Plio-Pleistocene vegetation changes in the North China Plain: Magnetostratigraphy, oxygen and carbon isotopic composition of pedogenic carbonates |
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Authors: | Zhengquan Yao Guoqiao Xiao Haibin Wu Yukun Chen |
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Affiliation: | a Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, Chinab SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'An 710075, Chinac Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan, 430074, Chinad Key laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, Chinae Earthquake Administration of Tianjin Municipality, Tianjin 300201, China |
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Abstract: | The Plio-Pleistocene history of C4 plant biomass in northwestern China has been documented from the loess-soil sequences of the Loess Plateau region. However, how C4 plants evolved in the warmer and low-elevation eastern China monsoon zone is still poorly known mainly because of the unavailability of well-dated geological records. In this study, a 203.6-m core of floodplain deposits was recovered from the North China Plain near Tianjin and dated magnetostratigraphically. The results define a chronosequence for the last 3.3 Ma. The late Quaternary portion of the core consists of fluvio-marine sediments while the rest of the section (3.3-0.6 Ma) contains abundant paleosols formed on the floodplain, as confirmed by soil micromorphological evidence. The stable carbon and oxygen isotopic composition of pedogenic carbonates was measured to document vegetation and climate changes. The results reveal mixed C3 and C4 vegetation with an estimated C4 abundance of ~ 40-60% from ~ 3.1 to ~ 2.2 Ma, and a subsequent gradual decline to ~ 25% until ~ 0.6 Ma. This trend is consistent with the data from the loess-soil sequences further west on the Loess Plateau, suggesting they are regionally significant changes. The lowering of growing-season temperature and/or drier conditions induced by global cooling would explain this overall decline. |
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Keywords: | Magnetostratigraphy Paleosol Stable carbon and oxygen isotopes C3 and C4 plants Monsoon |
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