Depositional environments and sequence stratigraphy of an exhumed permian mudstone-dominated submarine slope succession, KAROO BASIN, SOUTH AFRICA

The physical stratigraphy of a 470-m-thick, clastone-dominated exhumed middle to upper submarine slope succession was constrained within an area of 400 km2 in which five sand-prone units were characterized (Units D/E, E, F, G, and H). Units D/E to Unit F show an overall pattern of thickening upward and basinward stepping. This stacking pattern is reversed from the top of Unit F to the base of Unit H, above which basinward stepping is again observed. Different architectural styles of sand-prone deposits occupy predictable stratigraphie positions within the basinward-stepping section, starting with intraslope lobes through channel-levee complexes to entrenched slope valleys. Sandstone percentage is highest in the intraslope lobes and lowest in the slope valley fills, reflecting a change from depositional to bypass processes. The landward-stepping stratigraphy is dominated by claystone units with thin distal fringes of distributive deposits. The upper basinward-stepping succession (Unit H) is a distributive system possibly linked to a shelf edge delta. Across-strike complexity in the distribution of sand-prone units was controlled by cross-slope topography driven by differential compaction processes. Hemipelagic claystones separating the sand-prone units represent shutdown of the sand delivery to the whole slope and are interpreted as relative sealevel highstand deposits. Eleven depositional sequences are identified, nine of which are arranged into three composite sequences (Units E, F, and G) that together form a composite sequence set. The highly organized physical stratigraphie stacking suggests that glacioeustasy, during the Late Permian icehouse period, was the main driving process for the analyzed succession. Copyright © 2010, SEPM (Society for Sedimentary Geology).