NATURE AND EXTENT OF A LATE EDIACARAN (CA. 547 MA) GLACIGENIC EROSION SURFACE IN SOUTHERN AFRICA

摘要

Erosional surfaces within the late Ediacaran upper Kuibis and lower Schwarzrand Subgroups of the Nama Group, that extend from the Klein Karas Mountains in Namibia eastward to the Namibian-South African border and from southern Namibia to Nigramoep (near Springbok) in South Africa, are interpreted to form one discontinuous regional unconformity termed the Vingerbreek Unconformity (VGU). This unconformity formed by glacial, proglacial and fluvial erosion. The palaeochannels (palaeovalleys) associated with this unconformity in southern Namibia and northwestern South Africa are interpreted to have formed distant from major glaciers as a result of predominantly glacio-eustatic sea level fall. Our findings are consistent with a late Ediacaran (ca 547 Ma) glaciation, that is also recorded in South America and Eurasia. The evolutionary implications of a glacial event just before the Ediacaran/Cambrian are considerable, because climate deterioration could have acted as an evolutionary bottleneck and thus promoted the Cambrian explosion in its aftermath.