1 THE LATE MIOCENE THROUGH MODERN EVOLUTION OF THE ZHADA BASIN, SOUTH-WESTERN TIBET by Joel Edward Saylor A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 2 0 0 8 2 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE As members of the Dissertation Committee, we certify that we have read the dissertation prepared by: Joel E. Saylor entitled: The Late Miocene Through Modern Evolution of the Zhada Basin, South-western Tibet and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of: Doctor of Philosophy _______________________________________________________________________ Date: Peter DeCelles _______________________________________________________________________ Date: Jay Quade _______________________________________________________________________ Date: Paul Kapp _______________________________________________________________________ Date: George Gehrels _______________________________________________________________________ Date: Mihai Ducea Final approval and acceptance of this dissertation is contingent upon the candidate’s submission of the final copies of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. ________________________________________________ Date: Dissertation Director: Peter DeCelles ________________________________________________ Date: Dissertation Director: Jay Quade 3 STATEMENT BY THE AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department of the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. Signed: Joel Saylor 4 ACKOWLEDGEMENTS This dissertation would not have been possible without the help of many people. Foremost, my family: Jeannette, and Eirena for putting up with an absent (or busy) husband and father; Gary, Lita, and Nathaniel for their support and raising me. I owe a lifetime debt to my advisors: Drs. Pete DeCelles and Jay Quade for their patience, tutelage, and unending support. I also owe thanks to Dr. Paul Kapp for reading chapters (many times over) and many good comments and discussions; Dr. George Gehrels for his help with detrital zircon analyses and Dr. Mihai Ducea. Likewise, this work would not have happened without my field assistants: Jeannette Saylor, Scott McBride, Cai Fulong and our Tibetan crew. A special thanks to Facundo Fuentes, John Volkmer, Ross Waldrip, Lynn Peyton, Jerome Guynn, Andrew Leier, Aaron Martin, Matt Fabijanic, Adam and Amy Baker, Ari and Jane Heinze, Ryan and Janine Wilkinson, Jon Dyhr, Lise Johnson, Carrie Coykendall, Meghan Field, Sam Jayakanthan and many others from the Dept. of Geosciences, Graduate Christian Fellowship, and Northwest Community Friends Church for laughs, commiseration, and generally making life enjoyable. To others who have helped me work through ideas, given me pointers or hung out: thank you. Finally, I would like to thank those who I have worked with in the course of this project and hope to work with again: Dick Heermance for help with cosmogenic nuclide work; Mike Murphy and Ran Zhang for ideas and research help; Tank Ojha for assistance in the paleomagnetism lab; David Dettman for advice and assistance with stable isotope analyses; Majie Fan for assistance with organic material analyses and useful discussions; Victor Valencia for help with U-Pb analyses; and E. Lindsay and X. Wang for identification of mammal fossils and biostratigraphy. This research was supported by grants from the Geological Society of America, the American Association of Petroleum Geologists, ExxonMobil, Chevron-Texaco, The Galileo Circle of the U of A and National Science Foundation (grants EAR-0443387 and 0732436) and the National Science Foundation Tectonics Program. 5 DEDICATION Pro Veritas 6 TABLE OF CONTENTS LIST OF FIGURES………………………………................................………………...9 LIST OF TABLES……………………………............................……………………...11 ABSTRACT…………………………………....................................…………………..12 CHAPTER 1: INTRODUCTION……………………........................................……...13 CHAPTER 2: THE LATE MIOCENE THROUGH PRESENT PALEOELEVATION HISTORY OF SOUTHWESTERN TIBET...........................17 ABSTRACT………………………………………........................…………………17 INTRODUCTION……..…..……………………................................………....….19 Previous Paleoelevation Work…………………..……........................…....…..20 OXYGEN ISOTOPE PALEOALTIMETRY……………............................……..23 REGIONAL SETTING OF ZHADA BASIN……………....................…………..27 METHODS AND MATERIALS…………………........................…………....…..30 Age Control………………………....................................……………………...30 Modern Water…………………………....................................………………..32 Gastropods………………………………………............................……………33 Zhada Formation Plant Material…………………....................……………...34 RESULTS……………………………………........................................…………...36 Age……………………………………....................................………………….36 Modern Water………………………................................……………………..38 Gastropods……………………………………................................……………39 Zhada Formation Plant Material…………………........…....................……...40 APPLICATION TO PALEOALTIMETRY………………............................…...41 18 Calculation of Miocene δ Osw and Related Constraints and Corrections.....41 Source, pathway and amount effect constraints..............................................41 Shell preservation............................................................................................43 18 Calculation of Miocene δ Opsw.......................................................................43 Comparison with Models....................................................................................44 Effect of paleotemperature...............................................................................44 Modelling changes in lapse rate......................................................................45 Evaporation vs. Outflow..................................................................................46 Temperature of Modern Gastropod Shell Precipitation..................................48 Paleoelevation models.....................................................................................49 DISCUSSION AND CONCLUSIONS.....................................................................55 Oxygen Isotopes from Zhada Basin...................................................................55 Oxygen Isotopes from Zhongba..........................................................................58 Carbon Isotopes...................................................................................................59 Application to Tectonic Models..........................................................................60 CONCLUSIONS........................................................................................................62 7 TABLE OF CONTENTS – Continued CHAPTER 3: BASIN FORMATION DUE TO ARC-PARALLEL EXTENSION AND TECTONIC DAMMING: ZHADA BASIN, SW TIBET...................................95 ABSTRACT………………………………………....................................................95 INTRODUCTION………………………………….................................................96 GEOLOGIC SETTING…………………………………........................................98 SEDIMENTOLOGY OF THE ZHADA FORMATION.....................................100 Fluvial Association…………………………………………............................100 Lithofacies Association F1: Gcmi, Gch, Gt, Gcf...........................................100 Lithofacies Association F2: St, Sp, Sh, Sc.....................................................101 Lithofacies Association F3: Sm, Sc, Mm, Mc, Ml, Mh...................................101 Interpretation.....................................................................................................102 Supra-littoral (Lake Margin) Association.......................................................103 Lithofacies Association S1: Gct, Gcmi, Sp, St, Sh, Sm, Sr.............................103 Lithofacies Association S2: Sh.......................................................................104 Lithofacies Association S3: Sf........................................................................104 Interpretation.....................................................................................................104 Littoral Association............................................................................................105 Lithofacies Association L1: Ml......................................................................105 Lithofacies Association L2: Mr, Sr, Srw, Sp, Sh, Sm.....................................105 Interpretation.....................................................................................................106