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

我们建议研究前寒武纪-寒武纪界线（PCB，约543 Ma）沉积-地层变化的三个方面，以补充地球化学和古生物亚项目：(1)古技术记录的农艺革命的影响；(2)扬子地台PCB岩溶作用的意义；(3)比较扬子地台、塔里木/伊犁微大陆和哈萨克斯坦南部埃迪卡拉纪-寒武系剖面的地层构型。(1)埃迪卡拉纪至下寒武纪陆架沉积的化石记录表明，在农业革命期间，大量细粒沉积物是如何通过微生物封闭表面的消亡而被纳入全球化学-海洋交换的。迄今为止，地球系统扩大的时间尺度、相依赖关系和程度不能纳入地球化学模拟计算，也不能令人信服地将其与后生动物的扩大联系起来。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指标联系起来，并将这些指标与中国西部（塔里木和伊力微大陆）和哈萨克斯坦（卡拉托山脉）剖面的化学地层记录联系起来。(2)由于一个或几个时期的相对海平面下降和灯影组的陆下暴露，埃迪卡拉纪与寒武纪浅水相化石沉积的接触，使扬子地台几乎处处不整合和岩溶。碳酸盐岩，大约6-10 Ma的关键地质时间在PCB显然是缺失的。这一记录可以在四川、贵州和湖北等省大量暴露良好的地层剖面中进行研究。我们建议对这一事件进行评估，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参考剖面进行比较。我们的研究结果，加上同时进行的生物地层学研究（Steiner子项目），将填补我们对华南后生动物基底-寒武纪辐射的理解中一个被忽视但可能至关重要的空白。

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.