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High-Resolution Stratigraphy of Multiple, Vertically Stacked Slope Channel Complexes, Tanqua Depocentre, Karoo Basin, South Africa

Richard Wild1, David Hodgson1, Stephen Flint1, and Willem Van der Merve2
1 University of Liverpool, Liverpool, United Kingdom
2 Stellenbosch University, Stellenbosch, South Africa

Early Permian deepwater deposits of the Tanqua depocentre, 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 detailed time-stratigraphic relationship between deposition in the interchannel areas and channel fill aggradation remains elusive however, it is suggested that most of the turbidite sheet deposits outside of the channel systems represent older frontal splay deposits that are not genetically related to the channels.

Gravitational instability in the sheet deposits drove a range of deformation processes resulting in small-scale soft-sediment deformation structures (convolute lamination, dishes and pipes), intensely dewatered intervals and the development of low velocity slope ‘creep' bodies. Intervals of in-situ deformation formed lateral to known submarine channel complexes after incision and can be used to identify time ‘stored' in a stratigraphic succession and the presence of a sequence boundary. 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 5th order sequence.

This study provides a start point for high-resolution seismic modelling as a means to assess the implications of this model for submarine channel complex development versus the channel/levee model that is typically invoked for submarine slope systems and reservoir characterisation.