Controle estrutural dos depósitos de fluxos gravitacionais na borda leste da Bacia do Recôncavo – NE, Brasil

Abstract

The gravitational sedimentary flows are processes resulting from the transport of sedimentary materials or sediment-fluid mixtures under the direct influence of gravity. The occurrence of catastrophic tragedies in various parts of the world throughout history has been associated with gravitational flows, causing considerable damage to infrastructure and human lives. In rift-type sedimentary basins, such sediment deposits are often found in proximity to fault edges, manifesting as alluvial fans that record the onset of sedimentation during the rift phase overlaying the pre-rift phase discordance of the basement. Although current and past rifts have different evolutionary trajectories, these deposits consistently manifest in relation to the structural and environmental variations characterizing each stage. Therefore, a comprehensive understanding of the underlying mechanisms in the formation of these deposits is intrinsically linked to the appreciation of the morphostructural and paleoenvironmental evolution of the relevant basins. In this study, a detailed analysis of gravitational sedimentary flows observed in the Salvador Formation, located in the region adjacent to the border fault of the Recôncavo Basin in northeastern Brazil, was conducted. This analysis is set in the geological context of the formation of the Recôncavo-Tucano-Jatobá Rift System (RTJRS) during the Early Cretaceous. The research addresses the influence of geological structures on the directions and patterns of these sedimentary flows. The study area is subdivided into three distinct sectors: in Sector 1, paleocurrent orientations indicate basement influence, predominantly pointing to the north and northwest. In Sector 2, orientations suggest a strong association with a depocenter near the edge fault, with trends directed to the south and southeast. In turn, in Sector 3, paleocurrent directions predominantly point east and southeast, suggesting the influence of transverse structures with potential tectonic implications related to the Salvador Fault. The results highlight the direct influence of the Boa Viagem Fault structure on paleocurrent directions, indicating that sedimentation by gravitational flows was governed not only by the presence of the border fault but also by transverse faults present in the basin. The study proposes two hypotheses to explain the change in paleocurrent directions: the first considers the existence of a buried transfer fault, creating a relay ramp, diverting flows southeastward; the second hypothesis suggests the presence of a release fault, causing inclination in the region adjacent to the border fault, resulting in the formation of a depocenter near it. The findings of this research significantly contribute to understanding the relationship between geological structures and gravitational sedimentation processes in rifts, providing valuable insights for interpreting tectonic and sedimentary evolution, as well as significant implications for natural resource exploration and geological risk assessment in the region.