The sedimentology and stratigraphy of the Beaufort Group of the Karoo Supergroup in the vicinity of Thaba Nchu, central Free State province
Date
2009-09-11T07:33:29Z
Authors
Rutherford, Anthony Brian
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Abstract
Different basin fill models have been proposed for the retroarc foreland basin within which
the Karoo Supergroup of South Africa was deposited. The most recent of these proposals
suggests that the Karoo Basin behaved as a partitioned entity and that reciprocal infill
occurred either side of a hinge line in the centre of the basin. Detailed sedimentological,
palaeontological, stratigraphic and geophysical information for the Beaufort Group in the
eastern central Free State in the vicinity of Thaba Nchu is presented here enhances aspects
of this model. It is shown that the fossils assignable to the Dicynodon, Lystrosaurus and
Cynognathus assemblage zones occur within the sandstones and mudrocks of the Balfour,
Katberg and Burgersdorp formations in the study area. Using this combined data set it is
shown that parts of the Beaufort Group stratigraphic succession which are present in the
southern part of the Karoo Basin are absent in the central Free State. This suggests a
depositional hiatus at both the beginning of the Lystrosaurus Assemblage Zone and at the
end of Cynognathus Assemblage Zone times. During these hiatuses deposition was
restricted to the proximal sector i.e. south of the hinge line. This finding is in line with the
proposal that the Karoo Basin behaved as a partitioned basin with reciprocal fill.
Geophysical information defines a basement high north-east of Thaba Nchu that probably
accounts for a coarse-grained unit with anomalous palaeocurrent directions within the
study area.