A mid Cretaceous paleo-Karoo River valley across the Knersvlakte plain (northwestern coast of South Africa) : evidence from apatite fission-track analysis

Apatite fission track analysis of gneiss samples across the Knersvlakte plain in the coastal are of western South Africa reveals the existence of a relatively deeply incised paleovalley flanked by high ridges formed during the Mid Creataceous. This paleovalley coincides with the present course of the Krom River through the Great Escarpment. Modelling of the fission-track data suggest that the main stage of intense channel erosion, triggered by uplift of the catchment area, occurred between similar to 120 and similar to 110 Ma and was followed by a period of progressive hillslope erosion and interfluve degradation. It is suggested that the paleo-Karoo River and its tributaries were responsible for the formation of this relief. The present-day lower relief formed by continuing erosion starting at similar to 90 ma, time when all the analysed samples had already been exhumed to a depth corresponding to temperatures below 60 degrees C (similar to 2 to 3 km).