Structural controls on the morphology of an extremely narrow, low-accommodation, passive margin shelf (Eastern Brazil)

Abstract

The continental shelf adjacent to the municipality of Salvador (CSS), state of Bahia, Brazil, is one of the narrowest in the world (8 km) although it is located in a passive margin. This shelf is also shallow, with low accommodation space and sediment input. During the Quaternary, the area was exposed most of the time to subaerial conditions. This long period of erosion, controlled by the structural and lithological framework of the Cretaceous Northern Camamu Sedimentary Basin, was highly influential on shelf physiography. The paleo relief that was generated, in turn, controlled sedimentation during the sea-level rise since the Last Glacial Maximum (LGM). The present study used high-resolution shallow seismic surveys to investigate the influence of the structural framework of the Northern Camamu Sedimentary Basin on the erosion of CSS during lowstands and on sediment accumulation during highstands. Five seismic units were identified, representing the Crystalline Basement, the Northern Camamu Sedimentary Basin, and the Quaternary Sediments. Bathymetric highs and lows on the shelf are associated, respectively, with antiforms and synforms present in the syn-rift strata of the sedimentary basin. Normal and transfer faults related to the installation of the sedimentary basin controlled the incision of valleys during periods of subaerial exposure. This structural framework still presents a morphological expression on the shelf due to an immensely reduced sediment input, which precluded the burial of these structures.