Late Quaternary stratigraphic evolution of the inner continental shelf in response to sea-level change, Santa Catarina, Brazil

摘要

The inner continental shelf (0-50 m water depth) off Santa Catarina, southern Brazil was investigated using seismic stratigraphic methods to identify and interpret the major seismic stratigraphic units and to reconstruct the late Quaternary evolution of the inner shelf and coast. The stratigraphy comprises a bedrock basement overlain by a thick (30 m) unit that comprises, in the distal portion, laminated muds and sands, and in the coast-proximal zone, offlapping deltaic deposits, whose upper surface has been reworked to form alongshore-prograding barrier spits. Deposition of this unit is tentatively attributed to sea levels (-20 m MSL) during the late Pleistocene (MIS 5a, or 5c). A normal fault in the muddy units with a vertical offset of 3.5 m indicates episodic tectonic activity. Cut into this unit is a profusion of incised valleys, associated with sea level fall ultimately to -120 m at the last glacial maximum (LGM). The associated subaerial unconformity is only preserved close to shore, where it has escaped subsequent wave ravinement. This, coupled with the well-preserved incised valleys implies the underlying substrate to be weakly cohesive material (mud).