Sedimentary and geochemical evidence of Eocene climate change in the Xining Basin,northeastern Tibetan Plateau |
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| Authors: | Abu?Sadat?Md?Sayem Email author" target="_blank">Zhengtang?GuoEmail author Haibin?Wu Chunxia?Zhang Fan?Yang Guoqiao?Xiao Zhilin?He |
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| Institution: | 1.Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,China;2.University of Chinese Academy of Sciences,Beijing,China;3.Department of Geological Sciences,Jahangirnagar University,Dhaka,Bangladesh;4.CAS Center for Excellence in Life and Paleoenvironment,Bejing,China;5.State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences,China University of Geosciences,Wuhan,China |
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| Abstract: | The northeastern Tibetan Plateau began to grow during the Eocene and it is important to understand the climatic history of Asia during this period of so-called ‘doubthouse’ conditions. However, despite major advances in the last few decades, the evolutionary history and possible mechanisms of Eocene climate change in the northeastern Tibetan Plateau remain unclear. The Xining Basin in the northeastern Tibetan Plateau contains a continuous sequence of Early to Late Eocene non-marine sediments which provides the opportunity to resolve long-term climate changes during this period. In this study, we report the results of analyses of lithofacies, sediment color and geochemistry of bulk samples collected from the Xijigou section of the Xining Basin. An abrupt lithofacies change between the Early (～52–40 Ma) and Late Eocene (～40–34 Ma) indicates a change in the depositional environment from a shallow lake to a playa lake in response to a significant climatic shift. During ～52–40 Ma, higher values of sediment redness (a*), redness/lightness (a*/L*) and higher modified Chemical Index of Weathering (CIW’) indicate a relatively warm and humid climate, while from ～40–34 Ma the lower values of a*, a*/L* and lower CIW’ imply sub-humid to semi-arid climatic conditions. The paleoclimatic records indicate a long-term (～52–34 Ma) trend of decreasing chemical weathering, consistent with global climate change. An abrupt sharp excursion of the proxy records during ～42–40 Ma suggests a relatively brief warm interval, corresponding to the Middle Eocene Climatic Optimum (MECO). We suggest that global cooling substantially reduced humidity in inner Asia, resulting in sub-humid to semi-arid climatic conditions after 40 Ma in the Xining Basin, which may have been responsible for the long-term trend of decreasing chemical weathering during the Eocene. |
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