Lower Cretaceous paleosols and paleoclimate in Sichuan Basin,China |
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| Institution: | 1. Laboratoire de Géologie de Lyon, CNRS UMR 5276, Université Lyon 1, 69622 Villeurbanne, France;2. Institut Universitaire de France, France;1. Department of Geological Sciences, The University of Texas at Austin, Austin, TX, United States;2. Department of Geological Sciences, The University of Oregon, Eugene, OR, United States;1. CAS Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China;2. Department of Atmosphere and Ocean Sciences, School of Physics, Peking University, Beijing 100871, China;3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences (CAS), Beijing 100101, China;4. University of Chinese Academy of Sciences, Beijing 100049, China;5. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, China |
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| Abstract: | Abundant Lower Cretaceous (Berriasian–Hauterivian) paleosols have been recognized in the Sichuan Basin, along with the preserved pedogenetic features, e.g., soil horizons, soil structure, root traces and pedogenic nodules. Chemical, geochemical and mineralogical analyses were used to examine the paleosols. These paleosols were classified as Entisols, Inceptisols, Aridisols and Alfisols in terms of the modern soil taxonomic system. Early Cretaceous paleoprecipitation and paleotemperature in the Sichuan Basin were estimated from the degree of chemical weathering for non-calcareous paleosols, and from the depth to the calcic horizon and stable oxygen isotopic composition of pedogenic carbonates in calcareous paleosols, respectively. A temperate semi-arid climate generally prevailed in the Sichuan Basin as a part of the South China Block (SCB) and was controlled by subtropical high-pressure and a rain-shadow effect because the humid air masses from the Paleo-Pacific were impeded by the highlands of the South China Block. Further, several intervals of sub-humid paleoclimate occurred due to strengthened monsoonal circulation in the Early Cretaceous. Using the paleosol barometer, the paleoatmospheric CO2 levels of the Early Cretaceous are estimated to range from ～120 to ～520 ppmv, with a mean of 305 ppmv. Regional temperature is generally coupled with atmospheric CO2 concentration and is roughly consistent with the sea level fluctuation. |
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| Keywords: | Early Cretaceous Paleosol Pedogenic carbonates Paleoprecipitation Paleotemperature Weissert oceanic anoxic event Sichuan basin |
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