How inherited topography controls the development of incised valleys on coastal prisms: The case of southeastern Brazil inner continental shelf

The Southeastern Brazilian Continental Shelf (SBCS) is characterized by its great width (120 km), with the shelf break situated around 140 meters. The inner continental shelf, located between São Sebastião Island and Ubatuba, has a width of 50 km, and its outer limit is located at depths around 50 meters, exhibiting a gradient of 1:550. Thus, during most of the late Quaternary, the inner continental shelf was exposed to subaerial conditions favoring the formation of incised valleys, even though the sea level never fell below the shelf break. The inner shelf of the study area is inserted in the Neogene graben of Ubatuba, which is part of a Coastal Rif t System, whose limiting faults present preferential ENE orientation. Such faults seem to give origin to knickpoints, separating the inner from the outer shelf. This tectonostratigraphic architecture favored the creation of additional accommodation space, about which, during episodes of lowstand, a paleodrainage system has developed, in which sedimentary deposits were preserved in a complex of small incised valleys carved into the coastal prism developed in the highstand of 120 ka AP. The present work is ba sed on the analysis of 1200 km of CHIRP and sparker seismic records and aims to investigate how the geometric arrangement associated with this antecedent topography favored the development, during the last glacial period, of a complex of incised valleys c arved into the 120 ka BP coastal prism.