--> Abstract: Non-Foldbelt Provenance and Tectonic Influence on Sediment Supply Routes, Rates and Grain Size Range and Their Impact on Deepwater Sandstone Architecture, Early Karoo Foreland Basin, South Africa, by Stephen Flint, David Hodgson, Rosalind King, Richard Wild, Belinda Van Lente, Graham J. Potts, Daniel Andersson, Richard H. Worden, and De Ville Wickens; #90039 (2005)

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Non-Foldbelt Provenance and Tectonic Influence on Sediment Supply Routes, Rates and Grain Size Range and Their Impact on Deepwater Sandstone Architecture, Early Karoo Foreland Basin, South Africa

Stephen Flint1, David Hodgson1, Rosalind King1, Richard Wild1, Belinda Van Lente2, Graham J. Potts1, Daniel Andersson3, Richard H. Worden1, and De Ville Wickens2
1 University of Liverpool, Liverpool, United Kingdom
2 University of Stellenbosch, Stellenbosch, South Africa
3 University of Stockholm, Stockholm, Sweden

Understanding of the syndepositional tectonic controls on the timing, calibre and distribution of sediment delivered to deep-water depocentres is commonly hindered by later structural overprinting and poor preservation of coeval up dip strata. A tectono-stratigraphic approach with integrated petrographic and geochemical analysis has been used to elucidate the impact an evolving basin margin fold belt had on deep-water sedimentation styles. The SW Karoo Basin lies inboard (to the NE) of the arcuate Cape Fold Belt (CFB) in South Africa, and is divided into the early Permian Laingsburg and Tanqua depocentres. Petrographic, Sm/Nd isotopic and structural studies indicate that siliciclastics were transported from a common, fixed extrabasinal source (the North Patagonian massif) across the then submerged fold belt, which controlled the routeing and distribution of sediment, into the adjacent Karoo Basin sink but was itself not a source area. Sediment accumulation began first in the Laingsburg depocentre, which preserves a 2 km-thick fining-upward deep-water succession, whereas the 1 km thick Tanqua thickening-upward succession is interpreted to reflect a tectonic switch in sediment routeing from the same source area. More mud is present in the Laingsburg basin-floor fans, which preserve differences in gravity flow processes (more debrites) and architectural styles (more cohesive banks and spill facies) compared to the Tanqua fans. Earlier relatively mud-prone fans are interpreted to be due to a combination of low across-shelf transport efficiency, upslope excavation of MTC scars into a muddy shelf, seabed and erosional topography (limited spill), and profile position, rather than significant changes in provenance.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005