This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Chavez Lara, Claudia Title: Ecosystem changes and paleoclimatic implications from the Chihuahua Desert (Mexico) during the late Pleistocene and Holocene General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. 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Ecosystem changes and paleoclimatic implications from the Chihuahua Desert (Mexico) during the late Pleistocene and Holocene by Claudia Magali Chávez Lara School of Chemistry September 2018 A thesis submitted to the University of Bristol in accordance with the requirements for award of the degree of Doctor of Philosophy in the Faculty of Science Word count: 39616 i ii Abstract Climate change is affecting the subtropical northern Mexico by reducing the amounts of rainfall and increasing the severity of droughts. The rainfall system of this area is governed by the North American Monsoon which mechanism and dynamics regarding past global temperature change are still unclear. Hydroclimate variation of the northwest Mexico, specifically during the late Pleistocene and Holocene is an active area of debate, with uncertainty in the nature and sources of precipitation. Previous research has inferred the influences of winter storms, summer monsoonal rain and autumn tropical cyclones. Moreover, the impacts on regional and local ecosystems are not well constrained. In this thesis, I employ organic and inorganic geochemical methods, studying a variety of lipid biomarkers from aquatic and terrestrial sources, as well as the isotopic composition of endogenic carbonates to investigate two basins in central northern Mexico: the Satiaguillo and El Potosi basins at the western and eastern limits of the Chihuahua Desert. I investigate the response of lacustrine and terrestrial habitats of these basins to hydrological changes occurring since the late last glacial. Biomarkers from both sedimentary records reflect variable input of organic matter from algal and bacterial biomass, aquatic microfauna and surrounding vegetation. Changes in these inputs reveal distinct stages of ecosystem development and correlate with endogenic carbonate isotopic changes over the last 27,000 years on the Santiaguillo area and 20,000 years on the El Potosi area. Overall, the areas presented opposite environmental conditions during the last glacial maximum and deglaciation period. However, over the early- and mid- Holocene, both records reveal increasing aridity and a shrinking water body, while the late Holocene was characterized by less dry environment with higher proportions of C4 grasses. Finally, this thesis illustrates the great potential of biomarker applications for paleoenvironmental reconstructions of dry settings areas with poor pollen preservation and other fossil particulate matter. iiii iv To Lucía and Román iiv vi Acknowledgments First of all, I would like to thank my supervisors Richard D. Pancost, Jens Holtvoeth and Priyadarsi D. Roy for their support and guidance throughout my PhD. Very special thanks to CONACyT for funding me on this adventure. Thank you very much to all my friends and family who have always believed in me. viiiii viii Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University's Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate's own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED………………………………….. DATE…………………... ivix x Table of contents Abstract................................................................................................................ i Dedication............................................................................................................ ii Acknowledgments...……..................................................................................... iii Author’s declaration............................................................................................ iv Table of contents.................................................................................................. v List of figures....................................................................................................... ix List of tables......................................................................................................... xiv List of equations………………………………………………………………... xv Abbreviations........................................................................................................ xvi CHAPTER I. Introduction 1 1.1 Thesis aims and objectives 3 1.2 Thesis Structure 4 CHAPTER II. Scientific Background 6 2.1 The Chihuahua Deseret 6 2.2 The North America Monsoon 8 2.3 Climatic conditions during Late Pleistocene-Holocene 10 2.4 Hydroclimate of northwest Mexico and southwest USA during the Late 12 Pleistocene and Holocene 2.5 Lacustrine deposits and previous research on Santiaguillo and the El 14 Potosi basins 2.5.1 The Santiaguillo Basin 16 2.5.2 The El Potosi Basin 17 2.6 Organic Geochemistry 18 2.6.1 Lipid biomarkers 18 2.6.2 GDGTs 20 2.6.2.1 Isoprenoidal GDGTs 20 2.6.2.2 Branched GDGTs 22 2.6.2.3Relationship between iGDGTs and brGDGTs 24 2.6.3 Compound specific isotopes 25 2.7 Inorganic Geochemical Proxies 27 2.7.1 δ18O in endogenic carbonates 28 v 2.7.2 δ13C in endogenic carbonates 30 2.8 Unravelling paleoenvironmental conditions 31 CHAPTER III. Materials and Methodology 33 3.1 Material 33 3.2 Methodology 34 3.2.1 General sample preparation 34 3.2.2 Organic geochemical analyses 35 3.2.2.1 Biomarker analysis 35 3.2.2.1.1 Lipid Extractions 35 3.2.2.1.2 Hydrolysis and transmethylation of fatty acids 36 3.2.2.1.3 Derivatisation of hydroxy groups 36 3.2.2.1.4 GC and GC/MS analysis 36 3.2.2.2 GDGTs analysis 37 3.2.2.2.1 Filtering 37 3.2.2.2.2 HPLC/MS 37 3.2.2.3 Compound-specific isotopes analysis 37 3.2.2.3.1 Fractionation 37 3.2.2.3.2 GC-C-IRMS 38 3.2.3 Inorganic analysis 38 3.2.3.1 Analysis of carbon and oxygen isotopes of carbonates 38 3.2.3.1.1 Organic matter removal 38 3.2.3.1.2 CO2 acquisition 38 3.2.3.1.3 VG Optima MS 38 3.3 Data processing 39 3.3.1 Identification and quantification of lipids 39 3.3.2 GDGT analysis 39 3.3.3 δ13C values of FAMEs 40 3.3.4 δ13C and δ18O values of calcite 41 3.4 Uncertainty evaluation 41 CHAPTER IV. The Santiaguillo Basin 43 4.1 Abstract 44 4.2 Introduction 44 vi 4.3 Regional Setting 46 4.4 Materials and Methodology 48 4.5 Results 50 4.5.1 Lipid concentrations 50 4.5.2 Lipid composition (compound class inventory) 52 4.5.2.1 Saturated n-fatty acids (n-FAs) 52 4.5.2.2 Mono- and polyunsaturated fatty acids (MUFAs and PUFAs) 53 4.5.2.3 Hydroxy acids (OH-FAs) 53 4.5.2.4. Branched fatty acids 53 4.5.2.5 n-Alkanes 53 4.5.2.6 n-Alcohols (OH) 54 4.5.2.7 Methyl ketones 54 4.5.2.8 Sterols 54 4.5.2.9 Others 54 4.6 Discussion 54 4.6.1 Degradation 54 4.6.2 Inferred paleoenvironment from lipid assemblages 55 4.6.3 Interpretation of Changing Ecosystems and Land Surface Processes 61 4.7 Conclusions 69 CHAPTER V. The El Potosi Basin 71 5.1 Abstract 72 5.2 Introduction 73 5.3 Regional Setting 76 5.4 Sediment and analysis 77 5.5 Results 79 5.5.1 TOC contents, TOC/TN ratios and lipid concentration 79 5.5.2 GDGTs 82 5.5.3 Lipid composition (compound class inventory) 84 5.5.4 Carbon isotopes of fatty acids 86 5.6 Discussion 89 5.6.1 Ecosystem evolution 89 5.6.2 Ecosystem response to regional hydroclimate 100 5.6.2.1 Late Pleistocene 102 vii 5.6.2.2 Holocene 103 5.7 Conclusions 105 CHAPTER VI. Paleoclimatic implications for the Chihuahua Desert 107 6.1 Abstract 108 6.2 Introduction 109 6.3 Previous studies 111 6.4 Material and Methodology 113 6.5 Results 115 6.5.1 Endogenic calcite isotope data from the Santiaguillo Basin 115 6.5.2 Endogenic calcite isotope data from the El Potosi Basin 115 6.6 Discussion 117 6.6.1 Carbonate precipitation and dissolution in lakes 117 6.6.2 Unravelling the isotopic signature of lacustrine carbonates 118 6.6.3 Climate forcings 124 6.7 Conclusions 131 CHAPTER VII. Conclusions and Future Work 133 7.1 Conclusions 134 7.1.1 Records of environmental changes from subtropical Mexico 134 7.1.2 Climatic forcing 137 7.2 Final remarks 139 Appendix 1 142 Appendix 2 154 Appendix 3 166 References 167 viii List of figures Figure 2.1 Location of the North American Desert system. The Chihuahua Desert 6 forms the southern part of this desert system. (1) Chihuahua, (2) Coahuila, (3) Nuevo Leon, (4) Durango, (5) Zacatecas and (6) San Luis Potosi are the Mexican states that are part of the Chihuahua Desert.