Latest Proterozoic Microfossils from the Nama Group, Namibia (South West Africa)

Abstract

Gray to black shales from the Kuibis and Schwarzrand subgroups of the Nama Group, South West Africa/Namibia, contain a distinctive, if depauperate, assemblage of organic-walled microfossils. The assemblage is dominated by leiosphaerid acritarchs and fragments of the ribbon-like macrofossil <i>Vendotaenia</i>. Small unicells and non-septate filaments interpreted as the sheaths of oscillatorian cyanobacteria occur with variable frequency throughout the subgroups, while <i>Chuaria circularis, Bavlinella faveolata</i>, and a <i>Comasphaeridium</i>-like form (known from a single specimen) are found as rarer components of the biota. Assemblage composition shows no strong stratigraphic trends within the subgroups. The Nama assemblage compares closely with biotas previously described from upper-most Proterozoic (Valdaian) sequences of the Baltic region, Scandinavia, and Australia, and confirms a latest Proterozoic age for the Kuibis and Schwarzrand subgroups and their contained metazoan fossils. Although its significance is unclear, Nama microfossils tend to be strongly corroded. This diagenetic feature is widespread among Valdaian assemblages, but appears to be much less characteristic of older or younger biotas.