FORMATION AND GEOMORPHOLOGY OF CAVES IN CALCAREOUS TUFAS AND IMPLICATIONS FOR THE STUDY OF THE TAUNG FOSSIL DEPOSITS

SUMMARY

Models of cave site formation processes in calcareous tufa accretions are necessary for the interpretation of fossiliferous cave deposits exposed by quarrying and excavation. The ancient system of caves in the Thabaseek tufa at the Buxton Limeworks near Taung yielded the Taung hominid skull, type specimen of Australopithecus africanus, in 1924. Since then no consensus has been reached concerning the precise location of the Type Site, the geological age of the Taung hominid or the nature of the caves in which it became interred. Recent excavations of fossil deposits in the Thabaseek tufa, near the putative Type Site, in association with the historical records, have revealed new clues as to the provenance of the Taung hominid and the nature of the cave from which it was excavated. An investigation of caves in tufa accretions of the Ghaap escarpment and Eastern Transvaal has revealed four types of tufa caves that can be used as models for analysis of the fossil deposits. These include carapace caves, pipes (solution cavities and potholes), river-carved rock shelters, and vadose caves. The nature of the Taung fossil deposits suggest that the hominid and associated fossils were deposited within a series of successive carapace caves in the Thabaseek tufa. The relative positions of these deposits, with the putative Type Site being the deeper primary carapace cave within the Thabaseek tufa, suggest that the Taung hominid predates most of the fauna thus far used for dating of the formation.