Crustal Architecture, Sedimentation, and Petroleum Systems in the Sergipe-Alagoas Basin, Northeastern Brazil

摘要

An integrated, multidisciplinary study of the tectonic framework, sedimentation, and petroleum systems in the Sergipe-Alagoas Basin was carried out. The methodology was based on regional integration of geologic and geophysical data, particularly seismic reflection and potential field data (gravity and magnetics), results of exploratory drilling, paleontologic and paleoenvironmental analysis of the sedimentary succession, and geochemical data from oils and source rocks. The main topics addressed were the tectono-stratigraphic evolution of the sedimentary basins in northeastern Brazil, the crustal architecture of the Sergipe-Alagoas Basin, and the petroleum systems both onshore and offshore. Results of this study indicate that major synrift troughs are located in the proximal regions and are characterized by negative Bouguer anomalies. The proximal grabens are controlled by comparatively small synthetic and antithetic normal faults, while major rift blocks are controlled by crustal faults that dip seaward. These master faults cut through most of the crust and detach onto lower crustal horizons or even the seismic Moho. Deep-water rift blocks were affected by regional erosional episodes. The transition to pure oceanic crust is marked by wedges of seaward-dipping reflectors and igneous plugs. Some possible salt diapirs are located near the crustal limit. The petroleum systems for this basin include good source rocks in the transitional (evaporitic) and rift-phase sequences. Hydrocarbon generation and migration was effective from Late Cretaceous time onward. Exploratory plays include structural traps associated with synrift and postrift structures, as well as stratigraphic traps associated with deep-water turbidites.