Abstract:
Diverse foraminifera faunas occur in the Sundays River Formation of the onshore Algoa Basin that have allowed for the establishment of five Late Valanginian and ten Hauterivian interval biozones, formally proposed here. Previous work on ostracods had shown the presence of poor faunas in the earlier Late Valanginian and in the Early Hauterivian, with abundant, diverse faunas in the later Late Valanginian and Late Hauterivian, and this distribution pattern is duplicated by the foraminifera. The top of the Sundays River Formation is marked by intense planation, so that the most complete borehole sections are restricted to the basin depocentres. The relationship of the Sundays River Formation to the red and green beds of the underlying Kirkwood Formation is complex, but would seem to be a synchronous event across the basin, and is probably the same in the Pletmos Basin. From 20 deep boreholes, as well as shallow boreholes and outcrops, 122 species, one subspecies and 14 species-groups of foraminifera were identified. Twenty-three species and one subspecies are described as new. Species recognized show close similarities to those previously described from Valanginian and Hauterivian rocks from Brenton, borehole PB-A1 and Mngazana along the South African coast, and to faunas of the same age from the Neuquen and southern Patagonia regions of Argentina. Depositional environments of the Sundays River Formation vary from estuarine and nearly non-marine, and through littoral to outer shelf.