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Foraminifera distribution in surface sediment of the continental shelf is controlled by several environmental factors. Expansion and spreading of fluvial plumes significantly change environmental conditions at shelf areas facing river mouths. The present work contributes with an in situ reference study on the spatial distribution of foraminiferal assemblages in the surface sediments of the São Francisco delta clinoform and adjacent areas (outer shelf and homonymous submarine canyon). Four benthic foraminiferal biofacies were identified based on quantitative and qualitative analyses of foraminiferal microfauna from 116 sediment samples. Biofacies I and II, both dominated by Ammonia beccarii , perfectly delimit respectively the topset and upper foreset portions of the delta clinoform. Biofacies III characterizes the area around the São Francisco canyon head, which is partially buried by the clinoform. This biofacies is dominated by Globocassidulina subglobosa and Hanzawaia concentrica and typifies an important stratal surface, known as the Maximum Flooding Surface, over which the clinoform progrades. Biofacies IV, dominated by Textularia spp., characterizes the clinoform bottomset and outer shelf sediments. The outer shelf is typically covered by bioclastic sand and gravel. In this region, besides Textularia spp., biofacies IV also comprises macro-foraminifera species, such as Amphistegina spp., Archaias angulatus and Peneroplis spp., typical of reef bottoms. [ABSTRACT FROM AUTHOR]

The continental shelf off the coast of central Brazil, extending from 10 to 16°S, is unusually narrow (~20km) and rests on the São Francisco craton. The shelf break is located between the 45 and 50m isobaths and coincides with major hinge-lines of the marginal basins. The shelf was exposed for most of the Quaternary period, particularly during the last 1my, when the average sea level was −62m. Submarine geomorphology is strongly influenced by this extended sub-aerial exposure and reduced subsidence, resulting in widespread incisions on the shelf. During the limited episodes of shelf inundation, as is the case today, a few meters of non-framework grain assemblages dominated by coralline algae accumulated on the outer shelf, while quartz sands were restricted to water depths of less than 10–15m. Mud accumulation on this unusually shallow shelf is aided by additional accommodation space provided by incisions and canyon heads indenting the shelf. Artisanal fisheries, targeting high-value commercial species associated with hard bottoms located on the outer shelf and shelf break, are the most important human use of this shelf. Data used in this study have been compiled from theses and previously conducted surveys and consist of four piston cores, 509km of chirp subbottom profiles and side scan recordings, and 711 bottom grab samples that have been analyzed for various textural and compositional aspects. [ABSTRACT FROM AUTHOR]