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Sedimentary, Structural, and Provenance Record of the Cianzo Basin, Puna Plateau-Eastern Cordillera Boundary, NW Argentina

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Sedimentary, Structural, and Provenance Record of the Cianzo Basin, Puna Plateau-Eastern Cordillera Boundary, NW Argentina Copyright by Benjamin Charles Siks 2011 The Thesis Committee for Benjamin Charles Siks Certifies that this is the approved version of the following thesis: Sedimentary, structural, and provenance record of the Cianzo basin, Puna plateau-Eastern Cordillera boundary, NW Argentina APPROVED BY SUPERVISING COMMITTEE: Supervisor: Brian K. Horton Ronald J. Steel Kitty Milliken Sedimentary, structural, and provenance record of the Cianzo basin, Puna plateau-Eastern Cordillera boundary, NW Argentina by Benjamin Charles Siks, 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 May 2011 Acknowledgements This work could not have been completed without the support of my future wife, Ashley Bens, my mother Debbie Stann, my father Jan Siks, my siblings, my supervisor Dr. Brian Horton, my committee members Dr. Ron Steel and Dr. Kitty Milliken, as well as the members of my research group, and finally the loyal support of my border collie Pippin. iv Abstract Sedimentary, structural, and provenance record of the Cianzo basin, Puna plateau-Eastern Cordillera boundary, NW Argentina Benjamin Charles Siks, MS GeoSci The University of Texas at Austin, 2011 Supervisor: Brian K. Horton The fault-bounded Cianzo basin represents a Cenozoic intermontane depocenter between the Puna plateau and Eastern Cordillera of the central Andean fold-thrust belt in northern Argentina. New characterizations of fold-thrust structure, nonmarine sedimentation, and sediment provenance for the shortening-induced Cianzo basin at 23°S help constrain the origin, interconnectedness, and subsequent uplift and exhumation of the basin, which may serve as an analogue for other intermontane hinterland basins in the Andes. Structural mapping of the Cianzo basin reveals SW and NE-plunging synclines within the >6000 m-thick, upsection coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth stratal relationships within upper Miocene levels of the succession indicate syncontractional sedimentation directly adjacent to the Hornocal fault. Measured stratigraphic sections and clastic sedimentary lithofacies of Cenozoic basin-fill deposits show upsection changes from (1) a distal fluvial system recorded by v fine-grained, paleosol-rich, heavily bioturbated sandstones and mudstones (Paleocene‒Eocene Santa Bárbara Subgroup, ~400 m), to (2) a braided fluvial system represented by cross-stratified sandstones and interbedded mudstones with 0.3 to 8 m upsection-fining sequences (Upper Eocene–Oligocene Casa Grande Formation, ~1400 m), to (3) a distributary fluvial system in the distal sectors of a distributary fluvial megafan represented by structureless sheetflood sandstones, stratified pebble conglomerates and sandstones, and interbedded overbank mudstones (Miocene Río Grande Formation, ~3300 m), to (4) a proximal alluvial fan system with thick conglomerates interbedded with thin discontinuous sandstone lenses (upper Miocene Pisungo Formation, ~1600 m). New 40Ar/39Ar geochronological results for five interbedded volcanic tuffs indicate distributary fluvial deposition of the uppermost Río Grande Formation from 16.31 ± 0.6 Ma to 9.69 ± 0.05 Ma. Sandstone petrographic results show distinct upsection trends in lithic and feldspar content in the Casa Grande, Río Grande, and Pisungo formations, potentially distinguishing western magmatic arc (Western Cordillera) sediment sources from evolving eastern thrust-belt sources (Puna‒Eastern Cordillera). In addition to growth stratal relationships and 40Ar/39Ar constraints, conglomerate clast compositions reflect distinct lithologic differences, constraining the activation of the Cianzo thrust and coeval movement on the reactivated Hornocal fault. Finally, U-Pb geochronological analyses of sandstone detrital zircon populations in conjunction with paleocurrent data and depositional facies patterns help distinguish localized sources from more distal sources west of the basin, revealing a systematic eastward advance of Eocene to Miocene fold-thrust deformation in the central Andes of northern Argentina. vi Table of Contents List of tables ........................................................................................................... ix List of figures ...........................................................................................................x Chapter 1. Introduction and geologic context .........................................................1 Introduction .....................................................................................................1 Geologic setting ..............................................................................................3 Chapter 2. Tectonic, stratigraphic, and structural framework ................................7 Tectonic history ..............................................................................................7 Regional stratigraphy ....................................................................................10 Structural framework ....................................................................................13 Growth strata .................................................................................................16 Chapter 3. Sedimentology and stratigraphy ..........................................................19 Facies associations ........................................................................................19 40Ar/39Ar age geochronology ........................................................................34 Chapter 4. Depositional systems ............................................................................36 Chapter 5. Provenance ...........................................................................................40 Sandstone compositons .................................................................................40 Conglomerate clast compositions .................................................................46 Detrital zircon U-Pb geochronology .............................................................48 Chapter 6. Basin reconstruction and discussion ....................................................55 Santa Bárbara Group .....................................................................................55 Casa Grande Formation ................................................................................56 Río Grande Formation ..................................................................................57 Pisungo Formation ........................................................................................58 Chapter 7. Conclusions ..........................................................................................61 Appendix 1. Point count tables .............................................................................65 Appendix 2. Clast count tables .............................................................................67 Appendix 3. U-Pb geochronological results .........................................................69 vii Appendix 4. McBride, 2008 U-Pb results .............................................................85 References ..............................................................................................................89 viii List of Tables Table 1. Description and interpretation of lithofacies . ...................................20 Table 2. Summary of facies associations and interpretations .........................21 Table 3. 40Ar/39Ar data for interbedded tuffs ..................................................35 Table 4. Parameters for sandstone mineraloglical point counting. .................41 ix List of Figures Figure 1. Overview map of South America .......................................................4 Figure 2. Regional structures and provenace terranes in northern Argentina. ...6 Figure 3. Location of Cianzo basin and regional structures. ..............................9 Figure 4. Regional stratigraphy of the Cianzo basin ........................................11 Figure 5. Geologic map of Cianzo basin and surronding structures ................14 Figure 6. Growth strata within the Pisungo Formation ....................................18 Figure 7. Simplified stratigraphic section of Cenozoic fill ..............................22 Figure 8. Measured stratigraphic sections in the Cianzo basin ........................23 Figure 9. Lower Río Grande facies photographs .............................................26 Figure 10. Upper Río Grande facies photographs ..............................................29 Figure 11. Pisungo facies photographs...............................................................33 Figure 12. Depostional systems evolution diagram ...........................................39 Figure 13. Sandstone petrographic ternary diagrams .........................................44 Figure 14. Lithologic conglomerate clast count diagrams .................................47 Figure 15. Detrital zircon U-Pb relative probability plots ..................................51 Figure 16. 2D regional basin reconstruction diagrams .......................................60 x Chapter 1. Introduction and geologic context INTRODUCTION Many studies attribute crustal thickening and surface uplift in the central Andean fold-thrust belt and Puna‒Altiplano
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