Provenance of mudstones in the Karoo Supergroup of the Ellisras basin, South Africa: Geochemical evidence

The Karoo Supergroup in the Ellisras basin consists of sediments that were deposited predominantly during the Permian Period. Mudstone samples of the Swartrant and Grootegeluk Formations of the Ecca Group and the succeeding Eendragtpan Formation of the Beaufort Group were collected from borehole core. Based on the concentration and ratios of relatively immobile elements that have been shown to be directly related to their source rocks, the Grootegeluk Formation and Eendragtpan Formation mudstones have provenances which are approximately granodioritic in composition and have similar Late Proterozoic SmNd model t _Nd-DM ages (∼1.2 Ga). The provenance of the Swartrant Formation was relatively more mafic and has Early Proterozoic SmNd model t _Nd-DM ages (∼2.1 Ga). The model t _Nd-DM ages for all the sediments are too low to support a cratonic origin. It is not possible to identify a unique source for the Swartrant sediments from only the SmNd isotopic data, but a source from approximately the northwest of the coalfield in the Damaran mobile belt or from Antarctica to the east, in its Late Proterozoic to Late Palaeozoic palaeo-position, cannot be discounted. Palaeo-current data for the Swartrant Formation indicates a source from the east. This is consistent with palaeo-drainage patterns from Antarctica and therefore a fluvio-glacial source from Antarctica, in its Late Paleozoic geographic position, is favoured. The Grootegeluk and Eendragtpan mudstone Formations are most compatible with a source from retreating continental ice-sheets to the north of the Ellisras basin at the time of Early Permian deglaciation. Although the Swartrant and Grootegeluk Formations have been assigned to the same stratigraphic group (Ecca), the Grootegeluk Formation is geochemically distinct from the Swartrant Formation and indistinguishable from the overlying Eendragtpan Formation of the Beaufort Group.