An introduction to the Geology of the Drakensberg
An extended period of sedimentation, volcanic flow, massive continental upliftment and ultimately the erosion of the thick basalt cap defined Drakensberg’s geology. As a result, this escarpment is one of the world’s best examples of an erosional mountain.
Water-driven sedimentation
The lowest layer of the Drakensberg is the Molteno group of deposits. A sedimentary layer of approximately 450 metres thick in this region. It comprises sandstone and shale layers rich in insect and plant fossils, which reflect lush riverine or swampy vegetation over what we then knew as Gondwanaland. This supercontinent was established about 450 million years before the present until some 200 years before the present.
The Elliot Formation followed this layer. A layer of mudstones on what was a semi-arid floodplain. Dinasoar fossils have also been found in this layer.
Wind-driven sedimentation
The Elliot period was followed by wind-driven reddish fine sand deposits from an arid period over Gondwanaland. The Clarens Sandstone Formation was a narrower layer. This band is up to 90 metres in thickness. A softer yellow aerial deposit followed, sometimes called the Cave Deposits or Cave Formations.
The Gondwanaland split
Volcanic rock or magma forced its way up fissures in the sandstone about 180 million years ago. This magma formed a thick cap of basalt or a peneplain across much of what is now southern Africa.
Approximately 150 years ago, Gondwanaland was uplifted and began to split and drift apart into various continents. Africa was one of these.
Erosion
The eastern part of South Africa was uplifted before the split, creating fast east-flowing rivers. These rivers slowly eroded the basaltic layers to create the stark, rugged cliffs and peaks for which the Upper Drakensberg is renowned. The rapid fluvial erosion of the sandstone layers below established its deep valleys and the Little or Lower Drakensberg. The Drakensberg has slowly eroded some 150 to 200 kilometres from the present coastline at some 1.5 mm a year.
