Vertical stacking of multiple highstand shoreline deposits from the Cretaceous to the present: facies development and preservation

ABSTRACT Cooper, J.A.G., Green, A.N. and Smith, A.M. 2013. BARDEX II: Vertical stacking of multiple highstand shoreline deposits from the Cretaceous to the present: facies development and preservation. A sequence of vertically stacked shoreline facies exposed by unprecedented water level lowering in Lake St Lucia, South Africa, records multiple occupation of the same shoreline (5–6m amsl) on at least eight occasions since the late Cretaceous. The sequence involves a basal wave-cut surface that is the outcrop of a regional unconformity cut into Late Cretaceous siltstone with occasional borings, representing a hardground (Facies 1). This is succeeded by a limestone unit indicative of sedimentation in a region of low terrigenous input quite different to today. This commences with a 10cm-thick unit comprising corals and giant clams that colonised the hardground as a shallow reef (Facies 2). The reef has an erosional upper surface that is overlain by a 30–50cm thick coquina (Facies 3) with characteristic sand-...