The late Cretaceous to Holocene sequence stratigraphy of a sheared passive upper continental margin, northern KwaZulu-Natal, South Africa

High resolution single-channel seismic data reveal seven seismic units (A–G) from the narrow and steep upper portions of the sheared passive continental margin of northern KwaZulu-Natal. Several characteristic internal geometries are evident: onlapping sheet-like (Unit C), aggradational/progradational (Unit A and Facies D3), and progradational (Unit B, Facies D1/2 and Facies G1). On the basis of internal geometry and bounding unconformities, lowstand (Units B, Facies D3 and lowermost Unit G), possible transgressive (Unit C), highstand (upper Unit G) and falling stage (Facies D1 and D2) systems tracts are delineated. Units E and F are not reconcilable due to acoustic opacity. Overall, five incompletely preserved sequences are observed. Sequence one comprises Unit A of suspected Middle Maastrichtian age, separated from the overlying sequence by a subaerial unconformity surface SB1. Units B and C form sequence two and span the late Cretaceous (Late Maastrichtian) to mid–late Palaeocene. Two major hiatuses ensued (Angus and Jimmy) until mid Pliocene times when Unit D was deposited during shelf margin advance linked to hinterland uplift. These falling stage systems tract deposits are separated from latest Pliocene/early Pleistocene lowstand shelf edge deltaic deposits by a subaerial unconformity marking the deposition of sequence four (Facies D3). The age of Unit E is uncertain. Unit F represents a series of shorelines formed during Oxygen Isotope Stage (OIS) 5a to 2 on the regressive and transgressive limbs preceding and following the Last Glacial Maximum (LGM). The final partial sequence preserved is comprised of Unit G formed during the OIS 2 transgression to present mean sea level and subsequent development of the contemporary highstand wedge. In terms of stratigraphic architecture, this study shows an evolution from a ramp-style margin with a poorly defined shelf break to that of a shelf break profile with a narrow and steep shelf. In this respect, the narrowness of this shelf cannot be accounted for by the inheritance of shearing effects. Rather, the stratigraphic architecture reflects a period of slow and protracted subsidence with strong sediment dispersal, later punctuated by hinterland uplift. This formed the late Pliocene shelf margin clinoforms of Unit D and established the shelf break position at the offlap break of this wedge. The resulting narrow shelf may play a significant role in the preservation of later sequences, particularly in light of the continued uplift of the margin causing off-shelf sediment bypass where TST and HST sequences may not be preserved. This is reflected in the isolated preservation of shoreline and shallow marine deposits of the Pleistocene Units E and F.