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

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

ABSTRACT Facies Architecture and Paleobiology of a Terminal Proterozoic Carbonate Ramp, Kuibus Subgroup, Namibia John P. Grotzinger EAR-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.