Integrated constraints of tectonics, sedimentation and climatic regimes on the pre- and post-salt petroleum systems in the Santos Basin, Southeastern Brazil

Abstract

Recent hydrocarbon discoveries in the pre-salt section of the offshore Santos Basin have significantly advanced global deep-to-ultra-deep water hydrocarbon exploration. These successes highlight the vast potential of depositional successions formed during the Mesozoic breakup of Western Gondwana and the opening of the South Atlantic Ocean. However, the formation mechanisms of both the pre- and post-salt petroleum systems remain poorly constrained. This study aims to reconstruct the tectonic and climatic evolutions of the Santos Basin, and to examine how their multi-scale interplays controlled the development of these two petroleum systems. Source rocks, reservoirs, and seals were formed during the intracontinental rift stage and subsequent passive margin formation stage, respectively. During the transitional stage, an extensive salt layer was deposited under an arid regime in the Santos Basin, influenced by a southern paleo-geographic barrier. Several key events, including the eruption of Paraná–Etendeka Large Igneous Province (PE-LIP), pre- to syn-rift magmatism, the uplift of Serra do Mar coastal range, and the development of Australis and Paraíba do Sul river systems, collectively regulated water and sediment supply, facilitating the formation of the pre-salt source rocks and post-salt siliciclastic reservoirs. Active deep tectonic processes promoted rapid burial and heating of syn-rift deposits, enabling pre-salt source rocks to enter the oil window during the Albian−Cenomanian. Hydrocarbons generated at that time migrated into overlying lacustrine carbonate reservoirs and were effectively sealed by the massive Ariri evaporites. In contrast, post-salt source rocks, due to shallower burial depths and insufficient kitchen heating, remain immature to marginally mature and thus have less contribution to the discovered hydrocarbons. Nevertheless, some post-salt source rocks deposited in topographic lows, including those created by halokinesis, retain exploration potential. Synthesizing these findings from a perspective of Earth system science, emphasizing multi-spheric interactions, provides new insights into the mechanisms of hydrocarbon generation and accumulation in rift lacustrine basins. Applying this approach to other basin types could establish its predictive value and support exploration in areas with limited geological knowledge.