云南东部二叠-三叠系界线地质事件在含煤地层的元素地球化学响应

The evolution of geochemical elements in sediments can fully reflect the paleoenvironment and paleoclimate variation. The end Permian witnessed the largest mass extinction of marine and non-marine biota and a series of geological catastrophic events such as volcanic activity and climate variation in the Earth’s geologic history. All of above mentioned events may be recorded in the Latest Permian coal measures around the Permian-Triassic boundary. We take the nonmarine PTB coal measure of east Yunnan Prvince as a sample, based on the radioisotope dating data, the mineralogy, petrology, sporopollen assemblage and element geochemical characteristics of the coal measures samples were analysised. The evolution of paleoclimate, depositional environment and element geochemical characteristics were summarized and the relationship between migration and transformation of elements and geological events were deduced by the abnormal element distribution in the coal measure and provenance. This study was plan to establish the element geochemical responses of Latest Permian coal measures developed in nonmarine environment to a series of geological catastrophic events during the same period and discuss the inducing factors of PTB biotic extinction.

沉积物中地球化学元素的演化规律可以较为详尽地反映古环境、古气候变迁。晚二叠世末期发生于全球范围的主要事件如生物灭绝、火山活动、气候变化等信息都可能记录于同时期煤层及岩层中。本研究以滇东地区陆相和海陆过渡相晚二叠世末期含煤地层为研究对象，通过放射性同位素测年证实其确为界线煤系地层基础上，分析其矿物学和岩石学特征、孢粉组合特征及元素地球化学特征，总结古气候、沉积环境及元素地化特征演化规律，查明界线煤系地层中元素的物源及主要控制因素。通过煤系地层中元素的异常分布规律，结合物源推断元素的迁移转化与火山活动等地质事件的内在联系。本研究旨在建立非海相沉积环境下晚二叠世末期煤系地层元素地球化学特征对二叠-三叠纪之交生物灭绝、火山活动等同期地质灾变事件的响应关系，探讨PTB生物灭绝的可能诱发因素。

古、中生代之交是显生宙以来地质历史上重大的转折期，晚二叠世末发生于全球范围的一系列地质事件如生物集群灭绝、火山活动、气候变化等都可能记录于同时期沉积的煤层中。本研究以滇东宣威地区陆相晚二叠世末生物灭绝期煤层为研究对象，分析其孢粉学、矿物学和元素地球化学特征，揭示煤系地层中元素地球化学特征对火山活动等地质事件的响应。本研究通过SHRIMP U-Pb同位素方法确定了晚二叠世末最后一层煤—C1煤的精确地质年龄252.0±2.3 Ma，与生物灭绝主幕重合。上二叠统宣威组-卡以头组过渡地层中孢粉化石组合以蕨类孢子占绝对优势，裸子植物花粉贫乏，统计结果表明该地区古气候从炎热多雨的热带亚热带森林沼泽环境逐渐演变为温暖半潮湿的热带亚热带雨林环境。矿物学和稀土元素地球化学特征表明成煤期受含煤盆地西部康滇古陆峨眉山玄武岩碎屑物质输入影响，同时还受二叠纪末华南板块西南缘的古特提斯洋闭合引发的长英质火山作用影响，并在较小程度上受到过西伯利亚大火成岩省的影响；成煤期沉积环境以弱氧化-弱还原为主，成煤后期沉积环境动荡。C1煤中有12种元素W、Co、Mo、Cd、Pb、Be、Sb、Cu、Ni、Zn、Zr和V富集，其中Co、Mo、Cd、Cu、Zn、V以及并不富集的剧毒元素Tl在成煤末期含量突增，可能导致了晚二叠世末古植物的最终灭绝。煤中Zr元素地球化学特征异常富集，并与华南海相PTB粘土岩中Zr的富集规律一致。晚二叠世生物灭绝期煤中有毒有害微量元素的富集与宣威肺癌高发区可吸入颗粒物中高含量元素种类一致，这将现代的地方流行病与P/T之交的生物灭绝联系起来，具有重要的科学启发意义。