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Seismic Geomorphology and Evolution of Submarine Channels from the Angolan Continental Margin

¹ Basin Studies and Petroleum Geoscience, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL, U.K.; present address: Lukoil Overseas, Ltd. Moscow, 115035, Russia
² Basin Studies and Petroleum Geoscience, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL, U.K.; rob.gawthorpe{at}manchester.ac.uk
³ Norsk Hydro Research Centre, Sandsliveien 90, Bergen, 5020, Norway
⁴ Department of Geology, University of Maryland, College Park, Maryland 20742, U.S.A.; present address: Energy and Environmental Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A.

Three-dimensional seismic data from the shallow subsurface of the continental margin offshore Angola reveal two end-member morphological styles of submarine channel: (1) high-gradient, low-sinuosity, narrow channels with gull-winged levees, and (2) lower-gradient, deeply incised systems with moderate- to high-sinuosity channel axes. A third, and rare, channel form has moderate incision, low to medium sinuosity, and a moderate long-profile gradient. Based on channel parameters (incision depth, long-profile gradient, channel-axis sinuosity) and crosscutting relationships, we suggest that the channels evolved from initially steep and straight, with low sinuosity, to highly sinuous and deeply incised with lower channel-axis gradients. Correlation of long-profile gradient with both incision and sinuosity suggests that incised channels appear to remove convex-up curvature from the original slope as the channel axis evolves toward an equilibrium profile. Localized changes in channel planform, gradient, sinuosity, and incision reflect the complex morphology of the slope associated with growth of salt-related structures. Linear, high-amplitude seismic features, which correspond to weakly incised striations, or rills, on the open slope are considered to be precursors of submarine channels.

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