Geomorphic perspectives on the sterkfontein australopithecine breccias

Breccias in the upper Sterkfontein cave system levels have yielded artifact assemblages as well as Homo and Australopithecus africanus remains. As mapped by the author, this sytem can be subdivided into a northern sector, comprising small, bedding-controlled passageways, and a southern one with large galleries controlled by subvertical fracture zones and partly filled with two generations of external, detrital sediment. A four-stage model describes the development of these deposits. The implications of this study include: (1) The caves formed in one rather than two phases, as a result of structural rather than watertable controls. (2) The lowest strata of both depositional generations, 50–60 m below the hillcrest are probably the oldest. T. C. Partridge's Sterkfontein Formation only includes approximately the upper half of the stratigraphic column recognized here. Deposits underlying those he described are also fossiliferous and probably substantially older than the 2·8+ million year age attributed to the lower units of the Sterkfontein Formation. (3) The Sterkfontein Formation, as defined by Partridge, is a composite stratotype, comprising one surface exposure and another underground, at mid to upper levels in the system. Their stratigraphic relationships are obscure and since the lower boundary of the Formation also is in doubt, erection of a formal stratotype is premature. Deep-lying breccias may ultimately warrant another component, extending the Sterkfontein Formation to the lowest known levels of the cave system.