中国南方震旦系陡山沱组生物地层学研究

陡山沱组 生物地层 古环境 盖帽白云岩 华南
周传明 2008-01 项目
【英文摘要】The micropaleotological investigation has been systematically carried out in the Sinian Doushantuo Formation in the Yangtze Gorges area, Hubei Province, which reveals that while microfossil assemblages in the lower and upper Doushantuo Formation share some common elements, they are distinct taxonomically. Quantitative analysis shows that the two biozones are largely independent of taphonomic or facies controls, thus they can offer a viable tool for regional correlation of the Ediacaran System. High resolution carbon (inorganic and organic) and sulfur (pyrite and CAS) isotope studies suggest pulsed oxidation of the deep oceanic DOC reservoir, and the oxidation events appear to be coupled with eukaryote diversity in the Doushantuo basin of South China. Triple oxygen isotope composition of sulfate from ancient evaporates and barites shows variable negative 17O anomalies over the past 750 million years, and 17O anomaly of barites from the cap dolostone overlying the Nantuo diamictite in South China display a distinct negative spike, suggesting pCO2 was at its highest level in the past 750 million years, which is consistent with the snowball Earth hypothesis. Based on an extensive field survey of Marinoan cap carbonates in South China and detailed sedimentological, petrographic, and isotope data, a unified sequence of events concerning the formation of cap carbonate was proposed, the new model not only further supports the snowball Earth hypothesis, but suggests that the signal of methane hydrate was registered well after the cap dolostone deposition, which therefore could not be the trigger of termination of global glaciation. Micro-CT studies on some phosphatic embryo fossils with distinct outer ornamentation reveal their internal gastular structure, which provide convincing evidence for the early development stages of animal embryos.
【中文摘要】系统开展了湖北峡东地区震旦系陡山沱组燧石结核中保存的微体化石的生物地层学工作,发现陡山沱组下部和上部的微体生物群既有延续性,又有各自不同的代表性分子,相关性定量分析表明生物演替可能反映了由于环境和生态的改变而导致的生物演化过程,因此能够用以区域地层对比;综合利用碳(包括有机碳和无机碳)、硫同位素的系统研究,揭示出埃迪卡拉纪陡山沱期海洋和大气圈可能发生了幕次氧化事件,并发现氧化事件与生物演化在时间上密切相关;华南南沱冰碛岩之上盖帽白云岩中重晶石沉积的多氧同位素研究表明冰期结束时大气二氧化碳含量达到了7.5亿年以来的最高峰值,因此成为"雪球地球"假说的最直接证据;通过华南十余条盖帽白云岩剖面系统的沉积学、沉积岩石学和微区碳同位素分析,提出围绕盖帽白云岩形成过程中各个地质事件之间关系的新模式,新模式进一步支持"雪球地球"假说,同时表明甲烷渗漏发生在盖帽白云岩形成之后,因此很可能不是全球性冰期结束的诱因;对瓮安陡山沱组磷块岩保存的具有外部形态特征变化的胚胎化石进行Micro-CT内部扫描观察,发现其内部具有类似原肠腔的结构,可能是原肠胚动物化石,为该时期的胚胎发育提供了新的证据。