Taphonomy and sedimentology of an echinoderm obrution bed in the Lower Devonian Voorstehoek Formation (Bokkeveld Group, Cape Supergroup) of South Africa

Abstract

The Lower Devonian Voorstehoek Formation is a lithostratigraphic unit within the Ceres Subgroup of the Bokkeveld Group (Cape Supergroup) in South Africa comprised of essentially mudstones and siltstones. This fossiliferous unit contains typical cool to cold water benthic biota (e.g., brachiopods, trilobites, crinoids) from the Malvinokaffric Realm of SW Gondwana, however, to date, not only the taphonomy of Voorstehoek invertebrates is understudied, but in general those of the Early Devonian marine communities of this Realm. The palaeontological and sedimentological features of the Emsian Voorstehoek Formation suggest that deposition took place in a shallow marine environment within the storm-influenced, proximal part of an offshore transition zone. 3D microCT scanning of this obrution bed allows us to report, for the first time from South Africa, on the co-occurrence of fully-articulated remains of both ophiuroids and stylophorans within the same sedimentary layer. Taphonomic analyses of this ophiuroid–stylophoran assemblage suggest a marine obrution deposit, which formed due to the rapid burial of the benthic community during high-energy storms, smothered both autochthonous and allochthonous taxa. This uniquely preserved, mixed ophiuroid–stylophoran assemblage provides a taphonomic window into the marine ecosystems of the Early Devonian, including the structure of a benthic community within the Malvinokaffric Realm of SW Gondwana.