Lower- and Mid-Slope Submarine Slope Channel Complex Geometries: An Integrated Approach to 3-D Data Capture and Imaging within the Laingsburg Depocenter, Karoo Basin, South Africa

Jamie K. Pringle, Dave M. Hodgson, Rufus L. Brunt, Chris J. Haigh, Jon P. Kavanagh, and Steve S. Flint
Liverpool University, Liverpool, United Kingdom

Correct understanding of the stratigraphic evolution of slope channel complexes and spatially adjacent sheet sandstones is crucial in the accurate prediction and modelling of static and dynamic connectivity. This understanding is complicated by the preservation record of slope channel complex activity, with repeated phases of incision, aggradation and re-excavation. In the Laingsburg depocenter, the well-exposed Permian basin-floor/slope Laingsburg Formation includes a range of slope channel complexes at different profile positions (Units B-F). These include heterogeneous channel-fills and variable adjacent sheet-like elements preserved for tens of kilometres along regional fold limbs. Two slope channel complexes have been studied in detail.

A sand-prone, lower slope channel complex in Unit B, exposed at Skeiding, preserves a record of repeated erosion, aggradation and re-incision. Sand-rich channel elements stack sub-vertically, with a clear stratigraphic change in architecture. A heterolithic, mid-slope channel complex in Unit C at Laingsburg Garbage Dump includes at least four incisional channel elements that preserve lateral avulsion of the channel axes. Each channel is filled with a different facies, ranging from bypass-dominated thin-bedded sandstones to passive mudstone-filled.

A combination of traditional field geology techniques and modern 3D digital data collection has been utilised. Closely spaced (10-20 m) outcrop logs are correlated at individual bed scale by a combination of walking out and photopanel interpretations, complemented by an accurate dGPS stratigraphic framework survey. Subsurface data was acquired by selective use of Ground Penetrating Radar. Ground-based LIDAR surveys were utilised to rotate the channel complex to paleohorizontal and to quantify better erosion surface relief.