Submarine slope degradation and aggradation and the stratigraphic evolution of channel–levee systems

TLDR

Submarine channel–levee systems evolve through equilibrium shifts from low to high accommodation, with slope degradation, external levee development, and sediment bypass giving way to horizontal stacking and widening, then to slope aggradation, vertical stacking, and internal levee development—a pattern likely common to similar systems. In the Karoo Basin, two seismic‑scale channel–levee systems show that component channel fills first stack laterally and then vertically, revealing a common sequence of horizontal migration followed by aggradation. Supplementary correlation data are available at www.geolsoc.org.uk/SUP18456.

Abstract

Abstract: Two seismic-scale submarine channel–levee systems exposed in the Karoo Basin, South Africa provide insights into slope conduit evolution. Component channel fills in a levee-confined channel system (Unit C) and an entrenched channel system (Unit D) follow common stacking patterns; initial horizontal stacking (lateral migration) is followed by vertical stacking (aggradation). This architecture is a response to an equilibrium profile shift from low accommodation (slope degradation, composite erosion surface formation, external levee development, sediment bypass) through at-grade conditions (horizontal stacking and widening) to high accommodation (slope aggradation, vertical stacking, internal levee development). This architecture is likely common to other channel–levee systems. Supplementary material: A detailed correlation panel (presented schematically in Figure 2 ) is available at www.geolsoc.org.uk/SUP18456 .