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CALLEPERALTA-THESIS-2013.Pdf (6.086Mb) Copyright by Amanda Zulema Calle Peralta 2013 The Thesis Committee for Amanda Zulema Calle Peralta Certifies that this is the approved version of the following thesis: Neogene sedimentation and provenance record of the Subandean zone and Chaco foreland basin, southern Bolivia APPROVED BY SUPERVISING COMMITTEE: Brian K. Horton Lesli J. Wood Daniel F. Stockli Neogene sedimentation and provenance record of the Subandean zone and Chaco foreland basin, southern Bolivia by Amanda Zulema Calle Peralta, B. S. Geo. Thesis Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geological Sciences The University of Texas at Austin August 2013 Acknowledgements First, I thank my supervisor Dr. Brian Horton for the challenging and fruitful discussions, and professional guidance to further pursue many interesting geologic problems. Committee members Drs. Lesli Wood and Daniel Stockli are sincerely thanked for sharing their valuable time in discussions and suggestions to improve the manuscript. Special thanks for discussions with Jonas Kley, Victor Ramos, Daniel Starck, Kitty Milliken, Antonio Teixell, and Randy Marrett. This research was sponsored by the National Science Foundation NSF (EAR- 0908518) granted to Dr. Brian Horton, the Jackson School of Geosciences, Repsol E&P Bolivia, and research grants from the Geological Society of America and Society for Sedimentary Geology. Field and logistic assistance was graciously provided by Rodrigo Limachi, Gerardo Villacorta, Hernan Orellana, and Paul Muñoz. Discussions about Bolivian geology with Edgar Requena, Gonzalo Astorga and Rodrigo Limachi are greatly appreciated. Furthermore, I express my sincere thanks to Dr. Horton´s research group for stimulating discussions and laboratory training including Nicholas Perez, Meredith Bush, Mariya Levina, Joel Saylor, Renas Mohammed, Veronica Anderson, Ryan McKenzie, and Sebastian Ramirez. My family and friends were very supportive during the whole process. I sincerely thank my parents, siblings and relatives for encouraging me to achieve my goals. Finally, I am indebted to my friends Helene Baret, David Banda, Jess Lally, Jorge Gutierrez, Edgardo Pujols, Rosmery Fernandez, Marioly Yarhui, Chelsea Underwood, and Amanda Jeffrey for their continued support during this stage. iv Abstract Neogene sedimentation and provenance record of the Subandean zone and Chaco foreland basin, southern Bolivia Amanda Zulema Calle Peralta, M.S.GeoSci. The University of Texas at Austin, 2013 Supervisor: Brian K. Horton Evolution of the Subandean fold-thrust belt and adjacent Chaco foreland basin since their inception ~20 Myr ago has involved shortening, crustal thickening and flexural loading along the eastern margin of the central Andes in Bolivia. Few studies have assessed the linkages among surface processes and threshold responses to climate change, tectonics, and/or catchment-area modification in this thin-skinned fold-thrust belt and coupled foreland basin. Analyses of stratigraphic variations and sediment provenance within two of the proximal, westernmost sections of the Subandean zone (Bartolo and Emborozú localities) are consistent with an eastward advancing synorogenic fold-thrust system guiding deposition and facies migration within several foreland depozones. Results from Cenozoic detrital zircon U-Pb geochronology, conglomerate clast compositions, sandstone petrography and paleocurrent analyses provide information on the gradual eastward diachroneity of upward-coarsening successions and fluvial megafan deposits. New and published zircon U-Pb data for interbedded Miocene tuffs and an updated magnetostratigraphic analysis contribute to the interpretation of depositional v ages and changes in sediment accumulation rates. Regionally, the Neogene sedimentation history shows a gradually subsiding basin until 8 Ma with progressively coarser facies up to 6 Ma. High accumulation rates for proximal alluvial-fan facies and proximal fluvial megafan deposits after 6 Ma are identified and correlated with their distal counterparts in the Chaco basin. Evidence for the introduction of progressively younger rocks in uplifted sediment source areas, as documented by conglomerate counts and detrital zircon age populations, lead us to interpret protracted unroofing and sediment dispersal from the Eastern Cordillera–Interandean Zone commencing at ~23 Ma, followed by initial propagation of the deformation front into the Subandean Zone at ~20-15 Ma (as estimated from new tuff ages and accumulation rates). A temporal shift from axial to transverse fluvial drainage recorded by paleocurrent data reinforces evidence for an eastward advancing depocenter and structural partitioning of the older segments of the foreland basin, particularly from 6 Ma to present. Continued exhumation and enhancement of the drainage areas to the west (i.e., Eastern Cordillera, Interandean Zone, and actively deforming Subandean zone) reflect changes in the accumulation of coarser lithofacies in proximal areas and delivery of significant sediment volumes to modern fluvial megafans of the Chaco plain. vi Table of Contents List of Tables ......................................................................................................... ix List of Figures ..........................................................................................................x CHAPTER 1. INTRODUCTION AND GEOLOGIC FRAMEWORK ..................................1 Introduction .....................................................................................................1 Geological setting ...........................................................................................6 Andes Mountains ..........................................................................6 Central Andes................................................................................6 Topography ...................................................................................7 Mountain building and uplift ........................................................8 Shortening .....................................................................................9 Subandean foreland basin .............................................................9 Regional stratigraphic framework.................................................................13 CHAPTER 2. SEDIMENTOLOGY AND STRATIGRAPHY ............................................15 Cenozoic stratigraphy ...................................................................................15 Petaca Formation ........................................................................15 Yecua Formation .........................................................................16 Tariquia Formation .....................................................................16 Guandacay Formation .................................................................17 Emborozú Formation ..................................................................17 Sedimentology and depositional systems .....................................................19 Bartolo locality............................................................................19 Emborozú locality .......................................................................19 Facies associations ........................................................................................23 CHAPTER 3. PROVENANCE ANALYSES ..................................................................40 Conglomerate clast compositions ...............................................40 Sandstone petrology ....................................................................43 Paleocurrents ...............................................................................49 vii Detrital zircon U-Pb geochronology ...........................................52 CHAPTER 4. U-PB GEOCHRONOLOGY AND MAGNETOSTRATIGRAPHY ...............63 U-Pb geochronology of volcanic horizons .................................63 Magnetostratigraphy ...................................................................64 CHAPTER 5. CENOZOIC BASIN RECONSTRUCTION AND DISCUSSION ....................69 Oligocene-Miocene boundary (~23 Ma) ....................................69 ~23–20 Ma ..................................................................................71 20–6 Ma ......................................................................................71 6 Ma to present............................................................................75 CHAPTER 6. CONCLUSIONS ...................................................................................76 Appendix 1. Recalculated modal point-count data from the Bartolo locality .......80 Appendix 2. LA-ICP-MS analyses for detrital zircon U-Pb geochronology .........81 Appendix 3. SHRIMP U-Pb data from detrital zircon sample VLE07-109 from Escayola et al. (2011) ..................................................................................113 References ............................................................................................................115 Vita... ....................................................................................................................124 viii List of Tables Table 1. Lithofacies for the Petaca, Tariquia, Guandacay, Emborozú formations (after Miall, 1996; Uba et al., 2005 and Siks, 2011) ..................................24 Table 2. Facies associations and depositional systems for the Petaca, Tariquia,
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