The coastal plain between the towns of Cananéia and Iguape is very important as it contains the most extensive Quaternary coastal sedimentation in the State of São Paulo, Brazil. Comprida Island, the most prominent physiographic feature in this geological context, is essentially formed of shallow marine sands. Sedimentological analysis made it possible to characterize the texture and mineralogy of 126 samples of sediments from the different sub-environments of Comprida Island. Grain size analysis of the sands, treated by the SAHU method (1964), indicates high-energy and low-viscosity deposition in beach, shallow marine and eolian environments. Morphometric and heavy-mineral studies suggest that Holocene sands are derived from the Cananéia Formation (Pleistocene), the Precambrian Crystalline Complex, and the Upper Precambrian Açungui Group. The combined foraminiferal content of 26 of the samples consists of twenty-six species belonging to twenty-one genera, where Ammonia beccarii (Linné) and Nonionella atlantica (Cushman) are the dominant species. Data on these micro-organisms emphasize the importance of foraminifera in the interpretation of beach zone dynamics and show the necessity of considering the relations of these assemblages to the pattern of circulation of water masses and to such biological controls as the ecological succession of benthonic communities.
