新元古代—寒武纪硫同位素异常事件(Yudomski事件)的起源与结束

“Yudomski”Isotope Anomaly Event during Neoproterozoic-Cambrian:Its Origin and End

新元古代晚期—寒武纪早期是地球历史演化的关键时期,整个生物圈、大气圈和水圈在此期间都发生了巨大的变化,海水成分在其间也发生了明显的变化。而石盐流体包裹体恰恰记录了该时段海水主要离子成分的转变:海水成分从新元古代晚期的"文石海",快速转化为寒武纪的"方解石海";同时海水中的碳、锶、硫同位素都发生了剧烈的改变,其中海水硫酸根的硫同位素从新元古代冰期前的20‰左右,迅速升高到新元古代冰期后的35‰左右,甚至可以到45‰,海相蒸发岩沉积中的硫酸盐沉积(主要是石膏、硬石膏)则直接记录了当时海水中硫酸根的硫同位素变化。现有研究表明,新元古代晚期——寒武纪时期的海相蒸发岩沉积记录了当时海洋中存在着地质历史时期最大的硫同位素异常,即"Yudomski事件"。塔里木盆地的寒武纪早期、中期蒸发岩记录了"Yudomski事件"的硫同位素异常高值(35‰左右,甚至更高),表明这一起源于新元古代晚期的同位素异常事件持续到了寒武纪的早期和中期;塔里木盆地奥陶纪早期的蒸发岩、鄂尔多斯盆地奥陶纪中期蒸发岩和美国Williston盆地奥陶纪晚期地层的蒸发岩的硫同位素数据相似,都在+25‰左右则记录了较低的海洋硫同位素值,表明起源于新元古代冰期之后的"Yudomski事件"的硫同位素异常,持续到了寒武纪的中期,而结束于寒武纪的晚期。

In late Neoproterozoic-early Cambrian time major changes in earth’s climate and ocean chemistry occurred.Ocean chemistry compositionally shifted from aragonite to calcite in late Neoproterozoic-early Cambrian time interval and complex marine life was evolved during this time interval.Moreover,the rock records indicate sporadic fluctuations in the values of carbon and strontium isotopes in the same time interval and in Paleozoic,also.Similarly,analysis of sulfur isotope compositions of Neoproterozoic-Cambrian marine evaporates show anomalously high values of 34 S due to enrichment of brines inδ34 S.Holser termedδ34 S excursion as Yudomski Event after Yudomski and Motskaya Suit from late Proterozoic marine gypsiferous rocks of Siberia.Such high values ofδ34 S have been observed in marine evaporates of middle Cambrian in Tarim basin that indicate that Yudomski Event prolonged to middle Cambrian in China.