The sedimentary environment of the Deweras Group in Rhodesia

Abstract

THE sediments of the Deweras Group comprise a thick succession of alluvial deposits laid down in a fault-bound trough and bear a close lithologie and tectonic similarity to the broadly contemporaneous sediments of the Water-berg, Soutpansberg and Matsap successions further to the south. It is significant, therefore, that the troughs in which all these sediments were deposited show a marked alignment and it is suggested here that they may be interpreted as a palaeo-rift system between 2,100 and 1,300 Myr old. The Deweras Group (Figs 1 and 2) comprises a thick succession of clastic and argillaceous rocks, together with interbedded andesitic lavas. At the base of the sequence is a widespread but impersistent unit of continental tholeiitic basalts. These sediments crop out as a north-north-east (NNE) trending belt in central–north Rhodesia in a basin herein referred to as the Deweras trough.