Integrated Sequence and Chemostratigraphy of the Neoproterozoic Krol Platform, Lesser Himalaya, India

9614070 Christie-Blick 我们建议对印度北部小喜马拉雅山的新元古代（可能还有下寒武统）Krol 台地进行综合序列和化学地层学研究。 Krol 是厚度超过 6 公里的岩层的一部分，该岩层包括底部可能为 Varanger 年龄的冰川海洋岩层（Blaini 组）和顶部（Tal 群）的早期寒武纪时代（Tommotian 到 Botomian）的陆源岩石。 新元古代和早寒武纪的全球特征是 (13C，碳酸盐碳的范围为 12 至 -5) 的显着偏移。这些偏移反映了海水同位素组成的长期变化，并且偏移可用于全球对比。然而，碳酸盐偏移 (13C 低至 -5) 很难用整个海洋化学来解释，并且可能表明 a) 表面到海底同位素梯度大于现代海洋的约 2 分之一，b) 地层趋势可能部分归因于沉积古环境（水深）的变化。 Krol 平台可用于解决对新元古代化学地层学和我们对同位素偏移起源的理解至关重要的两个问题：1) (13C 作为相（和古水深度）的函数）的横向变化是什么？2) 已发表的 (13C) Krol 测量值与西伯利亚、中国南部、纳米比亚和马更些山脉潜在相关地层的数据之间是否存在差异（加拿大）由于之前的研究对 Krol 的成岩作用关注不够，或者 Krol 代表了异常完整且厚的碳酸盐层序（2 公里）并从中获取了样本，所以 Krol 可能特别适合层序地层学，因为可用的露头似乎涵盖了从浅层到深层的斜坡环境的过渡，以及碳酸盐岩与近岸砂岩的“交错”组合。化学地层学与层序地层学的结合将使我们能够建立一个独立的时间地层框架，通过该框架来观察（13C）的“垂直”和“横向”变化，并研究成岩作用在平台不同部分的作用。这项研究还应该解决前寒武纪-寒武纪边界是否位于磷虾顶部（如已发表的碳同位素数据所表明的那样）；并且它可能允许我们“指纹”几个层序边界（13C，因此可以比较这些表面的时间和在大致相同年龄的其他富含碳酸盐序列中解释的层序边界。

9614070 Christie-Blick We propose an integrated sequence and chemostratigraphic study of the Neoproterozoic (and possibly lower Cambrian) Krol platform in the Lesser Himalaya of northern India. The Krol is part of a succession more than 6 km thick that includes glacial-marine stata of probable Varanger age at the base (Blaini Formation) and terrigenous rocks of early Cambrain age (Tommotian to Botomian) at the top (Tal Group). The Neoproterozoic and early Cambrian interval is characterized globally by marked excursions in (13C, ranging from +12 to -5 for carbonate carbon. These have been taken to reflect secular variations in the isotopic composition of sea water, and that the excursions can be used for global correlation. However, excursions in carbonate (13C as low as -5 are difficult to explain in terms of whole-ocean chemistry, and may indicate a) a surface to seafloor isotopic gradient that was larger than the ~2 per mil of the modern ocean and b) that stratigraphic trends may be due in part to changes in the paleoenvironment of deposition (water depth). The Krol platform can be used to address two questions of importance to Neoproterozoic chemostratigraphy and our understanding of the origin of the isotopic excursions: 1) What are the lateral variations in (13C as a function of facies (and paleowater depth)? 2) Are differences between published (13C measurements for the Krol and data from potentially correlative strata in Siberia, southern China, Namibia and the Mackenzie Mountains (Canada) due to inadequate attention to diagenesis in the Krol in previous studies, miscorrelation or the fact that the Krol represents an unusually complete and thick succession of carbonate (2km) from which to obtain samples? Preliminary work shows that the Krol may be particularly amenable to sequence stratigraphy because available outcrop appears to encompass the transition from shallow to deep ramp settings, as well as "interfingering" of the carbonate rocks with nearshore sandstones. The co mbination of chemostratigraphy with sequence stratigraphy will allow us to establish an independent time-stratigraphic framework with which to look at both "vertical" and "lateral" variations in (13C, and to investigate the role of diagenesis in different parts of the platform. The study should also resolve whether the Precambrian-Cambrian boundary is located at the top of the Krill (as suggested by published carbon isotopic data); and it may allow us to "fingerprint" several sequence boundaries with respect to (13C, and hence to compare the timing of these surfaces and sequence boundaries interpreted in other carbonate-rich successions of broadly the same age.