Carbon and sulfur isotopic fluctuations associated with the end-Guadalupian mass extinction in South China

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• 作者：Yan Detian ; Zhang Liqin ; Qiu Zhen
• 关键词：Stable isotopes ; Mass extinctions ; End-Guadalupian ; South China
• 刊名：Gondwana Research
• 出版年：2013
• 出版时间：November, 2013
• 年：2013
• 卷：24
• 期：3-4
• 页码：1276-1282
• 全文大小：1147 K

文摘

Concentrations of total organic matter (TOC), carbon isotopic compositions of carbonate and organic matter (¦Ä¹³C_carb, ¦Ä¹³C_org), and sulfur isotopic compositions of carbonate associated sulfate (¦Ä³⁴S_sulfate) across the Guadalupian-Lopingian (G-L) boundary were analyzed from identical samples of Tieqiao section, Laibin, Guangxi province, South China. The ¦Ä¹³C_carb values show a positive excursion from ? 0.45¡ë to the peak of 3.80¡ë in the Laibin limestone member of the Maokou Formation, followed by a drastic drop to ? 2.60¡ë in the lowest Heshan formation, then returned to about 1.58¡ë. Similar to the trends of the ¦Ä¹³C_carb values, ¦¤¹³C_carb-org values also show a positive excursion followed by a sharp negative shift. The onset of a major negative carbon isotope excursion postdates the end Guadalupian extinction that indicates subsequent severe disturbance of the ocean-atmosphere carbon cycle. The first biostratigraphic ¦Ä³⁴S_sulfate values during the G-L transition exhibit a remarkable fluctuation: a dramatic negative shift followed by a rapid positive shift, ranging from 36.88¡ë to ? 37.41¡ë. These sulfate isotopic records suggest that the ocean during the G-L transition was strongly stratified, forming an unstable chemocline separating oxic shallow water from anoxic/euxinic deep water. Chemocline excursions, together with subsequent rapid transgression and oceanic anoxia, were likely responsible for the massive diversity decline of the G-L biotic crisis.