Stratigraphic evolution of the upper slope and shelf edge in the Karoo Basin, South Africa

Abstract

ABSTRACTThe Permian Ecca Group of the Karoo Basin, South Africa preserves an extensive well‐exposed siliciclastic basin floor, slope and shelf‐edge delta succession. The Kookfontein Formation includes multiple sedimentary cycles that display clinoform geometries and are interpreted to represent the deposits of a slope to shelf succession. The succession exhibits progradational followed by aggradational stacking of deltaic cycles that is related to a change in shelf‐edge trajectory, and lies within two depositional sequences. Sediment was transferred to the slope via overextension of deltas onto and over the shelf edge, resulting in failure and re‐adjustment of local slope gradients. The depositional facies and architecture of the Kookfontein Formation record the change from a bypass‐ to accretion‐dominated margin, which is interpreted to reflect a decrease in sediment transport efficiency as the slope gradient decreased, slope length increased and shelf‐edge trajectory rose. During this time the delivery system changed from point‐sourced basin‐floor fans fed by slope channels to starved basin‐floor with sand‐rich slope clinoforms. This is an example of a progradational margin in which the younger slope system is interpreted to be of a different style to the older slope system that fed the underlying sand‐rich basin floor fans.