Abstract: The position and process regime of paralic systems relative to the shelf edge rollover is a major control on sediment transfer into deep water. The depositional strike and dip variability of an exhumed Permian shelf edge succession has been studied in the Paardeberg Ridge, Karoo Basin. Siltstone-rich slope turbidites are overlain by 25–75 m-thick prodelta parasequences. These are truncated by a 30 m-thick sandstone-prone unit of tabular or convex-topped sandstones, interpreted as wave-modified mouth bars, cut by multiple irregular concave-upwards erosive surfaces overlain by sandstones, interpreted as distributary channels. The stratigraphic context, lithofacies and architecture are consistent with a mixed-influence shelf edge delta; the erosional base to the unit marks a basinwards shift in facies, consistent with a sequence boundary. Channels become thicker, wider, more erosive and incise into deeper-water facies downdip and correlate with sandstone-rich upper slope turbidites, all of which support the bypass of sand across the rollover. The overall progradational stacking pattern results in a stratigraphic decrease in channel dimensions. The results of this study suggest a predictable relationship between channel geometry, facies and position on the shelf-to-slope profile under a mixed wave and fluvial process regime.

Abstract The sediment source area for foreland-basin fills is typically inferred to be the adjacent fold-and-thrust belt. In the case of the Karoo Basin, South Africa, however, the Cape Fold Belt (CFB) was not the source during the early phase of basin filling. Instead, the Permian deepwater siliciclastic sediments of the lower Ecca Group were derived from a granitic source area outboard of the adjacent orthoquartzitic fold belt. Lithofacies, stratal thickness, and paleocurrent distributions indicate that seabed deformation occurred during deposition. Sediment was supplied across an evolving but submerged proto-CFB through a major syncline that acted as a long-lived single delivery point to the submarine slope. Northward migration of the deformation front and the subsequent uplift of the CFB, notably in the eastern parts of the syncline, forced another sediment route to develop 100 km north from the Laingsburg depocenter to the Tanqua depocenter.