Cenozoic evolution of the Pamir Salient; timing, mechanisms and paleo-environmental impacts: Constraints from the Aertashi section, western Tarim Basin. Tamsin Blayney Thesis submitted for the award of PhD June 2017 "Twenty years from now you will be more disappointed by the things you didn't do than the things you did. So throw off the bowlines, sail away from the safe harbour, catch the trade winds in your sails. Explore .... dream.... discover". Mark Twain ii Table of Contents Acknowledgements: ................................................................................................ ii Statement of work ................................................................................................... v Abstract ............................................................................................................... viii Introduction ........................................................................................................... ix Project Aims and Objectives .................................................................................. xii Thesis Outline ...................................................................................................... xiii 1. Geological Background .................................................................................... 1 1.2 The Himalayas and Tibetan Plateau ............................................................ 1 1.3 Western Kunlun mountain range ................................................................ 9 1.3.1 Western Kunlun Terranes.................................................................... 9 1.4 The Pamir ............................................................................................... 10 1.4.2 Pamir formation ................................................................................ 13 1.4.1 Pamir Terranes ................................................................................. 17 1.5 Tarim Basin............................................................................................. 20 1.5.1 Sediments of the Western Tarim Basin .............................................. 21 1.6 The Tian Shan ......................................................................................... 24 1.7 Global climate during the Cenozoic. ......................................................... 24 1.8 The Cenozoic Asian climate..................................................................... 28 1.8.1 C4 photosynthesis evolution in China ................................................ 31 1.9 The Aertashi section ................................................................................ 32 1.9.1 Sedimentology.................................................................................. 32 1.9.2 Existing age control in Aertashi......................................................... 33 2. Methods ........................................................................................................ 35 2.1 Construction of a reliable stratigraphy for the Aertashi section .................. 35 ii 2.2 Establishment of the age of the Aertashi section ....................................... 35 2.2.1 Magnetostratigraphic analysis ........................................................... 35 2.3 Determination of sediment provenance ..................................................... 39 2.3.1 U-Pb dating of detrital zircon grains .................................................. 39 2.3.2 Zircon fission track dating ................................................................. 42 2.3.3 Sm-Nd decay system ........................................................................ 44 2.3.4 Petrography ...................................................................................... 47 2.3.5 Heavy mineral analysis ..................................................................... 48 2.4 Determination of tectonic fabric ............................................................... 50 2.4.1 Anisotropy of magnetic susceptibility (AMS) .................................... 50 2.5 Determination of the regional climate ....................................................... 52 2.5.1 X-Ray Diffraction (XRD) ................................................................. 52 2.5.2 Organic δ13C on clays and sandstones ................................................ 56 2.5.3 X-Ray Fluorescence (XRF) ............................................................... 59 2.5.4 Magnetic susceptibility ..................................................................... 62 3. The Sedimentology of the Aertashi section ..................................................... 65 3.1 Depositional environment of Aertashi ...................................................... 65 3.2 Age control for the Aertashi section ......................................................... 69 3.3 Sampling and analysis of the Aertashi section ........................................... 70 3.4 Architectural elements of the Aertashi section .......................................... 73 3.5 The Aertashi sediments ............................................................................ 75 3.5.1 Non-marine Bashibulake Formation (0-720 m): Semi-arid fluvial floodplain. ..................................................................................................... 75 3.5.2 Unit A (760-800 m): Aeolian dune, inter-dune and arid flood plain..... 79 3.5.3 Unit B (800-1520 m): Flood-controlled lacustrine sandy delta plain.... 82 3.5.4 Unit C (~1520-2050 m): Meandering channel belts ............................ 85 iii 3.5.5 Unit C-D transition (Figure 3.20) ...................................................... 88 3.5.6 Unit D (2050-2790 m): Distal alluvial fan (Figure 3.27) ..................... 90 3.5.7 Unit D – E transition ......................................................................... 93 3.5.8 Unit E (2790-4050 m): Distal braid plain with ephemeral streams. ..... 95 3.5.9 Unit F (>4050 m): Proximal alluvial fan ...........................................100 3.6 Overall summary of the Aertashi continental section (Figure 3.40) ...........101 4. Indentation of the Pamir with respect to the northern margin of Tibet: constraints from the Tarim Basin sedimentary record. .............................................................104 Abstract ...........................................................................................................105 4.1 Introduction ............................................................................................105 4.2 Geological Background ..........................................................................109 4.2.1 The Pamir........................................................................................109 4.2.2 The West Kunlun Mountain Range (WKL) .......................................112 4.2.3 The Western Tarim Basin ................................................................113 4.3 Previous isotopic provenance studies on the Western Tarim sedimentary records. ............................................................................................................114 4.3.1 Oytag section...................................................................................115 4.3.2. Qimugen section ..............................................................................116 4.3.3 Sanju and Kekeya sections ..............................................................116 4.4 The study area - the Aertashi section .......................................................117 4.5 Approach, sampling and methods ............................................................120 4.5.1 Sampling ........................................................................................120 4.5.2 Petrography and heavy mineral analyses. ..........................................122 4.5.3 Sm-Nd bulk analyses .......................................................................124 4.5.4 Zircon U-Pb and fission track analyses. ............................................125 4.6 Results ...................................................................................................127 iv 4.6.1 Sedimentology and palaeocurrent data. .............................................127 4.6.2 Petrography and heavy mineral data. ................................................127 4.6.3 Sm-Nd data. ....................................................................................129 4.6.4 Zircon U-Pb data. ............................................................................129 4.6.5 Zircon fission track data, double dated with U-Pb ages. .....................131 4.6.7 Summary of provenance changes .....................................................134 4.7 Interpretations ........................................................................................135 4.7.1 Pre-Cenozoic and early Cenozoic times ............................................135 4.7.2 Late Oligocene (~25Ma) ..................................................................140 4.7.3 After the Early–Mid-Miocene (≤ 14 Ma) ..........................................140 4.8 Summary and conclusions: The palaeogeographic model .........................143 Acknowledgements: .........................................................................................144 5. Pamir tectonic evolution recorded in the western Tarim Basin: a combined magnetostratigraphic and sedimentological analysis of the Aertashi sedimentary section (China) .....................................................................................................145