The influence of the structural framework on the sedimentation of the Maracangalha Formation in the southern compartment of the Recôncavo Basin

Abstract

Sandy reservoirs formed by lacustrine gravity flows provide important insights into tectono-sedimentary processes associated with syn-sedimentary deformation, which is primarily controlled by tectonic structures that shape the lake-bottom relief. In the Recôncavo Basin, gravity-flow deposits within the Maracangalha Formation constitute significant gas reservoirs. However, their discontinuous and heterogeneous geometries pose challenges for predicting reservoir quality and hydrocarbon volume. The Maracangalha Formation represents a stratigraphic sequence deposited in a deep lacustrine environment during the syn-rift tectonic phase. Intense extensional tectonics, coupled with mud diapirism, generated earthquakes and gravitational destabilization of delta fronts, thereby triggering sandy-muddy gravity flows and their associated deposits. Additionally, syn-sedimentary deformational structures formed by gravity flows, along with subsequent liquefaction and fluidization processes, provide valuable evidence for reconstructing the dynamics and directions of these processes in the study area. A total of ten syn-depositional and late-to post-depositional lithofacies were identified in outcrops within the southern compartment of the Recôncavo Basin, including previously unpublished exposures on several islands in Todos os Santos Bay. These islands include Fontes Island, Bimbarras Island, the neighborhood of Santo Estevão – São Francisco do Conde City, Maria Guarda Island, Vacas Island, Bom Jesus dos Passos Island, and the northern portion of Maré Island. Tilting of depositional surfaces is observed across all sectors due to oblique displacement along extensional faults, with slip magnitude increasing southward. Analysis of syn-depositional sedimentary structures and late-to post-depositional deformational features suggests that sediment gravity flows were predominantly directed southward, with secondary variations toward the southeast, southwest, and west. The transport and deposition of these flows were controlled by a graben–horst system, likely characterized by a southward-dipping ramp geometry, bounded from northwest to southeast by the east-dipping Nova América, west-dipping São Domingos, and east-dipping Candeias faults. Additional controls were exerted by local depocenters associated with the hanging-wall blocks of the Capimirim and Lamarão faults.