Geochemical changes across the Ordovician-Silurian transition on the Yangtze Platform,South China |
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Authors: | DeTian Yan DaiZhao Chen QingChen Wang JianGuo Wang |
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Institution: | (1) Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan, 430074, China;(2) State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China |
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Abstract: | The trace element and rare earth element (REE) variations across the Ordovician-Silurian succession are presented from two
outcrop sections on the Yangtze Platform: the Nanbazi section, Guizhou Province, deposited in a shallow platform interior
setting, and the Wangjiawan section, Hubei Province, deposited in a deeper basinal environment. Geochemical analysis of closely
spaced samples through three intervals, the Wufeng, Guanyinqiao and Longmaxi, revealed vast palaeoceanographic changes. Some
geochemical proxies, including Th/U, Ni/Co, V/Cr, and V/(V+Ni) ratios, together with sedimentary facies and biotic data, indicate
that an anoxic condition on the most of the Yangtze Platform during the Wufeng and Longmaxi intervals, but an oxic condition
during the Guanyinqiao time. The shift of the anoxic to the oxic environment during the Guanyinqiao time coincided with a
global sea-level lowstand, in parallel with the global glaciation. The Longmaxian anoxic environment was a result of a global
sea-level rise, which may be synchronized with a mainly catastrophic event in the latest Ordovician. Although the two sections
generally show similar variation patterns of trace and REE concentrations and some element ratios, a minor difference occurs
between the Wangjiawan and Nanbazi sections, likely reflecting a difference in depositional setting during the accumulation.
Such an oceanic oxygen-level variation may add a useful constraint to the current arguments on the cause and consequence of
the latest Ordovician mass extinction.
Supported by National Basic Research Program of China (Grant No. 2005CB422101) |
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Keywords: | rare earth elements trace elements paleo-redox proxies mass extinction Ordovician-Silurian boundary Yangtze Platform |
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