High-resolution magnetostratigraphic study of the Paleogene-Neogene strata in the Northern Qaidam Basin: Implications for the growth of the Northeastern Tibetan Plateau |
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| Institution: | 1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China;3. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, PR China;1. Key Laboratory of Western China''s Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China;2. School of Earth Sciences & Key Laboratory of Western China''s Mineral Resources of Gansu Province, Lanzhou University, Lanzhou 730000, China;3. Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, 35137 Padova, Italy;1. Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Laboratoire Géosciences Rennes, CNRS-UMR6118, Université Rennes 1-Observatoire des Sciences de L''Univers de Rennes, Rennes, France;3. Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736202, China;4. Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China;1. School of Earth Sciences & Key Laboratory of Western China''s Mineral Resources of Gansu Province, Lanzhou University, Lanzhou 730000, China;2. Key Laboratory of Salt Lake Resources and Chemistry & Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 810008, China;3. Key Laboratory of Continental Collision and Plateau Uplift & Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China |
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| Abstract: | The Cenozoic terrestrial, intermontane Qaidam Basin on the northeastern edge of the Tibetan Plateau contains > 12 km of sedimentary rocks that potentially document the accommodation of India-Asia convergence and the growth of the plateau. The chronology remains incomplete, hindering cross-basin correlation between lithostratigraphic units and their further interpretation. Here we present a high-resolution magnetostratigraphy spanning > 5 km of Paleogene-Neogene sequence at Dahonggou in the Northern Qaidam Basin. Based on correlation with the geomagnetic polarity time scale (GPTS), we have dated the section to being between ~ 52 and ~ 7 Ma. The bottom conglomeratic unit, ranging from > 52 Ma to ~ 44 Ma, was deposited in high-energy environments (e.g., alluvial fan or braided river), reflecting the earliest deformation and uplift of the basin-bounding Qilian Shan fold-thrust belt in response to India-Asia collision. In addition, we identified two major increases in sedimentation rate at 25–16 Ma and after ~ 9.5 Ma and three phases of lesser increases at 52–44 Ma, 38–33 Ma, and 14.6–12.0 Ma. These increases in sedimentation rate are consistent with regional thermochronology and basin analysis studies, which revealed enhanced motion on basin-bounding thrust faults. We argue that these accelerated sedimentation rates indicate pulsed tectonism in the northeastern Tibetan Plateau. The pulse at 25–16 Ma may further relate to phases of strong rainfall linked to an intense monsoon at that time. |
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