Quaternary fault control on the coastal sedimentation and morphology of the São Francisco coastal plain, Brazil

Abstract

The role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of South America, but the level of the present-day tectonic stability of this margin is still a matter of debate. This paper presents an investigation of the effects of Quaternary fault reactivation on the São Francisco coastal plain (SFCP). This feature is a 56-km long progradational coastal plain located in the Sergipe–Alagoas Basin along the continental margin of Brazil. The SFCP is bounded on the west by a system of normal faults striking N–S to NE–SW. The horst that bounds this plain is capped by the Miocene Barreiras Formation and Quaternary debris-flow and fluvial deposits, whereas the graben is filled with braided stream deposits and sandy beach-ridge sediments. The faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain. These processes started with the reactivation of Cretaceous faults during the Miocene. During the Quaternary, fault reactivation and associated soft-sediment deformation occurred between 82 and 8.3ka, with minor pulses between 1700 and 60calyrBP. Several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope.