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

格罗青格9628257 该项目将试图通过研究从微生物和非生物碳酸盐形成的元古宙台地到钙化后生动物和后生植物骨骼形成的元古宙台地的过渡，提高我们对碳酸盐台地的一级长期演化的理解。 拟议的研究将试图记录几个碳酸盐岩平台和珊瑚礁的详细古环境的纳马和Witvlei组（纳米比亚），跨越终端新元古代的时间，和钙化的无脊椎动物和后生植物的沉积物生产，平台古生态学和相发展的第一个影响。 我们将具体研究：1）各种相的组成和分布，2）微生物岩形态与微组构之间的关系，3）微生物与钙化后生动物和干骺端细胞之间的关系，以及4）骨骼颗粒、微生物组分和胶结物的原生矿物学。 我们选择了三个有代表性的单位进行调查的基础上，他们的相，微生物和骨骼化石组合的多样性，并逐步年轻的地层位置和年龄。 按上升地层顺序，这些地层包括：1）Bushmanskippe地层（Witvlei组），其基础单位（Bildah成员）被认为是“帽碳酸盐”（2）具有三维地层出露的纳马群底部鄂木斯克段，含有壮观的微生物岩-Cloudina尖礁; 3）那马群中段匈奴段，含钙化的干骺端-微生物岩片礁和微生物岩-贝壳化石尖礁。 拟议的研究将提供重要的信息，将是有用的了解最早的钙化后生动物/后生植物和微生物生态系统，终端新元古代碳酸盐沉积物的来源，骨骼沉积物的影响和碳酸盐沉积系统的长期演化的相互作用。

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.