The Holocene highstand sedimentation in the inner continental shelf of southeastern Brazil, between São Sebastião Island (SSI) and Ubatuba, is composed by clinoforms prograding obliquely and longitudinally to the shoreline. These clinoforms exhibit a typically sigmoidal configuration, overlying wave ravinement surfaces (WRS), and exhibit distinct internal structures and progradation styles. The study area is characterized by two physiographic compartments separated by a chain of SW-NE trending islands: (i) the inner compartment, located between the shoreline and the 30-35 m isobaths, is topographically lowered and geomorphologically embayed, limited to the southwest by the SSI; (ii) the outer compartment extends from 35-40 m water depths to the boundary between the inner and outer continental shelf located at 60-70 m water depths. The clinoform located in the inner compartment is narrow and elongated, oriented approximately N-S, and slightly oblique to the shoreline. Its bathymetric expression is observed from the 10 m isobath, where it presents an average thickness of 4 m to a maximum thickness of 8 m at 16-20 m water depths. The inner clinoform progressively thins seaward to 30-35 m water depths. Internally it exhibits a sigmoidal progradational pattern downlapping the underlying WRS. The clinoform in the outer compartment is oriented SW-NE, longitudinally to the shoreline at water depths of 35-60 m, extending for around 32 km, with an average width of 15 km. This outer clinoform exhibits a compound sigmoidal-oblique configuration. Its lower portion is characterized by oblique reflectors at the base with toplap truncation at the top and downlap at the bottom, evolving upwards to a sigmoidal configuration. At water depths of 35-40 m, the inner clinoform is located between SSI and Búzios island, partially overlying the outer clinoform, generating a amalgamated clinoform pattern with crossing growth trajectories. This arrangement suggests multiple sediment sources for clinoform development. The inner clinoform would have been fed by local sediment sources, like small rivers that flow into the region. In contrast, the outer clinoform seems to have been fed by sediments from more distant sources brought to the area by a shelf-moving current such as the Brazilian Coastal Current.

Póster presentado en XIX Congresso da Associação Brasileira de Estudos do Quaternário: ABEQUA, 9-13 sep. 2024 Natal (Brasil)