The discovery of deep karstic features, associated with a sharp contact between the carbonate-containing Kombuis Member of the Matjies River Formation and the overlying shaley (lower) part of the Groenefontein Formation of the Cango Caves Group (CCG) in the southwestern Cape in South Africa, indicates that it represents an unconformity which was formed sub-aerially. Previous chrono-, chemo- and biostratigraphic data are supported by genetic stratigraphy, which suggest that the unconformity, called the Groenefontein Unconformity, can be correlated with the Vingerbreek Unconformity occurring in the southern Nama Group, Namibia. This information enables more reliable correlation of the stratigraphic units of the Cango Caves and the Nama Groups and indicates modification of previously proposed correlations. A correlation between the Kombuis Member of the Matjies River Formation (CCG) with the Kuibis Subgroup (Nama Group) as well as the Groenefontein Formation (CCG) with the Vingerbreek Member of the lower Schwarzrand Subgroup (Nama Group) is proposed. The correlation of the Nooitgedagt Member (CCG) with units of the Port Nolloth and Nama Groups is less certain. The Nooitgedagt Member may be a correlate of the Holgat Formation of the Port Nolloth Group or of the lower part of the Kuibis Subgroup of the Nama Group in Namibia. It may also be possible to correlate the Nooitgedagt Member with an even older formation of the Port Nolloth Group. The Groenefontein and Vingerbreek unconformities were probably formed as a result of a drop in sea level caused by a circa 547 Ma minor glaciation which occurred during latest Ediacaran times in southwest Gondwana.