The Formation of Plant Compression Fossils

THE FORMATION OF PLANT COMPRESSION FOSSILS: EXPERIMENTAL AND SEDIMENTOLOGICAL INVESTIGATIONS by G illia n Mary Rex Thesis submitted fo r the degree of Doctor of Philosophy in the University of London Department of Botany Bedford College University of London September 1983 ProQuest Number: 10098497 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10098497 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 To Bob ”The simple^ qudlitab’ive experiments described belcw are only justifiable in so fa r as they give good ideas and they can d isc re d it bad ones. For me they did both”. Professor Tom M. Harris (1974) ABSTRACT The mechanisms and processes that lead to the formation of a plant com pression fossil have been experimentally reproduced and studied in the present investigation. This research has used two main lines of in ve sti gation: f ir s t ly , experimental modelling of the fo ssilisa tio n process; and secondly, a detailed examination of plant compression fo ssils. Early experimental modelling was based on the simplest system possible. A dry compression apparatus was used in which a r tific ia l materials, represent ing plant and matrix, were subjected to vertical deformation. Forms were produced which closely resembled vertical sections of Sawdonia, Stigmaria, Calamités and Lepidodendron. Further apparatus was subsequently constructed, in which wet sediment and actual plant material were compressed, thus more closely reproducing the natural system of compacting sediment. Using this apparatus, factors, such as the role of grain size, change in dimensions of the plant organ, and rigidity of plant tissues were investigated. A recirculating labo ratory flume tank was used to examine the flow conditions, larid other parameters that were required to produce burial of plant material and in f ill of hollow stems. The results obtained formed a basis for inter preting the conditions of formation of observed fossil stem in fills . Experimental compression of the stems buried in the flume indicated the effect of an in f i l l on the eventual form of the fo s s il. Examination of plant compression fossils in the present investigation has been mainly based on a study of vertical sections through the matrix. These reveal the overall structure o f the compression, and the processes leading to its formation. The Carboniferous plants, Cyperites, A1ethopteris, Lepidostrobus and Trigonocarpus, have been investigated in this way. An understanding of the factors that dictate the fin a l form of the fo s s il, using the techniques described above, gives new insight into the fo s s ili sation process. This is of potential value in reconstructing plants from fossils only known in the compression state of preservation. This is illustrated with reference to Permian ovulate glossopterid fructifica- t i ons from Gondwanaland. Computer modelling provides an alternative method for studying the com pression process, and an account is given of a computer-based investiga- û^at-jon- process.' 11 ACKNOWLEDGEMENTS This work was carried out during the tenure of a NERC studentship which is gra tefully acknowledged. I should lik e to thank my supervisor. Professor W.G. Chaloner, fo r a ll his help and encouragement during the la st three years. I should also like to thank the following: the staff and technicians of the Botany Department, Bedford College, for all th e ir help, especially Mr P. Waite; Bedford College fo r providing research fa c ilitie s ; Dr Nils Gunnar-Ohlson fo r his considerable help with the computer modelling and for being my host during my v is it to Stockholm; Dr Dorothy Guy-Ohlson fo r arranging my v is it to Sweden and for all her help during my stay; Professor B. Llumblad for allowing me to v is it the Riksmuseum in Stockholm and to study the collections. I acknowledge the Central Research Fund, of the University of London, fo r funding the flume tank. I especially thank Mr S. White, of the Science Workshop at Bedford College, fo r building the tank and a ll my other apparatus used during this research. I am grateful to the Keeper of Palaeontology, British Museum (Natural History) and the Director of the Institute of Geological Sciences for allowing me access to the collections in their care. Many people have helped in discussion and in proof-reading parts of this thesis; I thank Hugh Pearson, Jane Francis and Else-Marie F riis fo r th e ir useful criticism s, and Simon Barber and Andy Davis fo r a ll th e ir photo graphic assistance. I extend grateful thanks to Rosemary Fris cher fo r a ll her patience during the typing of the thesis and fo r doing such a good job. I appreciate the support and encouragement given by my parents, especially during the last months of writing. Last, but not least, I thank my husband. Bob, whose patience, encouragement and understanding enabled me to complete this thesis. m PREFACE This thesis consists of two published papers and a submitted paper, and also the main part of the thesis. The order in which i t should be read is : the Introduction to the thesis, the paper in Appendix A, Chapter 3 of the thesis, the paper in Appendix B, Chapter 5 of the thesis, the paper in Appendix C, and then the remainder of the thesis, Unfortunately, there is some unavoidable repetition. This is mainly in the introduction of the thesis and in the introductions to the papers. This is because of the necessity to introduce the field of study to the reader in the publications. The references at the back of the thesis are a comprehensive lis t of a ll the references quoted in the published papers and those in the main part of the text. IV LIST OF PLATES page 1. The wet compression apparatus 18 2. The results of experimental compression of plant stems 28 3. The results of experimental compression of hollow plant stems 41 infilled and buried in a clay matrix 4. The results of the experimental compression of stems in fille d 49 and buried in the flume tank and then compressed in the wet compression apparatus 5. The structure of fossil stem compressions 52 6. The structure of compression borders in and bounding 56 fossil casts. 7. The structure of fossil pith casts 56 8. The structure o f Calamités pith casts in fille d with shale 68 9. The part and counterpart of the Pteridosperm leaves 72 10. The part and counterpart of A1ethopteris and Glossopteris 76 (both devoid of coaly matter) and Cordaftes 11. The structure of A1ethopteris compressions in transverse-section 78 12. The pathway the fracture plane takes to expose an 80 A1ethopteris pinnule 13. Permineralised specimens of A1ethopteris. Cordai tes and 84 Sphenopteri s 14. Experimental modelling of Rigby's (1978) hypothesis fo r the 112 compression of dorsiventral fructifications 15. Experimental modelling demonstrating the compression of 116 enrolled fructifications 16. Specimens of impression fossils of the ovulate glossopterid 119 fossils 17. The structure of the wing region in the ovulate glossopterid 121 fructifications 18. The arrangement of seeds in the impressions fo s sils of 122 ovulate glossopterid fructifications I9î Experimental modelling o f " Scutum" 127 20. The external structure of the cone compressions 139 21. Transverse-sections of cone compressions, showing the : variation in the structure of the cone axis -n -# ; : ïfs:: page 22. The structure of the sporangium and pedicels in cone 143 compressions 23. The structure of the lamina of the sporophylls in the cone 145 compressions 24. Sections of permineralised Lepidostrobus 147 25. The structure of Trigonocarpus 158 26. The internal structure of Trigonocarpus and Pachytesta 163 27. The hydraulic press apparatus 178 28. The compression of a solid cylinder of foam rubber in a 185 sawdust matrix in the dry compression apparatus 29. The compression of a hollow cylinder of foam rubber in a 194 sawdust matrix in the dry compression apparatus VI LIST OF FIGURES page 1.1 The terminology o f compression/impression fo ssils 10 used in this thesis 3.1 Simulated compression failures in plant axes (from Niki as 1978) 14 3.2a The wet compression apparatus 17 3.2b Plan drawing of the surface of the piston 20 3.3 The wet compression apparatus with core-catcher attached 21 3.4 The terminology of the uncompressed and compressed stems 23 used in this discussion 3.5 Results of the experimental compression of solid stems in 27 different grain sizes of matrix 3.6 The results of experimental compression of hollow rigid 31 pi ant stems 3.7 The results of experimental compression of plant stems 37 in fille d and buried in the same sediment 3.8 The proposed difference in mechanical behaviour of a sand 44 and clay matrix during compaction 3.9 The effect of a sediment i n f i l l on the form o f the stem 48 compression 3.10 The formation o f sediment ridges on a Calamités pith cast 58 5.1 The structure of clay infilled stems 66 7.1 Diagrammatic topography ®f!the part and counterpart of 74 A1ethopteris, Neu ropteri s, Glossopteris and Cordai tes 7.2 The pathway the fracture plane

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