The landscapes of southern Africa: the legacy of mantle dynamic or glacial erosion?

International audience ; The modern relief of southern Africa is characterized by high-standing plateaus surrounded by escarpments and dissected by a network of encased valleys that connect the plateaus to coastal plains. This topography is commonly interpreted as resulting from the activity of a mantle plume, the African superplume, and the resulting stepwise uplift of the lithosphere, generating planation surfaces through surface erosion processes since the Mesozoic. However, in this study, we argue that part of this landscape is inherited from the glacial processes of the Late Paleozoic Icehouse (LPI) that occurred 300 ma ago and during which southern Africa was largely covered in thick ice. Field and GIS-based sedimentological and geomorphological studies however revealed that LPI glacial activity tied to the Late Paleozoic Icehouse, that occurred 300 million years ago and during which southern Africa was largely covered in thick ice, greatly contributed to the shaping of the Earth surface at different spatial scales. Glaciers levelled continental-scale planation surface, carved large valleys, fjords and overdeepenings within topographic escarpments that already existed, ploughed grooves and striae on the bedrock and left behind typical sediments such as moraines, tills and ice-contact deltas. After glacial retreat, the sea invaded these glacial reliefs, as attested by preserved paleoshorelines. In postglacial times and for 120-180 million years, these glacial landforms were progressively filled and eventually sealed under thick non-glacial sedimentary accumulation and was later rejuvenated by erosion tied to the activity of the mantle superplume. Today, large portions of the desertic high-standing plateaus, escarpments and networks of valleys defining the relief of southern Africa actually corresponds to a relict though rejuvenated 300-Ma old glacial landscape.