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

9614070克里斯蒂-布里克我们建议对印度北部小喜马拉雅地区的新元古代(可能还有下寒武统)克罗尔地台进行综合层序和化学地层学研究。Krol是厚度超过6公里的序列的一部分，该序列包括底部(Blaini组)可能为Varanger时代的冰川-海相Stata和顶部(Tal群)早期CamBrain时代(Tommotian至Botomian)的陆源岩石。新元古代和早寒武世时期的全球特征是碳酸盐碳的(13C)显著漂移，范围从12到-5。这些变化反映了海水的同位素组成的长期变化，并且这些漂移可以用于全球对比。然而，碳酸盐(13C低至-5)的漂移很难用全海洋化学来解释，可能表明a)表面到海底的同位素梯度大于现代海洋的~2/mil，b)地层趋势可能部分是由于沉积古环境(水深)的变化。Krol地台可用于解决新元古代化学地层学和我们对同位素漂移起源的两个重要问题：1)Krol地台的横向变化(13C作为相(和古水深度)的函数)是什么？2)已发表的Krol地台(13C测量结果与来自西伯利亚、中国南部、纳米比亚和麦肯齐山脉(加拿大)潜在相关地层的数据之间的差异是由于以前研究中对Krol成岩作用的重视不够、对比错误或Krol代表了一个异常完整和厚实的碳酸盐岩系(2 Km)以获取样品？初步工作表明，Krol可能特别适合层序地层学，因为可用的露头似乎包括从浅到深的斜坡环境的过渡，以及碳酸盐岩与近岸砂岩的“相互作用”。化学地层学和层序地层学的结合将使我们能够建立一个独立的时间-地层学框架，用它来研究(13C)的“垂直”和“横向”变化，并研究成岩作用在地台不同部分的作用。这项研究还应该确定前寒武纪-寒武纪界面是否位于磷虾的顶部(正如已公布的碳同位素数据所表明的那样)；它可能允许我们对(13C)的几个层序界面进行“指纹”，从而比较这些表面的时间与在大体相同年龄的其他富碳酸盐序列中解释的层序界面的时间。

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.