The stratigraphy and formation history of fossil- and artefact-bearing sediments in the Milner Hall, Sterkfontein Cave, South Africa: New interpretations and implications for palaeoanthropology and archaeology

• We analyse six undescribed deposits found at the base of the Sterkfontein Caves.
• A multidisciplinary approach allowed the correlation of deposits to their sources.
• We recognise an early, distal and basal representative of the M2 deposit.
• Our work suggests that the deepest chambers contain some of the oldest sediments.

The Sterkfontein palaeokarst deposits, the richest repository of Australopithecus fossils in the world, are currently divided into six members (M1–M6) and named the Sterkfontein Formation ( Partridge and Watt, 1991). In this system, it was proposed that the passages and chambers deeper than the Silberberg Grotto formed most recently and are filled with comparatively young sediments from newer openings or reworked sediments from older, upper chambers. Here we describe the geomorphology, sedimentology, fauna and archaeological evidence from six deposits excavated near the base of the system in the Milner Hall. The use of a multidisciplinary approach enabled us to clarify the complex stratigraphic history, to track artefact-bearing deposits through multiple phases of deposition, and to identify an early deposit accumulated from the Silberberg Grotto to the base of the system. We propose that the Australopithecus-bearing Member 2 deposit originally extended down to near the base of the Milner Hall. We further propose that the vertical extent of the cave system was developed prior to the opening to the landscape surface, and that at that time the groundwater level was comparable to that seen now. We therefore argue that some of the earliest palaeoanthropological material in South Africa may have been deposited into the deepest chambers of the Sterkfontein Caves.