3-Gyr-old stromatolites from South Africa

Abstract

WE report here a new record of early Precambrian stromatolites from the 3.0-Gyr Pongola Supergroup of South Africa (Fig. 1), which is exposed in parts of the southeastern Transvaal, Swaziland, northern Natal and Zululand. These rocks occur in an almost complete section found in the Wit-Mfolozi River valley, about 200km north of Durban. In that part of Natal the volcanic-–sedimentary Pongola Supergroup attains a maximum thickness of about 2,500 m. It is subdivided into two distinct north-east-dipping stratigraphic units; the lower 1,800-m thick Insuzi Group and the upper 700-m Mozaan Group¹. Bedding and primary sedimentary structures are ubiquitously well preserved. Deformation is restricted to moderate cleaving of the argillaceous rocks. Evidence of regional metamorphism is restricted to incipient recrystallisation of the arenaceous and carbonate rocks; the lavas show evidence of deuteric alteration. Contact metamorphism is found where isolated diabase sills intrude the strata.