Architecture and stratigraphic evolution of multiple, vertically-stacked slope channel complexes, Tanqua depocentre, Karoo Basin, South Africa

Abstract

Abstract Early Permian deep-water deposits of the Tanqua depocentre, SW Karoo Basin, South Africa, include Unit 5, an extremely well-exposed 100 m-thick lower slope succession. Within the study area, Unit 5 comprises two partially-synchronous, vertically stacked, sub-parallel channel complex sets that lie 8 km apart along strike (the east-trending Klein Hangklip complex set and the NE-trending Groot Hangklip complex set). The detailed time-stratigraphic relationship between deposition in the interchannel areas and channel fill aggradation remains unresolved due to exposure limitations; however, it is suggested that most of the turbidite sheet deposits between the channels represent frontal lower slope splays from earlier slope feeder systems and are not genetically related to the channels. Gravitational instability in the sheet deposits drove a range of deformation processes from low velocity ‘slope creep’ to complete failure and slumping during times of maximum incision and bypass within the slope channels. Following the main phase of aggradation within the channels, periods of spill led to the formation of lateral splays and splay channels, which are distinct from the older frontal splay deposits. Each channel complex comprises two composite channel bodies and is interpreted to represent a fifth order sequence. In the absence of evidence of local (intraslope) tectonic controls, the vertical stacking of the channel complexes is interpreted to be due to fixed shelf edge entry points. Abrupt lateral facies changes along depositional strike, the ubiquity of instability features, the high proportion of sandstone preserved in the channel complexes and the absence of levees supports the interpretation that Unit 5 in the Hangklip area was deposited in a lower slope setting.