早-中奥陶世华南古海洋氧化还原变化及其对奥陶纪生物大辐射的意义

为了进一步探讨奥陶纪生物大辐射期间环境影响和控制因素, 对安徽南部将军岭剖面黑色页岩的有机碳含量(TOC)、总硫含量(TS)和黄铁矿硫同位素(δ³⁴S_py)进行测试分析。TOC与TS表现出正相关性, 说明可能是非硫化环境中的沉积产物。δ³⁴S_py在弗洛期表现出显著的负偏移, 在中奥陶世表现出相对幅度更大的波动。结合前人对全球碳酸盐岩晶格中硫酸盐硫同位素(δ³⁴S_CAS)和δ³⁴S_py数据的分析结果, 显示特马豆克期末期至弗洛期中期黄铁矿埋藏分数下降, 硫同位素分馏效应增大, 说明当时海水发生氧化, 对奥陶纪生物大辐射起到重要的促进作用。弗洛期晚期至达瑞威尔期, 不同地区δ³⁴S_CAS相继出现负偏移,δ³⁴S_py发生大幅振荡, 可能是由于海洋中硫酸根浓度较低以及硫化物再氧化所致。

Redox Variation during the Early and Middle Ordovician in South China and Its Implication to the Great Ordovician Biodiversification Event

To improve understanding of the environmental influential and controlling factors of the Great Ordovician Biodiversification Event (GOBE), total organic carbon content (TOC), total sulfur content (TS), and sulfur isotope of pyrite (δ³⁴S_py) of black shale of the Jiangjunling section, in southern Anhui Province, China are analyzed. TOC and TS show positive correlation, indicating non-euxinic environment.δ³⁴S_py exhibits obvious decrease in Floian and more oscillation in the Middle Ordovician. Combined with global sulfur isotope of carbonate-associated sulfate (δ³⁴S_CAS) andδ³⁴S_py data from previous researches, a marine oxygenation event is suggested by decreasing pyrite burial and increasing sulfur isotopic fractionation during the latest Tremadocian to middle Floian, which might boost GOBE. During the late Floian to Darriwilian,δ³⁴S_CAS from different areas decreases in succession, whileδ³⁴S_py is characterized by large oscillation, which is contributed to low sulfate concentration and sulfide reoxidation in the ocean.