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Microscopic organic-walled fossils are found in most sedimentary rocks. The organic particles - spores, pollen and other land- and marine-derived microfossils representing animals, plants, fungi and protists - can be extracted and used to date the rock, reveal details of the original sedimentary environment and provide information on the climate of the time of deposition. The mix within a sediment of these discrete organic particles - palynomorphs and palynodebris - form palynofacies. This book presents research work on the sedimentation of components of palynofacies and details their importance for sequence stratigraphy and the interpretation of ancient biologic and geologic environments. A comprehensive introduction to the subject is presented in the first chapter. Palynosedimentation in modern environments, the reconstruction of terrestrial vegetation and the application of the data to sequence stratigraphy are then considered. Later chapters detail the various quantitative methods and their specific applications in the subject. This is a valuable reference work for palynologists, sedimentologists and paleobiologists, and for professionals working in the hydrocarbons industries.

Sedimentation of organic particles

Sedimentation of organic particles edited by ALFRED TRAVERSE Department of Geosciences, The Pennsylvania State University

CAMBRIDGE UNIVERSITY PRESS

CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sao Paulo Cambridge University Press The Edinburgh Building, Cambridge CB2 2RU, UK Published in the United States of America by Cambridge University Press, New York www. Cambridge. org Information on this title: www.cambridge.org/9780521384360 © Cambridge University Press 1994 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1994 This digitally printed first paperback version 2005 A catalogue recordfor this publication is available from the British Library Library of Congress Cataloguing in Publication data Sedimentation of organic particles / edited by Alfred Traverse. p. cm. ISBN 0 521 38436 2 1. Palynology. 2. Sedimentation and deposition. 3. Micropaleontology. I. Traverse, Alfred, 1925— QE993.S43 1994 561'.13-dc20 92-39221 CIP ISBN-13 978-0-521-38436-0 hardback ISBN-10 0-521-38436-2 hardback ISBN-13 978-0-521-67550-5 paperback ISBN-10 0-521-67550-2 paperback

Contents

Editor's preface List of contributors

page ix xi

9 Maceral palynofacies of the Louisiana deltaic plain in terms of organic constituents and hydrocarbon potential 141 George F. Hart

I Introduction 1 Sedimentation of palynomorphs and palynodebris: an introduction Alfred Traverse

10 Organic sedimentation in a carbonate region Jason D. Darby and George F. Hart

II Studies of palynosedimentation in modern environments

2 The sorting of spores and pollen by water: experimental and field evidence Phillip L. Holmes

4 Pollen preservation in alkaline soils of the American Southwest 47 Vaughn M. Bryant, Jr., Richard G. Holloway, John G. Jones and David L. Carlson 5 Wind and water transport and sedimentation of miospores along two rivers subject to major floods and entering the Mediterranean Sea at Calvi (Corsica, France) 59 Maurice Streel and Claire Richelot 6 Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas 69 Alfred Traverse

B Palynofacies and palynodebris sedimentation The genesis and sedimentation of phytoclasts with examples from coastal environments Robert A. Gastaldo

777

11 An approach to a standard terminology for palynodebris 199 Michael C. Boulter

A Palynomorph sedimentation

3 Transport and deposition of pollen in an estuary: signature of the landscape Grace S. and Lucien M. Brush

8 Palynofacies of some recent marine sediments: the role of transportation 129 Claude Caratini

103

12 Relationships of palynofacies to coal-depositional environments in the upper Paleocene of the Gulf Coast Basin, Texas, and the Powder River Basin, Montana and Wyoming 277 Douglas J. Nichols and David T. Pocknall

III Reconstruction of late Cenozoic vegetation and sedimentary environments from palynological data 13 Quaternary terrestrial sediments and spatial scale: the limits to interpretation 239 Richard Bradshaw 14 Pollen and spores in Quaternary lake sediments as sensors of vegetation composition: theoretical models and empirical evidence 253 Stephen T. Jackson 15 Paleoecological interpretation of the Trail Ridge sequence, and related deposits in Georgia and Florida, based on pollen sedimentation and clastic sedimentology 287 Fredrick J. Rich and Fredric L. Pirkle

Vlll

Contents

IV Application of data on palynosedimentation to solution of geological problems A Sedimentary cycles 16 Palynology of sedimentary cycles 311 Daniel Habib, Yoram Eshet and Robert Van Pelt

20 Palynomorph concentration in studies of Paleogene nonmarine depositional environments of Wyoming 431 Martin B. Farley

D Specific examples of applications 21 Multivariate analyses of palynomorph data as a

B Sequence stratigraphy and sedimentation of organic particles 17 Particulate organic matter, maceral facies models, and applications to sequence stratigraphy 337 George F. Hart, Mark A. Pasley and William A. Gregory

C Quantitative methods and applications thereof 18 Association of palynomorphs and palynodebris with depositional environments: quantitative approaches 391 Warren L. Kovach and David J. Batten 19 A quantitative approach to Triassic palynology: the Lettenkeuper of the Germanic Basin as an example 409 W. A. Brugman, P. F. Van Bergen and J. H. F. Kerp

key to depositional environments of Upper Cretaceous and Paleogene coal-bearing rocks of the western United States 445 R. Farley Fleming and Douglas J. Nichols 22 Relationships between depositional environments and changes in palynofloras across the K/T boundary interval Arthur R. Sweet

461

23 Sedimentation of palynomorphs in rocks of 489 pre-Devonian age Paul K. Strother

V Appendix Modern pollen transport and sedimentation: an annotated bibliography 503 Martin B. Farley Index

525

Preface ALFRED TRAVERSE

My first job as a palynologist was with Shell Development Company in Houston, Texas. I was hired in 1955, and my assignment was to study pollen and spores in recent sediments in whatever way or ways I wished. For the next seven years I did this for Shell, and have, since then, been fascinated by the relationship between pollen, spores and other organic particles to the organisms from which they derive and to the sediments in which they occur as fossils. When Dr. Mary Dettmann invited me to organize a symposium on this subject for the 6th International Palynological Congress in Brisbane, Australia (AugustSeptember, 1988), I accepted enthusiastically. After the Congress I invited the participants in the symposium to produce chapters on this subject for a proposed book. However, as it worked out, there is very slight overlap between this volume and that symposium. For one reason or another, some of the participants in Brisbane did not prepare chapters. Others (including me) felt that the papers they had published in the Proceedings volume for the Congress (Review of Palaeobotany and Palynology, 64, 1990) need not be duplicated, and they produced something quite different for this book. It is also very significant for the shape of the present volume that I invited a number of people to write chapters who were not involved in the symposium at all, in order to assure a wide-ranging coverage of the subject. The new project was inspired by the symposium, but publishes a much different and broader array of material than was presented in Australia in 1988. The logic of the organization of this book seems right to me, but I realize from discussions with some of the authors that others might organize it differently. One of an editor's relatively few real privileges is to arrange the chapters! It seemed appropriate to me to begin with an introduction to the subject as I see it, including, where appropriate, references to individual chapters as they contribute to understanding organic particle sedimentation. The introduction is followed by chapters on palynosedimentation in modern environments, including discussion of the relatively new concepts of palynodebris and palynofacies. These matters seem to me basic to the whole field. Then come two chapters on the reconstruction

of terrestrial vegetation from palynological data. These chapters were added to the project on the basis of reviews of the original book proposal, which noted that this specialized application of palynosedimentation is important to a sizable group of researchers specializing in Cenozoic biology and geology. Next come chapters on the application of studies of palynosedimentation data to a number of currently important geologic problems, such as sedimentary cycles and sequence stratigraphy. Several concluding chapters on various quantitative methods and their specific applications seemed to me to provide a good counterbalance at the end to the general information at the very beginning of the volume. An appendix presents a previously unpublished annotated bibliography on the literature of palynomorph transport and sedimentation. The bibliography has been regularly updated for years, and this most recent version should be a very valuable tool for anybody interested in palynosedimentation. Because of the varied backgrounds of authors who contributed to this volume, there is some heterogeneity of usage. For example, in the bibliographies to chapters by George Hart and co-authors, references are made to privately circulated company reports. Citation of these is somewhat controversial, but Dr Hart indicates that he will provide photocopies of these reports to interested persons who write him. All of the chapters by my colleagues have been reviewed by at least one (usually two) highly qualified expert(s), and in every case this has resulted in considerable to extensive change. Some manuscripts unfortunately had to be rejected on the basis of review. The reviewers were mostly authors of other chapters. Practically all authors were involved as reviewers (generally anonymously), most with more than one manuscript, and they are acknowledged only by being listed as authors here. However, the help in evaluating manuscripts of the following 'external' reviewers is gratefully acknowledged: Jan Jansonius, Ronald J. Litwin, D. Colin McGregor and Cathy Whitlock. Two of my Penn State colleagues, Roy J. Greenfield and S. J. Mackwell, offered extensive computer assistance in the course of preparation of the

Preface final manuscript. Other Penn State colleagues, Lee R. Kump and Rudy L. Slingerland, were very helpful in editorial work with several chapters. Discussions with Martin B. Farley were central to initiation and continuation of this project. He has been very generous with help throughout the long time it has taken to complete the work. At the very end of the task I was a guest as Fulbright Professor at the Senckenberg Research Institute and Natural History Museum in Frankfurt am Main, Germany. Friedemann Schaarschmidt, the leader of the

Paleobotanical Section, and his co-workers, Karin Schmidt, Birgit Nickel, Kurt Goth and Volker Wilde, have all helped with the project. I am also grateful to Prof. Dr Willi Ziegler, Senckenberg's Director, for inviting me to work at the museum. Elizabeth I. Traverse has word-processed every letter in this book, mostly many times over, served as general editorial assistant and dealt with countless other problems, large and small, beginning years ago and not ending until the index was prepared and all proofread. Nobody has ever had a better assistant.

Contributors

David J. Batten Palynological Research Centre Institute of Earth Studies The University College of Wales Aberystwyth, Wales SY23 3DB, UK Michael C. Boulter Palaeobiology Research Unit University of East London Romford Road London E15 4LZ, UK Richard Bradshaw Faculty of Forestry Swedish University of Agricultural Sciences S-230 53 Alnarp, Sweden W. A. Brugman Royal Dutch/Shell 8 IPM-EPX 36 P.O. Box 162 2501 den Haag, Netherlands Grace S. Brush Department of Geography and Environmental Engineering The Johns Hopkins University Baltimore, MD 21218, USA Lucien M. Brush Department of Geography and Environmental Engineering The Johns Hopkins University Baltimore, MD 21218, USA Vaughn M. Bryant, Jr. Department of Anthropology Palynology Laboratory Texas A&M University College Station, TX 77843, USA

Claude Caratini French Institute BP33 Pondicherry, India 605001 David L. Carlson Archaeological Research Laboratory Texas A&M University College Station, TX 77843, USA Jason D. Darby United States Environmental Protection Agency Region IV 345 Courtland St. Atlanta, GA 30365, USA Yoram Eshet Geological Survey of Israel 30 Malkhei Israel Street Jerusalem 95501, Israel Martin B. Farley Exxon Production Research Co. P.O. Box 2189 Houston, TX 77252, USA R. Farley Fleming United States Geological Survey Federal Center, MS 919 Box 25046 Denver, CO 80225, USA Robert A. Gastaldo Department of Geology Auburn University Auburn, AL 36849-5305, USA William A. Gregory Exxon Exploration Company P.O. Box 4279 Houston, TX 77210-4279, USA

xii

Contributors

Daniel Habib Department of Geology Queens College City University of New York Flushing, NY 11367, USA George F. Hart Department of Geology and Geophysics Louisiana State University Baton Rouge, LA 70803, USA Richard G. Holloway Biology Department University of New Mexico Albuquerque, NM 87131, USA Phillip L. Holmes 243 Christchurch Ave Wealdstone, Harrow Middlesex, HA3 5BA, UK Stephen T. Jackson Department of Biological Sciences Northern Arizona University Flagstaff, AZ 86011, USA John G. Jones Palynology Laboratory Texas A&M University College Station, TX 77843, USA J. H. F. Kerp Westfalische Wilhelms-Universitat Abt. Palaobotanik Geol.-Palaont. Institut und Museum Hindenburgplatz 57-59 D-48143 Minister, Germany Warren L. Kovach Kovach Computing Services 85 Nant-y-Felin Pentraeth, Anglesey LL75 8UY, Wales, UK Douglas J. Nichols United States Geological Survey Federal Center, MS 919 Box 25046 Denver, CO 80225, USA Mark A. Pasley Amoco Production Co. P.O. Box 3092 Houston, TX 77253, USA

Fredric L. Pirkle E. I. Du Pont de Nemours and Co. Starke, FL 32091, USA David T. Pocknall Amoco Production Co. P.O. Box 3092 Houston, TX 77253, USA Fredrick J. Rich Department of Geology and Geography Georgia Southern University Statesboro, GA 30460, USA Claire Richelot Paleontology, The University 7, pi. Vingt-Aout B-4000 Liege, Belgium Maurice Streel Paleontology, The University 7, pi. Vingt-Aout B-4000 Liege, Belgium Paul K. Strother Weston Observatory 381 Concord Road Weston, MA 02193, USA Arthur R. Sweet Geological Survey of Canada Institute of Sedimentary and Petroleum Geology 3303 33rd St. NW Calgary, Alberta, Canada T2L 2A7 Alfred Traverse Palynological Laboratories Department of Geosciences Pennsylvania State University University Park, PA 16802, USA P. F. Van Bergen Netherlands Institute of Sea Research Division of Marine Biogeochemistry P.O. Box 59 1790 AB Den Burg, Texel The Netherlands Robert Van Pelt Westinghouse Savannah River P.O. Box 616 Merrill Lynch Bldg. Aiken, SC 29801, USA

Introduction

1 Sedimentation of palynomorphs and palynodebris: an introduction ALFRED TRAVERSE

Introduction The title above is really the subject of this whole book. Some time ago, Egon Degens (1965) estimated that about 2% of the total volume of sedimentary rocks on Earth is organic matter, that is, 20 m of a total of 1000 m of sediment in the whole of Earth history. All but 5 cm ( = coal and oil) of the 20 m (=19.95 m) is finely disseminated organic matter in shales, limestones and sandstones. Much of it is amorphous, much is from marine animals, algae and protists, either degraded or in recognizable particles. Since at least the Late Devonian, however, terrestrial plant biomass has been a (perhaps the) major source of the organic matter in sedimentary rocks (see discussion in Traverse, 1992). At present, approximately 150 xlO 6 metric tons of chemically resistant, particulate organic matter (POC) reaches the continental shelves from the major rivers of the world (Deuser, 1988; Ittekot, 1988). That can be compared with estimates of total sedimentation of 70 x 108 metric tons annually (Holland, 1978). As a rather rash guess, I would say that modern sedimentary rocks probably contain something like 10 times as much resistant-walled pollen-and-spore-like material as do 375 x 106-year-old Devonian shales and sandstones (Schuyler & Traverse, 1990). Nevertheless, land-derived plant debris in microscopic particles has been a very significant factor in building the organic bankroll of the Earth for some hundreds of millions of years, and much of it is recognizable as to source. In addition, marine-derived organic matter has been and is making a sizable contribution. Robust organic-walled, microscopic animal remains (chitinozoans, scolecodonts, 'microforams'), protists (for example, dinoflagellate cysts and some acritarchs), algae (various acritarchs, tasmanitids, among others) are obvious examples, but there is a much larger component of amorphous matter, as well as difficult to identify organic structures. It is clear from several chapters in Hue (1990) that organic matter in marine sediments includes important contributions from

both the indigenous marine realm itself (autochthonous) and from terrigenous material derived from the continents (allochthonous) (see Fig. 1.1). Palynologists have a keen interest in all of the fossil and potentially fossil organic matter just mentioned, but naturally are especially interested in identifiable particles, because their recognizability permits derivation of information about patterns of events on the continents and their shelves, such as climatic alteration, orogeny and other tectonic events, sedimentation patterns, and world oceanic current alterations. In addition, because of the relationship of organic particles to coal and oil formation, their study obviously is connected to investigations of coal and oil genesis and oil exploration. Hence, studies of the origin and eventual sedimentation of organic particles are currently an exciting frontier of both theoretical and applied paleontology. As is so often true in science, developments far removed from palynology-proper have had, and continue to have, obviously unpredictable impact on this area of study. Computer applications, including the automatic electronic recognition of particles, searching of records about them, and multivariate statistical programs are already in use. New fields of study such as the science and technology of particle systems (Hogg, 1989) may well have impact soon. Studies with their roots in well established basic geological and biological research are producing significant results. For example, studies of the origin and taphonomy of organic matter generally (Allison & Briggs, 1991) tell us much about what to expect in the sedimentation of organic particles. Conversely, the results of our research provide information that students of taphonomy of organic matter need to consider. Chapter 7 (Gastaldo, this book) is enlightening in this respect. Petrologists, paleobotanists, and other students of organic matter have for decades given order to our understanding of such diverse matters as the constitution of kerogen generally, and of coal in particular (Murchison, 1987; Scott, 1987). Their work has, for example, helped to clarify the lacustrine algal contribution to some oil shales (Goth

ALFRED TRAVERSE Formation of spores & pollen in sporangia/pollen sacs of plants

r-strategyM

k-strategy"

i Limited number of disseminules, carried by animal vectors, not abundant in sediments (Magnolia, Catalpa)

Very abundant spores or pollen, usually with flight-adapted morphology (isosporous ferns, Pinus, Ambrosia)

Mixed strategy

1 Some angiosperms, intermediate in pollen abundance (Tilia, Acer)

Chitinous-walled fungal spores and hyphae \ Transportation in the atmosphere

Weathering and erosion of sedimentary rocks, releasing palynomorphs: reworking and recycling

Transportation in stream water

Transportation to and in water of continental shelves

Structured & amorphous biomass debris (mostly plant tissue fragments and degradation residues) = palynodebris

Deposition on continental shelf: proximal marine

Deposition in lakes, fluvial environments, deltas

Marine animal production of palynomorphs: chitinozoans, scolecodonts, "microforams

Prasinophytes, acritarchs, dinocysts, and other algae of fresh and brackish water + autochthonous palynodebris

Transportation & deposition beyond the shelf in fully marine environments

Dinocysts, acritarchs, prasinophytes and other algae of marine environments: palynomorphs & palynodebris

MIXED SOURCE

(MOSTLY) ALLOCHTHONOUS

Figure 1.1. The complex origin, transportation and deposition as sediment, of robust organic (carbonaceous) particles. The shape of the boxes indicates whether particles concerned are produced mostly in the given fluid environment (autochthonous), or delivered mostly to that environment from outside of it (allochthonous), or have a mixed

source. (See legend at bottom of figure.) The size of the arrows indicates very roughly the relative magnitude of particle movements. More detail is provided for tracheophyte spores and pollen, because information derived from fossil sporomorphs is widely used for reconstruction of terrestrial climate and events.

Sedimentation of palynomorphs and palynodebris: an introduction et aU 1988). In this book, Chapters 9 and 17 (Hart and colleagues) present examples of the significance of various categories of particulate organic matter, not only for understanding the origin of sedimentary rocks, but also for correctly interpreting a great variety of sedimentary environments and evaluating them, for example, for sequence stratigraphy. The purpose of the entire book is to present recent contributions to the general study of the sedimentology of organic matter, the developent of which subject was heralded several years ago by Pelet and Deroo (1983).

Definition of the particle types While it has no force of law,' the preliminary Amsterdam Palynological Organic Matter Classification, drawn up on 27-28 June, 1991, by a committee which included David J. Batten, a co-author for this book (Batten, personal communication, 16 Dec, 1991), goes a long way toward explaining much of what we are talking about (underlined items, including the numbers, were added or slightly changed from the original; other modifications are explained): I.

PALYNOMORPHS sporomorphs pollen spores megaspores (> 200 small spores ( < 200 'algae' dinoflagellate cysts prasinophytes chlorococcales (cyanobacteria also included in original) acritarchs zoomorphs foram linings (= 'microforams') chitinozoans scolecodonts (tintinnids and rhizopods also included in original) fungal spores spores sclerotia indeterminate; opaque; microscopic seeds

II.

(PALYNODEBRIS): STRUCTURED DEBRIS woody plant epidermis/cuticle plant tissue (other) animal fungal opaque, indeterminate

III.

(PALYNODEBRIS): AMORPHOUS finely dispersed hom*ogeneous heterogeneous opaque

IV.

INDETERMINATE ( = not assignable to I-III) opaque other

The Amsterdam classification includes cyanobacteria under algal palynomorphs, and tintinnids and rhizopods under zoomorph palynomorphs, all of which I regard as inappropriate in the list and have removed. Scolecodonts were presented with a question-mark under zoomorphs, which seems unnecessary. 'Small spores,' which the new classification uses under sporomorphs, is a more felicitous word than 'miospore,' which has the disadvantage of being confusable with both meiospore and microspore. Sections II, III and perhaps IV comprise what some now call 'palynodebris,' an expression around long enough to have picked up contradictory attributes. Highton et a\. (1991), for example, classify palynodebris particles as > 200 /mi, whereas Boulter, in his classification of organic particles (Chap. 11, this book), describes palynodebris as not size-related. It is interesting that Combaz (1964) had, in his classification of the organic constituents of rock, a three-fold subdivision: (1) (what we now call) palynomorphs; (2) (what we now call) palynodebris; (3) amorphous and indeterminate organic matter. Gastaldo provides (Chap. 7, this book) a summary of how plant organics become phytoclasts and thus palynodebris. It is clear that the Amsterdam classification is strongly influenced by the detailed and profusely illustrated classification of Van Bergen et al. (1990). Brugman et a\. (Chap. 19, this book) employ this classification as a basic assumption. Boulter's related but different classification in Chapter 11, and that of Hart, Hart et al., and Darby and Hart (Chaps. 9, 17 & 10, respectively) are important additional contributions to this subject. For completeness one should also study the botanicallybased classification of Masran and Poco*ck (1981) and Habib's organic petrologic classification, which is referenced and used in Chapter 16 (Habib et al, this book).

Natural history of organic particles as clasts Elements of the Earth's biomass with resistant cell walls join other clastic particles in the atmosphere and hydrosphere, as suggested in Figure 1.1. Pieces of organic matter in the fluids of the Earth's surface are more than just passive fellow travellers of mineral clastic particles.

ALFRED TRAVERSE

It is known that living organic particles such as diatoms may tend to affect directly the stability of a stream bed (Heinzelmann et al, 1991). As generators of methanol and as substrate for sulfur-bacteria, organic particles undergoing taphonomic processes directly affect the properties of the co-sediment. In their final resting place they also provide raw material for hydrocarbon generation. From the point of view of palynology, these particles most significantly act as indicators or clues for the combinations of circ*mstances that put them where they are found in sediments, as suggested in Figure 1.1. As Robbins et al. (1991) point out, the biological information provided by palynomorphs/palynodebris must be coupled with their geological provenance to maximize the utility of the information their presence provides. Similarly, in Chapter 16 of this volume, Habib et al. show that the geochemistry of sediments is related to the suite of palynomorphs they contain. In Figure 1.1, I have indicated eventual sites of deposition, and thus incorporation in the sediments that become sedimentary rocks. The natural history of organic particles before they reach an eventual site of deposition is much more complicated than such a diagram can display.

Palynofacies It is now well known that when a particular assortment of palynomorphs/palynodebris in rocks is considered as a whole, it can yield information about (1) the biosphere segment producing the fossil particles, and (2) the environment of deposition in which the rock was produced, hence, the rock type produced. Combaz (1964) coined the term 'palynofacies' for the organic content of sedimentary rock, indicating both sedimentary environment of deposition and information about the producing biosphere elements.

Palynolithofacies I note from my company reports at Shell Development Company in 1960 that I was at that time using the term 'palynofacies' to refer to a more or less local concentration of particular palynomorphs, indicating a sort oi biofacies. It is clear that much of the application of the word since then has been geologically oriented, and 'palynofacies' is used primarily to indicate information about the enclosing rock, especially vis-a-vis its environment of deposition. I would call this a study of 'palynolithofacies.' LeNoir and Hart (1988), for example, described seven 'palynofacies' in Miocene sands of Louisiana. The palynofacies were characterized by dinoflagellate

assemblages, but the meaning is fe/iofacies, not biofacies. The dinocysts by themselves are not used to extract biologic information. Streel and Scheckler (1990) and Schuyler and Traverse (1990) similarly used Devonian miospore assemblages to characterize environments of deposition, from the point of view of the sedimentary rocks produced. In Chapter 19 of this book, Brugman et al. present detailed information about precise subdivisions of palynolithofacies, and in Chapter 18, Kovach and Batten describe computer-based quantitative methods for handling such data. Caratini (Chap. 8, this book) illustrates a helpful graphical technique for presenting such palynolithofacies.

Palynobiofacies The application of palynological studies to determine relationships between palynomorph concentrations and biosphere associations such as vegetation types I would designate with the term 'palynobiofacies.' Pleistocene palynologists use fossil pollen and spore assemblages to reconstruct plant associations. They are thus at pains to correct for over- and under-representation, and have developed very sophisticated quantitative methods to accomplish this end. Bradshaw and Jackson (Chaps. 13 & 14, respectively, this book) deal with aspects of such research. This is, in a sense, a way of eliminating biofacies concentrations from the data, to 'restore the norm.' All biofacies are to some degree counter to the norm, or average. That is why they are different 'faces' or facies. In Chapter 12 of this book Nichols and Pocknall describe the use of palynomorph-based plant association biofacies to determine the sorts of environments in which extensive ancient peats were formed. Traverse's Chapter 6 on palynomorph sedimentation in Trinity-Galveston Bay, Texas and vicinity, shows that in that set of environments, local sedimentary factors affect local total palynomorph concentrations, and it is clear that cores of sediment would yield quite different local palynofloras, depending on the location sampled. However, Brush and Brush's Chapter 3 on sedimentation in Chesapeake Bay shows that the overall pollen and spore flora of such a region at various stages in the recent past, determined from cored sediment, can be successfully used for interpreting climatic trends. Strother's Chapter 23 shows that, even in the early Paleozoic and before, organisms played an important role in sedimentation, either directly, or indirectly, as indicators of environment.

Palyno-biolithofacies Many studies of palynomorph/palynodebris-based facies are 'bi-facial.' That is, they have as goals both elucidation of the enclosing rock, and the biosphere association from which the palynological fossils were derived. This was

Sedimentation of palynomorphs and palynodebris: an introduction the emphasis in Farley and Traverse's (1990) study of Paleogene environments in Wyoming, and is further elucidated in Farley's Chapter 20 in the present volume. Obviously, palyno-biolithofacies studies tend to shift toward one or the other emphasis. Fleming and Nichols (Chap. 21, this book) show how multivariate analytical methods can be used to determine both sedimentary and biological environments. Rich and Pirkle (Chap. 15, this book) present a study of sedimentation in the southeastern USA, in which the emphasis leans toward understanding the source vegetation for palynofloras, but the plant associations indicated by the pollen assemblages are also used to help interpret the origin of various sedimentary types. Darby and Hart's study of carbonate deposition (Chap. 10, this book) uses palynologic data, especially on palynodebris, to determine depositional environment in the absence of clastic mineral particles. The goal is lithofacies analysis, but the means are very biological. Sweet (Chap. 22, this book) emphasizes floral changes across the K/T boundary, as they relate to lithofacies.

Palynosedimentation It is now quite well known that palynomorphs and palynodebris particles behave in the same way as do clastic particles of their size and specific gravity (see Traverse, 1988: Chap. 17; Spicer, 1991, makes a very significant contribution to understanding plant taphonomic processes that produce, among other things, most kinds of palynodebris). In general, palynomorphs/ palynodebris are transported to sites of deposition in water currents (see Fig. 1.1). An exception is found in arid regions, where all significant deposition is from the atmosphere. Bryant et al. (Chap. 4, this book) present a study of palynomorphs so sedimented. Also exceptions are some significant parts of the continental shelf, such as off northwest Africa (Hooghiemstra, 1988a,b; Dupont et a/., 1989), where wind transportation overwhelms the insignificant stream contributions. On the other hand, many studies of streams have demonstrated the dominance of water transportation of palynomorphs/palynodebris to continental shelves (Muller, 1959, for the Orinoco; Darrell, 1973, for the Mississippi; Federova, 1952, for the Volga, and many others). Holmes (1990, Chap. 2 this volume) has given a theoretical basis to the expectation of such transport by laboratory experiment. Darby and Hart's chapter on Florida (Chap. 10, this volume), and Traverse and Ginsburg's (1966) study of the Bahamas, have shown that 'pollen rain' delivered by either wind (virtually the only source in the Bahamas) or by wind and stream (as in Florida) is moved in non-clastic environments by water currents. Habib et al and Hart et al (Chaps. 16 & 17, respectively, this volume) both show that such large scale

phenomena/events at the marine/nonmarine boundary as transgression/regression can be traced by following the associated palynomorph/palynodebris sedimentation, both as to deposition of marine-derived palynomorphs (dinoflagellate cysts, for example) and as to sedimentation of different mixes of land-derived palynomorphs/ palynodebris.

Transportation of palynomorphslpalynodebris in water Although study of the transportation of pollen and spores in the atmosphere has a long history, relatively little has been done regarding the water transportation of palynomorphs/palynodebris. I have discussed the status of such studies recently (Traverse, 1990, 1992), as well as in Chapter 17 of Traverse (1988). Not surprisingly, as Koreneva (1964) and Chmura and Liu (1990) have pointed out, palynomorphs behave in the water as sedimentary particles, and their concentration is correlated strongly with mineral sediment concentration. Studies by Vronskiy (1975) in the Aral Sea and by Dupont et al. (1989), Hooghiemstra (1988a,b) and Hooghiemstra et al (1986) in the Atlantic Ocean off northwest Africa, and by Brush and Brush (Chap. 3, this volume), have shown, however, that in some situations airborne pollen exceeds or even dominates that brought by streams. For the most part, it seems clear that stream action and current movements on the continental shelf play the leading role in sedimentation of the palynomorphs/palynodebris found in shales and sandstones. Thus the experimental work reported by Holmes (Chap. 2, this book; see also Holmes, 1990) on the behavior of palynomorphs under laboratory conditions is an important contribution to basic understanding of the phenomena governing pollen suspension in and sedimentation out of water. Farley's annotated bibliography of the literature relating to all aspects of pollen/spore transportation in atmosphere and hydrosphere (Appendix, this book) should prove an invaluable resource to researchers in this field.

Sorting of palynomorphsl palynodebris during sedimentation Holmes (1990, Chap. 2 this book) has shown that sorting, mostly by size, can occur in the water transport of palynomorphs. As size sorting is possible in watch-glasses in the laboratory by 'swirling' (see discussion in Traverse, 1988, Chap. 6 this book), this is not surprising. Pleistocene palynologists have noticed sorting, or concentration, of certain forms and call it 'focusing.' Boulter and Riddick (1986) have noted that sorting of palynodebris elements occurs - and preferential deposition in different environments. Catto (1985) observed sorting into silts and sands in the somewhat unusual setting of a sub-arctic

ALFRED TRAVERSE

braided stream. Muller (1959), of course observed in his classic paper on the Orinoco drainage that smaller pollen becomes a larger percentage of total palynomorphs as one moves offshore. It must be mentioned that the 1:4 ratio of large to small palynomorphs on which the Hoffmeister (1954) method for finding ancient shorelines depended, was based on palynomorph sorting. However, there is little evidence that such sorting is efficient enough either to make the Hoffmeister method work reliably, or to prevent use of palynofloral analysis, for example, for stratigraphy based on joint occurrence of populations of many taxa of different pollen size.

Reworking, recycling and related matters The resilience of the walls of most sorts of palynomorphs and some kinds of palynodebris permits them not surprisingly to be resuspended and redeposited during depositional processes (Starling & Crowder, 1981). In Chapter 5 (this book), Streel and Richelot describe a situation in which pollen originally deposited in upland locations is carried downstream and out to sea during large floods. Palynomorphs also are frequently weathered and eroded out of rocks representing original sites of deposition, and recycled and redeposited. I am currently investigating cores of present-interglacial sediment from the Meadowlands complex, New Jersey. The 'native' pollen and spores are only poor to fair in quality of preservation, but (brown) Triassic (Corollind) and (yellowgreen) late Cretaceous (Rugubivesiculites, Normapolles, Cicatricosisporites) spores and pollen, obviously eroded from nearby outcrops when they were above sea level several thousands of years ago are beautifully preserved (Traverse, in press). Eshet et al. (1988) have shown that reworked palynomorphs in the fossil record, derived from previously exposed surfaces, have potential for study of source rocks and of depositional cycles that might not otherwise be observed. Reworked pollen found in the water of Trinity River, Texas, comes from all stratigraphic levels, Carboniferous to latest Cenozoic, intercepted by the river in its course toward the Gulf of Mexico (Traverse, 1990, 1992, Chap. 6 this book).

Sequence stratigraphy and organic sedimentation The relatively new development of sequence stratigraphy represents, among other things, acceptance of sedimentological insights and information into stratigraphic interpretation. The sedimentation of organic particles is ideally suited for a role in this new approach to stratigraphy, because many of the organic particles are age-specific and thus directly useful in stratigraphic interpretation, but all categories of organic particles can also be used in interpreting sedimentary environments.

Chapter 17 (Hart et al, this book) deals specifically with the contribution to sequence stratigraphy of palynofacies determined from the content of suites of particulate organic matter. Chapter 19 (Brugman et al, this book) describes use of an integrated palynofacies study in the Triassic of the Germanic Basin, revealing the sort of regressive, transgressive and mosaic environmental sequences that are useful for sequence stratigraphy. It seems clear, at least to this editor, that the future of paleopalynology is secure for some time, since it deals not only with fossil palynomorphs and their direct applicability to solution of stratigraphic problems, but also with resistant organic particles in general and their great potential for interpreting the genesis and subsequent history of sediments.

Suggestions for the Future Some of the blocks in Figure 1.1 indicate parts of the total subject that are especially open for research - areas about which relatively little is known:

Fungal spores, from sporu/ation to sedimentation and subsequent history in sedimentary rock The only fungal spores that are of interest palynologically are those with resistant walls, presumably all made of chitin (melanin probably plays a role as well; see Traverse, in press). Which super-taxa of Fungi this involves, what fraction of Fungi as a whole this comprises, the chemistry, the sedimentation, the geologic history, are all largely open questions.

Zoo-palynomorph sedimentation Sedimentation of such particles, especially of chitinozoans, scolecodonts and chitinous foraminiferal linings ('microforams'), has been relatively unstudied, although the stratigraphic range, especially for chitinozoans, has been extensively researched. The chemistry of these fossils is also very much an open question in need of solution.

Algal palynomorphs The sedimentation of prasinophytes, zygnemataceous zygospores, and various other categories of algal bodies, including most acritarchs, will be fruitful subjects for further investigation.

Organic particle transportation in the marine realm Movement of palynomorphs/palynodebris by various current systems, by turbidity currents, and by tidal action

Sedimentation of palynomorphs and palynodebris: an introduction would be well worth more study. The investigation of palynomorphs in ocean water is wide open. Farley's (1987) research in the Caribbean is practically alone as a systematic survey of pollen and spore transportation in the water of a significant segment of the oceans.

Reworking, recycling, redeposition These phenomena comprise a complex, fascinating and important subject that could constitute the basis of many very significant projects. The ability of resistant-walled palynomorphs to survive repeated attack on the substrate in which they are found and subsequent transportation should not be an embarrassment to palynology, but a source of very significant information about source rocks, cycles of erosion and deposition, differential diagenetic responses, and the courses of paleo-streams.

Sedimentation of palynodebris Discussed in a number of chapters in this book, this subject is still very new. We don't begin to know what the very diverse assemblages of such organic particles mean, except in the limited number of cases in which the materials have been carefully studied. This is clearly a very large subject which is now opening up ahead of us, and I hope this book stimulates study of it.

Acknowledgments As always, I acknowledge with gratitude the assistance of E. I. Traverse in preparation of the manuscript, and for many helpful suggestions. Discussions with Martin B. Farley at the beginning of this project were useful in designing the chapter. F. Schaarschmidt and members of his staff in the Paleobotanical Section of the Senckenberg Research Institute and Natural History Museum, Frankfurt am Main, Germany, were very cooperative in many ways during the final stage of this project, when I was a Fulbright Professor at that institution. B. Nickel was especially helpful in the preparation of Figure 1.1.

References Allison, P. A. & Briggs, D. E. G. (1991). Taphonomy of nonmineralized tissues. In Taphonomy: Releasing the Data Locked in the Fossil Record, ed. P. A. L. & D. E. G. B. Vol. 9 of Topics in Geobiology. New York: Plenum Press, 25-70. Boulter, M. C. & Riddick, A. (1986). Classification and analysis of palynodebris from the Palaeocene sediments of the Forties Field. Sedimentology, 33, 871-86. Catto, N. R. (1985). Hydrodynamic distribution of palynomorphs in a fluvial succession, Yukon. Canadian Journal of Earth Science, 22, 1552-6. Chmura, G. L. & Liu, K-b (1990). Pollen in the lower Mississippi River. Review of Palaeobotany and Palynology, 64, 253-61.

Combaz, A. (1964). Les Palynofacies. Revue de Micropaleontologie, 7(3), 205-18. Darrell, J. H., II (1973). Statistical evaluation of palynomorph distribution in the sedimentary environments of the modern Mississippi River delta. Ph.D. diss. Louisiana State University, Baton Rouge. Degens, E. T. (1965). Geochemistry of Sediments: A Brief Survey. Englewood Cliffs, New Jersey: Prentice-Hall. Deuser, W. G. (1988). Whither organic carbon? Nature, 332, 396-7. Dupont, L. M., Beug, H.-J., Stalling, H. & Tiedemann, R. (1989). 6. First palynological results from site 658 at 21° N off northwest Africa: pollen as climate indicators. In Proceedings of the Ocean Drilling Program, Scientific Results 108, ed. W. Ruddiman, M. Sarnthein, et al, 93-111. Eshet, Y., Druckman, Y., Cousminer, H., Habib, D. & Drugg, W. S. (1988). Reworked palynomorphs and their use in the determination of sedimentary cycles. Geology, 16,662-5. Farley, M. B. (1987). Palynomorphs from surface water of the eastern and central Caribbean Sea. Micropaleontology, 33, 270-9. Farley, M. B. & Traverse, A. (1990). Usefulness of palynomorph concentrations in distinguishing Paleogene depositional environments in Wyoming (U.S.A.). Review of Palaeobotany and Palynology, 64, 325-9. Federova, R. V. (1952). Dispersal of spores and pollen by water currents. Trudy Instituta Geografii Moskva, Akademiya Nauk SSSR, 52, 46-72. (In Russian). Goth, K., de Leeuw, J. W., Puttmann, W. & Tegelaar, E. W. (1988). Origin of Messel oil shale kerogen. Nature, 336(6201), 759-61. Heinzelmann, C , Baumgartner, B. & Rehse, C. (1991). Algal films stabilise the river bed: studying the effects of benthos settlement on bed erosion. German Research, 2/91, 12-14. Highton, P. J. C , Pearson, A. & Scott, A. C. (1991). Palynofacies and palynodebris and their use in Coal Measure palaeoecology and palaeoenvironmental analysis. Neues Jahrbuchfur Geologie und Paldontologie, Abhandlungen, 183(1-3), 135-69. Hoffmeister, W. S. (1954). Microfossil prospecting for petroleum. US Patent 2,686,108. Hogg, R. (1989). The science and technology of particle systems. Earth and Mineral Sciences (Pennsylvania State University, College of Earth and Mineral Sciences), 58(1), 1-5. Holland, H. E. (1978). The Chemistry of the Atmosphere and Oceans. New York: John Wiley & Sons. Holmes, P. L. (1990). Differential transport of spores and pollen: a laboratory study. Review of Palaeobotany and Palynology, 64, 289-96. Hooghiemstra, H. (1988a). Palynological records from northwest African marine sediments: a general outline of the interpretation of the pollen signal. Philosophical Transactions of the Royal Society of London, B 318,431—49. Hooghiemstra, H. (1988b). Changes of major wind belts and vegetation zones in NW Africa 20,000 - 5,000 yr B.P, as deduced from a marine pollen record near Cap Blanc. Review of Palaeobotany and Palynology, 55, 101-40. Hooghiemstra, H , Agwu, C. O. C. & Beug, H.-J. (1986). Pollen and spore distribution in recent marine sediments: a record of NW-African seasonal wind patterns and vegetation belts. 'Meteor' Forschung-Ergebnisse, C40, 87-135. Hue, A. Y., ed. (1990). Deposition of Organic Fades. AAPG Studies in Geology 30. Tulsa, Oklahoma: American Association of Petroleum Geologists.

ALFRED TRAVERSE Ittekot, V. (1988). Global trends in the nature of organic matter in river suspensions. Nature, 332, 436-8. Koreneva, E. V. (1964). Distribution and preservation of pollen in the western part of the Pacific Ocean. Geological Bulletin (Department of Geology, Queens College, City University of New York), 2, 1-17. LeNoir, E. A. & Hart, G. F. (1988). Palynofacies of some Miocene sands from the Gulf of Mexico, offshore Louisiana, U.S.A. Palynology, 12, 151-65. Masran, T. C. & Poco*ck, S. A. J. (1981). The classification of plant-derived particulate organic matter in sedimentary rocks. In Organic Maturation Studies and Fossil Fuel Exploration, ed. J. Brooks. London: Academic Press, 145-75. Muller, J. (1959). Palynology of Recent Orinoco Delta and shelf sediments. Micropaleontology, 5, 1-32. Murchison, D. G. (1987). Recent advances in organic petrology and organic geochemistry: an overview with some reference to 'oil from coal'. In Coal and Coal-bearing Strata: Recent Advances, ed. A. C. Scott. Geological Society Special Publication 32, 257-302. Pelet, R. & Deroo, G. (1983). Vers une sedimentologie de la matiere organique. Bulletin de la Societe geologique de France, 25(4), 483-93. Robbins, E. I., Zhou, Zi & Zhou, Zhi. (1991). Organic tissues in Tertiary lacustrine and palustrine rocks from the Jiyang and Pingyi rift depressions, Shandong Province, eastern China. Special Publications International Association of Sedimentologists, 13, 291-311. Schuyler, A. & Traverse, A. (1990). Sedimentology of miospores in the middle to Upper Devonian Oneonta Formation, Catskill Magnafacies, New York. Review of Palaeobotany and Palynology, 64, 305-13. Scott, A. C , ed. (1987). Coal and coal-bearing strata: recent advances and future prospects. In Coal and Coal-bearing Strata: Recent Advances, ed. A. C. S. Geological Society Special Publication 32, 1-6. Spicer, R. A. (1991). Plant taphonomic processes. In Taphonomy: Releasing the Data Locked in the Fossil

Record, ed. P. A. Allison & D. E. G. Briggs. Vol. 9 of Topics in Geobiology. New York: Plenum Press, 71-113. Starling, R. N. & Crowder, A. (1981). Pollen in the Salmon River system, Ontario, Canada. Review of Palaeobotany and Palynology, 31, 311-34. Streel, M. & Scheckler, S. E. (1990). Miospore lateral distribution in upper Famennian alluvial lagoonal to tidal facies from eastern United States and Belgium. Review of Palaeobotany and Palynology, 64, 315-24. Traverse, A. (1988). Paleopalynology. London: Unwin Hyman. Traverse, A. (1990). Studies of pollen and spores in rivers and other bodies of water, in terms of source-vegetation and sedimentation, with special reference to Trinity River and Bay, Texas. Review of Palaeobotany and Palynology, 64, 297-303. Traverse, A. (1992). Organic fluvial sediment: palynomorphs and 'palynodebris' in the lower Trinity River, Texas. Annals of the Missouri Botanical Garden, 79, 110-25. Traverse, A. (in press). Manifestations of sporopollenin, chitin and other 'non-degradable plastics' in the geologic record, as evidence for major biologic events. In Proceedings Birbal Sahni Birth Centenary Palaeobotanical Conference, ed. B. S. Venkatachala, K. P. Jain & N. Awasthi. Geophytology, 22. Traverse, A. & Ginsburg, R. N. (1966). Palynology of the surface sediments of Great Bahama Bank, as related to water movement and sedimentation. Marine Geology, 4, 417-59. Van Bergen, P. F., Janssen, N. M. M., Alferink, M. & Kerp, J. H. F. (1990). Recognition of organic matter types in standard palynological slides. In Proceedings: International Symposium on Organic Petrology, ed. W. J. J. Fermont & J. W. Weegink. Mededelingen Rijks Geologische Dienst 45, 9-21. Vronskiy, V. A. (1975). On modern 'pollen rain' above the surface of the Aral Sea. Doklady Akademii Nauk SSSR, 222(1), 167-70. (In Russian).

II Studies of palynosedimentation in modern environments A Palynomorph sedimentation 2 The sorting of spores and pollen by water: experimental and field evidence PHILLIP L. HOLMES

Introduction Palynologists extract fossil spores and pollen (collectively 'sporomorphs') from rocks representing many different sedimentary environments; these are used as indicators of the surrounding vegetation and climate as well as for stratigraphy. They are of particular use to stratigraphers, as they may be found in both marine and terrestrial sediments and can therefore be used as a link between the two environments. In the past it was common to believe that most of the pollen was transported to the sediment via the atmosphere as a 'pollen rain.' This pollen rain was considered to be relatively uniform over a wide area. The distribution of pollen through the atmosphere has been studied by many authors (for example, Lanner, 1966; Janssen, 1973). Numerous experiments have been carried out on the dispersion of pollen from both point sources (Colwell, 1951; Chamberlain, 1966) and from forests (Lanner, 1966). Some of these studies were initiated by investigators in other fields of study. May (1958), for example, was attempting to model the dispersion of radioactive particles in the atmosphere and she used Lycopodium spores to do this. As palynologists recognized the need to be able to differentiate between pollen that had travelled a few meters from that which had arrived at the site from several kilometers away, the pollen rain was interpreted as having three components with arbitrary boundaries: (1) 'local' (sporomorphs deposited within a few tens of meters of their source plant), (2) 'extra-local' (deposited within a few hundred meters of the source), and (3) 'regional' (deposited more than a few hundred meters from their source). The boundaries between these groups are vague, and many authors also use a fourth term, 'extra-regional,' for the long-distance transport of sporomorphs. As pollen analysis was extended to sediments other than peats (and their fossil derivative, coal) it became apparent that some of the pollen was transported to the site of deposition by water (e.g., Muller, 1959; Traverse

& Ginsburg, 1966), rather than by air. Quaternary investigators in particular, who have been using lake sediments as an alternative to moss polsters, have become increasingly aware of a substantial fluvial input of pollen to lakes. Among the more compelling evidence for this is the increase in absolute numbers of pollen found in sediments adjacent to river mouths in both lacustrine (Fletcher, 1979) and marine settings (Heusser & Florer, 1973; Heusser, 1988). Palynology is used in an increasing number of research fields, and a finer resolution time scale is demanded. Hence there is an increasing need to understand the taphonomic processes that act upon the sporomorphs. Nearly all of the work in this area has concentrated on field studies (e.g., Peck, 1973; Bonny, 1978; Crowder & Starling, 1980). There have been very few controlled laboratory experiments studying the behavior of sporomorphs in water, despite the unanswered questions raised by the field studies. For example, are the differences between sporomorphs great enough for physical processes to act upon? If they are, under what circ*mstances will sorting occur and is it possible to detect these effects? We have very little direct observation of the factors that affect sporomorph transport by water. In this chapter I review this limited experimental work and add new data based on my own studies. This will be followed by a discussion on the transport routes that sporomorphs may follow on their way to lake sediments. The processes that I describe, however, could be used in connection with any sedimentary system.

The pros and cons of experimental palynology Before we can interpret pollen records in taphonomic terms we need to know what factors affect their deposition rates. Of these processes we need to know which, if any, affect sporomorphs differentially (i.e., which processes can 'sort' them).

PHILLIP L. HOLMES

Among the problems of making field observations is the lack of control of variables such as water velocity and the suspended load of the flow. Sporomorphs may also reach the water via different routes, so the physical condition of the exine and protoplasmic contents may differ. Much of the sporomorph input to a stream or river is from surface runoff. Some will also be deposited directly from the atmosphere. The latter is more likely to be dry and uncorroded. The sporomorphs brought in by surface runoff may be partially degraded, having spent some time exposed on various substrates such as leaves, twigs and the soil, where they are open to microbial attack. These are also much more likely to be waterlogged. Rainfall is known to clear the atmosphere of much of its sporomorph load, by capture in raindrops (McCully et al, 1956; McDonald, 1962). These grains should be in good physical condition but will also be waterlogged. A whole range of preservation states and degrees of saturation will occur, and these may behave differently when they are incorporated into the sporomorph load of the river. By running laboratory experiments, it is possible to overcome these problems. Variables such as water velocity and depth can be controlled. The bed material over which the water flows is easily changed. The state of the sporomorphs used is also known. It is even possible to test for differences in behavior between fresh and partially degraded spores and pollen. Laboratory experiments also have disadvantages. The first of these is scale. The natural environment cannot be recreated in the laboratory. It is therefore only possible to test sporomorph behavior on a small scale, testing nature a piece at a time. The results from what appears to be a large flume in the laboratory should not be used to predict particle behavior in a river of varying width and depth, without careful consideration. One of the objectives of laboratory experiments such as those described in this chapter is to remove as many unknown quantities as possible from the scenario. Such simplifications should be remembered when trying to interpret the results in a meaningful and helpful manner. Laboratory experiments should not be run in isolation from the field, and all results should also be tested there. In common with many subjects, the results from experiments often raise as many questions as answers, especially in the early stages of the work. Even so, the results presented should prove to be of value, for example, in showing where future work may be directed.

The data base When sporomorphs are studied from a taxonomic viewpoint, the size of the grain and the thickness of the exine are frequently used for diagnostic purposes. These sorts of data are therefore relatively easy to come by. When looking at the behavior of sporomorphs in water,

other variables such as the specific gravity (or density) and volume of the grain are also of interest. Such characters are not routinely measured. Some data are available from the literature, but this is relatively sparse. Measurement of such characters is extremely timeconsuming. Table 2.1 summarizes our knowledge of some of the more important variables of pollen and spores. Not all sources are in agreement, because of differences in the techniques used for measurement. Values for grain density will vary with the water content of the grain. Most grains rapidly equilibrate with the external humidity (Harrington & Metzger, 1963). In this case, all of the measurements have been placed in the table, but more attention should be been given to the highest value, as this is most likely to represent the exine density. The density of a ragweed (Ambrosia) grain as a whole approaches that of the exine at 100% humidity (Harrington & Metzger, 1963).

Incorporation of sporomorphs into a water body The transport of sporomorphs through the atmosphere is adequately covered in the literature elsewhere (Tauber, 1967a,b; Bradshaw & Webb, 1985). Similarly, the processes involved in the degradation of sporomorphs have been studied (Havinga, 1964,1984; Sangster & Dale, 1964). In the following discussion, I therefore concentrate on the behavior of the sporomorphs beginning when they come into contact with the water surface. Spores and pollen that enter a water body via surface runoff may be considered to be saturated and will therefore be readily incorporated into the water body. I therefore ignore this input for now, concentrating instead on the input of sporomorphs from the atmosphere. Once a spore or pollen grain has landed on a water surface, the time taken for it to become incorporated into the flow depends on both the time taken to saturate the grain and on the turbulent nature of the water.

Saturation of sporomorphs Saturation has been studied by Hopkins (1950) who experimented with arboreal pollen. He tapped pollen from male inflorescences into a beaker filled with water and noted the time required for each to sink. Most deciduous pollen types sank within five to ten minutes, while bisaccate types tended to float. Bisaccate grains float because the sacci are sealed and thereby keep the grain buoyant even when the rest of the grain is saturated. The buoyancy of bisaccates is a well known phenomenon. Pohl (1933) noted that pine pollen could retain its buoyancy for up to four years, others have reiterated this

The sorting of spores and pollen by water: experimental and field evidence 11 Table 2.1. A compilation of pertinent spore/pollen characteristics. An asterisk (*) denotes measurements made on wet grains. It should be noted that difference authors use different techniques to obtain their results, hence the wide variation in, for example, sporomorph densities. Much of the variation in density measurements is probably due to differences in the level of saturation of the grains. In order to conserve space the information from different authors has not been segregated; thus the fall velocity quoted for a particular species does not necessarily relate to the other data on the same line. Data sources: ^ e a t h c o t e (1978); 2Fletcher (1979); 3 Niklas & Paw (1982); 4 Gregory (1961); 5 Chamberlain (1966); 6 Dyakowska (1937); 7 Brush & Brush (1972); 8 Durham (1946); 9 Harrington & Metzger (1963); 10 Davis & Brubaker (1973). Fall velocity (Vf) (cm/sec)

In Water

In Air Specific Gravity

Species

Size (/mi)

Acer sp. Abies sp.

39.9 1 86.2 1

Alnus sp.

21.22 1

A. glutinosa

A. viridis Ambrosia sp.

Betula sp. B. lutea B. nigra B. papyrifera B. pubescens B. verrucosa Corylus sp. C. americana C. avellana fa*gus sp.

23.6 24.2 6 47.0 1

F. grandifolia F. sylvatica Fraxinus sp. Lycopodium sp.

44.0 8 38.4 6 24.0 1 31.6 5 32.4 5

Pinus banksiana P. echinata P. resinosa P. strobus P. sylvestris

4 1

0.0202 1 0.110 1

1.171 1.167

0.00347 1 0.0037 7

0.00949 1 0.0285 1 0.0518 7 0.00438 1

1.74

1.2* 1.28*9 1.288 1.14

1.55*

31.22 24.6 8 28.79 1 27.5 6 24.5 8 8

1.236*1 1.270*1

1.98 2.59 8 2.59 8

1.41 1.3751 0.94

1.68

1.7

0.0037 1

O.OO351 0.0078 7

0.0048 1 0.019 7

0.0047 1

0.0197 1

0.0104

0.0102 1

0.0165 1

1.0068

22 7

Obs.

1.57 1.028

20.4 8 25.4 1 27.5 7

Calc.

Obs.

Calc.

1.468

26.0 8 30.0 8 30.0 8 19.52 1

187 Artemisia sp.

0.75 8 0.97 8 0.97 8

Density (g/cc)

1.3681 2.13 8 1.788

0.0023 7

l.l*7 1.098

1.83 2.96 8

0.71 6 0.94 8 0.94 8 0.713 4

1.31 2.5 4

1.081 5.52 8

1.175

1.3151

493 0.391 4

0.00452 1

0.00417 1

0.037 l 0.0175 1

0.01 I I 1 0.0105 1

345 38 3 523

0.00903 1

3.54 8 5.5 4

1.17*1 4

0.00955 1

1.76 1.905 2.14 5 2.0 3 2.0 3 2.3 3 2.1 3 2.5 3

2.49 3

543

577 528

0.8 7 1.2*7

28.5 8 34.0 8

1.01 8 0.98 4 0.91 8

0.0316 7 2.49

POACEAE

Capriola dactylon Dactylis glomerata

2.50 8 3.17 8

1.868 3.10 4 2.78 8

PHILLIP L. HOLMES

Table 2.1. Continued Fall velocity (V,) (cm/sec]1 In Water

In Air Species Phleum pratense Poa pratensis Secale cereale

Zea sp. Z. mays

Sixe (/*m)

Specific Gravity

34.08 28.08 30.08 608 49.5 5

0.98 0.98

81.61

1.421 0.358 1.08

90 Populus Quercus sp.

3O.131 247 32.661 2 9

Q. imbricaria Q. macrocarpa Q. robur Salix sp. Ulmus sp.

33.1 8 32.38 27.76 17.351 27.51

Density (g/cc)

Calc. 3.178 1.468 2.448 7.258

24.528

Obs.

1.748 4.3 4 6.08 8.84 18.08

1.161*1 1.311 1.1610 3.428 3.38 2.41 8

Obs.

2.88

1.02* 1.048 1.27 1.048 1.048

Calc.

0.00789' 0.00567 0.001781 0.0081 10

0.004511

0.001841 0.007151 0.00937

0.002781 0.005671

0.001341

0.0002891

2.28 1.838 2.94

1.1131 1.175*1

URTICACEAE

Cannabis sativa Urtica sp. U. gracilis

308 25 8 14.461 14.08

0.82

2.228 1.568

1.126*1 0.778

0.4

1.048 2.558 0.34

Notes: * = measurements on saturated grains. Further results for the observed V, of spores in air may be found in Gregory (1961).

point (e.g., Erdtman, 1943; Traverse & Ginsburg, 1966; Traverse, 1988). Hopkins' (1950) results show that there is some differential buoyancy between Pinus species. The grains that sank are those with smaller or deformed/broken air sacs. When placed on a water surface in a large water tank, over which a breeze of 13 km/h was blown, conifer pollen drifts at a rate of 0.16 to 0.32 km/h. When oak pollen (Quercus palustris) was put through a similar process most of it sank within the first meter (experiments by Hopkins, 1950). In Hopkins' experiments the surface of the water was calm. In nature the surface of streams and lakes are usually broken by wave action or turbulence within the flow. Most sporomorph types will therefore be rapidly incorporated into the water body.

Bisaccate grains will only sink if the bladders are pierced either by physical, chemical or microbial processes. They are therefore more likely to be saturated if they enter turbulent flow, or if they have been resident in a position (such as the soil surface) where they are open to microbial attack prior to introduction to the water. All of the pollen types tested by Hopkins had at least one pore or colpus. These provide an easy route for entry of water into the grain. Many pollen grains have mechanisms to prevent dessication but cannot prevent water uptake. Sporomorphs, many of which have no openings in the exine, have no inlet for water. Some, such as Lycopodium, also have an oily coat (Balick & Beitel, 1988). Attempts to saturate Lycopodium in the laboratory

The sorting of spores and pollen by water: experimental and field evidence 13 have shown that such grains are extremely resistant to water uptake. Extreme methods have to be invoked, such as placing the sporomorphs in a beaker in a vacuum for up to eight hours (own method) or boiling in water (Reynolds, 1979). This means that they are likely to remain afloat in the water, in nature, for long periods of time. This is consistent with results from the Volga River where Federova (1952) found Lycopodium spores over 700 km from their source.

They put this difference down to the differing specific gravities of the two pollen types. There is also a significant size difference. Peck (1974b) found down-lake decreases in many sporomorph types in two Yorkshire reservoirs. The larger sporomorph types were deposited in slightly higher numbers close to the stream mouth. Fletcher (1979) studied the sporomorph distribution in the surface sediments of Lake Michigan and found that lake currents carried small grains further than large grains, Ambrosia being particularly buoyant. Transport of sporomorphs in a water Davis et al (1971) and Davis and Brubaker (1973) explained differences in the distributions of oak (Quercus) body and ragweed (Ambrosia) in the sediments of several small Once they have been incorporated into the flow most North American lakes as resulting from sorting. The sporomorph types are transported as part of the smaller ragweed grains remain in suspension for longer suspended load. They are normally associated with the periods of time, allowing them to be transported to the fine silt/clay fraction (Muller, 1959; Cross et al, 1966; littoral areas of the lake by wind generated currents. Chen, 1987). This is the size class below that of the Sorting was also used to explain results presented by sporomorph size due to differences in their density Chen (1987) from the sediments of Lake Barine in compared to mineral sediment. The distribution of Queensland, Australia. Many of the grains are transported sporomorphs within a river channel will depend on the to the lake by surface runoff. On entering the lake the flow characteristics of the river. Peck (1973) assumed an runoff forms a current running from the lake's edge even distribution occurred in Oakdale Beck (Yorkshire) toward the center. Larger grains are deposited in the while Starling & Crowder (1980/81) found a concentration littoral areas, while smaller grains are carried to the lake of sporomorphs in the zone of maximum flow in the center by these currents. Salmon River (Ontario). They also found secondary areas Clearly, sorting of sporomorphs can occur in many with high counts in the bedload of the river. The Salmon depositional environments. The behavior of sporomorphs River is much larger than Oakdale Beck and is also in as sedimentary particles is, however, poorly understood. an area of lower relief; it is therefore likely to be less To date there has only been one other attempt at studying turbulent, allowing such patterns to persist. their transport in the laboratory, that of Brush and Brush On a smaller scale Brush and Brush (1972) found a (1972). Experiments were also run by Peck (1972); these, slight increase in the total numbers of sporomorphs with however, were designed to test the efficiency of the Tauber depth at the downstream end of the flume used in their Trap in water. Some of the data presented by Peck can experiments. The flume used for their study measured 4 m be used to provide useful information on sporomorph long by 0.23 m wide, water depth was 0.14 m and flow transport. velocity set at 33 cm/sec. Similar experiments run by the The experiments undertaken by Brush and Brush author in a larger flume (7.5 m x 0.3 m, water depth 0.26 (1972) were run in a small flume over a sand bed (grain size m) also show a slight increase of sporomorph numbers 0.63-2.0 mm) with a flow velocity of 33 cm/sec. A bed with depth over a distance of seven meters and at a range regime of dunes and ripples was established prior to the of low flow velocities (3 cm/sec-12.5 cm/sec). introduction of the sporomorphs. Total experiment time Several authors have found that water currents can was 15 minutes in each experiment. They found that sort sporomorphs. This was first seen in the field by sporomorphs were preferentially deposited with the finest Muller (1959) who was looking at the palynomorph sediments in the bottomset beds of the ripples. They also distribution in recent sediments in the Orinoco delta area. noticed that there was some selectivity in the transport He noted that the pollen of Rhizophora, which is relatively of the sporomorphs and of their inclusion in the bed. No small, was carried further out to sea than larger overall pattern for selectivity emerged from this study, sporomorphs from similar source areas. Cross et al. (1966) and the fate of many of the sporomorph types in the also found evidence of sorting in a marine setting as experiments could not be determined. They emphasized lighter, more buoyant, grains were carried further toward that a larger flume and longer experiment times would be needed for further investigation. the southern end of the Gulf of California. Peck's (1972) investigation of the Tauber Trap revealed Crowder and Cuddy (1973), looking at pollen spectra from Hay Bay (Lake Ontario), found that ragweed that at low velocities the trap would preferentially remove (Ambrosia) pollen was carried further from the mouth of larger sporomorphs from the water flow. Experiments Wilton Creek than was pollen from the grasses (Poaceae). with higher flow velocities showed no such differentiation.

PHILLIP L. HOLMES

Here the selection was thought to occur within the trap. It is possible, however, for the selection to have occurred at the trap orifice. In a more recent study of alluvial sediments from a canyon stream in the Chuska mountains of Arizona, Fall (1987) tested the assumption that the pollen in the alluvium was from local vegetation. She found that pollen concentrations in general were highest in the fine grained sediments. Non-arboreal sporomorph types however were found in higher numbers in the sandy sediments. Similar results have been reported from glacio-lacustrine sediments in Alaska (Goodwin, 1988) and braided stream deposits adjacent to the Caribou River in Yukon (Catto, 1985). These results may be due to differential transport (as suggested by Fall, 1987; Goodwin, 1988; Catto, 1985) or they may be due to the differing source areas of the tributaries involved (Hall, 1989). These results suggest that the deposition of fine grained sediments, sporomorphs in particular, is related both to the flow conditions of the water and the bed material over which the water flows. I undertook a series of experiments to investigate these relationships. The basic aims were as follows: (1) to elucidate those sporomorph characters (size, density) which control transport; (2) to determine at what flow velocities a significant level of differential transport ceases to occur; (3) to investigate the effect of bed material on sporomorph deposition.

Experimental methods Treatment of sporomorphs After collection (from living plants), all sporomorph types (except Lycopodium) were air dried for a period of up to ten days. Lycopodium spores were purchased from a chemical supplier. A few days prior to each experiment the sporomorphs were saturated with water by placing the required amount in a beaker of water in a partial vacuum. Pine pollen was saturated by putting the grains through an alcohol series as the vacuum treatment caused the air sacs to collapse. Some sporomorph types were also acetolysed, and the effect of this treatment was investigated in separate experiments.

Flume conditions The flume used for this study was an Armfield tilting flume. This has a sediment loop fitted so that it may continuously recycle the water and any suspended sediment. The main section of the flume measured 7.5 m x 0.3 m, the water depth varied between experiments from 0.23 to 0.26 m. The flow velocities used were in the range 0.03-0.3 m/sec, with Reynolds (Re) numbers in the range 14400-95000 and Froude numbers in the range

0.1628-0.2067. Experiments were run over two different sand beds as well as over the smooth base of the flume.

Basic experimental method Once the flume was set in the configuration required for the experiment the sporomorphs were added to the water over a period of several minutes. This, combined with the turbulence encountered on passage through the motor, sufficed to give a fairly hom*ogeneous distribution of sporomorphs in the water. Once in the flume three things could happen to the sporomorphs: (1) they could be deposited, (2) they could remain in suspension, or (3) they could be lost, either by lodging in the pipes or on the glass sides of the flume. Very few sporomorphs are found in the water after the flume has been cleaned, which suggests that a negligible amount lodge there during the experiments. The sporomorphs that stick to the sides of the flume form a visible line at the downstream end of the working section. Even so their number is small in comparison to the total numbers in the water. Such loss may therefore be ignored when considering the fate of the sporomorphs in each experiment. The total number of sporomorphs added to the flow at the beginning of each experiment can be calculated. By taking samples of the water throughout each experiment and counting the number of sporomorphs in one milliliter it is possible to estimate how many remain in suspension. This means that we can also calculate the numbers that have been deposited. A graph of the number of sporomorphs in suspension plotted against time can then be used to calculate a rate of deposition (see Fig. 2.1). The gradient of the regression line shown in Figure 2.1 describes the rate of loss of sporomorphs from suspension with time. As the only alternative site for the sporomorphs is on the flume bed, this can be translated as the rate of deposition to the bed. If the flow velocity were reduced we would expect sporomorph deposition to occur at a faster rate. This would be manifest as a steeper line on a graph of the type shown in Figure 2.1. This procedure has been used in Figure 2.1b where the inverse rate of deposition (taken as the reciprocal of the gradient) is plotted against flow velocity.

Statistical methods The data from each experiment were put through a least-squares regression analysis to give the best fit line. The gradient of each line was tested against the null hypothesis that it equalled zero (i.e., H o : j8 = 0) using analysis of variance and an F-test. The null hypothesis was rejected at the 95% confidence level for all of the data presented here. For experiments run at the same velocity, the gradients were tested against each other using the Student's t test, with the null hypothesis that all gradients were equal (Ho: /?i=/?2)-

The sorting of spores and pollen by water: experimental and field evidence 15 Data from experiments with Lycopodium (ave. diameter 32/im), flow over medium sand bed. r2 =coefficient of determination

fig.lb.

suspension

log e (spores/ml)

flow velocity (cm/sec)

flow velocity lOcm/sec 120

240 Time (minutes)

360

Figure 2.1. Calculation of a rate of deposition from the flume results. The main graph shows the relationship between sporomorph concentration in the flow (loge(spores/ml)) with time. The gradient of the least-squares regression line (m) in each case is equal to the rate at which sporomorphs are lost from the flow. Data points are given for one line only to retain clarity. The second graph (1b - inset) uses this relationship with the inverse of the gradient (m 1) plotted versus flow velocity. This illustrates clearly the changes in the deposition rate under different flow conditions; in this example the decreasing flow velocity results in a decrease in the inverse deposition rate (i.e., an increase in the deposition rate). The line drawn through these points is curved as there is a fourth data point (not plotted) from an experiment run at 25cm/sec with an inverse rate of deposition of 8000 (approx.). The data on this figure are derived from experiments with acetolysed Lycopodium spores and thus differ from the data points for Lycopodium in Figure 2.2.

480

Evidence for the sorting of sporomorphs Figure 2.2 displays a set of results I obtained from recent flume experiments, along with results recalculated from data given in Peck (1972). The inverse deposition rates of Lycopodium spores at several different flow velocities are shown. This provides a line for a 32 jim spore against which deposition rates for sporomorphs of various sizes may be compared. Peck's data for Lycopodium show a very close correspondence to this line, as do Dactylis and Quercus pollen, both of which are similar in size (33 fim and 28 /mi respectively). Quercus also has a specific gravity similar to that of Lycopodium (approximately 1.2); however, Dactylis is lighter, with a specific gravity of 0.98

PHILLIP L. HOLMES

600'

suspension

500-

400-

rate of deposition (l/m) 300«

200

to 7"

¥^ NA

\ — 1 _

West Texas Surf ace Samples

i 0

•

100

200

miles

I N

Figure 4.3. Location of collection sites for each of the 90 modern pollen surface samples.

Results Fossil pollen samples Of the 509 samples collected for analysis, only 243 (48%) contained sufficient fossil pollen to conduct statistically valid counts in excess of 200 grains, as recommended by Barkley (1934), Martin (1963), and others. We found the remaining 266 samples (52%) were almost entirely devoid of fossil pollen. The small amounts of pollen found in the productive samples represented: (1) taxa known to be highly resistant to various agents of destruction, (2) types that could still be identified even though they were severely degraded, or (3) highly degraded pollen grains that were no longer identifiable. This type of limited pollen recovery phenomenon is common in soils of the

American southwest and has been previously reported by Hall (1981), Holloway (1981), Bryant and Schoenwetter (1987) and Bryant and Hall (1993). The average number of pollen taxa per fossil sample was only 7.5, and the maximum of 17 was observed in only three samples. Two of the samples contained only one pollen type each (Fig. 4.4, Table 4.1). The five most frequent types in these samples were (1) Pinus, (2) cheno-ams [a combined term used to represent pollen taxa in both the family Chenopodiaceae and the genus Amardnthus], (3) genera of the Asteraceae family (including high and low spine composites, Artemisia, and Liguliflorae types), (4) Ephedra, and (5) various genera of the Poaceae family. Although these five pollen types represent plants common in the floral communities of the region sampled, they also represent distinctive pollen types that can be recognized easily even after being severely degraded. Pollen concentration values for each of the 243 fossil

VAUGHN M. BRYANT, JR., RICHARD G. HOLLOWAY, JOHN G. JONES AND DAVID L. CARLSON

Table 4.1. Descriptive statistics for the 243 fossil pollen samples

Number of taxa Pollen concentration Percent Indeterminable

Mean

Standard deviation

Median

Minimum

Maximum

7.5 6545 7.6

3.01 13 302 6.51

7 3688 6.1

1 674 0

17 165 828 34.1

Fossil Pollen Transect Number of Taxa (Count>199)

Number of Taxa

pollen samples were generally low (Table 4.1). That the distribution is skewed to the right is indicated by the difference between the mean and median statistics. While the mean concentration is 6545 grains/cm3, half the samples have fewer than 3688 grains/cm3. Table 4.1 also shows that the mean percentage of indeterminable pollen was 7.6 and that the distribution of these values is skewed as well. As we will show later, there is a tendency for the highest percentages of indeterminate pollen to come from samples with the lowest concentration values. Pollen listed in the indeterminable category included grains that were broken, corroded, degraded or folded in ways that made their identification impossible. This category included grains that were so broken or fragmented that accurate identification was impossible, grains that had so many areas missing from corrosion that accurate identification was no longer possible, grains that were so thinned and degraded that their accurate identity remained in question, and pollen that was so folded their identity remained uncertain. If pollen grains

Figure 4.4. Chart showing the number of pollen taxa in each of the 243 fossil pollen samples.

were broken, corroded, degraded, or folded, yet still identifiable, they were counted and included in the taxa to which they belonged and were not added to the indeterminable category. Although we did not split the indeterminable category into the groups listed above for counting purposes, almost all of the indeterminable grains in our study were those in the degraded category.

Modern pollen samples All 90 of the surface pollen samples collected for this study contained sufficient pollen to count more than 200 grains per sample. We have excluded one of these 90 samples from our analyses because it is unlike the rest and contained an extremely high pollen concentration value (sample 22, concentration 238 430). For the remaining 89 samples, the mean number of taxa per sample was 17.4

Pollen preservation in alkaline soils of the American Southwest

Table 4.2. Descriptive statistics for the 89 surface pollen samples

Number of taxa Pollen concentration Percent indeterminable

Mean

Standard deviation

Median

Minimum

Maximum

17.4 21311 6.6

3.04 13 854 3.23

18 17 374 6.2

11 2517 0.8

24 70625 15.9

West Texas Surface Pollen Samples Number of Taxa Per Sample 14

12 -

10 -

a. 8 ~

o 6 d 4 -

2 -

I 12

I 13

I 14

I 15

I 16

I 17

I 18

I 19

I 20

I 21

I 22

I 23

I 24

No. of Taxa Figure 4.5. Chart showing the number of pollen taxa in each of the 90 modern pollen samples.

(Fig. 4.5, Table 4.2). A difference of means test comparing the average number of taxa from the fossil and surface samples shows a significant difference between the two groups (t = 26.53, p< 0.0001). Pollen concentration values are significantly higher for the surface samples (t = 8.86, p < 0.0001), with mean values roughly three times those found among the fossil samples. Although the sample sizes are sufficiently large that the skewed distributions are not likely to affect the results of the difference of means test, a nonparametric difference of medians test (the Wilcoxon 2-sample test) was also used to compare the samples. Again the difference between the samples was significant (p< 0.0001). Even though the modern samples represented pollen that had been deposited fairly recently, some of the grains

already showed evidence of severe degradation. This is why the average percentage of indeterminable pollen is only slightly smaller for the surface samples. The difference is significant according to the Student's t test (£ = 2.03, p ;

I Forested areas I

Extensive marsh vegetation

GULF OF MEXICO 10

5 10

25 Miles

15 20

40 km

ALFRED TRAVERSE

bogs, swamps, marshes and strand. As a guide to approximate location and general proportions of the vegetation types, the map is useful for indication of possible relationship of vegetation types to pollen sedimentation. A very detailed map of the present situation has been published by White, et al. (1985). The forested areas indicated in the western half of the map represented gallery forests along the streams, typical of prairie country. The dominant species were Quercus nigra L. (water oak), Quercus phellos L. (willow oak), Ulmus crassifolia Nutt. (cedar elm), Carya illinoensis (Wangenheim) K. Koch (pecan), other Carya spp. (hickory), Taxodium distichum (L.) Richard (swamp cypress), and Fraxinus pennsylvanica Marsh (ash), and a variety of other, less important, species of trees. In the north-central part of the area (east of Houston), several tongues of East Texas forest occurred. These patches of forest included the species just named in the damper and less well-drained portions, plus woods on the sandier, better-drained portions, dominated by Pinus taeda L. (loblolly pine), Liquidambar styraciflua L. (sweet gum), and Quercus stellata Wangenheim (post oak). The prairies indicated were dominated by a variety of grasses, especially species of the genera Spartina and Andropogon. In moist places, thickets of trees and shrubs also were found. Acacia farnesiana (L.) Willd. (huisache) was especially abundant as a shrub or small tree in the dampest of such spots. Baccharis halimifolia L. (groundsel, a large shrub belonging to the Asteraceae = Compositae) and Myrica cerifera L. (wax myrtle) were also very common shrubs in the prairie. Next to the water, narrow rims of aquatic plants occurred that are not shown in Figure 6.3, except for the more extensive stands of marsh plants. Fringing the Trinity River delta, the marshes consisted of the giant grass (called 'reed'), Arundo donax L., various rushes (Juncus spp.), sedges such as Scirpus californicus (C.A. Meyer) Steudel and Scirpus validus Vahl, Typha spp. (cattails), and other water-loving plants. Along the edges of East and West Bays, extensive marshes of grasses, sedges, and rushes, occurred, and these were rimmed by prairies of the tufted coastal grass, Spartina spartinae (Trin.) Hitchco*ck. The marsh localities of the area were similar to, but much smaller than, some of those of coastal Louisiana described in the classic paper of Penfound and Hathaway (1938). True salt marshes were limited in extent in 1962 in this area. One large and typical salt marsh occurred on the western tip of Bolivar Peninsula, around the tidal ponds there. Others were found on the north side of Galveston Island and fringing West Bay. The bays have been described as surrounded by salt marshes (Reid, 1955), but, west of Trinity-Galveston Bay, water was too fresh and tidal flat area insufficient for true salt marshes to develop. Salt marshes depend on extensive tidal flooding,

because the characteristic plants are all salt-loving. At the latitude of the study area such vegetation consisted mostly of Salicornia perennis P. Mill, and other Salicornia spp. (the glassworts), Batis maritima L., Borrichia frutescens (L.) D C , and other halophytes. Certain areas around East and West Bays that have been described as 'marshes' were really damp prairies, dominated by Spartina spartinae and other grasses, not by Salicornia spp. (in salt marshes), or Typha spp., Juncus spp., Scirpus spp. (in freshwater marshes). Farther upstream in the drainage area, the Trinity River flowed through extensive prairies, oak savannas, and east Texas pine and hardwood forests, on its way to Trinity-Galveston Bay (Fig. 6.3B). Inasmuch as reworked spores and pollen from the whole river system (for example, Carboniferous spores from northwest of Ft. Worth) reach the mouth of the river (Traverse, 1992), it can be assumed that some modern pollen from the same area was also brought down by the river. But, as Chmura and Liu (1990) found for the Mississippi, it is doubtful that, say, Quercus pollen from far upstream, comprises a significant fraction of the oak pollen encountered in the lower river and bay.

Materials and methods Sample collections The surface sediment samples used in this study were collected during the years 1958-1962. Figure 6.4 shows the location and number for each sample. In each case uppermost surface sediment was sampled. Samples were taken from most parts of Galveston and Trinity Bays, and from West and East Bays, which are generally included under the comprehensive heading, Galveston Bay, but are really large lagoons protected by the barriers of Galveston Island and Bolivar Peninsula, respectively. Samples were also taken from many of the principal streams of the area, from backswamps (for example, sample 786), from ponds and lakes, and from tidal channels. Two groups of samples were taken in the adjacent portion of the Gulf of Mexico, to a depth of 14 m. The samples consisted of clays, sands, silts, shells, and organic matter, in varying proportions. Samples from streams, ponds, swamps, and other shallow, nearshore locations were collected by hand from a canoe or other small boat, or by wading into the water from shore. The sampling was accomplished by scooping up the sediment with a glass jar or, in deeper water, with a half-liter, weighted, scissor-levered, hand-operated grab sampler. The samples from deeper water were collected from a 9-m-long shrimp boat, using the grab sampler described above. All samples were stored in screw-top jars with polyethylene liners in the caps, using ethanol as a preservative.

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas

GULF OF MEXICO 15

20 Figure 6.4. Map of study area area showing location and numbers for samples studied. All samples were surface samples collected as described in text. For sediment-type descriptions, see Tables. The bracketed samples 820, 821, 822, were collected in Chocolate Bay, just off the map to the west.

25 Miles 40 km

ALFRED TRAVERSE

Sample maceration As nearly as was practical for samples of such diverse lithological composition, a standard maceration technique was employed: (1) 10% HC1; (2) 52% HF + con. HC1; (3) subsequent heating in 20% HC1 if silicofluoride complexes formed; (4) (for many peaty samples) oxidation in Schulze's solution (saturated solution of KC1O3 and enough H N O 3 to yield about 10% acid), followed by dehumification with 5% KOH; (5) (only for samples with excessive refractory mineral) a final float-sink treatment using bromoform-ethanol (s.g. 2.2) in a separatory funnel, followed by alcohol washes where the sample was very peaty; (6) staining with basic fuchsin solution and mounting in glycerin jelly.

Microfossil counting and concentration calculation The method later described in Traverse and Ginsburg (1966) for calculation of palynomorphs per gram of sediment (now called concentration; see Farley & Traverse, 1990) was already in use in my laboratory in Houston in 1958. The method, described in detail in Traverse (1988), depends, in principle, on counting all fossils on a slide. For some densely populated slides in this study half or one-quarter of the slide was prepared for counting, by ruling the coverslip with an India ink pen from one corner to the opposite corner to produce 'half-slides,' or, in a very few cases, connecting the other corners to produce 'quarter-slides.' The counts made for calculation of microfossils per gram also were used for percentages and ratios.

Baccharis cannot be readily distinguished in routine microscopy from pollen of many other composites.

'Reconstitution' of data obtained from the 1958-1962 studies In 1966, when I completed and sent to Shell in Houston a final report for this project, I made 35-mm Kodachrome photographs of the figures, and I retained a carbon copy of the typescript of the report, but not of the massive tables, which in pre-photocopying days were not practical to copy. When Shell several years ago released the information for publication, the original tables were apparently no longer in existence. However, the photographed figures included a map of the area with points for all samples, showing the numbers of the samples (Fig. 6.4). Another figure showed the sediment type (Tables 6.1-6.8; partially shown in Fig. 6.5A). Other figures displayed the concentration (and percentages or ratios in some cases) for total pollen and spores (Tables 6.1-6.8; Fig. 6.5B) and various individual microfossil types (Tables 6.1-6.8; Figs. 6.6-6.8). Another figure displayed my reconnaissance vegetation map (Fig. 6.3). Because enlargement prints failed to show all the numbers legibly, the original slides were studied at 32 x magnification with a dissecting microscope, using transmitted light. The numbers were easily legible under the microscope. The few numbers that were not legible using this technique account for most of the 'no data' (= +) entries in the tables. The others are instances where obvious errors were made in the original entering of the data. These numbers were eliminated from the tables.

Other calculations

Results

Ratios to pollen sum were also calculated. In the case of pollen of trees and shrubs included in the pollen sum, these are percentages, but for Taxodium, not included in the pollen sum, and for Gramineae, Compositae, Chenopodiaceae-Amaranthaceae ('cheno-ams'), and other non-arboreal forms, the calculations are ratios, not percentages. This is also true for non-pollen microfossils such as tracheary fragments and fungal spores. The pollen sum on which the ratios and percentages were based is the total of all wind-pollinated trees and shrubs, except for Taxodium and Baccharis. Taxodium was excluded from the pollen sum, because that was the practice of Shell palynologists with whom I worked. They excluded cypress pollen, because it is in some areas subject to local pollen floods, and thus, to over-representation. In fact (see Tables 6.1-6.8), this was not the case in the study area, where dense stands of Taxodium were relatively small and not widespread. Baccharis was excluded, because its family, Compositae (= Asteraceae), was mostly herbaceous in this area, and the echinate pollen of

Sediment type Tables 6.1-6.8 present the classification of the samples studied, as to sediment-type composition, from gross examination in the laboratory. The significance of these data can be best summarized by comparing the sediment types with total pollen and spores per gram of sediment (see Tables 6.1-6.8 and Fig. 6.5B). For example, the shelly sediment-type zones are for the most part impoverished in palynomorphs (see Fig. 6.5A). The most obvious explanation is the relative coarseness of the sediment, and the related fact that the areas were subject to tides and currents that swept fine sediment and microfossils away. However, for example in parts of Trinity Bay and southernmost Galveston Bay, there are shelly samples rich in pollen and spores, where, despite the shells, enough palynomorph-rich silt was present (see discussion in caption to Fig. 6.5A). It is clear that shells alone do not indicate palynomorph poverty of a sediment. This is only the case if the shells are part of a total silt-poor picture.

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas

Figure 6.5. (A) Location of samples consisting of sand and shells and of samples consisting of sand, shells and silt. Compare with Fig. 6.4 for sample location numbers, and with Tables 6.1-6.8 for sediment constituents. Comparison with Fig. 6.5B shows that sand and shell samples are barren, whereas sand-shell-silt samples may be palynologically rich. (A detailed surface sediment-type map of the Trinity-Galveston Bay area appears in White et ai, 1985.); (B) total pollen and spores per gram of sediment in all samples. Compare with Fig. 6.4 for sample location numbers and with Tables 6.1-6.8 for basic data.

WEST BAY AND THE SOUTHERN PART OF CENTRAL GALVESTON BAY, NEAR THE WESTERN TIP OF BOLIVAR PENINSULA (TABLE 6.2)

These areas were relatively low in palynomorph concentration. The most important factor was probably flushing resulting from tidal action and from storms. Sand and shells prevailed in the sediments, reflecting the same conditions. GULF OF MEXICO, OFFSHORE (TABLE 6.1)

Concentration of total pollen and spores per gram of sediment (Tables 6.1-6.8; Fig. 6.5B) The different environments and sediment types encountered in various parts of the study area should be emphasized. EAST BAY (TABLE 6.3)

This relatively quiescent, very shallow body of water, in 1962 was sedimenting (shoaling) rapidly. The sediment had a relatively high pollen concentration, reaching nearly 4 x 104/g. The sluggish bayous, marshes and small lakes near East Bay also had high concen-trations. Where rapid sedimentation of silt and clays was occurring, palynomorphs (fine silt-sized) were also accumulating. This agrees exactly with findings of Darrell (1973) for the Mississippi River delta area.

An area of high concentration existed in the Gulf of Mexico beyond the shelly zone swept by alongshore currents. This was especially marked offshore from the southwest end of Galveston Island (samples 69-72). Apparently this was a relatively low-energy environment, where silt sedimented out. That such silt sedimentation occurred in the Gulf in this manner, as a result of alongshore currents with local drops in energy level, was discussed by Price (1954). SMALL STREAM SYSTEMS AND SMALL LAKES (TABLES 6.3, 6.5)

Most of these areas, such as Clear Lake and its bayou, Lone Oak Bayou, as well as the bayous and lakes around East Bay already mentioned, had high concentrations in many samples, reflecting both silty deposition and large amounts of locally derived pollen.

ALFRED

TRAVERSE

SAN JACINTO RIVER, BUFFALO BAYOU, CEDAR BAYOU, AND THE LOWER TRINITY RIVER SYSTEM ITSELF (TABLES 6.7, 6.8)

Sediment from these areas yielded mixed results. Some samples were quite rich in palynomorphs, while others had moderate or low concentrations. This apparently reflects local sedimentation conditions and environment of deposition, with, for example, overbank samples yielding lower concentrations than channel fills (see Schuyler & Traverse, 1990, for Devonian riverine sediments). GENERAL OBSERVATIONS

Sediment type and environment of deposition were obviously the most limiting factors. For example, the low pollen samples from southern Galveston Bay consisted prevailingly of sand-shell sediment. Pollen supply is not a limiting factor. The studies I have previously published on palynomorphs in the water in this area (Traverse, 1990, 1992) demonstrate that abundant pollen was available in the water at all times of the year. Environment of deposition is of utmost importance, and it is not a simple matter. Schuyler and Traverse (1990), for example, showed for Devonian fluviatile sediments that coarse breccias can be rich in palynomorphs if they are channel breccias, not if they are breccias basal to a whole fluviatile unit. In the present study area, some peaty samples, for

Figure 6.6. (A) Distribution of tracheary fragments per gram of sediment; (B) leaf cuticle ( +epidermis) fragments per gram of sediment. Compare with Fig. 6.4 for sample location numbers and with Tables 6.1-6.8 for basic data.

example, those of Lone Oak Bayou, and other samples from near East Bay, were rich in pollen, whereas other peat-rich samples, for example, those from marshes at the tip of Bolivar Peninsula, and from the Trinity River delta, were low in pollen. This result does not surprise a paleopalynologist, who often encounters carbonaceous shales or even coals that are poor in palynomorphs. On the other hand, samples from many parts of the study area contain sediment poorly sorted enough that even a grossly shelly sample can contain enough fine silt-sized particles to be relatively pollen-rich.

Distribution of selected microfossil groups Tables 6.1-6.8 present the data for all the major types of palynomorphs, plus tracheary and cuticular palynodebris counted in this study. For some important forms, in terms of possible interest in connection with palynofacies studies, maps of the distributions are also presented (Figs. 6.6-6.8). Representatives of the forms discussed were illustrated photomicrographically in Traverse (1992).

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas

B Figure 6.7. (A) Fungal spores per gram of sediment; (B) Gramineae ( = Poaceae) pollen per gram of sediment. Compare with Fig. 6.4 for sample location numbers and with Tables 6.1-6.8 for basic data.

TRACHEARY FRAGMENTS (TABLES 6.1-6.8; FIG. 6.6A)

For the distribution of microscopic wood fragments, only particles larger than 15 /im with recognizable, lignified, cellular structure of wood or bark were counted. This was a very abundant microfossil type in the residues studied. As can been seen in Figure 6.6A, distribution was rather similar to that for total pollen and spores (Fig. 6.5B), except that areas of high concentration were geographically more limited. The area of high concentration in East Bay reflects the high rate of organic accumulation in the sediments from this area, while those of northern Galveston Bay and of Trinity Bay reflect the high rate of discharge of degraded vegetable matter from the streams of the area, especially the Trinity and San Jacinto Rivers. The very low concentrations in West Bay and western Bolivar Peninsula depended partly on low supply; the samples came mostly from marshy areas which did not produce much woody tissue, even though the sediment could be peaty. LEAF CUTICLES (TABLES 6.1-6.8; FIG. 6.6B)

Fragments of leaf epidermis with cutinized cell outline are usually called leaf cuticles.' It appears that the

explanation for the geographic distribution seen in Figure 6.6B is the same as that for wood fragments discharge of cuticular matter by the larger streams into Trinity and Galveston Bays, plus the relatively undisturbed accumulation of organic matter in the East Bay 'settling basin' area. One unusual feature of this distribution is the high number of samples with no cuticles at all. Leaf cuticle fragments are prevailingly much larger than pollen and spores; several hundreds of microns across and larger are common. Their sedimentation is probably sensitive to energy levels as well as to supply. The barren samples in the salt-marsh areas of western Bolivar Peninsula and West Bay were a direct result of no supply. Most salt-marsh plants apparently do not produce resistant cuticles. FUNGAL SPORES (TABLES 6.1-6.8; FIG. 6.7A)

Spores of a variety of fungi were encountered in these samples. Most of the forms (see illustrations in Traverse, 1992) are spores of saprophytic ascomycete fungi, and their supply in the area seems to have depended mostly on the supply of organic matter to the streams. The highest readings were in the Trinity River delta and adjacent northern Trinity Bay, plus a station in Chocolate Bay, just off the map to the west. However, there were sizable concentrations also in the samples from the southwest end of Galveston Island. Such high readings

ALFRED TRAVERSE

can only be explained by the sedimentary factors discussed earlier. These factors resulted in high concentrations in these samples for most microfossil categories. In general, this distribution is in accord with Muller's (1959) observation in the Orinoco River area that fungal spores are prevailingly a terrestrial phenomenon, with very sharp drop-offs in concentration offshore. PINUS POLLEN (TABLES 6.1-6.8)

At the time of this research, pine was of special interest because of the attention devoted to its behavior in water in my Shell report later published in part as Traverse and Ginsburg (1966). Pine pollen is very buoyant and is widely dispersed by both wind and water. It was ubiquitous in all samples that contained any pollen. For this reason, concentration of pine pollen tended to reflect that of total pollen. Only in a few environments in which other forms were dominant, such as the upper part of the Clear Lake complex (where Quercus, Ulmaceae and Compositae dominated), did pine pollen retreat from its dominant role. Of all pollen types, pine pollen was, therefore, least likely to indicate a local palynofacies. It occurred in all environments and comprised a large percentage of total pollen, even in most relatively barren samples. This is evident when stations in sandy offshore and marsh regions of the West Bay area and western Bolivar Peninsula are compared. QUERCUS POLLEN (TABLES 6.1-6.8)

Oak pollen distribution was similar to that of pine, although net as abundant, and therefore, a number of samples that were poor in pine pollen were barren of oak. Oak pollen had more of a tendency to predominate along streams than was true of pine pollen. In other words, oak pollen percentages showed some connection to environment and therefore to biofacies, whereas pine in this area showed little or none. COMPOSITAE (=ASTERACEAE) (THISTLE AND RAGWEED FAMILY) (TABLES 6.1-6.8)

Pollen of this family comprised a large proportion of all pollen in the samples, and its distribution per gram of sediment was very similar to that displayed in Figure 6.5B for total pollen and spores. Low-pollen sediments such as some of those off Galveston Island, showed a high percentage of composite pollen. That is, of the small concentration of pollen present, a high proportion was composite pollen (see Table 6.1). GRAMINEAE (=POACEAE) (GRASS FAMILY) (TABLES 6.1-6.8; FIG. 6.7B)

Grass pollen plotted per gram (Fig. 6.7B) shows its distribution in the samples well. Large concentrations of grass pollen were found in the same areas as for total

pollen, but the areas of greatest concentration were more restricted than for pine, oak, or composites. The frequency of samples with no or very little grass pollen in West Bay and upper Trinity Bay was probably some sort of response to sedimentary environment, as plants of the grass family were abundant at both locations. It is additionally significant in this connection that samples with no grass pollen were found immediately next to those with the highest readings, 10000 or more per gram, off the Trinity River delta. The samples with high grass concentrations also contained whole grass anthers. This demonstrated the general possibility of over-representation of grass pollen in some samples obtained from the neighborhood of deltas. This is the sort of distribution that Farley and Traverse (1990) found to be potentially useful in interpreting ancient depositional environments. Pine and oak pollen, on the other hand, are so ubiquitous as not to be helpful in determining environments except, along with all palynomorphs, in terms of total concentration. CHENOPODIACEAE-AMARANTHACEAE ('CHENO-AMS') (TABLES 6.1-6.8; FIG. 6.8A)

The periporate pollen of various representatives of these two related families are hard to separate in routine palynological analysis, and it is therefore customary to lump them as 'cheno-ams.' However, my field work in the area studied convinced me that most of the plants producing this pollen were either salt-marsh plants (Salicornia spp.) or weedy herbs such as Chenopodium spp. The distribution is most effectively displayed as the ratio to pollen sum (Fig. 6.8A). Production by Salicornia undoubtedly accounted for relatively abundant pollen of this type found in samples from the salty marshes of western Bolivar Peninsula. Elsewhere, relatively abundant chenopod pollen was probably the result of the very durable, thick pollen exines which the family produces. Because of this characteristic, it is a prime candidate for recycling. TYPHA (CATTAIL) POLLEN (TABLES 6.1-6.8)

Plants of this genus were common to abundant in moist places all over the study area, even in roadside ditches. The pollen is a monoporate-reticulate form found in obligate tetrads, monads, or dyads. Despite ubiquitous occurrence of the plants, cattail pollen was relatively abundant only in the 'settling basin' of East Bay and at just a few other stations in the deltaic systems of the Trinity and San Jacinto Rivers. Many stations in marshy places were absolutely barren of Typha pollen. It would appear that Typha pollen, when found as a fossil in older sediments, could be expected to be biofacies-related. I have noticed in my studies of sediments from a few hundred to a few thousand years old in cores from the coastal plain of the eastern USA, that Typha pollen may

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas

B Figure 6.8. (A) Chenopodiaceae + Amaranthaceae (cheno-ams) pollen as '%' = ratio to pollen sum; (B) Concentricystes (syn. Pseudoschizaea) sp. per gram of sediment. Arrows indicate the three regions of major occurrence. Compare with Fig. 6.4 for sample location numbers and with Tables 6.1-6.8 for basic data.

be very abundant in one sample and altogether absent in samples a few centimeters below or above. One would expect therefore that Typha pollen is an example of the sort of form that could be very useful for environmental interpretation. PSEUDOSCHIZAEA (SYN. CONCENTRICYSTES) ALGAL

at the time of this study I concluded that the form could well be a zygospore of the freshwater, green algal group, Zygnemataceae. A slide of the material was sent at that time to G. W. Prescott of Michigan State University, an authority on the group. He responded, in part, that it was '...certainly similar to a zygnemataceous zygospore, and that would be the best and about the only "guess" that I could make...' The distribution shown was very different from that of pollen in general, and corresponded to an ecological pattern that might be expected of a green algal form that grew at the edge of streams and in ponds. Cedar Bayou and Clear Lake Bayou were the two principal centers of distribution (see Fig. 6.8B and Tables 6.5, 6.8). Pseudoschizaea (syn. Concentricystes) is clearly a palynofacies indicator.

ZYGOSPORES (TABLES 6.1-6.8; FIG. 6.8B)

At the time I began this investigation I did not know the identity of this microfossil form, which was moderately abundant in certain samples. Since then, it has become rather well known, and it is discussed and illustrated by Rich and Pirkle (Chap. 15, this book). It is a more or less spherical body about 40 fim in diameter with a pattern of ridges and grooves reminiscent of a fingerprint. Chemically, the wall substance of this fossil type must resemble sporopollenin, since it responds to maceration in the same way and stains with basic fuchsin as do pollen grains. From study of many illustrations in the literature

OTHER FORMS FOR WHICH DATA ARE PRESENTED IN TABLES 6.1-6.8

Carya (hickory and pecan) The triporate pollen of wind-pollinated trees belonging to this genus was distributed very much like that of pine. It was ubiquitous in the sediments of the area. However, Carya pollen was absent or rare in certain groups of samples, for example, those from salt-marsh areas far from source stands of hickory, and from some sandy or shelly samples.

ALFRED TRAVERSE

Ulmaceae Elm pollen was present in most samples and was moderately abundant in some of them, especially in areas where abundant cedar elm stands were seen.

Liquidambar The very characteristic periporate pollen of sweet gum trees had a distribution in the sediment reflecting local abundance of these trees in the Trinity River - San Jacinto River - Buffalo Bayou drainage. Relatively abundant Liquidambar pollen in other places reflected the sedimentary environment. For example, the factors that encouraged pollen deposition in East Bay and discouraged it in West Bay led to relatively high Liquidambar pollen concentrations. Liquidambar trees are partly windpollinated, partly insect-pollinated. They produce large quantities of pollen, but not as much as pine or oak trees. Very low concentrations in Galveston and Trinity Bays, and in onshore samples from the area of pine-sweet gum forests (northern half of the study area) were a result of sediment type: Liquidambar pollen does not occur abundantly in sandy sediments.

Taxodium (swamp cypress) This is a tree of swamps and river bottoms. The pollen was locally concentrated in sediment associated with several of the stream courses, as well as in the 'settling basin' of East Bay, and in the offshore samples that were pollen-rich. There were many samples with absolutely no Taxodium pollen, even at stations with high general pollen abundance, for example, along Lone Oak Bayou on the east side of Trinity Bay. This tends to substantiate the idea previously mentioned that Taxodium is faciesinfluenced. The offshore concentrations showed, however, that this is not a simple relationship to the proximity of Taxodium swamps, or to rivers with swamp cypresses in the gallery forests.

Cyperaceae (sedges) The producing plants were abundant in the wetter parts of the entire area. The large amount of sedge pollen in the Trinity River delta, corresponding parts of the San Jacinto River-Buffalo Bayou drainage and in the East Bay area was a reflection of this abundance. Sedges are not major constituents of salt marshes but are subdominant in freshwater marshes. The extreme paucity of sedge pollen in upper Galveston-Trinity Bay must be related to sedimentary environment; many samples were absolutely void. I have noticed in my studies of modern sediments of coastal plains in the eastern USA that sedge pollen is very erratic in occurrence.

Summary and conclusions The distribution of pollen and spores in the surface sediment of Trinity and Galveston Bays and adjacent areas sampled in 1958-1962 was primarily a question of sedimentary factors that govern all clastic particles. Plant ecology played only a secondary role in the picture as a whole. However, some local effects related directly to autecology of the producing organisms were apparent. The probable algal zygospore, Pseudoschizaea (syn. Concentricystes), was found primarily in the vicinity of streams where the producing organisms grew. Abundant Typha pollen was mostly found fairly near cattail-rich areas. These 'biofacies' were, however, somewhat exceptional. The concentration of pollen and spores in the sediments studied was primarily explicable in terms of water movement and sedimentation patterns, not of wind patterns. Wind-driven water is a very significant factor in the area, however, as an agent of geological work. In that sense, wind phenomena are indirectly important to pollen sedimentation. Wind distribution is of course responsible for wide dispersal of pollen in very small quantities, as many studies have shown. Rowley and Walch (1972) showed that, at least in an exceptional case, pollen can even become airborne from the water medium as aerosol particles, and Valencia (1967) demonstrated the same thing experimentally. It should be noted that at least in the Atlantic Ocean off West Africa, Dupont et al. (1989) and Hooghiemstra (1988), among others, have indicated that wind delivery is the main source of pollen in surface sediment. Hooghiemstra found that the distribution of patterns of the pollen reflect the average atmospheric circulation, and Dupont et al state that the northeast trade winds and African easterly jet govern pollen supply and deposition. No evidence was seen for sedimentary sorting of pollen of various taxa. That does not mean, however, that this could not occur in some situations. In the laboratory, it is possible to concentrate different sizes of palynomorphs from each other and from debris by 'swirling' in watch glasses, using small-scale turbulence to sort the forms (see discussion in Traverse, 1988). Catto (1985) reports that such sorting occurs in silts and sands of a braided stream in northern Canada. He found that tree pollen concentrates in the silts and herbaceous pollen and spores in the sands. Holmes (1990) showed in laboratory experiments that some sorting based on size occurred as pollen moved through the flume he used. East Bay was nearly shut off from Galveston Bayproper at the time of this study by an oyster reef (Hanna Reef) and was filling rapidly with sediment. Because of this, it was also a 'settling basin' for the collection of pollen and other palynomorphs and palynodebris, in a

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas manner similar to that of lee areas in Great Bahama Bank (Traverse & Ginsburg, 1966). West Bay and lowermost Galveston Bay in the Galveston-Bolivar Peninsula area were flushed by tidal action and by high-energy wind storms, especially the winter 'northers.' For that reason, those areas were apparently not accumulating fine silty sediment in the palynomorph size range. Therefore, the surface sediment in those areas, on the whole, was poor in palynomorphs, because they were flushed out, along with other fine silt. Some samples studied from offshore, in the Gulf of Mexico, were rich in palynomorphs and other fine sediment. Other, nearby, samples consisted of coarse, shelly sediment containing few palynomorphs. The boundary between pollen-poor and pollen-rich was quite sharp. This is in accord with sedimentation studies of alongshore currents and deposition in the area. The pollen-poor coarse sediments were from the nearshore area swept by currents. This result is interesting as one exception to the usually cited regular decline of palynomorph concentration with distance from shore. Sediment from the bays-proper and from onshore locations such as rivers, backswamps and ponds were pollen-rich or pollen-poor, depending on the sedimentary environment. Silts from a bayou were usually pollen-rich, whereas sandy samples from the same bayou were usually pollen-poor. Sand-shell samples from all of the bays were pollen-poor, whereas silt-clay samples from nearby were often pollen-rich. Certain pollen types were ubiquitous, for example, Pinus and Quercus (and Carya, to a lesser extent). That is, they were abundant in all sorts of sediment, with a few exceptions. Other types, for example, Chenopodiaceae, Typha, and Taxodium were much more abundant in certain locations than in others, a response partly to presence of source vegetation, partly to sedimentary environment. Another example of a 'fades' indicator was the probable zygnemetaceous (green algal) zygospore form, Pseudoschizaea (syn. Concentricystes), which was principally found in sediment from bayous and rivers. In conclusion, one must compare the rather substantial seasonal fluctuations in the palynomorph load of the Trinity River and Trinity Bay I have previously reported (Traverse, 1990, 1992) with these results for the palynomorph content of the sediment produced over the whole area. Clearly the surface sediment reflected the vegetation of the area, but in a very generalized way. At the scale of the study presented, there is obviously evidence for sorting of pollen as a whole, with pollen-rich and pollen-poor environments; that is, palynolithofacies are clearly indicated. Sorting of palynomorphs, either by size characteristics for specific taxa, or according to the taxonomic groups encountered (palynobiofacies) was very limited in extent.

Acknowledgments I am grateful to Shell Development Company for permitting the publication of the major segments of research I did as a Shell palynologist, 1955-1962. At the time of the original research so many Shell employees were helpful in so many ways, that it would be difficult to pick out individuals to acknowledge. I must be content to thank them all jointly. I also acknowledge the help of Elizabeth I. Traverse with the preparation of this manuscript. Friedemann Schaarschmidt and members of his staff at the Research Institute of the Senckenberg Museum, Frankfurt am Main, Germany, were helpful with computer, drafting and in other ways at the end of the project. Martin B. Farley and Roy J. Greenfield also assisted me with advice and information necessary for the completion of the manuscript.

References Barbour, M. G. & Billings, W. D , eds. (1988). North American Terrestrial Vegetation. Cambridge: Cambridge University Press. Bernard, H. A., Major, C. F., Jr. & Parrott, B. S. (1959). The Galveston Barrier island and environs: a model for predicting reservoir occurrence and trend. Gulf Coast Association of Geological Societies Transactions, 9, 221-4. Catto, N. R. (1985). Hydrodynamic distribution of palynomorphs in a fluvial succession, Yukon. Canadian Journal of Earth Science, 22, 1552-6. Chmura, G. L. & Liu, K. B. (1990). Pollen in the lower Mississippi River. Review of Palaeobotany and Palynology, 64, 253-61. Darrell, J. H. II (1973). Statistical evaluation of palynomorph distribution in the sedimentary environments of the modern Mississippi River delta. Ph.D. diss. Louisiana State University, Baton Rouge. Dupont, L. M, Beug, H.-J., Stalling, H. & Tiedemann, R. (1989). 6. First palynological results from site 658 at 21° N off northwest Africa: pollen as climate indicators. Proceedings of the Ocean Drilling Program, Scientific Results, 108, 93-111. Farley, M. B. & Traverse, A. (1990). Usefulness of palynomorph concentrations in distinguishing Paleogene depositional environments in Wyoming (U.S.A.). Review of Palaeobotany and Palynology, 64, 325-9. Holmes, P. L. (1990). Differential transport of spores and pollen: a laboratory study. Review of Palaeobotany and Palynology, 64, 289-96. Hooghiemstra, H. (1988). Palynological records from northwest African marine sediments: a general outline of the interpretation of the pollen signal. Philosophical Transactions of the Royal Society of London, B 318,431—49. Lankford, R. R. & Rogers, J. J. W., compilers (1969). Holocene Geology of the Galveston Bay Area. Houston, TX: Houston Geological Society. LeBlanc, R. J. & Hodgson, W. D. (1959). Origin and development of the Texas shoreline. Gulf Coast Association of Geological Societies Proceedings, 9, 197-220. Lohse, E. A. (1955). Dynamic geology of the modern coastal region, northwest Gulf of Mexico. In Finding Ancient Shorelines, Society of Economic Paleontologists and Mineralogists Special Publication 3, 99-104.

ALFRED TRAVERSE

Matty, J. M., Anderson, J. B. & Dunbar, R. B. (1987). Suspended sediment transport, sedimentation, and resuspension in Lake Houston, Texas: implications for water quality. Environmental Geology and Water Sciences, 10 (3), 175-86. Mazzullo, J. (1986). Sources and provinces of late Quaternary sand on the East Texas-Louisiana continental shelf. Geological Society of America Bulletin, 97, 638-47. McEwan, M. C. (1963). Sedimentary facies of the Trinity River delta, Texas. Ph.D. diss., Rice University, Houston, TX. Muller, J. (1959). Palynology of Recent Orinoco delta and shelf sediments. Micropaleontology, 5, 1-32. Nixon, E. S. & Willett, R. L. (1974). Vegetative analysis of the floodplain of the Trinity River, Texas. Report for US Army Corps of Engineers, Ft. Worth District, Texas, Contract DACW63-74-C-0030. Penfound, W. T. & Hathaway, E. S. (1938). Plant communities in the marshlands of southeastern Louisiana. Ecological Monographs, 8 (1), 1-56. Prescott, G. W. (1966). Personal communication. Price, W. A. (1954). Shorelines and coasts of the Gulf of Mexico. In Gulf of Mexico: Its Origin, Waters and Marine Life, coordinater P. S. Galtstoff. US Department of the Interior: Fish and Wildlife Service Bulletin 89, 39-62. Reid, G. K., Jr. (1955). A summer study of the biology and ecology of East Bay, Texas, Part I. Texas Journal of Science, 1 (3), 316-43. Rich, F. J. & Pirkle, F. L. (this volume). Rowley, J. R. & Walch, K. M. (1972). Recovery of introduced pollen from a mountain glacier stream. Grana, 12, 146-52. Schuyler, A. & Traverse, A. (1990). Sedimentology of miospores in the Middle to Upper Devonian Oneonta

Formation, Catskill magnafacies, New York. Review of Palaeobotany and Palynology, 64, 305-13. Shepard, F. P. (1953). Sedimentation rates in Texas estuaries and lagoons. Bulletin of the American Association of Petroleum Geologists, 37 (8), 1919-34. Shepard, F. P. & Moore, D. G. (1960). Bays of central Texas coast. In Recent Sediments, Northwest Gulf of Mexico, ed. F. P. Shepard, F. B. Phleger & T. H. Van Andel. Tulsa, OK: American Association of Petroleum Geologists, 117-52. Traverse, A. (1988). Paleopalynology. London: Unwin Hyman. Traverse, A. (1990). Studies of pollen and spores in rivers and other bodies of water, in terms of source-vegetation and sedimentation, with special reference to Trinity River and Bay, Texas. Review of Palaeobotany and Palynology, 64, 297-303. Traverse, A. (1992). Organic fluvial sediment: palynomorphs and 'palynodebris' in the lower Trinity River, Texas. Annals of the Missouri Botanical Garden, 79, 110-25. Traverse, A. & Ginsburg, R. N. (1966). Palynology of the surface sediments of Great Bahama Bank, as related to water movement and sedimentation. Marine Geology, 4, 417-59. Valencia, M. J. (1967). Recycling of pollen from an air-water interface. American Journal of Science, 265, 843-7. Wantland, K. F. (1964). Recent foraminifers of Trinity Bay, Texas. M.A. thesis, Rice University, Houston, TX. White, W. A., Calnan, T. R., Morton, R. A., Kimble, R. S., Littleton, T. G., McGowen, J. H , Nance, H. S. & Schmedes, K. E. (1985). Submerged Lands of Texas, Galveston-Houston Area: Sediments, Geochemistry, Benthic Macroinvertebrates, and Associated Wetlands. Austin, TX: Bureau of Economic Geology Special Contribution.

Sedimentation of land-derived palynomorphs in the Trinity-Galveston Bay area, Texas

Tables 6.1-6.8 Basic palynological data for the sample locations displayed in Fig. 6.4. Table 6.1. Gulf of Mexico. Tables 6.2-6.4. Galveston Bay Area: Table 6.2. West Bay and associated land areas; Table 6.3. East Bay and associated land areas; Table 6.4. Central and Northern Bay. Table 6.5. Clear Lake complex. Table 6.6. Trinity Bay. Table 6.7. Lower Trinity River complex and delta. Table 6.8. Buffalo Bayou-San Jacinto River-Cedar Bayou complex. 'Sediment type' was based on gross examination in the laboratory; types are listed in order of apparent

abundance. All samples are surface samples. See text for details of sample collection. 'Spores & pollen/g' means total spores and pollen per gram of sediment, calculated from air-dried samples per method described by Traverse and Ginsburg (1966). All other 'per gram' data in the tables were calculated in the same way. '%' refers to percentage of the pollen sum (= all tree and shrub pollen except Taxodium and Baccharis). In the case of cheno-ams, Compositae, Cyperaceae, Gramineae, and Typha, these numbers are actually ratios to the pollen sum, as these taxa are not a part of it. * = sample barren; + = no data.

Table 6.1. Gulf of Mexico Sample #

Sediment type

sand shell

clay silt

sand shell

spores & pollen/g

11812

11196

20940

12456

389

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 1 0 4

0 7 1 1

* * * *

0 3 973 30 1135

0 2093 239 673

0 3 865 819 2 501

0 1987 151 1383

0 5 1 41

0 46 0 92

* * *

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

0 0 0 2 0 0 0 0 0 0 0 0 0 0 0

0 0 0 9 660! 4 0 0 1 100 0 0 0 0 0

* * * * * * * * *

134 1496 40 1290 35 175 402 31 2167 58 1073 29 196 61 186

55 1128 35 819 25 218 546 55 1656 51 1056 32 546 291 109

407 2298 20 2 665 24 610 1668 264 7119 63 2 278 20 936 540 447

114 757 15 1324 22 246 662 170 3150 64 1116 23 170 284 132

0 0 0 5 11 0 0 0 5 44 7 56 0 0 0

8 8 6 97 25 0 15 0 76 56 23 17 0 0 15

* * * * * * * *

* * * * *

* * *

* * * * * * * * *

* * * * *

Table 6.1. Continued Sample #

Sediment type

sand, shell silt, shell silt sand

silt sand

silt, sand shell

silt shell

sand shell

spores & pollen/g

4441

8 384

4486

6718

5 632

2 699

4311

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 46 5 59

0 3 1 1

0 17 6 79

8 203 61 384

0 219 0 416

15 107 56 214

25 308 234 824

0 88 59 343

0 31 4 156

0 35 25 219

* * * *

* * *

0 0 0 0 0 0 0

1 3 100 1 50 1 1

0 0 5 100 0 0 0

0 0 0 0 0 0 0

31 391 25 407 26 23 222 31 1081 68 337 21 115 84 46

66 810 34 744 31 129 350 66 131 7 853 35 219 88 44

0 214 19 534 47 122 366 46 549 48 351 31 31 31 96

74 431 16 1119 43 74 199 0 1648 64 579 22 62 62 86

98 480 23 392 19 59 372 39 1410 69 303 15 225 49 20

31 168 33 172 34 351 281 3 289 56 164 32 133 20 23

66 394 41 258 27 53 259 9 591 62 184 19 114 48 22

* * * * * * * * * * * * * * *

* * * *

0 6 95 7 105! 1 0 1 4 65 1 10 1 0 0

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

* * * * * * * * * *

Table 6.2. Galveston Bay area: West Bay and associated land areas Sample #

808

809

810

Sediment type

silt sand shell

silt shell sand

silt sand shell

silt shell sand

silt clay sand

spores & pollen/g

3 287

2 374

809

1675

1369

2120

2163

7 542

2199

1416

0 4 0 1

0 58 40 272

0 45 18 144

0 3 6 32

0 47 23 41

0 65 0 39

0 101 11 202

0 103 39 77

0 3 342 257 2914

4 237 39 406

0 139 35 307

0 0 0 3 13 1 3 0 13 70 5 27 0 1 0

58 156 11 369 27 46 13 6 1067 72 167 12 17 150 35

45 153 16 198 21 36 36 0 640 67 144 25 45 72 9

12 30 6 27 5 6 0 8 438 87 32 7 3 9 6

6 152 38 175 40 47 82 6 315 72 47 11 35 12 47

9 142 34 211 51 26 60 13 237 57 112 27 17 21 30

45 135 12 291 27 0 95 22 717 65 258 23 34 0 11

26 245 23 322 31 26 180 13 373 25 173 11 26 26 26

171 643 19 1207 34 43 300 86 1971 60 857 26 43 86 129

19 177 17 63 18 4 30 15 639 61 267 26 8 45 19

28 118 12 49 5 0 14 0 781 76 101 20 7 7 7

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

Table 6.2. Continued Sample #

814

815

820

821

822

823

824

825

826

827

828

Sediment type

silt clay sand peat

silt clay sand

silt clay

silt clay sand

clay sand silt

spores & pollen/g

354

938

503

1209

2 356

1861

545

5 890

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 5 0 0

0 97 11 210

0 1132 78 1757

278

0 439 32 331

0 98 0 392

0 146 16 421

0 511 0 255

3 24 0 15

0 3 337 36 8 485

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

0 0 0 0 0 0 5 0 0 0 0 0 0 0 0

0 22 12 44 24 0 0 0 177 91 0 0 0 0 0

78 78 40

0 0 0

16 142 64 63 36 0 16 0 142 64 47 27 0 16 0

33 98 21 65 14 0 33 0 359 79 0 0 0 0 0

65 250 27 97 14 16 97 0 236 35 275 41 16 32 32

0 547 118! 146 31 0 36 0 319 69 128 27 0 18 0

6 250 100 31 23 18 31 0 104 77 6 5 0 0 0

36 1030 65 1207 76 0 249 36 1402 89 107 7 0 533 0

+ 120! 0 0 0 195 100 0 0 0 0 0

368

25489

+ +

359 359 36

+ +

0 9 0 9 51

+ + 0 0 0

0 359 180

+ + + + 0 0 0

Table 6.3. Galveston Bay area: East Bay and associated land areas

Sample #

788

789

790

829

830

831

832

833

834

Sediment type

clay peat silt

silt peat clay

silt clay

silt sand clay peat

silt sand clay shell

silt peat sand clay

silt clay sand

clay silt peat

spores & pollen/g

24 780

23 380

23 878

1469

795

1541

1869

18981

23 047

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 1602 400 53 383

0 819 46 20967

0 9196 236 8 073

0 313 0 157

0 210 0 0

0 305 0 122

0 426 0 125

0 1086 384 10624

0 603 844 23 037

234 2402 34 1832 47 2069 2 602 133 6086 87 400 6 0 1335

46 289 6 3 270 41 675 1203 0 3 598 76 241 5 0 1301

78 4 598 53 7192 84 590 2 594 354 6013 70 2004 23 0 2 594

0 2 724 116! 39 12 0 78 0 276 53 117 35 0 0 0

0 180 72 30 12 0 30 0 253 100 0 0 0 0 0

0 429 122! 294 70 0 92 31 259 74 61 17 0 0 0

0 601 123! 251 51 0 75 0 388 79 75 15 0 0 0

128 1984 34 3 072 53 832 2496 192 3 360 58 1800 28 448 384 64

241 2 893 39 3 737 50 844 2 893 0 3 737 50 3 014 41 362 844 121

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

Table 6.3. Continued

Sample #

835

836

837

838

839

840

841

842

Sediment type

sand silt peat clay

silt clay sand

silt shell sand clay

silt clay shell sand

silt clay

silt sand

silt clay

spores & pollen/g

23 489

38188

20286

35 285

36 394

21390

7407

9401

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 377 283 10 334

64 512 64 6 340

0 28 59 2221

0 1293 366 4 324

0 4280 486 7101

0 126 24 421

0 318 53 1051

0 275 153 2 879

47 2 358 29 3 254 37 424 2095 236 2 672 55 1745 35 47 283 236

320 2818 18 3 586 30 512 2 626 192 11559 74 2818 18 768 768 512

171 1680 22 2620 33 114 1082 142 2286 83 365 13 28 456 228

73 2 785 46 2272 54 733 55 147 2 623 40 2418 40 1539 1026 73

389 2 724 30 4 864 54 778 5 837 389 4119 50 2 821 32 1556 389 97

126 1095 19 1852 33 84 942 126 2942 52 2064 36 337 169 42

0 478 19 584 22 159 590 189 2203 61 1062 29 0 372 53

122 794 16 855 17 92 763 82 3 662 73 1007 20 31 92 0

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

Table 6.4. Galveston Bay area: Central and Northern Bay Sample #

Sediment type

sand silt

silt clay

silt sand

silt shell

spores & pollen/g

2901

656

4 540

6134

9 370

5 707

867

2024

24158

692

2981

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 1024 0 1517

0 255 0 158

0 2059 0 281

0 2020 144 7 359

0 4062 131 2 359

0 1569 236 896

0 166 8 133

42 809 28 454

43 2 388 0 1023

0 160 23 206

0 609 31 836

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

0 38 14 190 10 38 38 38 1043 66 493 31 0 0 0

12 49 16 36 29 0 0 0 206 59 134 38 0 12 0

0 187 9 562 27 0 281 94 983 47 842 40 94 0 0

0 144 3 433 10 0 433 0 3102 73 846 20 0 0 144

0 393 14 1572 56 0 917 262 1638 58 393 14 0 0 262

47 330 13 802 30 94 330 47 1603 61 707 27 0 47 141

1 25 6 166 41 0 67 17 191 47 158 39 8 0 33

0 128 16 383 49 0 57 28 348 44 270 34 0 0 128

85 213 11 831 44 43 128 43 1151 61 490 26 43 21 43

0 100 12 80 27 23 34 11 154 53 92 31 0 0 23

52 237 25 382 40 0 93 31 547 58 258 27 10 10 21

Table 6.4. Continued

Sample #

Sediment type

silt shell

clay silt shell

silt shell

silt sand shell

silt

silt sand

spores & pollen/g

3159

3 392

854

10191

4 747

1698

4 336

6660

9 776

6 323

4105

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 134 153 940

26 993 128 633

0 168 17 93

0 984 81 539

0 1078 0 604

0 183 20 163

13 664 39 156

19 389 622 1535

47 94 1509 3 672

42 106 659 1081

12 98 624 982

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

34 182 17 465 43 21 75 16 706 66 192 18 16 5 37

60 205 13 318 20 60 120 17 1014 65 342 22 34 1 26

6 52 23 104 45 6 58 0 97 43 97 43 12 12 0

46 297 9 620 19 54 195 27 2716 83 317 10 88 40 61

43 259 15 733 44 43 235 43 1078 64 259 15 43 0 129

61 122 16 386 49 20 81 41 356 45 264 34 0 0 41

65 273 15 1167 60 13 299 52 1107 60 391 21 26 26 184

175 292 12 1788 68 19 428 78 1623 62 505 19 16 39 136

188 165 3 1106 17 0 400 118 5 485 84 636 10 0 0 94

127 403 12 454 29 21 339 127 3 078 62 1191 24 0 0 85

98 123 5 614 25 12 147 123 1265 52 823 34 0 0 86

Table 6.4. Continued Sample #

Sediment type

silt sand

silt

silt sand

silt shell sand

silt sand

silt shell sand

spores & pollen/g

838

10803

2612

2131

4386

9 376

12449

18 343

11658

8 604

3 885

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 27 9 128

0 1071 195 1849

0 506 0 111

0 468 16 145

0 614 75 509

0 1504 193 1918

0 1465 609 1961

0 2044 430 1184

0 322 161 724

0 823 57 670

0 223 56 989

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

0 46 11 210 53 9 46 18 178 45 137 34 0 0 18

195 681 19 1752 50 97 584 97 1752 50 823 33 0 97 195

56 222 22 111 11 0 0 0 444 44 444 44 0 56 56

32 194 33 387 67 16 81 32 178 31 210 36 16 0 48

45 360 16 404 18 30 210 15 1461 61 584 26 30 60 30

58 733 20 1330 37 154 521 19 2148 61 945 26 77 135 154

96 879 15 721 12 316 1059 90 3 832 66 1285 22 270 541 180

161 861 12 2 529 36 377 753 108 4492 64 1722 25 215 430 108

432 10 2251 45 322 482 241 3 658 73 724 14 241 80 80

77 670 24 1430 52 77 191 38 1713 62 574 21 230 115 134

57 306 18 434 25 40 129 88 1013 58 418 24 40 88 48

Table 6.4. Continued Sample #

806

807

Sediment type

silt shell sand

silt sand shell

sand silt

shell

silt sand shell

clay silt sand

spores & pollen/g

2191

6220

6 384

5 486

1896

3 819

4935

1508

5 489

2192

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 189 89 246

* * * *

0 1219 182 1057

0 1096 0 575

0 1518 51 810

0 566 0 149

19 662 50 666

11 642 146 434

0 57 0 325

83 330 1073 1156

44 385 105 561

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

89 233 26 179 21 45 112 0 290 33 402 46 0 124 22

* * * * * * * * * * * * * * *

52 598 23 468 18 78 236 52 1373 72 320 17 52 104 78

82 595 14 740 25 55 329 55 2219 74 520 17 110 164 0

34 354 12 1046 42 152 102 51 1619 66 557 23 17 101 67

37 112 19 321 35 22 67 45 520 58 224 25 7 7 30

85 297 17 425 25 89 112 50 1078 63 389 23 58 15 39

84 405 17 647 28 68 118 45 1430 63 602 26 56 45 90

0 38 7 229 40 38 141 19 257 60 229 40 57 19 0

41 206 8 908 36 124 413 41 1321 52 825 32 0 41 83

35 35 3 333 28 35 349 18 858 93 143 16 0 9 35

* * * * * * * * * * * * *

Table 6.5. Clear Lake complex Sample #

802

803

804

805

Sediment type

silt clay sand peat

silt clay sand

clay sand silt

spores & pollen/g

9 697

5 201

7 863

11610

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

128 2254 1063 723

79 1408 98 860

150 1090 101 989

217 1058 248 1610

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

43 0 0 1361 28 43 340 0 866 16 1999 42 0 43 1148

860 39 2 899 39 39 274 0 587 25 1290 56 235 0 156

178 101 3 1902 55 76 203 25 1578 46 1394 39 76 25 279

93 743 25 3 065 73 62 559 62 2074 50 1486 36 0 0 248

Table 6.6. Trinity Bay Sample #

Sediment type

silt clay

silt shell

silt peat

silt shell

spores & pollen/g

6 279

1527

656

6 236

164

462

4418

19701

13 371

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 3 540 84 1686

0 467 0 615

0 341 0 478

0 7 904 88 4215

0 54 0 52

0 378 0 84

0 431 0 1027

0 869 0 1998

0 1110 0 3 228

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

84 421 10 759 7 84 253 169 1138 43 1011 38 84 0 253

37 74 10 49 7 0 0 0 474 64 160 22 0 12 37

51 0 0 34 9 0 17 0 281 70 34 9 17 0 0

176 263 16 966 58 0 0 176 703 42 263 16 0 0 88

14 3 6 14 22 0 0 3 24 39 17 28 3 0 0

32 21 13 11 6 11 0 0 42 25 94 44 0 11 0

62 21 4 62 11 0 0 0 349 60 32 14 0 0 82

87 130 11 130 11 0 17 376 0 673 54 391 32 0 0 87

151 50 3 252 14 0 10088 50 958 54 303 17 0 0 252

0 10194 152

+ 152

+ 19 1369 49 0 228 304 1598 57 573 19 0 0 76

Table 6.6. Continued Sample #

Sediment type

silt shell

shell silt

silt shell

spores & pollen/g

2 382

15 794

2 649

1383

2158

2015

1161

1119

10442

5 353

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 838 0 658

0 724 0 2317

0 781 0 1115

0 377 0 587

0 458 65 1569

0 1343 42 1847

0 636 112 861

0 591 84 1266

0 11192 318 4 525

0 6447 365 2 748

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

66 66 6 197 17 22 132 66 845 71 154 13 0 0 0

48 48 4 241 20 0 11980 0 845 65 97 8 0 0 145

112 56 6 112 11 0 0 0 530 54 112 11 0 0 167

42 42 6 126 18 0 42 0 461 65 210 29 0 0 0

65 65 6 65 6 0 65 65 458 44 262 25 0 0 65

0 128 15 84 10 0 0 0 636 75 42 5 0 42 84

0 0 0 37 8 0 0 0 374 83 37 8 0 0 0

0 84 27 84 27 0 0 0 232 73 42 13 43 0 42

79 397 13 1111 37 238 159 79 2024 68 635 21 159 79 159

122 365 23 304 19 0 182 0 912 58 365 23 0 0 122

Table 6.6. Continued Sample #

597

598

599

600

603

Sediment type

silt shell

shell silt

sand peat silt

clay silt sand

silt clay sand

silt clay

clay silt

spores & pollen/g

8434

8 047

2 580

1974

1600

1679

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

0 8434 533 2989

0 7 934 609 3 449

0 5 521 303 2 580

0 99 4 352

0 4 342 79 1520

0 4110 52 1130

0 1610 48 137

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

320 320 10 854 27 214 747 167 1121 36 1068 34 0 0 214

345 460 19 690 29 115 230 0 1150 48 575 24 0 0 236

76 152 15 228 23 0 0 0 530 54 228 23 0 0 76

0 0 0 4 40 0 0 0 6 60 0 0 0 0 0

39 197 11 197 29 39 0 0 178 26 118 17 0 0 39

92 37 18 273 144! 0 0 0 141 26 43 8 34 0 19

43 48 5 88 10 0 20 0 639 75 65 8 0 20 48

Table 6.7. Lower Trinity River complex and delta Sample #

601

602

604

605

606

784

785

786

Sediment type

silt clay sand peat

sand

silt sand clay

silt clay sand

clay sand silt

silt peat clay

silt clay peat

1200

1928

643

410

104

6 354

3 056

2420

0 10320 144 1560

0 9 390 829 2 255

0 1555 0 877

0 1530 21 371

0 288 4 320

0 5 265 0 305

0 1107 27 54

33 4 507 33 133

0 0 0 180 100! 0 0 0 36 20 72 40 36 0 0

39 0 0 289 30 0 829 39 617 65 116 13 0 0 0

0 0 0 71 38 0 0 0 116 62 51 29 0 0 0

0 21 15 119 92 0 0 0 29 23 41 31 0 0 0

0 4 14 12 43 0 0 0 4 14 16 57 4 0 0

305 131 6 566 26 0 44 44 1175 43 1371 53 0 0 479

80 80 9 598 67 27 54 27 293 44 125 19 205 18 161

99 33 3 99 9 33 33 0 431 41 66 6 33 0 365

spores & pollen/g Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

Table 6.7. Continued Sample #

787

791

792

816

817

818

843

844

Sediment type

clay silt

silt clay sand

silt clay

spores & pollen/g

1904

5111

10028

1448

6 525

7 664

25 250

24996

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

67 1635 22 224

0 6414 0 36

82 3 324 494 2225

87 1216 0 1361

0 43 0 821

70 348 35 1114

110 1683 220 1706

132 5 795 44 287

0 22 2 224 24 22 45 0 762 83 67 9 0 0 0

218 0 0 725 39 36 109 109 1233 64 218 11 0 0 36

192 330 14 923 80 191 907 187 1159 49 357 15 0 82 357

29 145 26 87 16 0 0 0 463 89 29 5 0 0 0

0 173 7 605 23 0 432 86 2 203 84 302 11 43 43 43

76 330 20 826 38 283 488 0 1836 84 209 9 139 0 70

276 1764 31 8196 57 418 2204 110 2811 50 716 12 606 604 491

177 442 5 4 557 47 442 1194 644 6 658 68 131 1 310 0 442

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

Table 6.8. Buffalo Bayou - San Jacinto River - Cedar Bayou complex Sample #

793

794

795

796

797

798

799

800

801

819

Sediment type

silt clay sand

silt clay

clay silt

silt clay sand

spores & pollen/g

7 357

6381

3 356

5 638

4412

11104

3818

16 341

10 598

316

Concentricystes/g fungal spores/g leaf cuticles/g tracheary fragments/g

646 2062 15 369

775 1156 25 1784

108 260 76 454

250 654 0 453

50 50 99 843

58 1038 298 1483

14 281 42 477

53 4 577 0 1543

173 1990 303 1231

92 32 0 57

Carya/g cheno-ams/g cheno-ams % Compositae/g Compositae % Cyperaceae/g Gramineae/g Liquidambar/g Pinus/g Pinus % Quercus/g Quercus % Taxodium/g Typha/g Ulmaceae/g

92 46 3 2 786 154! 369 262 15 816 46 400 23 0 0 346

58 0 0 1407 50 75 176 100 3 392 49 728 10 201 75 276

76 54 4 985 66 43 195 87 628 42 390 26 11 11 195

252 0 0 1460 62 50 151 50 956 40 604 26 50 0 503

50 1154 14 644 45 99 392 50 942 66 299 21 0 99 0

0 198 32 2 307 65 408 750 115 2 769 77 519 15 115 404 58

28 548 57 800 83 84 239 70 659 68 140 14 0 14 28

160 3 832 30 2714 65 53 532 160 2 874 69 639 15 319 53 53

43 1168 92 1254 22 173 476 216 2465 63 908 23 87 0 216

8 8 7 24 21 4 8 0 48 41 4 3 0 0 44

B Palynofacies and palynodebris sedimentation 7 The genesis and sedimentation of phytoclasts with examples from coastal environments ROBERT A. GASTALDO

Introduction Significant quantities of biomass are produced yearly by vegetation in terrestrial communities. The fate of the majority of these plants is to be recycled through biodeterioration and soil-forming processes. A small quantity of all biomass generated is introduced into depositional environments. There it may be subjected to a complexity of preservational mechanisms, the results of which may be the development of identifiable fossil materials. In many instances, though, the plant parts are not preserved in their entirety. The number of fossil plant assemblages (phytocoenoses) that contain exquisitely preserved elements is low when compared to those assemblages in which 'unidentifiable' detritus litters bedding surfaces. In this latter case, select plant elements, predisposed to resist biodegradation, are mechanically fragmented by physical processes operating in the specific depositional environment into which the plant parts were introduced. These meso (2 mm-200 /im) and microtaphocoenoses (< 200 jam sensu Krassilov, 1975) composed of phytoclasts (sensu Cope, 1980) generally are overlooked by workers whose research is focused on macrotaphocoenoses. The potential data-set inherent in the nannodetrital assemblage may provide new and/or complementary information not generally available in macrofossil assemblages (see Tiffhey, 1989). Palynologists, on the other hand, often analyze this data set because this particulate organic detritus is recognized as residue from palynological preparations. Based on the physical characters of this residue, recovered plant parts may be placed into either of two broadly transcribed categories, structured or amorphous organic material. Organic geochemists, on the other hand, commonly lump all these elements into the generalized term, Organic Matter (OM; see Hue, 1988), which has been shown to be comprised of various chemical structures as reflected in their pyrolysis-gas chromatography patterns (Hue et a/., 1985). The elements recognized in 'nannodetrital' residues have been classified into major groups that include:

structured, terrestrially sourced materials; pollen and spores; charcoal; biodegraded, terrestrially sourced materials; amorphous materials colored yellow-amber; amorphous materials colored gray; biodegraded, aqueoussourced materials; and structured, aqueous-sourced materials (Masran & Poco*ck, 1981; Poco*ck et a/., 1987). Venkatachala (1981) has established categories for the differentiation of amorphous organic matter types in sediments, whereas Batten (1983) has attempted to establish an informal descriptive terminology for amorphous matter of land-plant and aquatic-plant origin, and these can be differentiated by their textural characters. It is principally the constituents of the structured, terrestrially sourced detritus category that will be addressed in this chapter. With the advent of plant taphonomic studies on the origin, assemblage composition, and destiny of terrestrial plant parts after their introduction into various depositional environments, we have begun to gain insights into those macrofossil assemblages that grace the exhibits of all major museums. As a byproduct, we have also been able to develop an understanding of those 'plant hash' assemblages once only recognized as 'comminuted detritus,' and those rocks that have been previously referred to as 'unfossiliferous' intervals.

Fate of organic detritus Plant biomass may be subjected to a complexity of processes in terrestrial ecosystems both during and after the functional life of the plant and/or plant part (Fig. 7.1). These interactions may ultimately play a role in the final state of preservation of any particular plant part or portion thereof. It is necessary to recognize that different plant parts of different systematic affinity are composed of different chemical constituents and, as such, have a wide range of susceptibility to biodegradational, chemical, and physical deterioration. Due to the fact that different plant parts are also constructed of a variety of tissue types, specific components of any plant part may 103

104

ROBERT A. GASTALDO

WIND-DISPERSED CHARCOAL

INSECT HERBIVORY FUNGAL INFESTATION

AQUATIC ENVIRONMENT

BANK FAILURE FLOODING

SOIL-AIR INTERFACE

SUSPENSION LOAD TRANSPORT FLOATERS CATABOLYSIS SATURATION

INSECT INTERACTION MACROPHAGES

SAPROTROPHS U / BACTERIAL COLONIZATION FUNGAL INFESTATION (ROT) CELLULOSE & LIGNIN DEPOLYMERIZATION

DEBRIS ACCUMULATIONS (JAMS)

PHYSICAL ABRASION \

CLAST SIZE REDUCTION

\ BACTERIAL COLONIZATION \ PYRFTE GENESIS INCORPORATION INTO SOIL

EMPLACEMENT BY SINKING

SAPROTROPHIC INTERACTION FUNGAL DECAY f> \ (e.g. Chytridiomycetes) /

SINKERS BEDLOAD TRANSPORT

SEDIMENT-WATER INTERFACE

CELLULOSE & LIGNIN DEPOLYMERIZATION CURRENTT REWORKING CLAST SIZE REDUCTION MACROINVERTEBRATE COLONIZATION (e.g. Teredo)

be more resistant than others. In the case of angiospermous leaves, for example, it will be re-emphasized that the lignin-bearing vascularization and the biopolymer (cuticle) coating the leaf epidermis are more resistant than the intervening mesophyll tissues composed of parenchyma. Physical disaggregation of such resistant parts provides much of the detritus found in processed residues. Several recent overviews of the taphonomic processes that help shape plant fossil assemblages have provided insights into mechanisms and conditions operating on plant biomass (Gastaldo, 1988; Spicer, 1989). It is not the purpose of this contribution to repeat, in detail, the concepts introduced in these publications. Rather, a brief discussion will establish the biotic and abiotic framework that will allow an assessment of the genesis of phytoclasts. Plant communities are heterogenous, with taxa distributed variably in space and time. Those plants living in close proximity to a depositional environment or a clastic pathway that leads into that site are more likely to contribute plant parts to that site than those plants living some distance from the area of accumulation (Spicer, 1981; Gastaldo et a/., 1987; Gastaldo, 1988). The generation of plant parts is a function of either

BURIAL

Figure 7 . 1 . Generalized diagram outlining the fate of aerial canopy parts in terrestrial and aquatic environments.

physiological or traumatic mechanisms. Physiological mechanisms include abscission of assimilating leaves and shoots, loss of lateral and annual branches, bark shedding resulting from volumetric growth, and dispersal of reproductive structures (Gastaldo, 1988). Traumaticinduced loss, in contrast, is the result of anomalous abiotic circ*mstances. For example, wind rarely transports canopy leaves any significant distance from the parent plant, and even the tallest temperate trees must be within approximately 50 m of an open body of water to contribute detritus to that depositional site (Ferguson, 1985). Under extreme conditions, such as gale to hurricane force winds, large areas may be defoliated, resulting in the introduction of upper story canopy biomass into adjacent depositional sites. The community is selectively sampled, either with regard to the position of the plants within the tiered community structure (understory and ground cover are rarely damaged except by branch fall from the primary canopy-Scheihing, 1980; Dittus, 1985), or to the differences in histological and morphological features between taxa in the same

The genesis and sedimentation of phytoclasts with examples from coastal environments geographical area (Craighead & Gilbert, 1962). In either case, the plant parts arrive essentially whole in the depositional environment. Although leaves and ultimate branches may be damaged under hurricane-gale conditions by severe abrasion, transport by wind does little to fragment the plant part once disarticulated from the producing organism.

Interaction at the soil-air interface Biomass introduced onto the soil in which the community grows is subjected to degradation. Decay of litter can be highly selective, with taxa of various histological characteristics reacting differently to deterioration processes (Ferguson, 1985; La Caro & Rudd, 1985). There is little chance of these plant parts or their structural components (e.g., more resistant tracheary elements) entering an aquatic depositional environment once resident on top of the soil. The biodegradational processes operating on these plant parts, though, provide some insight into the biochemical changes that facilitate the formation of phytoclasts. There is a wide assortment and variable proportion of the principal constituents of plant cells (cellulose, hemicellulose, and lignin) across the plant kingdom, not only with regard to systematic affinity but also to the age and maturity of the plant. In arborescent forms, an inverse relationship exits between the proportions of proteins and water soluble components, and cellulose, hemicellulose, and lignin. This is a function of age. The susceptibility of any plant part to microbial decomposition, then, is an index of its 'palatability', energy content (carbon compounds), nutritional value (such as nitrogen and phosphorus and the molecular form of the nutrient source; Ross, 1989), and the physicochemical environment under which degradation proceeds (Swift et a/., 1979). In general, rates of microbial decomposition can be related to the quantity of lignin and nutrient mobilization in any particular plant part. This nutrient mobilization is partly a function of the solubility of the cellular contents, including polyphenols which act as decay-limiting compounds, and susceptibility to catabolic reactions (Swift et al, 1979). In those cells where lignin plays a minor role in cellular structure, mobile elements are quickly lost (Gosz et a/., 1973). The bulk of the remaining plant litter, composed of lignitic cells, is decomposed via catabolic (energy-yielding enzymatic) reactions and comminutive (reduction by ingestion and digestion) processes within a few years (Swift et aU 1979). Taxonomic diversity characterizes the decomposers in terrestrial environments. These include necrotrophs, biotrophs, and saprotrophs. It is the saprotrophic microorganisms, fungi and bacteria, that are two of the principal agents that 'soften' plant tissues during decomposition. This 'softening' is the result of microbial attack, first onto the surface of the plant part, followed

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by substrate penetration at the cellular and molecular level (English, 1965). Fungi possess a wide spectrum of extracellular enzymes. They are responsible for mechanical penetration of cuticularized leaves, seeds, and pollen/ spores by the production of'boring' hyphae (Alexopoulos & Mims, 1979). This process has been studied extensively with respect to plant parasites, but not directly with regard to saprotrophs. The processes may be similar (Swift et al, 1979). Mechanical disruption of the cuticle is sometimes preceded by enzymatic activity on cutin and cell wall polymers, but this is not requisite in all cases. Resource exploitation by fungi occurs over relatively long intervals of time. The detritus on which fungal action occurs is generally large. Spores may be produced as the resource is depleted. As will be discussed below, the action of fungi on leaf degradation in aquatic depositional environments does not appear to be the principal biotic component responsible for leaf deterioration. Unicellular microbes interact with resources over relatively short durations, as they are adapted to surface habitats. Their exponential growth rate allows them to exploit rapidly the available resources. Bacteria do not easily penetrate resistant materials, but their small size provides an advantage in colonization of all available surface topographies. They are well adapted to occupy detritus that has a high surface to volume ratio and produce significant quantities of extracellular depolymerizing enzymes. These substances result in the 'softening' necessary for cellulolysis. Both aerobic and anaerobic bacteria are variable in their physiological processes, and may utilize a particular enzymatic capacity in one set of conditions and not in another. Their surface-bound enzymes restrict their depolymerization to erosion of the surface in the immediate vicinity of the cell. Many bacterial species are closely associated with fungal hyphae and, as such, may occupy an adjunct role to fungi in decomposition in terrestrial environments (Swift et a/., 1979). Under anaerobic conditions they may be the primary agents to the almost total exclusion of other organisms. Their role may be more significant in detritus degraded in aquatic systems in that they probably initiate the process of organic maturation.

Factors affecting decomposition Resource quality affects the rate of decomposition. Each major plant organ - leaves, stems/shoots, roots, reproductive organs - undergoes characteristically different rates of deterioration. In both temperate deciduous and tropical forests, the rate of turnover for reproductive organs is greater than that for leaves, which is greater than that for wood (Swift et a/., 1979). Differences in rates of degradation of specific plant parts appear to be consistent, no matter what climatic conditions prevail. Particular components of any plant part, though, may play an inhibitory role in the

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degradation process. The presence of intra- or extracellular organic compounds that are of a fungitoxic or fungistatic nature will prevent or retard the colonization activity of fungi. Their persistence in senescent tissues most likely affects the decomposition process. Other inhibitory components that act as protective mechanisms include coverings found on the outer surfaces of plants. These are impregnated or composed of resistant chemicals that include waxes, cutin, cutan, and suberin. These operate as barriers in two ways: first, many chemical constituents have a direct fungistatic effect; and second, the cuticle is a physical barrier because it is generally resistant to decomposition. However, recent investigations of the properties of cuticles have demonstrated that two distinctly different polymers occur. One of these polymers is easily degraded, the other not (a non-saponifiable highly aliphatic bipolymer; Nip et al, 1986a,b). This fact, in itself, may bias the potential fossil record. The physical attributes of different plant parts influence decomposition. Leaf degradation may be initiated while the leaf is still functional, as in the case of fungal introduction via insect damage (Fig. 7.1; see below), but in the majority of cases degradation begins after senescence. During the functional life of a leaf, the hydrophobic character of the cuticle interferes with the development of water films. This, in turn, prevents the germination of fungal spores, their subsequent growth and development, and the potential activity of exoenzymes. In addition, epidermal hairs and scales protect stomatal openings, those potential conduits through which fungal spores could be introduced into the interior of the leaf. The original position of a leaf on a plant may also influence the leafs potential for deterioration. Heath and Arnold (1966) have shown that in fa*gus and Quercus, shade leaves (thin soft leaves from beneath the outer regions of the canopy) are more readily attacked by decomposers and degrade more rapidly than the tough, heavily cuticularized sun leaves. The thickness of the cuticle does not necessarily inhibit the mechanical penetration by fungal hyphae, as infection-pegs from germination tubes have been shown to penetrate various inert substances including gold foil and paraffin wax (Swift et al, 1979). There is, though, a correlation between cuticle thickness and toughness (as measured by a penetrometer), and resistance to fungal penetration (Dickinson, 1960). Once penetration has occurred, catabolic reactions, both of resource-specific and nonresource-specific fungi and bacteria, proceed generally unabated. The resistance of wood to decay, as compared with leaf litter, is partly due to high lignin concentrations, low concentrations of soluble carbohydrates and nutrients,thick hydrophobic bark, and the presence of a spectrum of modifiers that may be taxon specific. Some decomposers (both microbial and macrobial forms) have evolved lignases and tolerances to a wide range of

aromatic modifiers that overcome some of these factors. Insects play a large role in the initial stages of wood decay, with bacteria and fungi relegated to a secondary role. It must be noted that these microorganisms are associated with insects either as a symbiotic gut flora or as a food source for larvae or nymphs (e.g., 'fungal gardens' of ant and termite colonies). Once these microorganisms are introduced into the wood by the activity of insect borers (Gastaldo et al, 1989), their activities can be divided into two phases - passive colonization and active destruction (Levy & Dickinson, 1981). Extracellular enzymes are secreted, which begin to destroy the wood cell walls. Mainly gram-positive bacteria have been noted to colonize exposed woods (Clubbe, in Levy & Dickinson, 1981) but other forms have been reported (Rossell et ah, 1973). The main wood rotting fungi are Basidiomycetes, but wood may be infected by various other groups which Levy and Dickinson (1981) term primary molds, secondary molds, stainers, and soft rots. The architectural framework of wood is considerably different from that of other plant organs such as leaves. Wood has a distinct anisotropy, the result of cell elongation parallel to the axis of growth and a marked localized lateral elongation of cells in a direction perpendicular to that of the primary growth. This cellular organization has a marked effect on the rate of fungal colonization. Colonization of wood by fungi occurs more rapidly along the grain (longitudinal) rather than across the grain (developing radially rather than tangentially). Cellular structure also plays a significant role in wood type and, in turn, its susceptibility to infection and degradation. For fungal decay to begin, the moisture content of the wood must be above 20% (the fiber saturation point in most woods is 30%). Where woods are immersed in waters and completely saturated, microbial activity may be inhibited, but degradatory processes can be initiated by other organisms. Wood can be subjected to degradation processes at any time, both during life and afterwards. The effects of decay are focused on the cell walls and may include the formation of chains of cavities in the middle layer of the cell wall (soft rots), boreholes through the wall and erosion of the wall from the lumen (white rots), and chemical deterioration of the inner layers of the wall through extracellular enzymatic diffusion, resulting in a friable and disorganized appearance (brown rots; Rayner & Boddy, 1988). It has been demonstrated in the former two enzyme-retentive groups that mucilage is associated with the fungal hyphae, whereas in the latter group no mucilage is found associated with hyphae (Highley, 1976; Green, 1980). This may explain why micromorphological features of degradation can be found associated with the soft and white rots, and are absent where brown rots are the infection agent.

The genesis and sedimentation of phytoclasts with examples from coastal environments The chemical sequence of cellulose depolymerization is well detailed (Swift et al, 1979), and the enzyme systems involved in the breakdown of other cell wall polysaccharides is now gaining more attention. Most evidence indicates activity of multi-enzyme systems. The ability to depolymerize lignin is held by a wide variety of organisms, but it is not a common feature among decomposers. The Basidiomycetes are the only group able to metabolize the intact molecule (Swift et al, 1979). Because of their ability to modify the microchemical environment in which they grow, most decomposers are not affected by changes in pH. In fact, fungi appear to be able to regulate their internal pH, maintaining it between pH 5 and 6.

Depositional environments and phytomacrodetritus The processes and vectors of deterioration active in the terrestrial environment provide the basis from which to evaluate processes operating on plant detritus introduced to depositional regimes. Fossil plant assemblages are best preserved in depositional environments where the biological, physico-chemical, and mechanical degradation processes have been retarded or suspended for various reasons. It is the effects and efficiencies of these processes that probably constrain the type(s) and degree of maturation recognized in 'nannodetrital' residues. Plant detritus may be introduced into an aquatic environment by various mechanisms: wind, abscission of vegetative parts that have become non-functional, dispersal of spores, pollen, fruits, seeds. For the purposes of this chapter, it will be assumed that the plant parts under consideration have been introduced by physiological processes and transported in a fluvial regime to their initial depositional site. Pollen and spore dispersal, sedimentology, and taphonomy will not be addressed here, as this topic is considered elsewhere in this volume. Many other scenarios can be visualized, but these may not be directly responsible for the development of phytoclasts (e.g., volcanogenic accumulations; see Spicer, 1989). The following descriptions and examples of plant part alteration are derived from studies in Holocene coastal and nearshore environments where degradation processes are the most active, and in the biased opinion of the author, the sites where phytoclasts are most efficiently generated. Leaves Upon entry into the aquatic realm, leaves undergo changes similar to those operating on the forest floor. The leaf will become saturated, with accompanying loss of soluble materials (sugars, mobile elements, and some polyphenols) from inter- and intracellular components

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(Fig. 7.1). The rapidity of saturation will be dictated by cuticle and epicuticular polymer thickness, stomatal and glandular hair (e.g., hydathode) density, leaf anatomy, laminar or petiolar damage (prior to or post introduction), water temperature, and water chemistry (Spicer, 1981; Ferguson & De Bock, 1983; Ferguson, 1985). Soluble chemicals will be lost to the surrounding environment until equilibrium is achieved (Nykvist, 1959a,b, 1961a,b, 1962). This progressive alteration, accompanied by microbial biodeterioration under long-term exposure, will affect the suspension load residence time of any particular leaf. Experimental data regarding flotation time of leaves in quiescent waters suggest that a complex of factors is responsible for residency time at the air-water interface (Spicer, 1981; Ferguson & De Bock, 1983; Ferguson, 1985). Flotation times vary from several hours to several weeks; thin papery leaves tend to settle before thick coriaceous leaves. Thinner leaves break down quickly and saturate faster than thicker leaves. Damage to leaves, such as injury sustained through insect damage or petiolar loss, decreases experimental flotation time due to the more rapid uptake of water. Residency time under flowing water conditions is difficult to support empirically, and most of our data are anecdotal. It is probable that residency times parallel those documented experimentally (see discussion below). The 'softening' of leaves may be a function of the timing of leaf litter fall (Garden & Davies, 1988) and may be dramatically affected by their polyphenolic constituents. Insoluble polyphenols can delay microbial degradation due to their antifungal and antibacterial properties (Williams, 1963; Benoit, Starkey & Basaraba, 1968). This, in turn, allows catabolic reactions to dominate over the biodegradational processes. Where biodegradational processes occur in aquatic systems it has been assumed that fungal activity predominates over bacterial action (Spicer, 1989), as fungi appear to be the most important agent in leaf decay (Kaushik & Hynes, 1968, 1971). This may not necessarily be the case when the leaves have been introduced either directly into an aquatic regime with a high suspension-load, or they have been transported considerable distances. Fungal activity may play an insignificant role in degradation under these conditions. The minimal role played by fungi in leaf degradation is exemplified in whole leaves recovered from sediments at depth from various depositional environments in the tropical Mahakam River delta, Kalimantan, Indonesia, and the temperate Mobile-Tensaw River delta, Alabama, USA (Gastaldo et a/, 1987; Gastaldo, 1989; Gastaldo et al, in press). Figure 7.2 illustrates this phenomenon. Leaves dehisced from tropical hardwood angiosperms, recovered from a vibracore (Hoyt & Demarest, 1981) extracted in an abandoned, infilling tidal channel of the upper region of the Mahakam delta, show a distinct partitioning in the effects of fungal activity and degree

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of degradation (Fig. 7.2 A). The figured leaf (Fig. 7.2B-2D) was recovered from within the upper 75 cm of core, in which aerial plant detritus was concentrated and interbedded horizontally with suspension-load mud. Total organic carbon averaged 12.4% in the sample (range 6.57-20.02%). The pH of the sample ranged from 6.48 near the surface to 6.82 at a depth of 50 cm, with accompanying Eh potentials averaging —256 mV at 24.8 °C. The leaf was partially damaged by insects prior to dehiscence from the canopy. It is common to see an entire canopy composed of these insect-damaged leaves, and it appears that they remain functional after insect attack (personal observation, 26 October 88). Their duration

Figure 7.2. Bedded leaf-dominated litter illustrating the supressed role of fungal activity in subaqueous sites of burial. (A) Vibracore 16 recovered from an abandoned upper delta plain tidal creek showing the interbedded organic fill and tidal mud, Mahakam River delta, eastern Kalimantan, Indonesia. Vibracore lengths are one meter. Scale in cm. (B) Scanning electron micrograph (11582) of dicot leaf with insect damage recovered from vibracore 16. Insect damage in the bottom left of the lamina occurred while leaf was still attached to the tree. Bar scale equals 1 mm. (C) Scanning electron micrograph (11584) of the broken edge of the leaf a few millimeters from the site of insect damage. There is no evidence of fungal degradation in these parenchymatous cells. Bar scale 10 fim. (D) Scanning electron micrograph (11581) of the edge of insect-damaged leaf with fungal hyphae (fh) permeating the mesophyll tissue. Bar scale 10 fjm.

The genesis and sedimentation of phytoclasts with examples from coastal environments

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time in the canopy afterwards is unknown, but it must the accumulation have either been transported short be long enough for replacement leaves to develop in distances (these are leaves tidally flushed from the growth areas. In these recovered leaves the only area mangrove swamp forests fringing the lower delta plain) affected by fungal degradation, as evidenced by the or great distances (a minimum of at least 50 km remnant fungal hyphae permeating the mesophyll tissue, originating from the upper delta hardwood community is that directly adjacent to the site of injury. The fungal or the interior of the island of Borneo). Leaves that have hyphae do not appear to have colonized or permeated remained intact during long distance transport and the remainder of the mesophyll tissues, as other areas of subsequent deposition appear similar to those recovered the leaves examined have no evidence of fungal infection. from aquatic environments in the Mobile-Tensaw River One may suggest that fungal growth was slow and that regime. Such oxidized, blackened leaves generally lack the remainder of the leaf would eventually be degraded structural integrity, that is, they are 'softened'. The as infection spread. Also, if sedimentation rates in this majority of whole leaves recovered from the deposit are abandoned channel parallel those in other organic-rich those of the mangroves, Avicennia and Rhizophora. The channel infill sequences, the 75 cm thick deposit could parenchymatous tissues within these leaves have been represent several hundred years of accumulation. This degraded resulting in a cuticular envelope surrounding time frame would provide sufficient opportunity for the xylary conducting elements (Fig. 7.3). This condition fungal degradation to proceed if the chemical conditions is similar to that described by Spicer (1981) for leaves were amenable, but moderately reducing conditions are resident in a limnic setting. Examination of these indicated by the pH-Eh phase relationships. This, alone, degraded leaves utilizing SEM reveals that very few fungal may be responsible for the inhibition of fungal growth, hyphae occur within the leaves, if any, and no fungal and it appears that these environmental conditions reproductive bodies are present. If degradation of these suppressed fungal activity soon after the introduction of leaves was principally by fungi, some sort of sporethe leaves into the aquatic site. This does not appear to producing body should ensue once the food source was be an exception, but rather the rule. utilized and no longer available. Either the entire Depositional sites into which leaves are transported spore-producing body released spores, or remnants of have also been examined with regard to the bio- the structure(s) should be present within these cuticular degradational processes operating within them. Gastaldo envelopes. Such conditions have been observed in detrital et al (1987) described an allochthonous plant assemblage plant material collected from Florida Bay (pers. observ., deposited in an interdistributary bay of the Mobile- Feb. 1989, Laboratoire de Sedimentologie, Universite de Tensaw River delta. The plant components derived Paris-Sud, Orsay). principally from levee community inhabitants were Other leaf fragments display a different style of transported a minimum of 10 km in suspension load degradation, albeit without evidence of fungal infection (some parts such as fascicles of Pinus were transported (Fig. 7.4). These leaves/leaf fragments appear to begin at least 60 km; the producing plants grow extrabasinally) degradation from areas adjacent to the venation without before settling at the sediment-water interface of a specificity to the level of vein architecture. Deterioration crevasse splay channel. Leaves were in various stages of results in the separation of the intervein lamina, imparting degradation, ranging from oxidized blackened leaves an irregular aspect to the leaf. It is interesting to note which maintained their structural integrity to leaves in that this not only affects the parenchymatous mesophyll which the laminae were partially decayed. Evidence of tissues but also the cuticle. Nip et al. (1986a, 1986b, 1989) fungal activity within these leaves was not found. Leaves have demonstrated that two different polymers may recovered at depth in sites that contain moderate comprise plant cuticles; one polymer that is easily bioturbation appear to be chemically degraded by degraded, the other resistant. Although geochemical data fluctuating oxygen conditions rather than by activity of for the cuticle composition of the illustrated specimen either fungi or invertebrate detritivores (Rindsberg & are not available, it is probable that this style of break Gastaldo, 1989). up may be related to chemically degradable cuticle. As Plant components deposited within the major discussed above, bacteria are capable of colonizing the depositional environments of the Mahakam River delta surfaces of leaves rather than penetrating the leaf tissues. are presently under study. Some of the plant parts This predisposes the leaf to decay. The colonized leaf accumulate in thick deposits (up to two meters in surface originally in contact with the epidermal walls may thickness) along the seaward margins of tidal flats (Fig. be affected, resulting in the initial degradation of the 7.3; Gastaldo et al, in press). These detrital peat beaches anticlinal cell walls where the cutin is first to be altered originate in the tidally dominated interdistributary zone (De Vries et al, 1967). Continued chemical alteration of (Allen et al., 1979). Few whole leaves are found intact in the cell walls would lead to their separation. Because the deposit, and the mechanisms for their destruction will these intervenal areas are small (generally less than 2 be discussed below. Those whole leaves that do occur in 1 mm ), separation and re-entrainment in the water

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column would be one means to introduce structured phytoclasts into the water column. Although it is difficult to observe the types of bacteria responsible for leaf deterioration, the products of their activity remain (Fig. 7.4B,C). The obvious byproduct of sulfur-reducing bacterial processes is the formation of pyrite framboids, signaling early biochemical (diagenetic) activity. Framboidal pyrite has been found to occur on surfaces of leaves recovered from the upper delta plain of the Mahakam. Additionally, framboids have been observed within parenchymatous tissues that border areas that have been damaged by insects. Insects, therefore, seem not only to be a vector for the introduction

Figure 7.3. Leaf degradation processes, detrital peat beach, Tandjung Bayor, Mahakam River delta, eastern Kalimantan, Indonesia (see Gastaldo et ai, in press). (A) View of detrital peat beach. Photograph taken near the shoreline with the perspective looking downdrift. Note reworking of beach face by tidal activity resulting in size-sorting of detritus. Large macrodetritus is commonly found behind the beach berm. (B) Mangrove leaf recovered from the surface of the detrital peat beach. Degradation has proceeded to the point where only the tracheary elements and cuticle are preserved. Scale in cm. (C) Scanning electron micrograph (11563) of mangrove leaf with upper cuticle removed showing complete deterioration of parenchymatous tissues and accompanying absence of fungal hyphae between xylary elements. Bar scale 1 mm. (D) Scanning electron micrograph (11586) illustrating the extent of fungal infection within these leaves. Note that very few fungal hyphae (fh) occur between xylary elements and that some residual amorphous organic material is figured in the lower left. Scale 100 fim.

The genesis and sedimentation of phytoclasts with examples from coastal environments

Figure 7.4. Various states and byproducts of leaf degradation. Plant parts recovered from subaqueous sites in the Mahakam River delta, eastern Kalimantan, Indonesia. (A) Scanning electron micrograph (12072) showing degradation of leaf lamina and cuticle proceeding within the intervein areas of a dicotyledonous leaf recovered from a vibracore extracted from an upper delta plain tidal channel undergoing abandonment. Scale 1 mm. See Fig. 7.4B. (B) Scanning electron micrograph (12074) of the cells in the separated parenchymatous area adjacent to the resistant venation. No evidence exists such that the degradation can be attributed to fungal infection. Dicotyledonous leaf recovered from vibracore extracted from an upper delta plain tidal channel undergoing abandonment. Scale 10 /xm. (C) Scanning electron micrograph (12069) of the surface of a leaf on which framboidal pyrite has resulted from bacterial activity. Pyrite also has been observed within parenchymatous tissues, especially those damaged by insects. Leaf recovered from the upper delta plain. Scale 100 /im. (D) Photograph of Nipa palm petiole with attached worm tubes recovered from dredge sample of upper delta plain within a hardwood swamp. Scale in cm.

of fungi into the mesophyll of the leaf, but also for the contemporaneous direct or indirect introduction of bacteria. It appears to the author that the principal biological degradation of leaves resident in aquatic regimes is the result of bacteria. The predisposition of leaves to invertebrate detritovore activity is enhanced by microbial action (Kaushik

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& Hynes, 1971; Petersen & Cummins, 1974). This degradational vector, though, is operative when the leaf has settled out of suspension load into a site where invertebrates exist. Their absence, and hence inability to interact with the plant detritus, may be the result of physical and/or chemical conditions of the specific environment. These would include substrate instability, water column agitation, dysaerobic or anaerobic phases, chemical toxicity, etc. Where macroinvertebrates interact with deposited plant detritus, several mechanisms appear to be responsible for its degradation. The most obvious interaction is that of scavenging, feeding, and physical manipulation of the leaf that might introduce nannodetrital residue either into the sediment or back into the water column. The undigested or indigestible components would be defecated from the macroinvertebrate and concentrated in the sediment either as fecal pellets or as fecal castings. A second less obvious interaction is the utilization of the detritus as a hard substrate for attachment of organisms in sediment of soupy consistency. Although this is more commonly associated with wood and stem detritus (e.g., barnacles, bivalves), leaves are also utilized (Gastaldo et al, in press). For example, it is common to find worm tubes attached to leaves or leaf

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parts (both recent and fossil) recovered from estuarine and near shore environments (Fig. 7.4D). Evidence for such nannodetrital generation comes from processed residues of moderate to heavily bioturbated sediments (Fig. 7.5). Delta front sands in the Mahakam River delta are characterized by medium-dark gray fine sand with a slight admixture of mud. Isolated or fragmented invertebrate valves are commonly found intermixed in the facies. The site is heavily bioturbated, yet the dark appearance of the sand suggests organic

Figure 7.5. Mesodetritus in bioturbated sediments. (A) Vibracore recovered from delta front of the Mahakam River depicting various facies including bioturbated sand with shell fragments (bsf) and sandy mud with sands bioturbated into the mud (sm). Vertical burrows are a common feature in the lower part of the core. Vibracore lengths are one meter. Scale in cm. (B) X-radiograph of vibracore recovered from Conway Creek, lower delta plain, Mobile-Tensaw River delta, Alabama. Bayfill sediment is silty mud interlayered with organics and flat-laminated sand. Small burrows can be seen to penetrate the mud. Additional bioturbation in which the sediment is hom*ogenized is also evident. Scale in cm. (C) Photomicrograph of dispersed cuticle recovered from vibracore 6 (sample 6.1/65) taken in the delta front, Mahakam River delta, eastern Kalimantan, Indonesia.

The genesis and sedimentation of phytoclasts with examples from coastal environments components dispersed throughout the sediment. The TOC (Total Organic Carbon) in these samples averages a little more than 1% (range 0.61-3.84; average 1.21%). Nannodetrital remains recovered from these sediments include cuticle (see below). Similar assemblages have been recovered from an interdistributary bay fill sequence in Chacaloochee Bay, Mobile-Tensaw delta. The bioturbated bay fill sediments vary from silty mud to sandy silt to muddy sand with TOC contents below 2% (range 0.83-1.15, average 1.25%; D. Felton, unpublished data). Little discernible plant detritus is seen in core or x-radiographs, but dispersed cuticles and few palynomorphs are recoverable (Fig. 7.5C). hom*ogenization of the deposits at the sediment-water interface appear to occur only where accumulations of macrodetrital plant parts are less than 2-4 cm in thickness (Rindsberg & Gastaldo, 1989). The principal mechanism by which leaf material is broken ultimately into nannodetrital-sized fragments appears to be physical degradation. As Spicer (1989) notes, one would believe intuitively that the movement of plant parts under high flow regimes operating in fluvial systems would cause the plant parts to fracture. This might be true if a leaf were transported in the bedload and moved along the river bottom by saltation. This, though, is probably a rare occurrence for leaves (see below for wood). This might affect leaves in bedload that had been subjected to microbial attack, because under these circ*mstances the leaves lose their robustness (Spicer, 1981). If the plant parts were freshly abscised, their degree of fragmentation would be minimal because they retain their structural integrity (Ferguson, 1971, 1985; Spicer, 1981). Transport of leaves occurs primarily in suspensionload where the leaf is moving at the same rate and speed as the fluid surrounding it. This movement may be either through fluvial, tidal, or storm processes, and the velocities that directly affect the plant part may impart a complex history on the deposition and final burial site of that detritus. It is this complex transport and depositional history of any plant part that probably is responsible for nannodetrital generation. Once the specific gravity of any detrital part exceeds unity, it will settle from the water column. The specific gravity of some plant parts, such as some woods (see below), is already greater than one, and they sink immediately upon introduction to the water column. In other cases, these plant fragments remain floating and undergo progressive water uptake until saturated. Spicer (1989) contends that the final settling site of such debris is determined to a large degree by the objects' submerged density and shape, the two factors affecting settling velocity and entrainment behavior. We must also consider the rate of discharge of the fluvial system and the possible total residence time in suspension-load transport before saturation of the plant part causes it to begin settling. In addition, differences in temperature in the water column and, hence, differences in water density,

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will affect the site of transport within the water column. If one were to judge the quantity and quality of transported biomass by that which is observable on the water surface of either the rivers in the Mobile-Tensaw or Mahakam deltas, this biomass could not account for the estimated quantity deposited throughout these regimes. The recovery of whole leaves, intact mosses, and insect parts from depositional sites in which active riverine processes occur (lateral channel bars [Mahakam], channel bedload deposits [Mobile], distributary mouth bars [Mahakam, Mobile], tidal flats [Mahakam]), is suggestive that the plant parts were either resident in suspension load for a short time interval (days) or were never transported in bedload. It seems more likely that, as the specific gravity of these leaves changes with continued saturation, they move progressively down in the water column, being transported at different depths through time. This would be correlative with transport of woods of various densities. It appears that settling from the water column is controlled principally by fluctuations in water velocity, particularly by velocity reduction. In the Mahakam River delta, where sedimentation is affected strongly by microto mesotidal processes, the lateral distributary channel bars are characterized by a cyclical depositional pattern. Although the competence of the Mahakam River is low (fine to medium sand), it has a very high capacity. The channels are extremely muddy. It is not possible to see your hand when it is held more than a few centimeters below the surface of the water. Bedload sand is deposited in migrating ripples along the inside bends of fluvial channels, where water flow is less than that on the outside of the curve. Mud and/or plant litter beds overlie these sand ripples, and are deposited in response to flood tidal energy that moves upriver (maximum spring tidal displacement is greater than two meters). The spring tidal bore causes some, but not all, of the saturated plant detritus to settle out of suspension. The litter beds are composed of leaves, mosses, and insect fragments, and they occur across the entire width of lateral channel bars. The same process may result in the settling of leaves along the shoreline on tidal flats, but grounding of this detritus at the sediment-water interface also occurs as current flow wanes over these depositional sites. Leaves may undergo deposition and entrainment several times before final burial (Gastaldo, 1988; Spicer, 1989). Variations in discharge rates and/or migration of a channel system will re-entrain plant parts initially deposited in fluvial environments. It is this potential for continued re-entrainment of saturated leaves, whose structural integrity has already been jeopardized, that provides the biomass requisite for the genesis of vast quantities of phytoclasts. The activity of waves and tides in coastal and nearshore shallow waters best accounts for the re-entrainment and ultimate maceration of leaves after they are transported

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into the estuarine and nearshore marine environments (Rindsberg & Gastaldo, 1989; Gastaldo et al, in press). It is within these sites that leaves, resident in the water column and/or resident at the sediment-water interface, are subjected to continous agitation when they are above wave base (Fig. 7.6A,B). Leaves may be brought to these sites either directly through fluvio-marine processes, by which the biomass is transported to the delta front and redistributed along the coastal zone by wave and tidal action, or after some residence time offshore (it is not uncommon to find leaf fragments on which colonies of bryozoa have developed [Fig. 7.6D], these reflecting clear quiet-water offshore conditions). In both cases, the leaves have been subjected, to some degree, to catabolic and microbial degradation subsequent to their introduction into the fluvial regime. This loss in structural integrity predisposes plant parts to mechanical fragmentation in the organic slurry that is found inside the breaker zone (Fig. 7.6A). Agitation and breakup continues while the plant part is entrained within the breaker zone, and is stopped (sometimes only temporarily) when the plant

Figure 7.6. Process site and results of macrodetrital physical degradation, detrital peat beach, Tandjung Bayor, Mahakam River delta, eastern Kalimantan, Indonesia (see Gastaldo et al.. in press). (A) Photograph of low tide shoreline along detrital peat beach. Continued agitation of plant debris occurs in the organic slurry (osl) at the margin of the beach. (B) Photograph of select sample of detrital peat fragments from peat beach including wood (w), leaf laminae (I), fibers of a Nipa petiole (n), and detrital dammar (r). Scale in cm. (C) Scanning electron micrograph (12075) of a dicot leaf fragment in which the cuticle (c) is undergoing separation from the epidermis (ep). (D) Scanning electron micrograph (11606) of a leaf fragment showing epiphytic bryozoan growth on the leaf. The bryozoan colony is represented by the raised geometrical pattern. Scale 100 fim.

parts are deposited on the tidal flat/peat beach during tidal flux. The plant parts that are generated reflect the contributing biomass (Gastaldo et al, in press) and include leaf petioles, intervenal leaf laminar fragments, incomplete tracheary elements (leaf venation), and isolated cuticle (Fig. 7.6B,C). The size of the leaf pieces range from rare whole leaves to fragments, the most common size being less than 1 cm in maximum dimension.

The genesis and sedimentation of phytoclasts with examples from coastal environments

Figure 7.7. Photograph of rippled sandstone in which nannodetrital fragments are concentrated in ripple troughs. Lower Pennsylvanian 'Pottsville' Formation, Black Warrior basin, Alabama. Scale in cm.

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particularly in ripple troughs (Fig. 7.7). These accumulations are often found in offshore depositional sites, at or below wave base. Gastaldo et a\. (1987) also reported that plant part and The burial of plant detritus does not preclude it from size sorting of the detritus occurs in these deposits. In degradation or further alteration. In fact, depending upon the case of peat shoals in the Mobile-Tensaw delta, the the depositional environment in which leaves accumulate, 'shoreface' of the shoal (that adjacent to open water they may be more subject to continued degradation and conditions and subjected to tide and wind-generated wave alteration. Of the environments of deposition examined activity) was composed more of woody fragments than to date, sand-rich sites seem to be the environment in the 'back barrier' sites. These latter sites included more which these processes operate most effectively. Rindsberg leaf fragments, which was interpreted to indicate that and Gastaldo (1989) note that leaf litters buried in some winnowing of less dense leaf materials occurred in distributary mouth bar sand at a depth of less than one the swash zone. Additionally, there were more smaller meter are quickly degraded where the water level plant parts (size category 0-0.5 cm) in the front of the fluctuates in response to variation in discharge rates, shoal than behind its crest. Comparative data do not exist prevailing wind patterns (strong directional winds may for the peat beaches in the Mahakam delta, although lower water levels particularly in protected bays), and differences were noted to occur in particle sizes composing tidal cyclicity. The porosity of the sand will subject the bedding features within the peat beach. buried litter to some flushing which may accelerate the When examining bulk samples of these organic-rich loss of soluble compounds. The change in water level, accumulations (TOC as high as 39.4%), it is evident that which may subaerially expose the distributary mouth bar plant part fragments less than or equal to 1 mm are not sand body, introduces oxygen to the litter accumulation(s) a large component of the deposit. In fact, they are which, in turn, accelerates chemical degradation. In other conspicuously low quantitatively. This size category of instances, where litters have been buried and isolated plant fragment probably is maintained within the water from oxygenating waters, bacterial-induced methane column and remains in suspension-load. As tidal production occurs. Although the distributary mouth bar fluctuations rise and wane, these nannodetrital particles is bioturbated mostly by polychaete worms, these are transported away from their site of mechanical organisms do not utilize the plant resource for food deterioration, and may be retained in the water column (Rindsberg & Gastaldo, 1989). Rather, when they for some time before settling to the sediment-water penetrate a buried leaf, an oxidation rind occurs at the interface. Often, this mesodetrital fraction behaves edge of the burrow in contact with the plant debris. The sedimentologically in a manner similar to that of mica. worm does not exploit the buried litter horizon, and this Once meso- and microdetrital particles sink, they may is possibly due to microenvironmental chemical conditions. be dispersed across the bedding surface or concentrated Where the sand is colonized by plants (aquatics and

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semiaquatics), aerobic decomposition of buried leaf debris proceeds most effectively where aerenchymatous roots provide oxygen to the rhizosphere. The result of these processes is the formation of an amorphous organicstained horizon in which the most resistant plant parts (e.g., tracheary elements and cuticles) occur. Distributary mouth bars are ephemeral coastal features, and when the site is breached by higher discharge flood waters, phytoclasts are reintroduced into the water column and transported to a new depositional site. Other coastal sites may be subjected to tidal and wave reworking, and the leaf litters that were deposited contemporaneously with primary sedimentological structures are also reworked mechanically to nannodetrital size. The best documented example studied, to date, occurs in Mayor Bayor within the interdistributary zone of the Mahakam River delta. The area is an inactive fluvial regime now subjected to tidally dominated processes. In the conversion from fluvial to tidal domination, the lateral channel and distributary mouth bars are exposed to higher tidal and wave energies because of the abated influence of fluvial discharge in the area. Plant litter horizons recovered from vibracores extracted from these sites are composed of nannodetrital fragments of leaves, wood, cuticle, and unidentifiable materials. Most plant parts have been physically abraded to a size equivalent to that of the fine sand comprising the clastic fraction. Again, these sites may be ephemeral, and when they are affected by higher energy, lowfrequency events, phytoclasts would be entrained in suspension load and flushed from the interdistributary zone. This would result in the transport offshore of the plant fragments.

Dispersed cuticles This structured phytoclast is generally viewed as being composed of resistant cuticles that have been separated from leaves. Most dispersed cuticles can be identified systematically, although some cannot be interpreted as parts of well definable plant organs or entities (Kerp, 1989; Upchurch, 1989). Cuticle segregation and subsequent transport theoretically results in the accumulation of isolated fragments with the same hydrodynamic properties as other parts of similar size and density. Dispersed cuticles occur within a variety of continental and marine depositional environments (open marine, deltaic and nearshore coastal, fluvial, lacustrine, paludal, and volcanogenic) and a variety of sedimentary rocks (claystone, limestone, shale, siltstone, sandstone, carbonaceous shale and coal, and tuff; e.g. Batten, 1979; Clark et a/., 1986). Indeed, recovered specimen suites may represent isolated cuticles dispersed within a sedimentary environment, or they may represent residual resistant structures in an environment where degraded leaves are dispersed and not identifiable as macrofossils.

The segregation of cuticle from a leaf may occur either by biochemical activity, physical manipulation, or a combination of processes. Complete degradation of parenchymatous tissues within a plant organ can result in the isolation of the protective cuticle (Figure 7.3; Gastaldo et a/., in press). This is not only applicable to aerial plant parts, but also to subterranean rootlets. For example, rootlet cuticles account for greater than 65% of the maceration residuals processed from Nipa palm and hardwood swamp soils in the Mahakam River delta. Accessory plant parts in these settings include resistant fibrous and woody components, leaf laminae, and a small proportion of dispersed leaf cuticle. This assemblage appears to be a common feature of subaerially exposed environments. Bacterial attack on the anticlinal walls of parenchymatous tissues in leaves is probably responsible for initiation of weak areas between these cells and the overlying cuticle. Once this plane of weakness is established, separation of the cuticle can begin. In marginal sites of aquatic environments that are subjected to wetting and drying, the alternation of tissue swelling and contracting may accelerate separation (Fig. 7.8). Cuticle dispersal occurs as small fragments that are mechanically separated, either through the action of wind, moving the leaf along a subaerially exposed strandline, or in water by bedload transport by either littoral currents or tides (Fig. 7.6A,B). The density, size, and complement of accessory hairs and papillae of any cuticular fragment generated in this mode will play a role in subsequent transport and ultimate deposition. Assessments of each major depositional environment in the Mahakam River delta have been made as to the contribution of plant part categories (unidentifiable millimeter-sized resistant detritus, mosses, woody and fibrous detritus, Nipa palm petiole, leaf laminae, dispersed cuticle, reproductive structures [fruits and seeds], roots and rootlets, and damar [resin]) to each litter-bearing accumulation. Subaerial swamps, fluvial and tidal channels, subaqueous tidal flats, interdistributary tidally influenced sites and peat beaches, and the delta front have been analyzed. Samples recovered from vibracores were hand-picked to recover isolated cuticle from dried litter accumulations. Complementary samples from each of these environments were processed for dispersed cuticle (using methods of Upchurch, 1989), even where there appeared to be no bedded or identifiable plant remains in the sediment. In general, the frequency of occurrence of isolated cuticles recovered from dried samples was low. Quantitatively, isolated cuticles comprise less than 2.3% of all plant parts recovered from bedded litters (range 0.7% in Nipa swamps and upper delta tidal channels to 5.1% in detrital peat beaches). It is difficult to assess the weight percentage of dispersed cuticle residuum from processed samples (these account for less than 0.01 gm of residue), but well preserved cuticles have been

The genesis and sedimentation of phytoclasts with examples from coastal environments

Figure 7.8. Genesis of dispersed cuticle from leaf deterioration. Recovered leaf from tidal strandline along margin of Mobile Bay, Fairhope, Alabama, showing separation of cuticle from underlying parenchymatous and xylary tissues. This appears to be the result of alternating wetting and drying. Scale in cm.

recovered from every conceivable depositional site sampled. Some of these may not represent actual dispersed cuticles, but rather the remnants of either fragmentary or whole leaves dispersed within the sediment. The ubiquitous character of dispersed cuticle in palynological residues from various lithofacies has permitted the use of cuticles as a criterion for interpreting facies relationships (e.g., Parry et al, 1981; Batten, 1982; Batten et al, 1984), but their utility for facies discrimination is just now being tested.

Wood The physical properties of any particular wood circ*mscribe the way in which that wood will behave during transport and subsequent interactions after initial deposition. The mechanical and nonmechanical wood properties are affected by fluctuations in the quantity of water present. Water in wood occurs both as bound water located in the cell walls and as free water within cell lumina. When the liquid phase of water exceeds a wood's fiber saturation point (generally between 25 and 30% moisture content) it accumulates in the cell lumina, and maximum moisture content is reached (Panshin & De Zeeuw, 1970). The total amount of accommodated water is limited by the void volume of the wood. Living trees will not contain more than one-half to two-thirds as much moisture as is theoretically possible. Wood that is resident in an aquatic system may become completely saturated.

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The specific gravity (density index) of wood depends on the size of the cells, the thickness of cell walls, and the interrelationships between secondary xylem elements (fibers, wood parenchyma, tracheids and/or vessel elements). This characterization is based on oven dry weight, and although this is only a relative index of the cell wall materials, it provides a guide to indicate whether a particular wood is considered to be light, moderately light to moderately heavy, or heavy. Such parameters, in turn, reflect the ability of any wood to be a 'floater' or a 'sinker' upon initially entering an aquatic regime. This is important with regard to the residency time in suspension load prior to settling to the sediment-water interface. The ability of a non-degraded piece of wood to float is determined by the buoyant force that develops in response to the difference between the wood density and that of the water displaced by the fully submerged part (Panshin & De Zeeuw, 1970). Whereas woods that consist of at least two-thirds cell wall substances will sink immediately in water, most woods must first become saturated, whereupon the air spaces within are filled until the density of the wood equals or exceeds that of the displaced water. At this point, the wood moves to the bedload. It must be noted that decayed wood absorbs water more quickly than wood that has not been subjected to degradational mechanisms. Rot affects wood in a variety of ways. 'Dry rot' (attack by Merulius lachrymans) causes shrinkage and cracking into rectangular blocks, and the tracheid wall composition is significantly altered and grossly degraded (Harris, 1958). Wood density is changed through a reduction in dry weight. These factors will reduce residency time in suspension load because the wood will equilibrate more rapidly with the surrounding water.

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The mechanisms responsible for the introduction of wood into aquatic systems are varied (physiological or traumatic loss, flood-derived, stream bank failure, etc.). Wood may be subjected to alternating periods of submergence and exposure prior to final burial. Although wood is more resistant to deterioration by microorganisms than are most other plant tissues, it may be degraded to varying degrees before introduction into and transport in an aquatic system. Insect damage can occur both to living and dead wood in emergent environments. Changes in the physical properties can be caused, for example, by beetle mining (e.g., families Scolytidae and Platypodidae), larval development under the bark or within the wood, termites (dry-wood and damp-wood types), and carpenter ants (Camponetus). Once wood is submerged and resident at the sediment-water interface, it can become the site of anchorage for various macroinvertebrates and also subjected to the activities of marine borers including the molluscs and crustaceans (Fig. 7.9). The molluscan genera - Teredo, Bankia, and Martesia - attach themselves by their caudal end to wood and begin to burrow by grinding (Turner & Johnson, 1971; Hoagland & Turner, 1981). Grinding is accomplished through the action of a pair

Figure 7.9. Wood as a host for endobionts. (A) Bored drift wood lying on top of detrital peat beach, Tandjung Bayor, Mahakam River delta, Indonesia. (B) Enlargement of wood borings referable to Teredo. (C) Transverse section of a bored Paleocene wood (boring cf. Teredolites), Clayton Formation, Alabama. Borings are infilled with marl, calcite, and pyrite/marcasite. Scale in cm.

of toothed shell valves. It is believed that these molluscs not only use the wood for a habitat, boring into and becoming imprisoned within the wood, but also utilize it as a food source. Crustaceans use wood both as a site for inhabitation during some part of their life as well as for a food source (e.g., Chelura; Barnes, 1974). They bore using a pair of toothed mandibles and seldom extend their burrows very far into the wood. The role that wood plays in the dietary requirements of these animals is still speculative. Some authors contend that wood passes unaltered through their digestive tracts. Chemical analyses of wood passed through the gut of Limnoria (an isopod) indicates that these borers are capable of removing nearly all the hemicellulose and about half of the cellulose (Lane, 1959; Ray, 1959). In either case, nannodetrital-sized fragments of structured wood are mechanically separated during boring and can be introduced into the water

The genesis and sedimentation of phytoclasts with examples from coastal environments

Figure 7.1 Q. Characteristics of bedload-transported detrital woods. (A) Variously shaped wood fragments recovered from detrital peat shoal deposit, Chacaloochee Bay, Mobile-Tensaw River delta, Alabama. Wood illustrated represents the 0.5-1.0 cm size fraction. Scale in cm. (B) Scanning electron micrograph (11573) showing angularity of cell walls that have been mechanically fragmented during transport. Wood specimen recovered from detrital peat beach, Mahakam River delta, eastern Kalimantan, Indonesia. Scale 10 /im. (C) Scanning electron micrograph (12057) illustrating wood parenchyma and fibers, neither of which are infected by fungi and, hence, predisposed to microbial biochemical degradation. Fibers appear to show mechanical fracture along walls. Specimen recovered from vibracore 22.6/55. The vibracore was taken in a lateral channel bar of an active distributary channel, Mahakam River delta, eastern Kalimantan, Indonesia. Scale 10 /xm. (D) Scanning electron micrograph (12061) of a wood fragment in which early diagenetic framboidal pyrite has formed in response to bacterial activity within a cavity. Specimen recovered from vibracore 8.2/15, taken in the tidally influenced lower delta plain, Mahakam River delta, eastern Kalimantan, Indonesia. Scale 1 mm.

column. Ingested wood, chemically altered through digestive processes, may also be introduced into the water column, possibly as amorphous organic matter. Consequently these phytoclasts should show some signs of organic maturation. In most instances, though, the reduction of wood to

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nannodetrital-sized clasts is more a function of its long distance transport and/or interactions with bedloads of sand-sized or larger clasts. Channel lag deposits that may or may not be ephemeral are comprised of material with the highest settling velocities. Organic constituents are commonly logs and larger, robust, fruits and seeds (Spicer, 1989), and this fact has been used often to identify the bounding surfaces of fluvial architectural systems. Under unusual transport conditions, however, log accumulations may be found terminating a channel fill sequence reflecting their role in abandonment processes (Degges & Gastaldo, 1988). As discussed by Gastaldo et al (1987), the residency time of wood in bedload and the distance transported in bedload affect its physical aspect. Transport of wood in suspension load and subsequent residency time at the sediment-water interface might allow for the propagation of fungal degradation, if active, thereby chemically altering the cell walls. This would predispose the wood to size and shape alteration when abraded. Woods sampled from vibracores and detrital peat beach environments have been examined. To date, these show little sign of fungal infection that might cause them to be 'softened' after which mechanical alteration of shape could proceed quickly (Fig. 7.10). Rather, it is generally

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believed that water retention within wood (to the point of fiber saturation) appears to be the principal mechanism responsible for softening of wood when submerged. It has been demonstrated that the addition of polar liquids to the cell wall constituents affects the microfibrillar arrangement and results in its expansion, a volumetric change in the cell wall (Panshin & De Zeeuw, 1970). The dimensional changes in any particular wood are a function of both the moisture quantity and the amount of cell wall substance. The more cell wall material present in any particular wood, the greater the dimensional changes (e.g., swelling) when moisture is added. This swelling of the cell wall and expansion of the architectural fabric predisposes the cell wall to simple fracture when subjected to mechanical stresses during bedload transport. Bacterial colonization of wood clasts may occur, and their activity is reflected in the chemical byproducts of their respiratory activity. As demonstrated for transported leaves, the presence of early diagenetic pyrite in wood can be documented (Figure 7.10D) in certain environments in which specific chemical conditions operate. Wood containing pyrite framboids has been recovered at depth from vibracores extracted in estuarine conditions in the Mahakam River delta. Pyrite appears not to occur on exposed surface areas, but is confined to cavities within the wood where interaction with flowing waters would be minimized. These degradation products may result more in incipient permineralization near the site of pyrite formation than in large scale degradation resulting in nannodetrital production. The physical abrasion of the cells on the exterior of any wood particle being moved in bedload mechanically breaks portions of saturated cell walls from the phytoclast. This results in the progressive rounding of wood clasts during transport and may be a relative indicator of residency time in bedload (Gastaldo et a/., 1987). The alteration in clast shape from sharply angular to smooth and rounded is analogous to that of lithoclasts. The parts of cell walls and/or groups of cellular constituents broken from the phytoclast are commonly nannodetrital-sized. Their removal results in an irregularity in the form of the wood clast when viewed under SEM (Fig. 7.10B). Because this phytoclast is principally composed of residual lignin (presumably the cellulose and hemicelluloses have been degraded), the mesodetrital-sized clasts can be transported in suspension-load over significant distances and incorporated into a wide diversity of depositional environments.

Resin, copal and dammar Resins are plant secretions that solidify when exposed to air, and approximately 10% of extant plant families living in temperate and tropical climates synthesize them (Langenheim, 1990). Resins are characterized as mixtures

of either terpenoid or phenolic compounds, although the chemical composition is variable. The terpenoid resins have been examined in more detail because these commonly fossilize (Grimalt et a/., 1988). Resins are common in certain gymnosperms and angiosperms, and resins from plants of different systematic affinity commonly have been given distinct appellations. All conifers produce terpenoid resins, but only the members of the Pinaceae and Araucariaceae synthesize large quantities. These secretions are generally referred to as resins or ambers. The production of resins in angiosperms is limited to a few families. Several genera of the Leguminosae with a South American-African distribution produce large quantities of diterpenoid resins, and these hardened masses are referred to as copals. Members of the tropical Burseraceae and Dipterocarpaceae produce resins that contain triterpenoids and have been termed dammars (an Indo-Malay word for resin). These secondary substances are produced either within ducts found in various tissues/organs or in specialized surface glands. The function and ecological role of this exudate is speculative (e.g., Fraenkel, 1959; Ehrlich & Raven, 1964; Langenheim, 1990), but one thing is certain, copious quantities can be produced and accumulate on the exterior of a plant after wounding has occurred. Polymerization of these terpenoids may be initiated by light and oxidation (Cunningham et a/., 1983) resulting in their hardening within weeks to months after exudation. The masses so produced are highly resistant to environmental influences (Mills et a/., 1984). Resins may be dissociated from the tree in various ways, and this unstructured plant synthate may be introduced to and incorporated within various depositional regimes. These plant-derived secretions can be a common component in nannodetrital residues of fluvial and nearshore facies. Resin ducts are most commonly found in wood. They may be a characteristic feature of some while their occurrence in other wood types is the result of injury (traumatic resin ducts). Resin ducts can be vertically oriented or oriented both vertically and horizontally within the wood, and lined with thick-walled epithelial cells (Fahn, 1969). The ducts are generally filled with synthate. Upon death of the plant, and exposure to degradation processes, the resin within the ducts undergoes polymerization and hardens in place. Pieces of wood with polymerized resin ducts may be transported in bedload and subjected to physical abrasion releasing small cylindrical masses (on the order of 300 fxm in diameter) into the sediment load (Fig. 7.11). In litters recovered from vibracores extracted in fluvial, delta front, and tidal flat environments of the Mahakam River delta, small cylindrical fragments of dammar occur, in addition to angular to rounded wood fragments in which polymerized resins can be identified.

The genesis and sedimentation of phytoclasts with examples from coastal environments

Figure 7.11. Occurrence of detrital plant resins. (A) Scanning electron micrograph of solidified dammar in resin ducts of hardwood angiosperm wood (?Dipterocarpaceae). Wood is an allochthonous fragment recovered from vibracore 22.6/55. The vibracore was taken in a lateral channel bar of an active distributary channel, Mahakam River delta, eastern Kalimantan, Indonesia. Scale 10 /im. (B) Suite of allochthonous dammar clasts taken from detrital peat beach samples, Tandjung Bayor, Mahakam River delta, eastern Kalimantan, Indonesia. Borings (b) occur in dammar of various size, and larger pieces may act as a substrate for bivalve (oy) attachment. Scale in cm.

Larger quantities of resin may be incorporated when masses of hardened exudate are introduced into the transport system. Trees damaged by trauma or insects respond by producing vast quantities of resin, deposited on the exterior of the tree around the injured site. For example, Thomas (1970) estimated that resin accumulated from Agathis australis in New Zealand over, presumably, the past 1000 years amounts to 25 tons per km 2 within the geographical distribution of the species. This resin polymerizes and hardens both around the wounded area and adjacent to the tree, where the viscous material has been deposited. If trees grow adjacent to waterways, resins may fall into the river system and be transported

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downstream. The densities of the various terpenoid resins are all slightly greater than one. This property causes resin masses of different sizes to sink to bedload and be transported by rolling and saltation. The dominant trees of some southeast Asian forests belong to the Dipterocarpaceae, a family of plants known to produce prodigious quantities of dammar. Although dipterocarpaceae triterpenoid resins do not polymerize as easily as the diterpenoid resins (Langenheim, 1990), angular to rounded pieces are common components of higher energy depositional sites in the Mahakam River delta (Fig. 7.1 IB). Where present, dammar generally accounts for less than 1 % of identifiable plant parts, but in specific depositional environments (delta front, tidally influenced interdistributary area, and detrital peat beach) this component may account for as much as 4.5% of the recovered plant parts. Individual irregularly shaped pieces of dammar show features acquired during transport including rounding and fracturing. In addition, they may shown signs of macroinvertebrate interactions that include boring and utilization as a firm substrate. Coloration, translucence/opacity, and friability of the dammar do not appear to be characteristics that can be used to infer age of individual clasts. Gastaldo et al. (in press) report 14 C dates for two dammars recovered from a detrital peat beach. One piece appeared to be 'young' based on its amber coloration (dark yellowish-orange, 10 YR 6/6) and translucent appearance; another piece appeared to be 'older' based on its 'weathered' opaque appearance (bluish-white coloration 5 B 9/1). The 14 C age of the translucent specimen is 2645 ±215, whereas the opaque specimen has yielded an age date of 930 ± 205. Whitish-colored opaque dammars generally are more brittle and friable than translucent pieces. Some are easily crushed under slight pressures. The structural integrity of translucent dammars appears to be better, although these may fracture conchoidally. With regard to both conditions, nannodetrital-sized fragments can be broken from these materials during initial transport and subsequent re-entrainment in the water column. Accumulations of such detritus may remain as a residuum in palynological preparations most often identified as resinous droplets and lumps.

Charcoal Terrestrial plant parts in various climatic regimes may be subjected to combustion during naturally occurring wildfire. Pyrolysis of unburnt plant tissues may accompany the rapid temperature increase resulting in the formation of charcoalified detritus (Chaloner, 1989), which is chemically inert (Mantell, 1968). Although charcoal is generally thought of as derived from wood, softer parenchymatous tissues of leaves and flowers may also be preserved (Scott, 1989). This physico-chemical plant

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byproduct can be identified by megascopic, microscopic, and chemical features (Harris, 1958, 1981; Cope, 1981; Cope & Chaloner, 1985). Megascopically, charcoal is lustrous and brittle. This latter character is best demonstrated by the development of a black 'streak' when a specimen is rubbed on paper. Charcoal fragments are commonly cuboidal, due to rigidity and the development of longitudinal and transverse shrinkage cracks during pyrolysis. Shrinkage estimates approach 45% by volume (McGinnes et al, 1974). Charcoal may also form short, angular, rounded or amorphous clasts (Harris, 1958; Herring, 1985), often splintery in appearance in residues (Batten, 1973). Its density is low, the specific gravity of uncompressed fusain powder has been reported to be 0.28 (Harris, 1958). Charcoalified plant parts are relatively resistant to oxidizing chemicals (which accounts for their presence in palynological residues), have a high reflectivity, and appear porous, a reflection of the configuration of hom*ogenized cell wall structure. Charcoal particles retain more of their original identifiable cellular constituents when found in nearshore waters, as compared to particles recovered from open ocean sites (Herring, 1985). The oldest sedimentary occurrence of charcoal in a noncarbonaceous rock has been reported from the Lower Carboniferous (Scott & Collinson, 1978). It also has been recognized in carbonaceous rock from a transitional Devonian-Carboniferous 'coal' (Warg & Traverse, 1973). It is a common component of many sedimentary regimes. Microbial and chemical interactions with charcoal during transport, deposition and subsequent diagenesis are minimized because of its inert character, consisting of almost pure carbon (Mantell, 1968). It is easily transported both by wind and water. Large pieces of charcoal cannot be moved far by wind, and most of the charcoal generated remains near the site of pyrolysis and is incorporated into the soil. Erosion of these particulates may introduce them into fluvial and nearshore regimes, and this fraction rarely is transported beyond coastal waters (Herring, 1985). Wind transport of charcoal is often the result of the injection of meso- and microdetrital-sized carbon particles into the air by thermal currents generated during wildfire propagation. Canopy temperatures can exceed 800 °C for short periods (one minute or less), and can be maintained at 300 °C for almost twenty minutes (Ahlgren, 1970; Rundel, 1981). Ground temperatures range between 200 and 500 °C, with temperature extremes reaching 1000 °C. Particles 1-100 jam (or larger) may remain airborne for quite some time and wood carbon may constitute up to 36% of atmospheric carbon particulate matter (Griffin & Goldberg, 1979; Herring, 1985). Eolian charcoal is transported from the continents to ocean basins via tropospheric winds operating at altitudes less than 10 km (Palmer & Northcutt, 1975). Upon introduction into the ocean waters, it is believed that

sedimentation rates of the particles are accelerated by particle ingestion by zooplankton and excretion of fecal pellets (Herring, 1985). Because of its low density, charcoalified debris may be water transported for significant distances and deposited in various aquatic environments, commonly accumulating in nearshore continental sediments. Herring (1985) believes that these coastal sites are probably the primary reservoir for charcoal in the open oceans. As Harris (1958) discusses, each fusain-rich deposit may not represent a single forest fire event, as buried charcoal may be excavated by subsequent erosional processes and redeposited in other sites. He contrasts this with other plant detritus which he believes would be destroyed by re-entrainment, but as demonstrated above, this does not necessarily occur.

Discussion The physical and geochemical characteristics of phytoclasts have gained more attention recently because of their potential as indices for and/or sources of oil and natural gas, particularly in nonmarine and deltaic coastal settings (Combaz & de Martharel, 1978; Thomas, 1982; Nwachukwu & Barker, 1985; Bustin, 1988). Variations in abundance and type of detritus (amorphous organic material versus structured woody material; terrestrial versus open marine) with depositional environment and with stratigraphic age have been demonstrated in various geographical settings (e.g., Dow & Pearson, 1975; Hedges & Parker, 1976; Bustin, 1988). The recognition of different nannodetrital categories that can be isolated from preparation residues allows for an assessment of their provenance and resultant biofacies relationships. An understanding of the characters of the taphonomic assemblage, by assessing the individual plant part components, may provide data useful in assisting interpretations of depositional environment and studies of hydrocarbon source-rock potential. Structured terrestrially sourced phytoclasts comprise a variety of plant part tissues and/or cells that include cuticles of various origin (leaves, aerial stems, and roots), xylary and fibrous elements (leaf venation, sclerenchymatous bundles, and secondary woods), phytoliths, resistant small fruits and seeds, and charcoalified debris. Unstructured accessory chemical exudates, such as coniferous resins, and angiospermous copals and dammars, may be important elements in the amorphous residual fraction. The characteristics of micro- and mesodetrital residue are the result of various biogeochemical and physical degradational processes acting upon plant parts throughout their functional and post-functional existence. Biodegradation may be the result of interaction by bacteria and fungi, and the role each of these decomposers

The genesis and sedimentation of phytoclasts with examples from coastal environments may play with respect to any plant part varies. To date, plant parts recovered from various subaqueous depositional environments in temperate and tropical coastal regimes appear to be minimally affected by fungal degradation. Bacterial colonization and enzymatic degradation (catabolism possibly in response to cellular senescence) may play a more significant role in the degradation of the intracellular contents and celluloserich cell walls than the purported effects of fungal action. Timing and duration of, and susceptibility to, degradation appear to play the pivotal role in the quantity and quality of plant material available for incorporation and ultimate preservation in sediments. Plant parts that are subjected to prolonged alteration processes ultimately are reduced to the nannodetrital fraction. As has been demonstrated and discussed before (Gastaldo, 1988; Spicer, 1989), resistant plant parts are more prone than less resistant parts to being incorporated into sedimentary regimes even after physically disaggregated. Less resistant tissues are those most rapidly affected after physiological or traumatic loss. Biogeochemical degradation of different plant parts occurs at different tissue and cellular levels, with parenchymatous tissues undergoing deterioration first. For leaves, cuticle chemistry may be a significant factor with regard to the systematic distribution of identifiable cuticles in processed residues. Those composed of a resistant bipolymer (Nip et al, 1986a,b) do not undergo as severe deterioration as do cuticles lacking this particular bipolymer. The difference in preservation potential is aptly demonstrated in the comparison of plant leaves recovered from the Mahakam River delta cores. Within the same sample suite leaves may either be well preserved or may have undergone selective degradation, beginning at the interface between intervenal parenchymatous tissues and the xylary elements and continuing into the intervenal areas. In other instances, cuticular envelopes with venation architecture are found to coexist with leaves in various stages of deterioration (Gastaldo et ai, in press). The loss of soluble substances and the oxidation (blackening) of the material seems to be a universal property after plant detritus is exposed to saturating conditions. This 'softening' of the detritus predisposes the material towards degradation to nannodetrital-sized phytoclasts through various and, at times, sustained biotic or abiotic interactions. Biotic interactions include colonization by saprotrophic bacteria and/or fungi. In addition, macroinvertebrates may utilize the plant debris for food (resulting in hom*ogenization of the sediment through bioturbation), may use the resource as a habitat (either through epibiont growth or endobiont colonization), or a combination of these activities may exist. Macroinvertebrate behavior, including that of necrotrophs and biotrophs, may be responsible for the introduction of saprotrophs that promote tissue deterioration (e.g.,

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Gastaldo et a/., 1989). The principal abiotic interaction apparently responsible for phytoclast generation is the physical abrasive breakup of 'softened' plant parts in moderate to high energy environments. Although this may occur during residence and transport in bedload of a fluvial or nearshore setting, it appears that in coastal sedimentary regimes the majority of mechanical sizereduction occurs within the coastal zone through reworking of previously deposited detritus. Without a doubt, macrodetritus may be subjected to a complex transport history before it is finally buried. Often plant parts may undergo deposition and re-entrainment several times, and each time the plant part is subjected to potential and continued physical breakdown. The timing of this re-entrainment may be prior to burial, shortly after initial burial (within days to decades either due to the ephemeral character of the depositional site or to subsequent high-energy storm activity), or it may occur some time afterwards (on the order of 10 3 -10 4 years). Short-term eustatic sea level fluctuations in coastal zones must not be overlooked as a mechanism in the generation and redistribution of phytoclasts. With the recognition of sequence stratigraphic processes and the concomitant development of transgressive erosional surfaces that planate former nearshore and coastal terrestrial environments (ravinement surfaces; e.g. Galloway, 1989; Larue & Martinez, 1989; Liu & Gastaldo, 1992), any plant litter that would have accumulated and buried in these sites would be reintroduced into the water column upon erosion of the place of burial. Because pieces of plant litter would have been subjected previously to various degrees of degradation by a multiplicity of processes, their erosion during shoreface transgression would place them directly in a wave zone in which they would be mechanically fragmented. Their redistribution to the subsequently developed ravinement bed or to sites offshore would be a function of coastal energy operating within any particular part of the coastal regime. In situ degradation of buried litter may result when fluctuating water conditions introduce oxygenated waters into a site. This will result in the chemical alteration of plant parts and the development of micro- to mesodetritalsized materials, without necessarily meaning that the physical degradational processes operated at that specific time at that specific site. The generally ephemeral nature of coastal subaqueous to subaerial sites provides a means to reintroduce the degraded (and possibly partially matured) detritus into the water column, to be deposited in other parts of the coastal regime. Phytoclasts, such as particles of charcoal and resins, may be introduced into the sedimentary environment in a variety of ways. Inert charcoal enters the sedimentary regime most commonly through wind and/or water action, and is concentrated in nearshore environments

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(Herring, 1985). Resins, including copals and dammars, are transported either within their host wood or as part of bedload transport. The concentration of these amorphous plant parts in nearshore environments probably parallels that of charcoal. Redistribution of these particles results in alteration of their form, accompanied by size reduction. This is probably a function of brittleness. The vast majority of terrestrially derived phytoclasts recovered in coastal and nearshore facies appears to have originated from communities in which deciduous plants predominate. In the case of deltaic settings, the ecosystems contributing detritus are those of the upper delta and interior (extrabasinal) sites (Gastaldo et al, 1987; Gastaldo et a/., in press). The herbaceous vegetation growing in 'lower delta plain' settings (marsh grasses and Nipa palms) have a tendency to retain their aerial parts and undergo degradation in situ (Gastaldo, 1989; Gastaldo, 1990). When these sites are inhabited by arborescent vegetation (e.g., Orinoco River delta; Scheihing & Pfefferkorn, 1984) the plants tend to dehisce and shed canopy parts during growth. It is more common that the deciduous elements may be transported away from their initial depositional site by tidal flushing (Dame, 1982), but this does not preclude some of the degraded herbaceous material from dispersal by this mechanism, particularly under spring tidal conditions. In fact, the various kinds of amorphous and degraded material of terrestrial origin may be generated under these circ*mstances. The recognized early stages of color differentiation and maturation in these particles (e.g., Caratini, Chap. 8, this volume) may reflect the various phases of the initial biochemical alteration and/or chemical manipulation of the organic matter in the depositional setting. The loci where fluvial systems debouch into coastal environments can be acknowledged as the principal sites where large quantities of terrestrial detritus enter into the nearshore and littoral regimes. This detritus may be distributed by transport along coastlines by longshore currents and/or prevailing circulation patterns, and be deposited within various depositional settings, ranging from lagoonal to offshore barrier sands. But not all coastlines are perforated by river systems emptying into a basin. In most instances, long stretches of vegetated shoreline exist that are subjected only to the influence of tides. Differences in daily and monthly tides, and those tides amplified by localized storm conditions, generate variable conditions that affect vegetated coastal zones. When tidal velocities increase to the point where plant detritus of varied degradational states can be entrained in the water column (either moved in suspension or in bedload), litter can be flushed into nearshore sites where accumulation may result in organic-rich deposits (e.g., Risk & Rhodes, 1985; Bird, 1986). Low clastic sedimentation rates in these sites would allow for

preferential degradation of the least resistant tissues, resulting in concentration of those resistant parts, such as cuticular biopolymers. What are now considered to be 'dispersed' cuticles in facies that appear organic-rich but do not 'preserve' identifiable macrofossils might represent, in part, facies in which clastic sedimentation rates are lower than rates of degradation. The fragmentary character of these sample suites may not be entirely a function of cuticle separation from leaves and differential concentration, but rather may be the result of sample preparation. The biofacies resulting from the accumulation of phytoclasts mirror the regional terrestrial communities that flank either the distributary fluvial regimes or the marginal coastal vegetation. The temporal variations in the quality of contributed material are indicative of the changes in ecosystem structure of the provenance communities. The accessory nannodetrital components may be a signal of short-term ecosystem disruption on a localized or regional scale rather than evolutionary or long-term, climatically induced floristic turnover, as might be interpreted from the recovered palynoflora. This may be particularly applicable where palynofloras also contain quantities of charcoal (fusain). The ecological repercussions caused by wildfire have been reviewed by many authors (e.g., Rundel, 1981; Raup, 1981), and it is apparent that this disruption causes community turnover. When this is expressed on a regional scale and where k-strategy plants are eliminated, fecund r-strategists quickly become established. This alteration of community structure will be reflected quickly in changes of the palynoflora. This disruption is best manifested in contemporaneous depositional sites with the addition of wind-borne and/or water-transported charcoal fluxes. The recognition of this accessory component in higher than background concentrations might provide the clues necessary to filter out the short-term from long-term causes of vegetational change. With a developing understanding of the relationships between palynofacies generation and the taphonomic processes responsible for their nannodetrital component, a more accurate picture can be derived of their discrete utilization.

Acknowledgments Data collected for and discussed within this chapter have been collected over the past decade with the assistance of many undergraduate students, graduate students, and colleagues too numerous to cite individually. I would like to express my appreciation to them for their help in some inhospitable localities. Phytotaphonomic research in modern environments has been supported by several agencies. Acknowledgment is made to the Donors of the Petroleum Research Fund, as administered by the American Chemical Society, for grants ACS PRF 18141 B2 and ACS PRF 20829 AC8 in partial support of these studies. The National Science Foundation is acknowledged for grant NSF EAR 8803609 that supported research in eastern Borneo. Dr. George P. Allen and Mr.

The genesis and sedimentation of phytoclasts with examples from coastal environments Choppin de Janvry, TOTAL, Compagnie Franchise des Petroles, are gratefully acknowledged for providing logistical and field support for our vibracoring program in the Mahakam River delta, Kalimantan. Dr. Alain Yves-Hue and the Institut Frangais du Petrol are thanked for their assistance in developing a cooperative project in Indonesia and financial support allowing me a residence in France to begin sample processing and preparation. Professor Bruce Purser, the Universite de Paris-Sud, Orsay, is gratefully acknowledged for his cooperation and use of laboratory and electon microscopy facilities. Mr David Felton is thanked for providing data and unpublished x-radiographs of vibracores extracted in the Mobile-Tensaw River delta, Alabama, and Dr Charles E. Savrda is acknowledged for the loan of the Paleocene bored wood. The author would like to thank the editor and two anonymous reviewers for suggestions that led to the improvement of the manuscript.

References Ahlgren, C. E. (1970). Some effects of prescribed burning on Jack Pine reproduction in Northeastern Minnesota. Minnesota Agricultural Experimental Station Miscellaneous Report, 94, 1—14. Alexopoulos, C. J. & Mims, C. W. (1979). Introductory Mycology. New York: John Wiley & Sons. Allen, G. P., Laurier, D. & Thouvenin, J. P. (1979). Etude sedimentologique du delta de la Mahakam: TOTAL. Compagnie Frangaise des Petroles, Paris, Notes et Memoir es, 15, 1-156. Barnes, R. D. (1974). Invertebrate Zoology. Philadelphia: W. B. Saunders. Batten, D. J. (1973). Use of palynologic assemblage-types in Wealden correlation. Palaeontology, 16, 1-40. Batten, D. J. (1979). Miospores and other acid-resistant microfossils from the Aptian/Albian of Holes 400A and 402A, DSDP-IPOD Leg 48, Bay of Biscay. In Initial Reports of the Deep Sea Drilling Project, V. XLVIII, ed. L. Montadert and D. G. Roberts. Washington, DC: US Government Printing Office, 579-87. Batten, D. J. (1982). Palynofacies, palaeoenvironments and petroleum. Journal of Micropalaeontology, 1, 107-14. Batten, D. J. (1983). Identification of amorphous sedimentary organic matter by transmitted light microscopy. In Petroleum Geochemistry and Exploration of Europe, ed. J. Brooks. London: Blackwell Scientific, 275-87. Batten, D. J., Creber, G. T. & Zhou, Zhiyan (1984). Fossil plants and other organic debris in Cretaceous sediments from Deep Sea Drilling Project: their paleoenvironmental significance and source potential: Initial Reports of the Deep Sea Drilling Project 80. Washington, DC: US Government Printing Office, 629-41. Benoit, R. E , Starkey, R. L. & Basaraba, J. (1968). Effect of purified plant tannin on decomposition of some organic compounds and plant materials. Soil Science, 105, 153-8. Bird, E. C. F. (1986). Mangroves and intertidal morphology in Western Port Bay, Victoria, Australia. Marine Geology, 69, 251-72. Bustin, R. M. (1988). Sedimentology and characteristics of dispersed organic matter in Tertiary Niger delta: Origin of source rocks in a deltaic environment. Bulletin of the American Association of Petroleum Geologists, 72, 277-98. Chaloner, W. G. (1989). Fossil charcoal as an indicator of palaeoatmospheric oxygen level. Journal of the Geological Society of London, 146, 171-4.

125

Clark, D. L., Byers, C. W. & Pratt, L. M. (1986). Cretaceous black mud from the central Arctic Ocean. Paleoceanography, 1, 265-71. Combaz, A. & de Martharel, M. (1978). Organic sedimentation and genesis of petroleum in Mahakam delta, Borneo. Bulletin of the American Association of Petroleum Geologists, 62, 1684-95. Cope, M. J. (1980). Physical and chemical properties of coalified and charcoalified phytoclasts from some British Mesozoic sediments: an organic geochemical approach to palaeobotany. In Advances in Organic Geochemistry, 1979, Physics and Chemistry of the Earth, 12, ed. A. G. Douglas and J. R. Maxwell. Oxford: Pergamon Press, 663-77. Cope, M. J. (1981). Products of natural burning as a component of the dispersed organic matter of sedimentary rocks. In Organic Maturation Studies and Fossil Fuel Exploration, ed. J. Brooks. London: Academic Press, 89-109. Cope, M. J. & Chaloner, W. G. (1980). Fossil charcoal as evidence of past atmospheric composition. Nature, 283, 647-9. Cope, M. J. & Chaloner, W. G. (1985). Wildfire, an interaction of biological and physical processes. In Geological Factors and the Evolution of Plants, ed. B. H. Tiffney. New Haven, CT: Yale University Press, 257-77. Craighead, F. C. & Gilbert, V. C. (1962). The effects of Hurricane Donna on the vegetation of southern Florida. The Quarterly Journal of the Florida Academy of Science, 21, 1-28. Cunningham, A., Gay, I. D., Oehlschlager, A. C. & Langenheim, J. H. (1983). 13 C NMR and IR analyses of structure, aging, and botanic origin of Dominican and Mexican ambers. Phytochemistry, 22, 965-8. Dame, R. R. (1982). The flux of floating macrodetritus in the North Inlet estuarine ecosystem. Estuarine, Coastal and Shelf Science, 21, 1-28. Degges, C. W. & R. A. Gastaldo (1988). The use of fossilized logs as paleocurrent indicators in fluvial systems - A note of caution. Geological Society of America, Abstracts with Program, 20(7), A264. De Vries, H., Bredemeijer, G. & Heinen, W. (1967). The decay of cutin and cuticular components by soil microorganisms in their natural environment. Acta Botanica Neerlandische, 16, 102-10. Dickinson, S. (1960). The mechanical ability to breach the host barriers. In Plant Pathology, ed. J. G. Horsfall & A. E. Dimond. London & New York: Academic Press, 2: 203-32. Dittus, W. P. J. (1985). The influence of cyclones on the dry evergreen forest of Sri Lanka. Biotropica, 17, 1-14. Dow, W. G. & Pearson, D. B. (1975). Organic matter in Gulf Coast sediments. Offshore Technology Conference Proceedings, 3, Paper 2343. Ehrlich, P. R. & Raven, R. H. (1964). Butterflies and plants: A study of coevolution. Evolution, 18, 568-608. English, M. P. (1965). The saprophytic growth of nonkeratinophilic fungi on keratinised substrates and a comparison with keratinophilic fungi: Transactions British Mycological Society, 48, 219-35. Fahn, A. (1969). Plant Anatomy. Oxford: Pergamon Press. Ferguson, D. K. (1971). The Miocene Flora of Kreuzau. Western Germany: 1. The Leaf Remains. Amsterdam: North Holland Publishers. Ferguson, D. K. (1985). The origin of leaf-assemblages - new light on an old problem. Review of Palaeobotany and Palynology, 46, 117-88. Ferguson, D. K. & De Bock, P. (1983). The bryophyte and

126

ROBERT A. GASTALDO

angiosperm leaf-remains from the Holocene sediments of Deggendorf. Documenta Naturae, 9, 16-33. Fraenkel, G. (1959). The raison d'etre of secondary plant substances. Science, 121, 1466-70. Galloway, W. E. (1989). Genetic stratigraphic sequences in basin analysis I: Architecture and genesis of flooding-surface bounded depositional units. American Association of Petroleum Geologists Bulletin, 73, 125—42. Garden, A. & Davies, R. W. (1988). Decay rates of autumn and spring leaf litter in a stream and effects on growth rate of a detritovore. Freshwater Biology, 19, 297-303. Gastaldo, R. A. (1988). A conspectus of phytotaphonomy. In Methods and Applications of Plant Paleoecology: Notes for a Short Course, ed. W. A. DiMichele and S. L. Wing. Paleontological Society Special Publication, 3, 14-28. Gastaldo, R. A. (1989). Preliminary observations on phytotaphonomic assemblages in a subtropical/temperate Holocene bayhead delta: Mobile Delta, Gulf Coastal Plain, Alabama. Review of Palaeobotany and Palynology, 58, 61-84. Gastaldo, R. A. (1990). Phytotaphocoenoses in Late Quaternary temperate and tropical coastal deltaic regimes. Paleofloristic and paleoclimatic changes in the Cretaceous and Tertiary. In Proceedings of the International Symposium - Paleofloristic and Paleoclimatic Changes in the Cretaceous and Tertiary, International Geological Correlation Programme Project No. 216: Global Biological Events in Earth History, ed. F. Knobloch & Z. Kvafcek. Prague: Geological Survey of Czechoslovakia, 285-90. Gastaldo, R. A., Allen, G. P. & Hue, A. Y. (in press). Detrital peat formation in the tropical Mahakam River delta, Kalimantan, eastern Borneo: Formation, plant composition, and geochemistry. Geological Society of America Special Paper. Gastaldo, R. A., Demko, T. M , Liu, Y., Keefer, W. D. & Abston, S. L. (1989). Biostratinomic processes for the development of mud-cast logs in Carboniferous and Holocene swamps. Palaios, 4, 356-65. Gastaldo, R. A., Douglass, D. P. & McCarroll, S. M. (1987). Origin, characteristics and provenance of plant macrodetritus in a Holocene crevasse splay, Mobile delta, Alabama. Palaios, 2(3), 229^0. Gosz, J. R., Likens, G. E. & Bormann, F. H. (1973). Nutrient release from decomposing leaf and branch litter in the Hubbard Brook Forest, New Hampshire. Ecological Monographs, 47, 173-91. Green, N. B. (1980). The biochemical basis of wood decay micromorphology. Journal of the Institute of Wood Science, 8, 221-8. Griffin, J. J. & Goldberg, E. D. (1979). Morphologies and origin of elemental carbon in the environment. Science, 206, 563-5. Grimalt, J. O., Simoneit, B. R. T., Hatcher, P. G. & Nissenbaum, A. (1988). The molecular composition of ambers. Organic Geochemistry, 13, 677-90. Harris, T. M. (1958). Forest fire in the Mesozoic. Journal of Ecology, 46, 447-53. Harris, T. M. (1981). Burnt ferns from the English Wealdon. Proceedings Geological Association of London, 92, 47-58. Heath, G. W. & Arnold, M. K. (1966). Studies in leaf-litter breakdown. II. Breakdown rate of 'sun' and 'shade' leaves. Pedobiologia, 6, 238-43. Hedges, J. I. & Parker, P. L. (1976). Land-derived organic matter in surface sediments from the Gulf of Mexico. Geochimica et Cosmochimica Acta, 40, 1019-29.

Herring, J. R. (1985). Charcoal fluxes into sediments of the North Pacific Ocean: the Cenozoic record of burning. In The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present. Geophysical Monograph, 32, 419-22. Highley, T. L. (1976). Hemicelluloses of white and brown rot fungi in relation to host preference. Material und Organismen,

11, 33—46.

Hoagland, K. E. & Turner, R. (1981). Evolution of woodboring bivalves. Malacologia, 21, 111-48. Hoyt, W. M. & Demarest, J. M. (1981). Vibracoring in coastal environments: The R.V. Phryne II Barge and associated coring methods. University of Delaware, Sea Grant College Program, Newark, Delaware, DEL SG 01 81. Hue, A. Y. (1988). Sedimentology of Organic Matter. In Humic Substances and Their Role in the Environment, ed. F. H. Frimmel & R. F. Christman. London: John Wiley & Sons, 215-243. Hue, A. Y., Durand, B., Roucachet, J., Vandenbroucke, M. & Pittion, J. L. (1985). Comparison of three series of organic matter of continental origin. Advances in Organic Geochemistry, 1985. Organic Geochemistry, 10, 65-72. Kaushik, N. K. & Hynes, H. B. N. (1968). Experimental study on the role of autumn leaf shed in aquatic environments. Journal of Ecology, 56, 229-43. Kaushik, N. K. & Hynes, H. B. N. (1971). The fate of the dead leaves that fall into streams. Archives Hydrobiology, 68, 465-515. Kerp, H. (1989). Cuticular analysis of gymnosperms: A short introduction. In Phytodebris: Notes for a Workshop on the Study of Fragmentary Plant Remains, ed. B. H. Tiffney. Paleobotanical Section of the Botanical Society of America. Krassilov, V. A. (1975). Palaeoecology of Terrestrial Plants: Basic Principles and Techniques. New York: J. Wiley & Sons. La Caro, F. & Rudd, R. L. (1985). Litter disappearance rates in a Puerto Rican montane rain forest. Biotropica, 17,269-76. Lane, C. E. (1959). The general histology and nutrition of Limnoria. In Marine Boring and Fouling Organisms, ed. D. H. Ray. Seattle: University of Washington Press, 34-45. Langenheim, J. H. (1990). Plant resins. Scientific American, 78, 16-24. Larue, D. K. & Martinez, P. A. (1989). Use of bed-form climb models to analyze geometry and preservation potential of clastic facies and erosional surfaces. American Association of Petroleum Geologists Bulletin, 73, 40-53. Levy, J. F. & Dickinson, D. J. (1981). Wood. In Microbial Biodeterioration (= Economic Microbiology, 6), ed. A. H. Rose. London: Academic Press, 19-60. Liu, Yuejin & Gastaldo, R. A. (1992). Characteristics of a Pennsylvanian ravinement surface. Sedimentary Geology, 11, 197-213. Mantell, C. L. (1968). Carbon and Graphite Handbook. New York: Wiley-Interscience. Masran, T. C. & Poco*ck, S. A. J. (1981). The classification of plant-derived particulate organic matter in sedimentary rocks. In Organic Maturation Studies and Fossil Fuel Exploration, ed. J. Brooks. London: Academic Press, 145-61. McGinnes, A. E , Szopa, P. S. & Phelps, J. E. (1974). Use of scanning electron microscopy in studies of wood charcoal formation. Scanning Electron Microscopy/1974, part 2, 469-476. Mills, J. S, White, R. & Gough, L. J. (1984/85). The chemical composition of Baltic amber. Chemical Geology, 47, 15-39. Nip, M , Tegelaar, E. W , De Leeuw, J. W., Schenk, P. A. & Holloway, P. J. (1986a). A new non-saponifiable highly aliphatic and resistant biopolymer in plant cuticles: Naturwissenschaften, 73, 579-85.

The genesis and sedimentation of phytoclasts with examples from coastal environments Nip, M., Tegelaar, E. W., Brinkhuis, H., De Leeuw, J. W., Schenk, P. A. & Holloway, P. J. (1986b). Analysis of modern and fossil plant cuticles by Curie point Py-Gc and Curie Point Py-Gc-Ms: Recognition of a new highly aliphatic and resistant biopolymer. In Advances in Organic Geochemistry 1985, ed. D. Leythaeuser and J. Rollkotter. Organic Geochemistry, 10, 769-78. Nip, M., De Leeuw, J. W., Schenk, P. A, Windig, W , Meuzelaar, H. L. C. & Crelling, J. C. (1989). A flash pyrolysis and petrographic study of cutinite from the Indiana Paper coal. Geochimica et Cosmochimica Acta, 53, 671-83. Nwachukwu, J. I. & Barker, C. (1985). Organic matter: size fraction relationships for recent sediments from the Orinoco delta, Venezuela. Marine and Petroleum Geology, 2, 202-9. Nykvist, N. (1959a). Leaching and decomposition of litter. I. Experiments on leaf litter of Fraxinus excelsior. Oikos, 10, 190-211. Nykvist, N. (1959b). Leaching and decomposition of litter. II. Experiments on leaf litter of Pinus silvestris. Oikos, 10, 212-24. Nykvist, N. (1961a). Leaching and decomposition of litter. III. Experiments on leaf litter of Betula verrucosa. Oikos, 12, 249-63. Nykvist, N. (1961b). Leaching and decomposition of litter. IV. Experiments on leaf litter of Picea abies. Oikos, 12, 264-79. Nykvist, N. (1962). Leaching and decomposition of litter. V. Experiments on leaf litter of Alnus glutinosa, fa*gus silvatica and Quercus robur. Oikos, 13, 232-48. Palmer, T. Y. & Northcutt, L. I. (1975). Convection columns above large experimental fires. Fire Technology, 11,111-18. Panshin, A. J. & De Zeeuw, C. (1970). Textbook of Wood Technology. Vol. 1. New York: McGraw Hill. Parry, C. C , Whitley, P. K. J. & Simpson, R. D. H. (1981). Integration of palynological and sedimentological methods in facies analysis of the Brent Formation. In Petroleum Geology of the Continental Shelf of Nor th-West Europe, ed. L. V. Illing & G. D. Hobson. London: Institute of Petroleum, 205-15. Petersen, R. C. & Cummins, K. W. (1974). Leaf processing in a woodland stream. Freshwater Biology, 4, 343-68. Poco*ck, S. A. J., Vasanthy, G. & Venkatachala, B. S. (1987). Introduction to the study of particulate organic materials. Journal of Palynology, 23-24, 167-88. Raup, H. M. (1981). Physical disturbance in the life of plants. In Bio tic Crises in Ecological and Evolutionary Time, ed. M. H. Nitecki. New York: Academic Press, 39-52. Ray, D. L. (1959) Nutritional physiology of Limnoria. In Marine Boring and Fouling Organisms, ed. D. L. Ray. Seattle: University of Washington Press, 46-61. Rayner, A. D. M. & Boddy, L. (1988). Fungal Decomposition of Wood: Its Biology and Ecology. Chichester: John Wiley & Sons. Rindsberg, A. K. & Gastaldo, R. A. (1989). The roles of wave action, bioturbation, and diffusion of oxygen from aerenchymatous roots in degradation of leaf debris. 28th International Geological Congress Abstracts, 2, 701. Risk, M. J. & Rhodes, E. G. (1985). From mangroves to petroleum precursors: an example from tropical northeast Australia. Bulletin of the American Association of Petroleum Geologists, 69, 1230-40. Ross, S. (1989). Soil Processes: A Systematic Approach.

127

London and New York: Routledge. Rossel, S. E., Abbot, G. M. & Levy, J. F. (1973). Bacteria and wood (a review of the literature related to presence, action, and interaction of bacteria in wood). Journal of the Institute of Wood Science, 6, 28-35. Rundel, P. W. (1981). Fire as an ecological factor. In Physiological Plant Ecology 1. Response to the Physical Environment, ed. O. L. Lange, P. S. Nobel, C. B. Osmond & H. Ziegler. Berlin: Springer-Verlag, 501-38. Scheihing, M. H. (1980). Reduction of wind velocity by the forest canopy and the rarity of non-arborescent plants in the Upper Carboniferous fossil record. Argumenta Palaeobotanica, 6, 133-8. Scheihing, M. H. & Pfefferkorn, H. W. (1984). The taphonomy of land plants in the Orinoco Delta: A model for the incorporation of plant parts in clastic sediments of Late Carboniferous age of Euramerica. Review of Palaeobotany and Palynology, 41, 205-80. Scott, A. C. (1989). Observations on the nature and origin of fusain. International Journal of Coal Geology, 12, 443-75. Scott, A. C. & Collinson, M. E. (1978). Organic sedimentary particles: results from Scanning Electron Microscope studies of fragmentary plant material. In Scanning Electron Microscopy in the Studies of Sediments, ed. W. B. Whalley. Norwich, UK: Geoabstracts, 137-67. Spicer, R. A. (1981). The sorting and deposition of allochthonous plant material in a modern environment at Silwood Lake, Silwood Park, Berkshire, England. United States Geological Survey Professional Paper 1143. Spicer, R. A. (1989). The formation and interpretation of plant fossil assemblages. Advances in Botanical Research, 16, 95-191. Swift, M. J., Heal, O. W. & Anderson, J. M. (1979). Decomposition in Terrestrial Ecosystems. Studies in Ecology, 5. Thomas, B. M. (1982). Land-plant source rocks for oil and their significance in Australian basins. Australian Petroleum Exploration Association Journal, 22, 164-70. Thomas, B. R. (1970). Modern and fossil plant resins. In Phytochemical Phytogeny, ed. J. B. Harborne. London: Academic Press, 59-79. Tiffney, B. H., ed. (1989). Phytodebris: Notes for a Workshop on the Study of Fragmentary Plant Remains. Paleobotanical Section of the Botanical Society of America. Turner, R. & Johnson, A. C. (1971). Biology of marine woodboring molluscs. In Marine Borers, Fungi and Fouling Organisms, ed. E. B. G. Jones & S. K. Eltringham. Paris: Organization for Economic Cooperation and Development, 259-301. Upchurch, G. R. (1989). Dispersed angiosperm cuticle. In Phytodebris: Notes for a Workshop on the Study of Fragmentary Plant Remains, ed. B. H. Tiffney. Paleobotanical Section of the Botanical Society of America. Venkatachala, B. S. (1981). Differentiation of amorphous organic matter types in sediments. In Organic Maturation Studies and Fossil Fuel Exploration, ed. J. Brooks. London: Academic Press, 177-85. Warg, J. B. & Traverse, A. (1973). A palynological study of shales and 'coals' of a Devonian-Mississippian transition zone, central Pennsylvania. Geoscience and Man, 7, 39—46. Williams, A. M. (1963). Enzyme inhibition by phenolic compounds. In The Enzyme Chemistry of Phenolic Compounds, ed. J. B. Pridham. New York: Pergamon Press, 87-95.

8 Palynofacies of some recent marine sediments: the role of transportation CLAUDE CARATINI

Introduction

The concept of palynofacies

Palynological study of the organic matter content of sediments reveals information about the nature and state of preservation of constituent elements of both the sediments in general and the organic matter in particular. These observations have led to the establishment of a number of criteria to assist in reconstruction of the paleogeographical and sedimentological conditions prevailing at the time of deposition, as well as the geological history of the sediment. Several authors have proposed relationships which may have existed between paleogeography, in the broadest sense, and the microscopic character of the sedimentary organic matter. The ultimate aim of these investigations has been to understand the origin and alteration of this organic material, and, more generally, of the sediment in which it is preserved (Haseldonckx, 1974; Hart, 1986; Poco*ck et a/., 1987). Most often these studies have concentrated on Pre-Quaternary sedimentary formations. The paleogeography prevailing at the time of deposition can be deciphered only from reconstructions where hypotheses sometimes become important, reducing the validity of the proposed conclusions. It was to alleviate such difficulties, and particularly to understand and consequently interpret the geological data more accurately, that the ORGON project, a series of French scientific cruise-expeditions with organic geochemical goals, was undertaken during the years 1976-1983, to study the organic content of Late Pleistocene to Holocene deposits from various ocean environments (see Fig. 8.1). Only extant phenomena which can be described or quantified are taken into consideration. This project, essentially based on observed facts, enables us to delimit, in some well-defined cases, the role and importance of the various factors affecting the nature and state of preservation of organic matter in marine sediments.

Palynofacies is the description, by means of transmission light microscopy, of the organic constituents of the rock and estimation of their relative proportions (paraphrase of definition by Combaz, 1964; 1980).

Organic matter The organic matter observed does not represent the totality of organic matter present in sedimentary rock, but only the fraction which remains unhydrolysed after destruction of the mineral phase by hydrochloric and hydrofluoric acids (Durand & Nicaise, 1980). This fraction is designated as 'palynological residue' in preference to the term 'kerogen,' as the definition of the latter has become too inaccurate. 'Kerogen' is often used with different meanings in organic geochemistry and palynology. In the ORGON sediments, the palynological residues constitute an average of 60-70% of the total organic carbon fraction of the sediments and are therefore representative of the entire fraction.

Elements and criteria for characterizing a palynofacies Combaz's (1964, section Ib) classification is adopted here. Each element is sufficiently well defined so as not to give rise to divergent interpretations by different observers. This simplified method facilitates use, without reducing possibilities of interpretation.

Structured organic matter Structured organic matter is composed of elements which show a well-defined structure or form when viewed with a transmission light microscope. They are: (1) microfossils - pollen, spores, microplankton; (2) plant and animal 129

130

CLAUDE CARATINI

*6 Demerara abyssal plain

/)/ '//INDIAN Figure 8.1. the text.

OCEAN

Location of the ORGON cruises and sites mentioned in

Palynofacies of some recent marine sediments: the role of transportation

131

debris (their dimensions and color are characters which are easy to measure or evaluate); (3) opaque particles - from reflectance examination these are found to be mostly charcoal. Pyrite, which has not been considered in quantitative estimates, can be easily distinguished from organic matter by its crystalline, cubic or framboidal shape.

the majority of ORGON sediments, the structured/ amorphous ratio is strongly correlated with the most useful geochemical parameters for defining sedimentary organic matter: H/C and N/C atomic ratios. To represent this value, the increasing percentages of amorphous organic matter are plotted on the same graph axis, graduated from 0 to 100 from left to right (Fig. 8.2.1). This disposition implies that the values of structured organic matter, which are complementary, increase from Amorphous organic matter right to left on this graph axis. Hence, a sample on this Amorphous organic matter is composed of particles graph would be positioned as a function of its smaller than one micron in size, making it difficult to composition. Thus, the sample from the North Sea (cited define precisely. It is not possible to observe any structure earlier) is placed in A, while the sample from the Sukra in this fraction with the light microscope, even at the transect appears in B. highest magnification. I have refrained from describing the different aspects in which amorphous organic matter Maximum dimension of detrital structured elements The may be present because of difficulties in agreeing to a maximum dimension of detrital structured elements is a vocabulary usable by different observers without very useful criterion for interpreting transport and ambiguity. Moreover, by definition, this fraction of sedimentation of organic matter. This dimension, organic matter is called 'amorphous,' indicating lack of expressed in micrometers, is plotted on a logarithmic descriptive criteria. scale y-axis. In the example, sample A, where the largest

Numerical analysis of the palynofacies As early as 1964, Combaz established the basis for a quantitative method to estimate the fraction of the microscopic field occupied by each category of the palynofacies, using circular charts showing different percentage classes. The results obtained by trained observers are always of the same order, which testifies to the validity of this method. For example, the palynofacies of a sample from ORGON I in the North Sea (Combaz et al, 1977; see Fig. 8.2.1 - ORGON I sample KS14) is composed of 95% structured organic matter and 5% amorphous organic matter. In the Sukra transect, Gulf of Aden, ORGON IV (Caratini et al, 1981; see Fig. 8.2.1 - ORGON IV sample KL5), the composition is reversed, namely 10% and 90%, respectively.

Graphic representation of the palynofacies The simplest way to master and compare vast quantities of data is to adopt a standardized system into which each datum is entered as it is obtained.

Choice of criteria and mode of representation NUMERICAL CRITERIA

Proportion between amorphous and structured organic matter The most obvious character is the relative abundance of the two main categories of organic matter, structured versus amorphous. This relationship is very significant, as Caratini et al. (1983) have shown that, for

detrital structured elements measure 60 /mi, is clearly distinguishable from sample B, where they attain only 15 /im (Fig. 8.2.II). Proportions of the different types of structured elements The most common types of structured elements, i.e., microfossils, ligneous fragments, and opaque particles (excluding pyrite), can be represented quantitatively. For this purpose, the segment corresponding to the maximum dimension of the structured elements is divided proportionally into the different constituent percentages. This results in a stacked histogram, where the proportions of each category appear clearly (Fig. 8.2.III). Colors The importance of the color of organic matter in evaluating the degree of maturation and state of preservation is well known (see Correia, 1969). Without attempting extreme precision, the major trends in the color of each type of structured organic matter may be limited to three shades: black to dark brown, yellow to light green, and an intermediate of ochre between these two extremes. Each of these shades is seen as a well-defined hatching of obvious significance, the denser the hatching, the darker the color (see Fig. 8.2). Opaque particles are distinguished by another kind of pattern. Although, as stated above, amorphous organic matter is difficult to describe, it is nevertheless possible to estimate one character without too much controversy, namely, the color. This is especially true if we classify it into only three classes: light, dark, and intermediate. Samples A and B are examples of light and dark amorphous organic matter, respectively. To represent these colors without crowding the already dense diagram, a rectangle 5 mm high is added to the lower part of each

132

CLAUDE CARATINI B OMAN

NORWAY Orgon I KS14. 10cm

Orgon IV KL 5. 20cm

0%5% Amorphous O.M.

0% 10% -Structured O.M.

50'%

jum --- T 60jum 50-

n -s-

il5um

10-1 0

0% 5% Amorphous O.M. •

|um

50-

10% 0% -Structured 0. M.

50%

Proportions between structured debris

-microfossils 3% ^dark ligneous debris 2 %

microfossils < | % ligneous debris 5%

20-Opaque particles 9 0 % 1000% 5% Amorphous O.M.

Opaque particles 5 % 50%

microfossils ligneous fragments "Opaque particles 10% 0% Structured O.M.

Proportions between structured debris microfossils

204

ligneous fragments Opaque particles Colour amorphous O.M

10-1 50%

0 % 5% Amorphous O.M.

10% 0% -Structured O.M.

Colour

1 . | EEI!

dark middle

Opaque particles

light Figure 8.2. Principles of the graphic representation of palynofacies. Explanations for I, II, III, IV are in text.

bar, corresponding to the composition of the palynofacies, and explicitly hatched to demonstrate the colors (Fig. 8.2.IV). A graphic representation of the palynofacies is obtained which is clear enough for understanding the quantitative and qualitative features, and simple enough for practical use.

Palynofacies and conditions of transportation of the organic matter Reappraisal of some palynofacies selected from those studied following the ORGON cruises reveals the major influence of transportation conditions existing at the time

Palynofacies of some recent marine sediments: the role of transportation

•HiocH KL 10 (3765 m)

50-

KL II (3263m)

133

Proportion between KL 14 structured debris (1885m) KL 15 I KRI3 (2552m) t OlOm.) microfossils — _ ligneous fragments

20 H

Opaque particles 0

Colour amorphousO.M. 0% Amorphous O.M.

50%

92 95

-Structured O.M. Colour dark middle

1. ' .1 Opaque particles

light Figure 8.3.

ORGON III, Cape Blanc transect, Mauritania: graphic

representation of the palynofacies.

of deposition on the character of organic matter deposited in a marine environment. All the sediments are modern or very recent. In no case was the organic matter subjected to any significant diagenetic transformation. In this chapter I use only essential descriptions (for further information see Caratini et al, 1975,1979,1981; Caratini & Coumes, 1979; Combaz et al., 1977; Debyser & Gadel, 1979; Debyser et al, 1978; Moyes et al, 1978, 1979; Pelet et al, 1981).

The role of wind THE CAPE BLANC TRANSECT, MAURITANIA: ORGON III

The investigations carried out off Mauritania, along the Cape Blanc transect (Fig. 8.1) were aimed at studying the organic sedimentation on the continental margin of an old platform to which the vast Sahara Desert now extends. Several reasons a priori justified this choice (Caratini & Coumes, 1979; Pelet et al, 1979): (1) The contribution of organic matter of continental origin is low, due to the highly scattered Saharan vegetation, as well as to the nearly total absence of a perennial hydrographic network capable of transporting sedimentary deposits to the marine environment. Thus, the organic constituents of continental origin are solely those brought by wind. These are known to be significant (Simoneit, 1977), as the trade winds sweep the Sahara continuously. The importance of these constituents was verified by aeropalynological studies during the ORGON III cruise (Caratini & Cour, 1980). (2) Strong and regular trade winds also play a role, although indirectly, on organic sedimentation. They induce seasonal upwellings responsible for considerable primary production, evidence of which

should be found in the form of organic matter of planktonic origin in the sediments. We could infer that this organic matter of marine origin would be predominant when compared to that transported by wind. (3) The Canaries current, generally oriented NE-SW, could also be the source of organic material from regions further north which it traverses. However, results obtained from the ORGON III investigations do not indicate an important role for this current as a vector for supplying organic matter. Palynological analyses and detailed studies of sedimentary organic matter were carried out at 5 sites along the 21° N parallel (Caratini et al, 1979), ranging from the slope (station 13: 910 m) to the abyssal plain (station 10: 3765 m). The corresponding palynofacies are represented in Fig. 8.3, according to the method described above. The nature of the palynological residue varies in a regular manner with increase in depth and distance from the coast. Variation in the structured/amorphous organic matter ratio

The percentage of amorphous organic matter decreases away from the coast, from 95% in station 13, 92% in station 14, 87% in 15, 73% in 11, to only 30% in station 10. Thus, the structured/amorphous organic matter ratio increases as a function of depth and the distance from the coast. It seems as if the fragile amorphous organic matter had become altered and had disappeared in part when the movement necessary to attain marine depths increases, whereas, in contrast, the more resistant structured organic matter was relatively better preserved (Fig. 8.3). From the results of geochemical analyses (Debyser & Gadel, 1979) the amorphous organic matter is shown to be characteristically of marine origin, while the structured organic matter generally comes from the continent. Surprisingly, in a marine environment, as the depth and distance from the coast increase, the

134

CLAUDE CARATINI

W __ continent Continental organic microfossils Marine organic microfossils

ocean—:

Continental shelf

Abyssal plain

•

Vegetal fragments

Opaque particles

Amorphous organic matter

Figure 8.4. Progressive change in the composition of palynological residue from the shelf to the abyssal plain along the Cape Blanc transect Mauritania. ORGON I KS8 (440m) Pleistocene pm (glacial)

ORGON

500ORGON •8

Amazone

Demerara abyssal plain

Proportions between structured debris

100-

50microfossils

20100 0% 5 Amorphous O.M

50 55

ligneous fragments Opaque particles Colour amorphous O.M. 90 95 97 0 % -structured O.M.

1. ' . j opaque particles

Figure 8.5.

continental, rather than the marine markers, become more abundant. Such an apparent anomaly can be explained logically by the fact that when organic matter of continental origin reaches the marine environment it has already undergone some alteration. Hence, only the least labile fractions remain, and they will be transported further and further without any significant transformation. On the other hand, marine organic matter deteriorates

ORGON I, II, III, & IV: graphic representation of the

palynofacies studies.

rapidly as soon as it is produced. The sedimentation pattern of pelagic to semi-pelagic materials (Moyes et a/., 1979) is mainly one of 'decantation' and is therefore continuous and regular, and is without noticeable reworking, which also explains the progressive changes of the organic matter seen along the transect.

Palynofades of some recent marine sediments: the role of transportation Variation in the proportions of structured elements

The

proportions of the different types of structured elements vary depending on the site. Evolution of the composition of the palynofacies can be demonstrated as functions of depth of the sites and their distance from the coast. Organic microfossils constitute less than 1% of the palynological residue. When this residue is concentrated for palynological analysis it is observed that organic microfossil composition varies throughout the transect. The percentage of pollen decreases seaward with a corresponding increase in dinoflagellate cysts. This quantitative progression is accompanied by qualitative changes: disaccate pollen grains, almost exclusively represented by Pinus, become proportionally more abundant at station 10 (the deepest), where logically the pelagic cysts of the genus Impagidinium replace genera found in neritic or coastal environments, such as Tuberculodinium or Lingulodinium. The percentage of ligneous fragments and opaque particles increases with distance from shore. While in the shallower cores, KR13 and KL14, these detrital elements constitute an average of 5% of the palynological residue, their percentage progressively increases from about 10% in site KL15 to 25% in KL11, and reaches about 70% in the deeper water core, KL10. These detrital elements generally measure 5-10 /mi, the maximum size decreasing progressively away from the shore, from 50 to 30 /an. The reflectance of the coal particles is generally low, less than 1.5%, which indicates low maturity. These coal particles as well as the ligneous fragments are quite comparable to the corresponding elements present in desert aerosols collected from a source region in Niger (Caratini et a/., 1988). This is a further proof of their Saharan origin, and of transportation by wind to the marine environment. Variation in coloration Studies on the evolution of organic matter coloration confirm the seaward changes. Indeed, the color of the two fractions, amorphous and structured, evolves along the transect, and this evolution corresponds to an alteration towards greater depths. The color of the amorphous organic matter becomes lighter, while the ligneous fragments become darker, from light yellow in the KR13, KL14, KL15 and KL11 cores to a fairly dark ochre color in the KL10 core. Thus, in this example, first the wind from the Sahara, then a regular decantation by pelagic to semipelagic suspensions in the sea water, explain the main patterns of transport responsible for the relationship between the sources of the organic material and the resultant composition of the sedimentary organic matter. THE SUKRA TRANSECT, OMAN SEA: ORGON IV

The Sukra transect is located in the Oman Sea along the 57°30' meridian (Pelet et a/., 1981). It is over 200

135

km long (Fig. 8.1), extending from the edge of the continental shelf (station 6: 200 m) to the abyssal plain (station 5: 4010 m). Like the Cape Blanc transect, this region is now bordered by a vast desert zone, and upwellings are active here also. On the other hand, the winds which give rise to the upwellings blow alternately from east and west (Currie et al, 1973) and hence do not traverse the neighboring desert regions immediately north of the region studied. In all the sites of the Sukra transect, the palynological residues are characterized by an extreme abundance of amorphous organic matter which represents 97% of the total in station 6 (the shallowest), and 90% in the abyssal plain (Figs. 8.2, 8.6.2). The structured organic matter is composed of small elements, less than 15 /im in size. In spite of such hom*ogeneity, the ratio of amorphous/ structured organic matter decreases away from the shore. This diminution is accompanied by a change in color indicating a deterioration and is comparable to that observed off Mauritania. Thus, the alteration of organic matter off Oman is the same as that described for the Cape Blanc transect. Along the two transects investigated, Cape Blanc and Sukra, the potential sources of organic matter are similar and, consequently, the sedimentary organic matter shares common features. Their main dissimilarity is due to the difference between the eolian fluxes, heavily loaded off Sahara but not off Oman, because of the orientation of the winds in this region of the Arabian Sea. Role of sub-marine canyons and slumping THE KAYAR CANYON, SENEGAL, AND THE ABYSSAL PLAIN OF GAMBIA: ORGON III

The Kayar canyon is a major geomorphological feature of the continental margin off Senegal and Gambia (Caratini & Coumes, 1979). It begins near the Senegalese coast and, after a wide curve in the north, stretches over the abyssal plain of Gambia. This whole zone extends off a humid region covered by forests of the Sudanian and Guinean domains and is drained by short rivers with abundant flow. Three sites were studied in detail (Fig. 8.1): one in the middle of the canyon (station 17: 3871 m), another at its opening in the Gambia abyssal plain (station 6: 4450 m), and the third at the foot of the slope (station 4: 4000 m; see Dewaele, 1980). Sedimentological studies of Moyes et al. (1979) have shown that slumping on the slope and reworking in the canyon dominate the deposition of the sediments, mainly silty clay, which is too fine for clearly revealing turbidite sequences. The most striking feature of the palynofacies of the three cores studied is their uniformity (Fig. 8.5). Ligneous fragments, constituting 30-40% of the total organic residue, can attain dimensions up to 250 /mi. They are

136

CLAUDE CARATINI

fWMM

wmMh A*

100 / / m light yellow in color, a good index of immaturity. The opaque particles, also comprising 30-40% of the total, belong to two granulometric classes: small-sized elements (5-15 /im), which are the most abundant, and larger elements measuring 50-100 /xm. The reflectance of the large-sized particles is low, always less than 2%, indicating low maturity. The well-preserved state of structured elements is due to transportation followed by rapid deposition, the rivers being short and the continental plateau relatively narrow. The percentage of amorphous organic matter is about 30%, and the color of this fraction is quite dark, an indicator in this case of its well-preserved condition. The heterogeneity of the opaque particles denotes a double origin, regional and probably aquatic for largesized fragments, distant and eolian for small-sized ones. Several arguments favor an eolian origin for these small-sized fragments. They are identical to those

Figure 8.6. Magnification indicated by bar. (1) ORGON I, KS14 (0.20 m). Sea of Norway. Palynofacies with predominance of structured elements: ligneous fragments and highly colored microfossils; opaque particles. (2) ORGON IV, KL5 (0.20 m). Sea of Oman. Palynofacies dominated by amorphous organic matter. (3) ORGON III, KL14 (2.50 m). Offshore Mauritania. Cape Blanc transect. Station near the coast. Palynofacies dominated by amorphous organic matter. (4) ORGON III, KL10 (3.15 m). Offshore Mauritania. Cape Blanc transect. Station away from the coast. Palynofacies dominated by opaque particles.

observed in the Cape Blanc transect, where eolian origin is certain. The eolian source is also evident in the nature of the pollen associations: pollen from the Sahara predominates (about 40%); there is also a fair amount (about 5% on the average) of Mediterranean pollen. The deposition of the sediments, dominated by the preponderant role of turbidity currents and rapid

Palynofacies of some recent marine sediments: the role of transportation transportation by canyons, insures the preservation of the organic material, producing numerous reworkings of the sediments, and leading to their hom*ogenization. Thus, the similarity between sites 17, 4 and 6, despite the difference in their locations in terms of both depth and distance from the coast, is remarkable and is explained by the mode of transport on the continental slope.

The role of sea level THE AMAZON CONE AND THE ABYSSAL PLAIN OF DEMERARA, BRAZIL: ORGON II

The Amazon River drains a huge basin now covered almost completely by tropical evergreen forests. This river then flows into the Atlantic Ocean where, in the course of geological time, it has accumulated a gigantic cone prolonged by a deep sea fan which grades laterally into a long continental rise to the abyssal plain of Demerara. The Holocene Period All these ocean floors are covered by a thin (a few decimeters) layer of biogenic ooze, consisting of foraminifera and pteropods. This ooze has been deposited during the Holocene by a pelagic sedimentation pattern (Moyes et a/., 1978), excluding the irregular fluxes of sediments by slumping. The palynofacies in all the sites studied (Fig. 8.1) are very hom*ogeneous (Fig. 8.5). They are dominated by dark yellow amorphous organic matter (85%, on the average) and also contain small-sized ( . W A , | ACTIVE DELTA FRESH-WATER INFLUENCED SHORELINE

147

148

GEORGE F. HART

1 UU%

Qrt(V

I I i T0 T A L 0 RGrANIC CARBON

orjcv

\ \

LU 7 0 %

\ \ \ \

Z
m

LU X ^ CO oco _|LL 100

Eh (mV)

oxidized >400

natural levee. Abandonment results in subsidence and the blanketing of the organic sediments with saline marsh peat and bay deposits. These interdistributary areas of peat accumulation are characterized by abrupt facies changes and rapid sedimentation rates. The marginal deltaic, high-organic environments are laterally extensive, fine grained, and exhibit slower depositional rates but complex hydrodynamic changes. The marshes are at present depositing a blanket peat in response to the transgression of the Gulf of Mexico. Beckman (1984) showed that the thickness of the peat is controlled by the physiographic nature of the local basin.

Effect of water characteristics Salinity is probably the most important aspect of water affecting particulate organic matter in sediments. In organic rich environments Penfound and Hathaway (1938) and Penfound (1952) divided the Louisiana marshes into four types on the basis of salinity: fresh, slightly brackish, brackish, and saline. This is a result of the interaction of tidal action and freshwater runoff. There are gradational boundaries between the marsh types on both an areal and temporal scale and only the three main types (fresh, brackish, saline) were used for the investigations of maceral distribution reported in this chapter. The characteristics of the overlying water mass are given in Table 9.3, and those of the surficial sediments in Table 9.4. There is a strong relationship between the salinity of the overlying water mass, the salinity of the surficial sediment and the salinity of the interstitial water of the depositional environment (Fig. 9.5; Tables 9.3-9.5). In the depositional environment there is a general trend for decreasing TOC content with increase in salinity (Fig. 9.6). Palmisano (1970) and Chabreck, (1972) also observed this in the surficial environment, and noted that saline marshes (average salinity 15%) contain a low diversity of plant species dominated by the halophyte, Spartina alterniflora Loisel. The TOC content averages 25%. The brackish marshes (average salinity 7%) are more diverse and are dominated by Spartina patens, in association with four to five other common species. The TOC averages 35%. The freshwater marshes are the most diverse, with 92 species dominated by Panicum hemitomon. TOC content reaches 50% or more. The amount of water over an organic sediment affects the quantity of organic matter, as is seen in the scatter plot of water depth versus TOC (Fig. 9.6). Beckman (1984) pointed out that shallow water depth, or the absence of water, allow the diffusion of molecular oxygen to the surficial sediments. This encourages the development of a fungal and bacterial aerobic biocoenosis: pathways which facilitate the degradation of organic matter. This

150

GEORGE F. HART

Table 9.4. Characteristics of surficial sediment: Louisiana deltaic plain Key: A = acidic; B = basic; Br = brackish; F = fresh; MA = moderately acidic; MiA = mildly acidic; MiB = mildly basic; M R = moderately reduced; N = neutral; Ox = oxidized; S = saline; SBr = slightly brackish Environment

Salinity

1.1 1.2 1.3 1.4 1.5 2.1 2.2 2.3 2.4 2.5 2.6 3.1 3.2 3.3 3.4 3.5 4.1 4.2 4.3 4.4 4.5 5.1 5.2 5.3 5.4 5.5

MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR MR Ox Ox MR

N MiB MiB MiB MiB MiB MiB MiA MA A MiA B B MiB MiB MiB MiB MiB MiB N MiB MiB A MiA MiA N

S Br SBr SBr Br Br Br Br Br F F Br S S S S Br S Br S S F F SBr SBr SBr

is seen in the fresh marsh environment (which has the lowest water level) which contain a greater abundance of infested and scleratoclastic macerals. The lower TOC of the saline marsh also may be a result of the more complete biodegradational pathway. However, there is a high exportation of organic matter from these environments (by tidal flushing), and sedimentation rates are higher.

Organic degradation The great bulk of sedimentary organic matter produced by living systems is destroyed by the biochemical activities of monerans, protozoans, and fungi, rather than by abiologic chemical reactions. Although much of this takes place in the water column, the process of conversion of POM to DOM by bacterial action at the sediment/ water interface and in the depositional environment is important in the organic chemical cycle (Degens et al, 1964; Hart, 1986; Litchfield et al, 1974).

Structural carbohydrates are the main energy source left in the debris that accumulates at the surface/water interface. The most abundant materials that are comparatively resistant to decay include lignin (which is the most common natural product containing aromatic rings), some proteinaceous substances, and lipids. Sporopollenin and chitin also are resistant but are not quantitatively as significant. In addition, humic substances (fulvic acid, humic acid, and humin) are quite resistant to microbial decay and may form the bulk of organic matter in both the water column and at the sediment/ water interface. It is for this reason that plant debris (lignin rich), algal remains (lipid rich) and amorphous kerobitumen (often predominantly colloidal particulate humic substances) dominate POM. 'With respect to all sedimentary organic matter, the rapidity with which it passes through the surficial zone of intense degradation has a direct effect on the probability that the organic matter will be retained at depth.' (Hart, 1986) Sieburth (1979) and Odum (1971) point out that the destruction of POM is really a bacterial-protozoan partnership, in which flagellated protozoans in the POM supplement the osmotrophic work of the monerans. Although the bulk of this activity takes place in the aerobic zone of the sediments important bacterial induced changes occur in the anaerobic zone. In continental environments fungi may be equally or more important than monera in biodegradation, but the monerans are definitely the most important degrading organisms in the marine environment. Sieburth (1979) notes that within the anaerobic zone the processes are basically the same, irrespective of habitat, and the same types of organisms are involved. Chemically the phytoclastic macerals contain the following major polymeric biomass compounds: hom*opolysaccharides (cellulose and starch), heteropolysaccharides (hemicellulose), lignins, pectins, proteins, and lipids. The hom*opolysaccharides are the most abundant, and cellulose comprises 45-98% of most virgin phytoclasts. In woody cell walls cellulose occurs as lignocellulose. Under aerobic conditions the fungi are extremely active in cellulose degradation. Heteropolysaccharides (hemicellulose) may form up to 40% of phytoclastic biomass.These short, branch-chained polysaccharides are readily degraded by fungi and bacteria. Lignin (an aromatic compound) comprises 20-30% of phytoclastic biomass. It is poorly degradable but experimentally will produce low molecular weight, aromatic compounds. This has been done at high temperatures and pH (Sleat & Mah, 1987). Under strict anaerobic conditions at least eleven degraded products of aromatic lignins can be converted to methane (Healy & Young, 1979; Healy et al, 1980). Pectin and starch are complex polysaccharides that

Maceral palynofacies of the Louisiana deltaic plain 36

20 CO

"5 12

Surface Salinity

•• c

• ••• • ••• • •• •

I16

20 25 30 35 Six Inch Sample Salinity

Figure 9.5. Scatter plots of constituents in environments of the Louisiana deltaic plain: (a) salinity of overlying water versus surficial bottom sediment; (b) salinity of overlying water versus depositional environment sediment.

151

152

GEORGE F. HART

Table 9.5. Characteristics of depositional environment sediments: Louisiana deltaic plain Key: A = acidic; B = basic; Br = brackish; F = fresh; h = high; l = low; m = medium; M = moderate; MiA = mildly acidic; MiB = mildly basic; MOx = moderately oxidized; M R = moderately reduced; N = neutral; na = not available; O x = oxidized; R = reduced; S = saline; SBr = slightly brackish

Environment Eh

Salinity

Sulfate

Sulfide

Org. sulfur

Sand %

TOC

C:N Methane ratio

1.1 1.2 1.3 1.4 1.5 2.1 2.2 2.3 2.4 2.5 2.6 3.1 3.2 3.3 3.4 3.5 4.1 4.2 4.3 4.4 4.5 5.1 5.2 5.3 5.4 5.5

MiA MiB MiA N MiB MiB MiB MiA MiB A A B MiB MiB MiB MiB MiB MiB MiB MiB MiB MiA A MiA A MiA

S Br Br Br Br Br Br Br S SBr F S Br S S

h m 1 1 m h h h h 1 1 h h h h h h h h h h 1 1 1 1 m

1 1 1 1 I I I I I I I 1 I I I

m 1 1 1 m h h h h h m 1 m 1 m m m 1 1 1 1 1 1 1 1 1

m 1 1 1 m h m h h h m 1 1 1 m m 1 1 1 1 1 1 1 1 1 1

1 m 1 mixed 1 1 mixed mixed mixed mixed mixed h h h 1 1 mixed h h 1 1 mixed 1 mixed mixed 1

M M M M M m M h h h h 1 1 1 M M M 1 1 M M M h M 1 M

1 1 M h M 1 1 1 1 h h 1 1 1 1 1 1 1 1 1 h h h h 1 h

R MR MR MR MR R R R R R MR M MR MR R MR R MR MR MR MR MR MR MR Ox MR

Br S Br S S F SBr SBr SBr F

Descriptive codes used for Table 9.5 Sulfate (mg/1) Sulfide (wt %)

low 0-500

medium 500-1500

low 0-0.1

high >0.1

Total sulfur (wt %)

low 0-0.1

medium 0.1-0.5

high >0.5

Organic sulfur (wt %)

low 0-0.1

medium 0.1-0.5

high >0.5

Sand %

low 0-25

medium 26-75

high 76-100

Total organic carbon = TOC (wt %)

low 0-0.4

moderate low 0.4-0.8

moderate 0.8-5.0

Methane (ppm)

low 0-1000

medium 1000-2000

high >2000

C:N ratio

low

high

high >1500

high >5.0

I 11 I 12 h 13 I 14 hi 15 h21 h22 h23 h24 h25 h26 tia31 h32 133 134 135 141 142 na43 144 145 h 51 152 153 154 155

are readily decomposed by bacterial activity. The anaerobic digestion of lipids (mainly glycerol, with long chain monocarboxylic acids) may be inhibited by high H 2 content but generally takes place at a slow pace. However, Lindblom and Lupton (1961) noted a progressive increase in lipids with depth in the Orinoco deltaic sediments. This was possibly a result of bacterial 'upgrading,' as suggested by Zhang and Chen (1985) and Hart (1986). The major product after digestion by the hydrolytic bacteria are fatty acids. This is converted to a methanogenic substrate by the acetogenic and hom*oacetogenic bacteria (Table 9.6). It is important to realize that bacterial degradation may increase the proportion of some compounds in the organic matter they are degrading. For example, proteins may comprise more than 50% of bacterial cells, and much of this material may be left behind when the bacterial population dies. BACTERIAL GEOCHEMISTRY AND SULFUR CONTENT

Winogradsky (1888) first noted the existence of monerans that derived energy by oxidation of sulfur compounds.

Maceral palynofacies of the Louisiana deltaic plain TOC 55 + 50 + 45 + 40 + 35 + 30 + 25 + 20 + 15 + 10 + 5+ 0+

a Legend: A = 1 obs, B = 2 obs, etc.; Depth in meters. TOC in wt %. TOC 55 • 50 •

B^V.

A 40 •B 35 A 30 G 25 L 20 H 15 ND 10 •Z AAA 5 JAUXEA 0 ZYZVVZDC

45 •

B A B A G KA E C H AED LBEL ECB ZDGFMA

153

A A A A DAB HBD L I C C A A A J A SAE O F F GAEC A G N I

WDEP A A B BGHZ ED

NLJBB 10

WDEP

Legend: A = 1 obs, B = 2 obs, etc.; Salinity in PPT, TOC in wt %. TOC 55 • 50 •

45 • 40 •

35 30 25 20 15 10 5 0

TOC 55 + 50 + 45 + 40 + 35 + 30 + 25 + 20 + 15 + 10 + 5 + AB 0+

A BA A

A AA BBBB A GB C A AA ABAABB AB EAA CBBC 15

A B AB A AA AD B A BA A BA C BC A DADG 20

WSAL C A V A ZH AA

GED AAAA BAAAB fa*gEAAC EDBJFGDCAED EEEE C A CBTCF 10

AAA 35

WSAL Variable WDEP WSAL TOC

N 505 328 519

Minimum 0 0.010 0

Maximum

Mean

Std Dev

35.99 33.83 52.02

5.65 12.94 4.05

9.965 10. 549 7. 418

Figure 9.6. Scatter plots of constituents in environments of the Louisiana deltaic plain: (a) water depth versus total organic carbon; (b) salinity versus total organic carbon. Plots to the right are enlargements of important areas in the main plots. WSAL = water salinity in parts per thousand; WDEP = water depth in meters; TOC = total organic carbon in wt %; obs = observation(s).

The sulfur-oxidizing bacteria involved were reviewed by Schlegel (1975). Species belonging to Thiobacillus are important organisms causing the oxidation of sulfide to sulfate in the oxygenic zone. Although sulfide oxidation is principally facilitated by bacterial activity, slow

154

GEORGE F. HART

Table 9.6. Levels of bacterial activity in surficial and depositional environments (cf. Chynoweth & Isaacson, 1987, P. 3) 1. DEPOSITION OF MACERALS (Proteins, Lipids, Carbohydrates) 2. ALTERATION BY HYDROLYTIC BACTERIA (to Organic Acids, Neutral Compounds, CO 2 , H, Alcohols) 3. ALTERATION BY ACETOGENIC (and hom*oACETOGENIC) BACTERIA (to CO 2 , H 2 , Acetate) 4. ALTERATION BY METHANOGENIC BACTERIA (to CH 4 , CO 2 )

inorganic oxidation can take place. The sulfate-reducing bacteria degrade organic matter and simultaneously convert the sulfate to sulfide. The sulfate-reducing bacteria remove oxygen from S O | " and then reduce the sulfur to S 2 ~ under anaerobic conditions (Nedwell & Banat, 1981). This activity occurs to a depth at which sulfate no longer diffuses downward. In general, the methanogenic bacteria are inhibited by the sulfate bacteria, probably as a result of the competition for H 2 and acetate (Hobson et al. 1974; Kristjansson et al.9 1982; Oremland & Taylor, 1978; Schonheit et al, 1982; Thauer, 1982). Sulfur analyses were performed on both the interstitial water (sulfate and sulfide) and the sediment of the depositional environment (total sulfur, organic sulfur, and inorganic sulfide by subtraction). As seen in Table 9.5, the sulfur-rich environments are essentially the shoreline environments. Statistical analysis of the sulfur data emphasizes the dominance of salinity in determining the sulfate concentrations found in the interstitial water. High salinities in the depositional environment cause high interstitial water sulfate values as seen in Figure 9.7. Analyses of bulk sediments indicate that the total sulfur and organic sulfur for the most part are dependent upon TOC. Particularly, in sediments with a high organic content the interstitial sulfate values correlate positively with the amount of total sulfur and organic sulfur found in the sediment. This agrees with the findings of Casagrande et al. (1979) and Casagrande and Ng (1979), who noted that: (1) 30-50% of total sulfur in peat from the Everglades is in the organic form contributed from both plant sources and microbial activity converting SO 4 to H 2 S, and (2) the formation of a significant portion of the organic sulfur content of a sediment is related to sulfate concentration. Thus, fresh waters high in organic matter and low in sulfate have low total sulfur and organic sulfur, whereas areas high in sulfate and organic matter have high total sulfur and organic sulfur (see Fig. 9.8). Because of the relationship between sulfate concentration and salinity of the interstitial water (high salinities

causing high sulfate values), Beckman (1984) suggested that transformation of sulfate to organic sulfur may show a strong correlation to the salinity of the overlying marsh water. Thus, organic sulfur content might provide an indication of paleosalinities. TOC, organic sulfur, and salinity analysis of the 60 samples from the three marsh environments (Hart, 1979c) had indicated that high salinities relate to greater concentrations of organic sulfur. Using these data, Beckman calculated the mean TOCsulfur ratios for each of the three marsh environments as: fresh 6.87, brackish 10.12, and saline 21.06. He then measured the organic sulfur content of 13 samples in a core from the Barataria Basin, which core he had previously shown to include a sequence of the three marsh types. His analyses indicated that the simple TOCsulfur ratio could not be used to indicate paleosalinities. The sulfur is apparently leached and migrates downward. Moreover, sulfur may be formed below the surficial sediment zone. For example, Lord (1980) noted that seasonal oxidation events destroy pyrite and release sulfur into the pore water. The sulfate is then reduced microbially to H2 S at depth, and reacts with organic matter to produce organic sulfur. Clearly, the pore water systems of organic-rich deposits are highly reactive and play an important part in changing the chemical imprint in subsurface sediments. BACTERIAL GEOCHEMISTRY AND METHANE CONTENT

The presence of light hydrocarbons (C1-C7) was measured on all samples. Using the occurrence of butane as an indicator of the presence of petrogenic (nonbiogenic) gas, the data-set was divided into petrogenic and non-petrogenic samples. It is recognized that this method does not unequivocally isolate all non-petrogenic material, but only that it provides some indication of the amount of biogenic methane production in a sample. The distribution of methane in the depositional sediments of the Louisiana deltaic plain is summarized in Table 9.5 and Figure 9.9. It is well known that below the sulfate zone the methanogenic bacteria take over. These monerans cannot use complex organic compounds but grow on substrates such as CO 2 , H-methanol, and acetate (Gottschalk, 1979; Sorensen et al, 1981). Methane production in the depositional environment is the result of bacterial degradation, but this activity is inhibited by the presence of sulfate in the interstitial water in quantities as small as 0.2 mM (Zeikus, 1977; Nikaido, 1977). The scatter plot (Fig. 9.9) shows that a distinct relationship exists between methane production and sulfate in the interstitial water. This relationship is expressed by the formula: log[CH 4 ] = 7.17 -1.51 logCSOj"] 2

(r = 0.85), where methane and sulfate are expressed in parts per thousand.

Maceral palynofacies of the Louisiana deltaic plain

155

Sulfate

Offshore Barrier Island Shoreline Onshore Active Delta Alluvial Valley

Salinity

Figure 9.7. Triplot of sulfate in the interstitial water. Eh, and salinity of the environments of the Louisiana deltaic plain. DMB = distributary mouth bar; IDB = interdistributary bay; FM = fresh marsh; Eh = redox potential.

The statistical analyses performed in the present study also indicate that both sand percentage and TOC influence methane production. The highest methane production is found in freshwater environments that have high TOC and low sand content. Microbial methanogenesis occurs only under strict anaerobic conditions and involves a mixed bacterial population of obligate anaerobes acting at three levels (Chynoweth & Isaacson, 1987), as illustrated in Table 9.6. This activity occurs efficiently at a depth in the sediment at which oxygen, nitrates, and most of the sulfates have been depleted. Eh requirements in a sediment are probably less than — 300 mV; pH optimally in the 6.0-7.7 range; and a temperature optimally in the 4-45 °C range (Zhang & Chen, 1985). Figure 9.10 shows the distribution of Eh and pH in the depositional environment samples studied from the Louisiana deltaic plain. As a result of their biodegradation the hydrolytic bacteria produce organic acids, hydrogen, carbon dioxide

and alcohols from the macerals (lipids, proteins, and carbohydrates). This is the rate-limiting step in the overall conversion of macerals to methane. Acetogenic and hom*oacetogenic bacteria then work over these compounds to produce acetate, hydrogen and carbon dioxide. This involves a complex interspecies association of bacteria primarily driven by the flow of electrons (as H2) (Boone & Mah, 1987). The methanogenic bacteria then convert the acetate, hydrogen and carbon dioxide to methane and carbon dioxide. The final gas often includes traces of hydrogen sulfide. It should be noted that certain macerals (lignin rich organic matter) are little effected by the biodegradational processes under anaerobic conditions, even under long residence times (a factor in the formation of coals). The hydrolyzed products are peptides which are converted to amino acids and used as carbon and energy sources by the acetogenic bacteria. MACERAL DEGRADATION

The degradation state of a sediment is an important parameter for differentiating environments of deposition. In addition, knowledge of the degree of organic degradation is useful in determining the potential of a sediment to produce hydrocarbons. Two independent

156

GEORGE F. HART 100%

90%

SULFATE IN INTERSTITIAL WATER

80%

70%

•

z £ 60% o Q_

jjj 50%