Relict periglacial slope deposits in the Hex River Mountains, South Africa: observations and palaeoenvironmental implications

Shattered bedrock near the summit of Matroosberg, Western Cape Mountains, is closely associated with several blockstreams which grade downslope into broad terraces. With an increase in slope angles the regolith grades into broad bands of coarse but sorted material parallel to the maximum gradient. The width of the coarse stripes increases in the downslope direction, where they merge into openwork block deposits several tens of metres long and wide. Whereas the terraces near the summit plateau closely resemble gelifluction sheets, the large sorted stripes and coarse debris mantles are analogous to the stone-banked terraces described for the Colorado Front Range. The landforms are primarily related to seasonal frost creep at the Last Glacial Maximum (LGM) when mean annual temperatures are estimated to have been around 0°C, i.e., winter temperatures 7–8°C lower than present. Snowcover must have been limited to allow deep frost penetration.