Transition from Shelf Margin Delta to Slope Fan—Outcrop Examples from the Tanqua Karoo, South Africa
Grant D. Wach, Arnold H. Bouma, Ted Lukas, H. Deville Wickens, R. K. Goldhammer, 2013. "Transition from Shelf Margin Delta to Slope Fan—Outcrop Examples from the Tanqua Karoo, South Africa", 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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Outcrop sections containing excellent physical and biogenic sedimentary structures within the Late Permian Ecca Group are exposed within the Tanqua Karoo that show the transition from shelf margin delta through to slope and basin floor fans. The Tanqua submarine fan complex comprises six regionally distinct fan systems, five of which form a progradational stack with the sixth fan, to the south, downlapping onto the fifth fan. Progradation of the deltaic deposits across the basin has been in response to a decrease in accommodation space created by relatively high rates of sedimentation within the foreland basin setting. The sedimentology and sequence stratigraphy of the Hangklip Fan represents a shelf margin delta feeding downdip slope fan deposits. Wave ripples, swaley cross-stratification and trace fossils, including Gyrochorte, suggest substantially shallower depositional conditions than slope fan deposits, which are devoid of such features. Erosional slump scars, cutting into laminated shale with chaotic infill of sand intraclasts, point toward slope depositional processes that are not in evidence in the underlying submarine fan deposits.