Early Cretaceous marine incursions into South Atlantic rift basins originated from the south

The breakup of Gondwana resulted in sedimentary deposits recording lacustrine to marine environmental transitions in the South Atlantic rift basins during the Early Cretaceous. Currently, ambiguity pervades our understanding of the timing and orientation of the initial seawater incursion. Here we investigated hydrocarbon biomarkers in sediments from two drill cores off West Africa with stratigraphic coverage from the Berriasian-Barremian to Albian. Based on biomarkers that can distinguish non-marine from marine-influenced settings, initial seawater influx occurred through the southern entrance across the Rio Grande Rise-Walvis Ridge during the early Aptian stage. Transitional conditions prevailed during the Aptian stage as the seawater incursion induced microbial community and environmental reorganization until the Albian when fully marine conditions prevailed. Overall, results of this study are valuable in deciphering the final opening of the South Atlantic Ocean, fulfilling the global comparison of paleoenvironments, and facilitating future petroleum exploration along the South Atlantic conjugate margins.

Automated summary

The sedimentary deposits in the South Atlantic rift basins during the Early Cretaceous, resulting from the breakup of Gondwana, reveal transitions from lacustrine to marine environments. Through biomarker analysis, it is found that the initial seawater incursion occurred during the early Aptian stage, entering through the southern entrance across the Rio Grande Rise-Walvis Ridge. This study contributes to understanding the final opening of the South Atlantic Ocean, global comparison of paleoenvironments, and future petroleum exploration in the South Atlantic conjugate margins.