Orderly hydrocarbon accumulation pattern in passive continental margin basins on both sides of the South Atlantic

Based on the plate tectonics theory, the sedimentary environment of paleotectonics along the passive continental margins on both sides of the South Atlantic Ocean was reconstructed using the paleomagnetic, regional geological, and seismic data, and the intrinsic relationships of hydrocarbon distribution in the passive continental margin basins and the differential hydrocarbon accumulation patterns were analyzed. Results show that basins on both sides of the South Atlantic experienced two major extensional phases—rift and depression—and four evolutionary stages: the Early Cretaceous Berriasian-Barremian intracontinental rift stage, the Early Cretaceous Aptian-Albian intercontinental rift to initial drift transition stage, the Late Cretaceous-Paleogene drift-related marine transgressive depression stage, and the Neogene-Quaternary drift-related marine regressive depression stage. According to basin architecture and superposition style, the passive-margin basins are classified into two principal types: rift-continental marginal depression composite and continental marginal depression-dominated. The basins in the study area were further divided into six types based on the development degree of salt tectonics and the type of dominant sand bodies, i.e. salt-free rift-continental marginal gravity-flow composite type, salt-free rift-continental marginal delta composite type, salt-bearing rift-continental marginal gravity flow composite type, delta-dominated salt-bearing rift-continental marginal delta composite type, gravity-flow-dominated continental marginal depression type, and delta-dominated continental marginal depression type. The salt-free rift-continental marginal gravity flow and delta composite basins are mainly distributed in the southern segment. The salt-bearing rift-continental marginal gravity flow and delta composite basins are mainly distributed in the central segment. The gravity-flow-dominated continental marginal depression basins are mainy distributed in the northern segment. The delta-dominated passive-margin depression basins are distributed in three segments from north to south. In different types of basins, distinctive depositional systems and source-reservoir-caprock assemblages were formed in each upper/lower structure layer. The superimposition and evolution of multi-phase prototype basins result in the orderly hydrocarbon accumulation vertically and laterally, which are “segmented along-strike, zoned across-strike, and layered vertically”.