Ecological and environmental change recorded through stratigraphy and sedimentology at selected Ediacaran-Cambrian boundary sections in East and Central Asia

我们建议调查前寒武纪-寒武纪界线（PCB;约）沉积地层变化的三个方面。这些研究补充了地球化学和古生物学子项目：（1）古遗迹学记录的农业革命的影响;（2）扬子地台PCB岩溶作用的意义;（3）扬子地台、塔里木/伊犁微大陆和哈萨克斯坦南部埃迪卡拉-寒武纪剖面的地层结构比较。(1)埃迪卡拉纪至下寒武纪陆棚沉积物的化石记录表明，在农学革命期间，通过微生物密封表面的消亡，大量细粒沉积物如何融入全球化学海洋学交换中。到目前为止，地球系统的这种扩大的时间尺度，相依赖性和程度不能纳入地球化学建模计算，也不能令人信服地与后生动物的扩张。在这个子项目中，我们将把PCB关键剖面的生物扰动指数与地球化学代用指标联系起来，并将其与中国西部（塔里木和伊犁微大陆）和哈萨克斯坦（卡拉套山脉）剖面的化学地层记录联系起来。(2)由于埃迪卡拉纪和寒武纪沉积在含盐浅水相接触，扬子地台几乎到处都是不整合和岩溶，这是一个或几个时期的相对海平面下降和灯影组陆上暴露的结果。碳酸盐岩，大约6-10百万年的关键地质时间在PCB显然是失踪。这一记录在川、黔、鄂等地大量出露良好的地层剖面中均有研究。我们建议评估这一事件，以推断化学风化的持续时间和强度，并将我们的结果与全球其他暴露良好的PCB参考部分进行比较。我们的研究结果，辅以同期生物地层学研究（子项目施泰纳），将填补一个被忽视的，但潜在的关键差距，我们的理解后生动物基地寒武纪辐射在中国南方。

We suggest investigating three aspects of sedimentary-stratigraphic change at the Precambrian-Cambrian Boundary (PCB; ca. 543 Ma) that complement geochemical and paleobiological subprojects: (1) the effects of the agronomic revolution, recorded by paleoichnology; (2) the significance of karsting at the PCB on the Yangtze Platform; and (3) the comparative stratigraphic architecture of Ediacaran-Cambrian sections from the Yangtze Platform, the Tarim/Yili microcontinents, and southern Kazakhstan.(1) The fossil record of Ediacaran to Lower Cambrian shelf deposits demonstrates how significant volumes of fine-grained sediment became incorporated in the global chemicaloceanographic interchanges through the demise of microbially sealed surfaces during the agronomic revolution. To date, the timescale, facies dependency and degree of this enlargement of the Earth system cannot be incorporated in geochemical modeling calculations nor can it be convincingly linked to the expansion of the metazoa. In this subproject, we will link the bioturbation index from key sections across the PCB to geochemical proxies and relate those in turn to the chemostratigraphic record from profiles in West China (Tarim and Yili microcontinents) and Kazakhstan (Karatau Range).(2) Because the contact between Ediacaran and Cambrian deposits in the fossiliferous shallow-water facies the Yangtze Platform is virtually everywhere unconformable and karsted, resulting from one or several periods of relative sea level fall and subaerial exposure of Dengying Fm. carbonates, approximately 6-10 Ma of critical geologic time at the PCB is apparently missing. This record can be studied in numerous well-exposed stratigraphic sections of Sichuan, Guizhou and Hubei Provinces. We suggest to assess this event to infer duration and intensity of chemical weathering and compare our results to other well-exposed PCB reference sections worldwide. Our results, complemented by a concurrent biostratigraphic study (subproject Steiner), will fill in a neglected but potentially critical gap in our understanding of the metazoan base-Cambrian radiation in South China.