Geological Setting of the Hofmeyr Locality

Abstract

The Hofmeyr skull was discovered from the banks of the Vlekpoort River, which traverses a broad plain northeast of the town of Hofmeyr, located in the hinterland of the Eastern Cape Province of South Africa. The fossil locality is directly underlain by the reddish siltstones of the Burgersdorp Formation, while the resistant sandstones of the overlying Molteno Formation form the slopes of the Bamboesberg mountains more than 10 km to the east. Both these formations accumulated through deposition by northwards-flowing rivers draining the Cape Fold Belt to the south, during the Triassic (251–201 Ma), filling the main Karoo Basin, which was at that time situated in southern Gondwana. The modern landscape, dominated by the Great Escarpment, was formed during a long, erosion-dominant period, which started right after Gondwana break-up, was accelerated during the predominant humid tropical climate associated with the Cretaceous, and continues to this day. Short, steep south-flowing river systems, such as the Great Fish River drainage, which encompass the Vlekpoort River, drains the landscape across and south of the Great Escarpment. Quaternary deposits drape the hill slopes and plain north of Hofmeyr. The Late Pleistocene age obtained from the Hofmeyr specimen overlaps with the fluvial record from central South Africa, which is a time when a dry climate is assumed to have predominated over central South Africa. Locally the Vlekpoort River valley is bounded by resistant Karoo bedrock, with a prominent dolerite dyke approximately 4 km south of the fossil locality, one of several to intersect the modern landscape, controlling the local channel profile. Over the past century the construction of numerous dams and weirs in the river channel has interrupted the natural river evolution processes by raising the local base level, which has resulted in in the silting-up of the channel floor and the Hofmeyr fossil locality.