New chronology for the southern Kalahari Group sediments: implications for sediment cycle dynamics and early hominin occupation

The Kalahari Group covers an extensive part of the southern African continent and forms a low-relief landscape dominated by extensive unconsolidated sand. Current depositional models assume that the Kalahari Group sediments accumulated gradually throughout the Cenozoic, but an absence of absolute chronology beyond ~60 ka has left this premise untested. Here, we challenge this age model with new cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments at Mamatwan Mine near the southern edge of the Kalahari basin. Our results indicate that the majority of the existing section was emplaced rapidly at ~1 Ma. At this time the basin filled to its present level and established the Kalahari sand belts, which fostered the modern savannah. Our data suggest a dynamic landscape, with punctuated cycles of erosion and deposition, in contrast to the accepted concept of a stable basin filling slowly throughout the Cenozoic. The sedimentology and cosmogenic nuclide measurements from the lower Mamatwan Mine section reveal the existence of an extensive Early to Middle Pleistocene water body, persisting at least 420 ka prior to the rapid filling event at ~1 Ma. This water body is contemporaneous with a significant hominin occupation as evidenced by neighboring archaeological excavations. We thus provide the first evidence of association of the high-density hominin occupation in southern Africa with an extensive water body. © 2014 The Geological Society of America (GSA)

Keywords

Africa, Sand, Sediments, Geological deposits, Pleistocene epoch, Water, Isotopes

Citation

Matmon, A., Hidy, A., Vainer, S., Crouvi, O., Fink, D., Erel, Y., Arnold, M., Aumaître, G., Bourlès, D., Keddadouche, K., Horwitz, L., & Chazan, M. (2014). New chronology for the southern Kalahari Group sediments: implications for sediment cycle dynamics and early hominin occupation. Paper presented at the GSA Annual Meeting 19-22 October, 2014, Vancouver, BC, Canada.