Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Dissertations, Master's Theses and Master's Reports - Open Reports 2013 Spatial and Temporal Evolution of the Volcanics and Sediments of the Kenya Rift Alexandria L. Guth Michigan Technological University Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Geology Commons Copyright 2013 Alexandria L. Guth Recommended Citation Guth, Alexandria L., "Spatial and Temporal Evolution of the Volcanics and Sediments of the Kenya Rift", Dissertation, Michigan Technological University, 2013. https://doi.org/10.37099/mtu.dc.etds/484 Follow this and additional works at: https://digitalcommons.mtu.edu/etds Part of the Geology Commons SPATIAL AND TEMPORAL EVOLUTION OF THE VOLCANICS AND SEDIMENTS OF THE KENYA RIFT By Alexandria L. Guth A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Geology MICHIGAN TECHNOLOGICAL UNIVERSITY 2013 © 2013 Alexandria L. Guth This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Geology. Department of Geological and Mining Engineering and Sciences Dissertation Advisor:" James Wood Committee Member: " Jacqueline Huntoon Committee Member: " Aleksey Smirnov Committee Member: " Carol MacLennan Department Chair: " Wayne Pennington Dedication This work could not have happened without the field geologists who came before me and spent years working on the ground, collecting rocks, and doing analyses. My first and foremost dedication is to these scientists, whose hard work has allowed this synthesis to occur. On a personal level I would like to thank my advisor, Jim Wood who took me to Africa, my parents Sharon Alley (1981) & Lawrence Guth (1991) who raised me in a science-filled home, and my partner in science & life: Bryan Franklin (2009). In case anyone ever reads this: as all who have written likely know, it is difficult and time consuming to distill your thoughts into a single page, and I am sure most academic writers do not do so unless compelled by page limitations. Thus, to paraphrase Blaise Pascal (1656): I apologize that this work is so long, I lacked the time to make it short. Table of Contents List of Figures!.............................................................................vii List of Tables!................................................................................ix List of Files!....................................................................................x Acknowledgments!.......................................................................xi Definitions!...................................................................................xii List of Abbreviations!.................................................................xiii Abstract!......................................................................................xiv Introduction and Summary!..........................................................1 Document Structure!.................................................................................6 Recommendations!....................................................................................8 1. Geological mapping in the Kenya Rift!....................................9 1.1. Introduction!........................................................................................9 1.2. Geologic Survey Publications!..........................................................9 1.3. Non-Survey Maps and Reports!.......................................................11 1.4. The Era of Age Dating!......................................................................14 1.5. A Digital Map of the Kenya Rift Geology!.......................................17 1.5.1 Digital Mapping Techniques & Sources of Map Error".................17 2. Rift characterization & current state of research!................20 2.2. Current State of Knowledge: Rift Origins!......................................24 2.2.1. One Plume"................................................................................26 2.2.2. Several Small Plumes"...............................................................26 2.2.3. Superplumes, Piles, and LLSVPs"..............................................29 iii 2.2.4. Modified Single Plume"...............................................................31 2.2.5. The Plate Model".........................................................................33 2.2.6. Brief Argument Summary"..........................................................34 2.3. Current State of Knowledge: Timing of rift development!............36 2.4. Current State of Knowledge: Crustal Structure!............................37 2.5. Current State of Knowledge: Plate Motions!..................................41 3. Geologic development of the Kenya Rift: trends and patterns!........................................................................................44 3.1. Methods!............................................................................................44 3.2. Trends & Paleomaps!.......................................................................45 3.2.1. Composition:"..............................................................................46 3.2.2. Spatial and Temporal Trends:"....................................................49 3.3. Volume Analysis!...............................................................................59 3.3.1. Seismically derived thickness estimates"...................................66 3.3.2. A note on volume estimates; sediments and dense-rock equivalents"..........................................................................................70 3.3.3. Volume estimate comparisons"...................................................71 3.3.4. Reconciling seismic and map-derived volume estimates"..........71 3.4. Volcanic pulses and eruptive rate comparisons!..........................74 3.4.1. Eruptive Rates"...........................................................................76 3.4.2. Comparisons with other large eruptive events - LIPs and SLIPs ".............................................................................................................79 3.4.3. Volcanic mass flux & comparisons with other systems"..............83 3.5. Chapter Conclusions: spatial, temporal & volumetric trends!.....86 4. Lake and hominin site distributions from Miocene to present in the Kenya Rift!............................................................88 iv 4.1. History of Lake Sedimentation in the Kenya Rift!..........................88 4.1.1. Basics of Climate in the Rift".......................................................89 4.1.2. Lacustrine deposits: volcanic and hominin synergies"................91 4.1.3. Volcanic and Lake Sedimentation trends in the Kenya Rift".....100 4.1.4. Lake Deposition History"...........................................................104 Oligocene: the earliest rift sediments!.................................................107 Early Miocene: 15-18 Ma!.......................................................................107 Mid-Miocene: 9-13 Ma!...........................................................................107 Late Miocene: 6-7 Ma!............................................................................108 Pliocene: 3-4 Ma!....................................................................................110 Late Pliocene - Early Pleistocene: 1.7-3 Ma!........................................110 Discussion of Pliocene - Pleistocene Climate!...................................111 Middle Pleistocene: 0.5-1.5 Ma!............................................................112 Late Pleistocene: 100-200 ka!...............................................................114 Holocene: the last 10 ka!.......................................................................115 Holocene: Present lacustrine settings!................................................115 4.2. Hominin developments in reference to rift and lake basin development!..........................................................................................117 4.2.1. Background to hominin research".............................................117 4.2.2. Hominin trends in the Rift"........................................................121 4.3. Conclusions: rift-related lacustrine & hominin trends!...............126 4.3.1. Open questions and future research needs:"............................127 5. Discussion & Conclusions!..................................................132 5.1. Conclusions!...................................................................................140 References!................................................................................143 v Appendix A!................................................................................169 Appendix B!................................................................................171 Appendix C!................................................................................176 Appendix D!................................................................................177 Appendix E!................................................................................178 vi List of Figures Figure 1.1." Outline of Kenya showing location of the available maps produced by the Kenya Geologic Survey. 9 Figure 1.2. " Geologic maps for regions affected by rift volcanism. The number in each box is the report number or degree sheet. 13