Environmental and Biologic Controls on Carbonate Platform and Reef Development, Terminal Neoproterozoic Nama Group, Namibia

格罗青格9628257这个项目将试图通过研究从由微生物和非生物碳酸盐形成的元古界台地到由钙化的后生动物和玄武岩骨架形成的显生界台地的过渡，来提高我们对碳酸盐台地一级、长期演化的理解。这项拟议的研究将试图记录(纳米比亚)Nama和Witvlei群中跨越新元古代末期的几个碳酸盐台地和生物礁的详细古环境，以及钙化的无脊椎动物和形而上学对沉积物生产、台地古生态和相发育的首次影响。我们将具体研究：1)各种相的组成和分布，2)微闪石形态与微组构的关系，3)微生物与钙化后生动物和变质岩的关系，4)骨骼颗粒、微生物成分和胶结物的原生矿物学。我们选择了三个具有代表性的单位进行调查，根据它们的相、微闪石和骨骼化石组合的多样性，以及逐渐年轻的地层位置和时代。按地层升序排列，它们包括：1)Bushmanskppe组(Witvlei群)，其基本单位(Bildah段)被认为是“盖层碳酸盐”(特殊的碳酸盐)，可能与新元古代冰盖的消融有关；2)基本Nama群的Omkyk成员，具有三维地层暴露，包含壮观的微闪石-Cloudina尖顶生物礁；以及3)Nama群中部的匈奴成员，包括钙化的干玄武岩-微闪石斑块生物礁和微闪石-贝利化石顶尖生物礁。这项研究将提供重要的信息，有助于了解最早的钙化后生动物/形而上学与微生物生态系统之间的相互作用，新元古代末期碳酸盐沉积的来源，以及骨骼沉积对碳酸盐沉积体系的相变和长期演化的影响。

Grotzinger 9628257 This project will attempt to improve our understanding of the first-order, long-term evolution of carbonate platforms by investigating the transition from Proterozoic platforms formed of microbial and abiotic carbonates to Phanerozoic platforms formed of calcified metazoan and metaphyte skeletons. The proposed research will attempt to document the detailed paleoenvironments of several carbonate platforms and reefs in the Nama and Witvlei groups (Namibia) that span terminal Neoproterozoic time, and the first influences of calcified invertebrates and metaphytes on sediment production, platform paleoecology, and facies development. We will specifically study: 1) the composition and distribution of various facies, 2) the relationships between microbialite morphology and microfabric, 3) the relationships between microbialities and calcified metazoans and metaphyytes, and 4) primary mineralogy of skeletal grains, microbial components, and cements. We have selected three representative units for investigation based on their diversity of facies, microbialite and skeletal fossil assemblages, and progressively younger stratigraphic positions and age. In ascending stratigraphic order these include: 1) the Bushmanskippe Formation (Witvlei Group), whose basal unit (Bildah Member) is considered to be a "cap carbonate" (peculiar carbonates possibly associated with deglaciation of Neoproterozoic ice sheets; 2) the Omkyk Member of the basal Nama Group which has 3-D stratigraphic exposures and contains spectacular microbialite-Cloudina pinnacle reefs; and, 3) the Huns Member of the middle Nama Group which contains calcified metaphyte-microbialite patch reefs and microbialite-shelly fossil pinnacle reefs. The proposed research will provide important information that will be useful in understanding interactions within the earliest calcified metazoan/metaphyte and microbial ecosystems, the sources of terminal Neoproterozoic carbonate sediment, and impact of skeletal sediment on the f acies and long-term evolution of carbonate depositional systems.