Spatial and Temporal Diversity Trends in an Extra-Tropical, Megathermal Vegetation Type: the Early Palaeogene Pollen and Spore Record from the Us Gulf Coast
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SPATIAL AND TEMPORAL DIVERSITY TRENDS IN AN EXTRA-TROPICAL, MEGATHERMAL VEGETATION TYPE: THE EARLY PALAEOGENE POLLEN AND SPORE RECORD FROM THE US GULF COAST by Phillip Edward Jardine A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Geography, Earth and Environmental Sciences College of Life and Environmental Sciences University of Birmingham July 2011 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT During the early Palaeogene warm interval megathermal climatic regimes expanded beyond their current tropical limits. The early Palaeogene sporomorph (pollen and spore) record of the US Gulf Coastal Plain (GCP) indicates an extra- tropical vegetation type that developed under these megathermal climatic conditions. It is therefore suitable to address hypotheses concerning the importance of tropical climates in controlling low latitude spatial and temporal diversity patterns. Here, I construct a new sporomorph dataset comprising 151 samples, 41831 counted specimens and 214 sporomorph morphotypes. Fifty-nine of these morphotypes were not found in the published literature and are newly described. I demonstrate that previous studies of the GCP sporomorph record that have relied on biostratigraphic datasets have underestimated the true species richness of this region. Compositional heterogeneity was important for maintaining regional species richness on the GCP. The rate and scale dependency of spatial turnover in Holocene tropical and extra- tropical sporomorphs records precluded associating the GCP vegetation more closely with any particular modern biome, however. Finally, I show that warming extra- tropical regions to megathermal levels did not stimulate increased speciation there, which does not support a direct control of temperature on speciation rate in the low latitudes. ACKNOWLEDGEMENTS Thanks awfully to: My PhD supervisor, Guy Harrington, for several years of help, support and intellectual input, while this project took shape, and then proceeded to change shape into something rather different. Paul Smith, for his role as second supervisor, who provided quick and insightful comments on grant applications and the like when requested, but never felt the need to interfere the rest of the time. In essence, an ideal second supervisor. Ivan Sansom and, in the early stages of the project, Tim Reston, who made many improving comments during panel meetings. Ivan also took over as second supervisor, apparently. Aruna Mistry, for creating a pleasant and enjoyable working environment for my teaching support role, and for being ever-so-nice when things got a bit busy on the PhD front. The rest of the staff and all the post-grads based in Earth Sciences, for making the whole process a lot more enjoyable than it might have been otherwise. Special thanks to the various inhabitants of room 116 over the last few years, for injecting some much needed fun into the humdrum of PhD life. On the funding front, thanks to the School of Geography, Earth and Environmental Sciences for paying me to do this project (it took about 18 litres each of hydrofluoric and hydrochloric acid, 4 litres of nitric acid, and 2000 litres of aterw to process the 70 kilograms of sediment. I hope it was good for you too), and the Palaeontological Association, the Geological Society of London, the American Association of Stratigraphic Palynologists, the Micropalaeontological Society, and the Linnean Society Palynology Specialist Group, for providing much needed financial support for fieldwork, courses and conference attendance. Andy Moss for his help with the aforementioned lab work. Dan Kowalski of Walnut Creek Mining Company, Keith Wallis of U.S. Silica Mine, David Dockery III, Richard Carroll and Tracy Janus for their help and logistic support during fieldwork on the U.S. Gulf Coast. Carlos Jaramillo, Hermann Behling, Juan Carlos Berrio and Francis Mayer are thanked for providing additional data that are used in Chapters 6 and 7. Carlos Jaramillo, Surangi Punyasena and Thomas Demchuk provided helpful reviews for two manuscripts that form Chapters 5 and 6 of this thesis. John Alroy, Mike Foote, Tom Olszewski, David Polly and Pete Wagner are thanked for their inspirational teaching on the PBDB summer school, which greatly broadened my statistical horizons, and vastly elevated the quality of data analysis that has gone into this thesis. My family, and in particular Jodie the dog, for providing a much-needed haven in the Berkshire countryside. And walkies, of course. And finally, thanks to Sania Reddig for almost five years of emotional, financial and gastronomic support. CONTENTS Chapter 1: Introduction Page 1 1.1 The early Palaeogene greenhouse world 1 1.2 The US Gulf Coast paratropics 4 1.3 Global and regional climatic trends 6 1.4 Aims of thesis 9 1.5 Structure of thesis 11 Chapter 2: Geological setting 15 2.1 Structural and stratigraphic architecture of the GCP sedimentary sequence 15 2.2 Lithostratigraphy 17 2.3 Dating the GCP sedimentary succession 20 Chapter 3: Materials 23 3.1 Sampling strategy 23 3.2 Sample processing 27 3.3 Data collection 28 3.4 Potential reworking of sporomorphs 30 Chapter 4: Systematics 33 Trilete isospores 33 Zonoporate pollen 37 Tricolpate pollen Page 39 Zonocolpate pollen 50 Tricolporate pollen 51 Zonocolporate pollen 81 Triprojectate pollen 85 Chapter 5: The Red Hills Mine palynoflora: a diverse swamp assemblage from the Late Paleocene of Mississippi 93 5.1. Introduction 93 5.2 Geological setting 96 5.3 Materials and methods 97 5.3.1 Rarefaction 97 5.3.2 Evenness 97 5.3.3 Non-metric multidimensional scaling (NMDS) 98 5.4 Results 99 5.5 Discussion 105 5.5.1 Environmental interpretation 105 5.5.2 Comparisons with other Late Paleocene palynofloras 107 5.6 Conclusions 109 Chapter 6: Regional-scale spatial heterogeneity in the Late Paleocene paratropical forests of the U.S. Gulf Coast 111 6.1 Introduction 111 6.2 Sampling spatial patterns in the fossil sporomorph record 115 6.3 Materials Page 117 6.4 Age model 119 6.5 The biogeographic structure of the Paleocene GCP palynoflora 123 6.5.1 Methods 123 Additive diversity partitioning 124 Sample ordination - NMDS 128 Cluster analysis 129 6.5.2 Results 130 Additive diversity partitioning 130 NMDS 132 Cluster analysis 134 6.5.3 Compositional heterogeneity in the Paleocene GCP palynoflora 135 6.6 Relating the Paleocene GCP to Holocene biomes 139 6.6.1 Methods 139 Holocene dataset details 139 Data analysis 143 6.6.2 Results 146 6.6.3 The Paleocene GCP versus Holocene tropical and extra- tropical biomes 148 6.7 Summary and conclusions 150 Chapter 7: An early Palaeogene record of extra-tropical plant diversity patterns 153 7.1 Introduction Page 153 7.2 Materials and methods 157 7.2.1 Dataset description and overview 157 7.2.2 Data analysis 158 Individual- and sample-based rarefaction 158 Within-sample evenness 159 Species richness estimation 165 NMDS 166 Proportional first and last appearances 167 Origins of first appearances: speciation versus immigration 169 7.3 Results 175 7.3.1 Palynofloral diversity on the GCP and in Colombia 175 Within-sample richness (observed) 175 Within-sample richness (estimated) 177 Within sample evenness 177 Within-Age richness (observed) 177 Within-Age richness (estimated) 180 7.3.2 GCP compositional changes 183 NMDS 183 GCP turnover (first and last appearances) 183 7.3.3 Immigration versus speciation on the GCP 185 7.4 Discussion and conclusions 188 7.4.1 GCP versus Neotropical diversity during the early Palaeogene Page 188 7.4.2 The influence of temperature on paratropical speciation, and implications for the form and maintenance of the LDG 189 Chapter 8: Conclusions 193 8.1 Restatement of thesis aims 193 8.2 Major findings of thesis 193 APPENDIX 1: ADDITIONAL SYSTEMATICS 197 APPENDIX 2: R CODE 373 REFERENCES 401 CD (enclosed on inside back cover) R code as .rtf files Appendix 3: Count data and sample information Appendix 4: Taxon index list with occurrence information LIST OF FIGURES Figure 1.1. δ18O and estimated ice-free temperatures for the Cenozoic Page 2 Figure 1.2. Reconstructed positions of the continents during the Early Eocene 2 Figure 1.3. Global and US Gulf Coastal Plain climatic trends during the early Palaeogene 8 Figure 2.1 Stratigraphy for the US Gulf Coastal Plain 18 Figure 3.1. Map of U.S. Gulf Coast showing sampling localities, and stratigraphic coverage for each locality 24 Figure 3.2. Sedimentary logs for cores and outcrops sampled 26 Figure 3.3. Sampling intensity for formations in Mississippi and Alabama (Porters Creek to Zilpha formations) and Texas (Calvert Bluff Formation) 29 Figure 5.1. Typical exposures of lignite beds in the Red Hills Mine 95 Figure 5.2. Individual-based rarefaction curves for Red Hills Mine samples 100 Figure 5.3. Rank/abundance plots for Red Hills Mine samples 102 Figure 5.4. Sample-based rarefaction curves for lignite and non- lignite samples 102 Figure 5.5. NMDS biplot of Red Hills Mine samples and selected taxa 104 Figure 6.1. β diversity (among-sample heterogeneity) and spatial turnover in ecological systems 113 Figure 6.2. Sampling coverage and biostratigraphic correlation 118 Figure 6.3. Sampling scheme used in Chapter 6 Page 126 Figure 6.4. Additive partitioning of species richness 131 Figure 6.5.