The holocene sequence of the central continental shelf of the State of Bahia, Brazil

Abstract

Fifty cores were recovered from the sea bottom in the central portion of the continental shelf of the State of Bahia, between the Marau Peninsula and the city of Olivença. Thirty six of these cores were collected by divers at up to 40 m deep waters. Fourteen cores were collected by piston cores in areas ranging from the continental shelf to the upper slope. All cores were described, photographed and sampled for grain size and biostratigraphic analysis. These data were used to prepare textural and facies maps of the continental shelf. The piston cores were run parallel to sub-bottom profiling surveys. Results show that there is a strong reflector located 3 - 4 m below the sedi-ment-water interface, which limited the penetration of the piston cores. This reflector represents a sequence boundary separating the holocene from the pleis-tocene sequences. A transgressive system tract has been deposited on the top of this surface along with the early stages of the highstand system tract, particularly on the inner shelf. Because of the starved character of this shelf, notably on its external portion, a detailed application of sequence stratigraphy concepts has not been possible. Only at the inner shelf/shoreface there is evident progradation of siliciclastics over carbonates. Several submarine valleys dissect the outer shelf/upper slope, thus acting as channels that transport continental shelf sediments to the deeper portions of the basin.