Facies Architecture and Paleobiology of a Terminal Proterozoic Carbonate Ramp, Kuibus Subgroup, Namibia

纳米比亚Kuibus亚群末元古代碳酸盐岩斜坡的表面结构和古生物本项目将通过研究纳米比亚南部末元古代Kuibis碳酸盐台地的三维地层结构和古生物学，提高我们对碳酸盐岩台地一级、长期演化的认识。柯伊比斯地台具有斜坡几何结构，其特点是相变得相对平缓，从晶内椭圆形梯度岩浅滩到深水异石器组合，由薄层石灰泥岩、血栓/叠层石纹岩和页岩组成。泥沙输运主要由波浪和风暴产生的水流控制，如散布的丘陵状交叉层状和准平面层状方解石床所显示的那样，此外还有可能是由稀释浊流沉积的细粒级配床。坡道还包含许多礁相，由血栓岩、叠层石和可能是最古老的钙化后生动物组合之一的各种化石组成。珊瑚礁具有不同的几何形状，在上倾位置形成片状生物礁或明显的斑块生物礁，或者在较深水域、较低倾斜位置形成大型尖顶生物礁。这项研究的目的是：1)通过三维绘制Kuibis地台的详细古环境图，2)量化准层序界面之间的相空间排列，3)检验各种关于血栓结构起源的假说，4)利用新的数字三维重建技术量化钙化化石的分类多样性。拟议的研究将提供重要的信息，有助于了解最早的钙化后生动物和微生物生态系统中的相发育，准序列中相的定量分布，以及最古老的钙化后生动物的形态和分类多样性。

ABSTRACTFacies Architecture and Paleobiology of a Terminal Proterozoic Carbonate Ramp, Kuibus Subgroup, NamibiaJohn P. GrotzingerEAR-0001018 This project will attempt to improve our understanding of the first-order, long-term evolution of carbonate platforms by investigating the three-dimensional stratigraphic architecture and paleobiology of the terminal Proterozoic Kuibis carbonate platform of southern Namibia. The Kuibis platform has ramp geometry, marked by relatively gentle gradients in facies from intraclast-ooid grainstone shoals into deeper-water heterolithic assemblages of thin-bedded lime mudstones, thrombolitic/stromatolitic laminites, and shales. Sediment transport was dominated by wave- and storm-produced currents, as shown by interspersed beds of hummocky cross-stratified and quasiplanar stratified calcarenites, in addition to finer-grained graded beds probably deposited from dilute turbidity flows. The ramp also contains numerous reefal facies, formed of thrombolites, stromatolites and diverse fossils of what may be one of the oldest assemblages of calcified metazoans. Reefs have variable geometry, forming sheet-like biostromes or distinct patch reefs in updip positions, or large pinnacle reefs in deeper-water, more downdip positions. The objectives of this research are to: 1) document the detailed paleoenvironments of the Kuibis platform by mapping it in three dimensions, 2) quantify the spatial arrangement of facies between parasequence boundaries, 3) test various hypotheses for the origin of thrombolite textures, 4) quantify the taxonomic diversity of calcified fossils using new digital 3D reconstruction techniques. The proposed research will provide important information that will be useful in understanding facies development within the earliest calcified metazoan and microbial ecosystems, the quantitative distribution of facies within parasequences, and the morphology and taxonomic diversity of the oldest calcified metazoans.