Sequence stratigraphy and sedimentology of the Neoproterozoic Kuibis and Schwarzrand Subgroups (Nama Group), southwestern Namibia

Abstract

The Kuibis and Schwarzrand Subgroups of the Nama Group form a succession of shallow-marine and minor fluvial sedimentary rocks that is exposed over much of central and southern Namibia. Ediacaran-type body fossils and the stratigraphic carbon-isotope variability indicate a Vendian age for much of these strata; the Precambrian-Cambrian boundary is in the uppermost part of the Schwarzrand Subgroup. Radiometric dating of abundant volcanic ash beds which span much of the Vendian and extend into the Cambrian part of the section could make the Nama Group the best calibrated reference section for Vendian chronostratigraphy. Here we describe the sedimentology and sequence stratigraphy of exposures of the Kuibis and Schwarzrand Subgroups in southwestern Namibia. We place tighter environmental constraints on the paleontology and geochemistry and we identify seven depositional sequences. The boundaries of the depositional sequences correspond to the more important disconformities in the Kuibis and Schwarzrand Subgroups; their identification is crucial for defining rates of organism evolution and isotopic differentiation.