oa South African Journal of Geology - Author's reply to discussion - discussion

Volume 102 Number 4
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590



Marshall (1999) raises several issues in his discussion of our paper 'Tidalites in the Natal Group' (Liu and Cooper, 1998). Although, obviously, Marshall is keen for us to follow his view regarding the Ordovician age (Thomas et al., 1992) and non-correlation of the Natal Group with the Msikaba Formation, our citation of these views merely reflects current opinion and is hardly support for hypotheses which still require rigorous testing. In fact, this hypothesis was introduced without addressing two fundamental questions, namely, if the Natal Group rivers did not ultimately flow into the Samfrau Sea much further to the south, where did they go and what happened to all their fines? It also makes the elementary error of assuming that the presence of 'Devonian' fossils in the Msikaba sandstone makes the entire formation Devonian. By their very nature, quartz-arenite successions are notoriously condensed and the base of the formation could be substantially older; likewise, the top could be significantly younger. In this respect, we are sure Marshall and his coworkers would be particularly interested in a reference they missed: Anderson and Anderson (1985) redescribed the Msikaba plants as Longicicatrix bulbosa and noted that because the material was ' ... quite unlike any from the Cape Fold Belt ... we judge the host strata to be younger than the Witteberg Group'; Cooper (1986) showed that the Upper Witteberg was Lower Carboniferous. Does this mean, now, that the Msikaba Sandstone is entirely Middle to Upper Carboniferous?

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