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

小行星9614070 我们建议在印度北方的小喜马拉雅地区对新元古代（可能还有下寒武统）克罗尔台地进行综合层序和化学地层学研究。 克罗尔是一个超过6公里厚的连续层的一部分，该连续层包括底部可能是瓦兰格时代的冰川-海洋地层（Blaini地层）和顶部的早期Cambrain时代（Tommotian到Botomian）的陆源岩石（Tal群）。 新元古代和寒武纪早期的全球特征是碳同位素13 C的显著偏移，范围从+12到-5。 这些都反映了长期变化的同位素组成的海水，并可用于全球相关的偏移。 然而，碳酸盐（13 C低至-5）的偏移很难从整个海洋化学的角度来解释，这可能表明：a）表层到海底的同位素梯度大于现代海洋的每千分之2; B）地层趋势可能部分归因于沉积古环境（水深）的变化。 Krol平台可用于解决新元古代化学地层学和我们对同位素漂移起源的理解的两个重要问题：1）13 C的横向变化是什么样的相（和古水深）的函数？2)公布的克罗尔13 C测量值与来自西伯利亚、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否是由于以前的研究中对克罗尔的成岩作用关注不够、相关性不佳或克罗尔代表了一个异常完整和厚的碳酸盐岩序列（2 km）的事实而导致的？ 初步工作表明，克罗尔可能特别适合层序地层学，因为可用的露头似乎包括从浅斜坡到深斜坡的过渡，以及碳酸盐岩与近岸砂岩的“交指”。 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-地层格架，用它来观察（13 C）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。 这项研究还应该解决前寒武纪-寒武纪边界是否位于磷虾的顶部（如已发表的碳同位素数据所示）;它可能使我们能够“指纹”几个序列边界相对于（13 C），从而比较这些表面和序列边界的时间解释在其他碳酸盐丰富的继承大致相同的年龄。

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.