Cosmogenic nuclide burial dating of an alluvial conglomerate sequence: An example from the Hexi Corridor,NE Tibetan Plateau |
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| Institution: | 1. College of Geographical Sciences, East China Normal University, Shanghai 200241, China;2. The Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China;3. Key Laboratory of Earth Surface Processes of Ministry of Education, Peking University, Beijing 100871, China;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, Rennes 35042, France;3. Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736202, China |
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| Abstract: | The thick alluvial conglomerate sequences around the Tibetan Plateau have been notoriously difficult to date. Here we use the cosmogenic nuclide burial dating method to date the Yumen and Jiuquan formations, a ∼900 m thick fanglomerate found in the Hexi Corridor, the foredeep of the Qilian Shan, and exposed in the Laojunmiao anticline. We date 16 sites with simple burial dating and 2 sites with isochron burial dating, and use these dates to reinterpret the magnetostratigraphy of the section. We suggest that the bottom of the Yumen Formation, defined by a progressive unconformity, is around 5 My. Taking this timing as the initiation of anticline growth, the long-term crustal shortening rate at the ramp zone in western Qilian Shan is about 0.72 mm/yr, consistent with those obtained from middle and eastern Qilian Shan. The boundary between the Yumen and Jiuquan Formations is near ∼1.2 My. Three other angular unconformities are dated to ∼2.6–3.1, ∼2.2–2.5, and ∼1.2–1.7 My, respectively. Burial dating offers a robust chronology for these deposits, and when combined with paleomagnetic stratigraphy offers much tighter precision. |
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| Keywords: | Cosmogenic burial dating Isochron burial dating Alluvial conglomerate sequence Hexi Corridor Qilian Shan |
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