SHELF MORPHOLOGY AND SUBMERGED SHORELINE PRESERVATION: EXAMPLES FROM KWAZULU-NATAL, SOUTH AFRICA
The northern shelf sector is 2-4 km wide with a gradient ca. 2.7°. Three seismic units are preserved and represent calcareous sedimentary barriers (shorelines), back barrier sediments and a highstand sediment wedge. Barriers are best preserved at -100m and -60m with an intervening erosional surface between each. Scarps in the surface represent now buried headland-embayment cells separated by rocky headlands on the high gradient coast.
The central shelf sector is 8-15 km wide with a gradient of ca. 1°. Five seismic units are identified that record a large-scale cemented barrier complex with back-barrier systems comprising lake/lagoon depression and extensive, well-preserved parabolic dune fields.
Differences in shelf setting cause variations in the style of barrier-preservation and associated transgressive stratigraphy. A much thicker post-transgressive sediment drape, higher degrees of ravinement and only partial barrier preservation exist on the steeper and narrower shelf section. A simpler transgressive arrangement of shelf elements is produced. In contrast, the more gently sloping shelf shoreline complex contains large-scale equilibrium forms, dune fields and significantly higher degree of preservation of the shoreline features.