Abstract

Late Mesozoic palaeosoils and Cenozoic deposits in the Northern Province, South Africa, centered on Vaalputs, Namaqualand are exposed in radioactive waste disposal trenches and buried beneath the surficial sands that cover much of the Bushmanland region. The sediments are preserved in a depression, in the “Vaalputs Basin”, inland of the Great Escarpment. They overly a kaolinized and silicified basement of Late Mesozoic arenites (Dasdap beds) and by high grade rocks of the Namaqualand Metamorphic Complex. The Vaalputs sediments are interpreted to be fluvial in origin, possibly deposited as unchannelized floodouts from a provenance area in the west. Extensive bioturbation and pedogenesis accompanied deposition. The age of the sediments is poorly constrained but post-dates ~67 Ma volcanic pipes of the region. The Vaalputs sediments are influenced by north-northwesterly trending faults which also displace the underlying kaolinized and silicified basement. To the east of Vaalputs faulting in this orientation has produced a local depression (the Santab-se-Vloer). The distribution and apparent ages of the kaolinized and silicified surface, the Dasdap and Vaalputs sequences, and the position of the Santab-se-Vloer depression suggest to us that the continental margin has been characterized by an easterly migrating arch of uplift since the opening of the Atlantic, accompanied by increasing aridification of the region.

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