Shelf-to-Slope Depositional Systems
2013. "Shelf-to-Slope Depositional Systems", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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Deposition of deep-water fan systems is, in part, influenced by a variety of shelf margin and slope processes that affect the sediment pathways into the receiving basins. Shelf and slope seafloor topographic changes that resulted from tectonic movement, mobile substrate deformation and/or relative sea level fluctuations, may lead to switching of the sediment pathways leading to deep-water basins and result in depositional pulses of shelf and slope material that interrupt the background pelagic and hemipelagic sedimentation in different areas through time. The sediment pathways of the Permian deep-water deposits in the Tanqua and Laingsburg subbasins seen in outcrops in the southwest corner of the Karoo Basin, South Africa, have been influenced by fluctuations in seafloor topography caused by tectonic forces associated with the adjacent fold thrust belt. The two subbasins have geologically near-contemporaneous formation and filling, and in part contain deep-water sediments. Studies on these deep-water deposits have allowed reconstruction of the shelf and slope environment. Tectonic compression in the area has led to the formation of a basin floor high (anticlinorium) that separates the subbasins and influenced sediment transport. The Tanqua subbasin has developed into a broad, open basin that received five stacked submarine fan systems, while the Laingsburg subbasin has built into a deeper, longer and narrower basin that also has received five stacked submarine fan systems. Petrologic and microprobe analysis of the sandstones in the submarine fan systems indicate that they have come from a common source area that is an extended distance away (as great as 400 km). The subbasins, most likely, share a single shelf edge canyon and slope transportation system that involves enough length to allow for switching of the slope pathways through the evolving topographic highs and lows over time.