EVIDENCE OF NEOGENE TO QUATERNARY FAULTING AND SEISMOGENIC DEFORMATION ALONG THE NAMAQUALAND COAST, SOUTH AFRICA

Abstract

This paper reports on the results of a systematic investigation into evidence of near-surface and surface deformation of Late Cenozoic sediments along the West Coast of South Africa. Regional studies were supplemented by the investigation of pit faces in diamond mines owned by De Beers Consolidated Mines (Pty) Ltd between Hondeklip Bay and Kleinsee and inspection of exploratory trench logs kept by Alexkor at Alexander Bay. The results provide the first substantiation for previous unverified reports of neotectonic faulting in Pliocene to Pleistocene formations along the Namaqualand coast. Associated deformation of unconsolidated marine sediments suggests that the faulting was seismogenic. The interpretations of some of the observed features remain preliminary and the age of the structures is in most cases not well constrained. Some of the faulting at Hondeklip Bay is clearly younger that 3 Ma and the youngest surface rupture observed may be of latest Pleistocene age. This style of reactivation of coast-parallel Mesozoic or older faults is similar to that recently described in Namibia, and known Quaternary reactivation of the Kango fault system in the Southern Cape.