Discussion on 'The stratigraphy and origin of the Natal Group' (S. Afr. J. Geol., 102, 15-25)

Abstract

Marshall and Von Brunn (1999) have ably analysed the lithology and revised the lithostratigraphy of the Natal Group (SACS, 1980) to a stage where the characteristic cyclical sedimentation in depositional basins is revealed. We provide evidence from developing sequence chronostratigraphic techniques (Vail et al., 1977; Wilgus et al., 1988; Van Wagoner et al., 1990; Vail et al., 1991) that endorses previous correlations with the Cape Supergroup. Based on references such as these and relevant articles on local stratigraphy, we point out where we consider that insufficient research was done to modify or drop these correlations in favour of their conclusion that the sediments occupy an older rift valley or foreland-type basin. Both the Cape Supergroup and their redefined Natal Group are bounded by the same upper major unconformity (Levorsen, 1960; Fatti and Du Toit, 1970; Winter and Venter, 1970; Fatti, 1970, quoted in Fatti, 1972). Winter (1984; 1989; 1991; 1992) consequently followed a current conclusion that the former is a passive margin basin comprising three global time-equivalent Sloss-type sequences (Sloss, 1963). Both are lithostratigraphic units belonging to the same major regional chronostratigraphic unit and thus share the same tectonic style of depositional basin (Winter, 1989; Salvador, 1994; SACS, 1996). In both outcrop …