Late Cenozoic paleoclimates of the Gaap Escarpment, Kalahari margin, South Africa

Abstract

The Gaap Escarpment is a dolomite cuesta demarcating the southeast margin of the Kalahari. Since Miocene-Pliocene times, thick masses of lime tufa have repeatedly accumulated at several points along this escarpment, and four regional sequences are described. These allow discrimination of six major depositional complexes, commonly characterized by basal cryoclastic breccias or coarse conglomerates that reflect frost shattering and torrential runoff, followed by sheets and lobes of tufa generated in an environment substantially wetter than today. A chronostratigraphy for the last 30,000 yr is provided by 14C dating, with direct or indirect correlations to the Vaal River sequence. The regional stratigraphy as well as faunal dating indicate an early Pleistocene age for Australopithecus africanus at Taung. Repeated episodes of protracted cold or wetter climate or both begin in terminal Miocene times, and the last Pleistocene cold-moist interval began after 35,000 yr B.P. and ended 14,000 yr B.P. Early and late Holocene times were mainly wetter, whereas the middle Holocene was drier than today. The paleoclimatic sequence differs from that of the southern and southwestern Cape or that of East Africa, but close parallels are evident throughout the lower Vaal Basin and the southern Kalahari. The tufa cycles provide a unique, 5,000,000-yr record of climatic variation in the Kalahari.summer-rainfall belt that can be related to complex anomalies of the general atmospheric circulation.