Western South Atlantic Margin Sedimentary Basins: Petroleum Systems and New Exploration Potential
The characteristic structural style and sedimentary fill of South Atlantic continental margin basins derives from Late Paleozoic taphrogenic events related to initial separation of Africa and South America. Extensional forces generated aulacogens and margin-parallel rift chains that contained growing depressions filled with non-marine sequences during the Neocomian. Mid-Cretaceous paleo-bathymetric evidence suggests an internal sea with conditions favorable to preserve organic matter and develop hydrocarbon source rocks until the 85 Ma opening of the Mozambique - Agulhas gateway through Africa. These organic-rich sequences have been identified in DSDP boreholes and exploration wells. Multi-channel seismic shows thinning/truncating beds beneath the margins, augmenting reconnaissance mapping from potential field data of external depocenters filled with Early Cretaceous and Tertiary sequences.
Despite limited well coverage (<160 wells) in the shallow waters of the San Jorge and Austral - Malvinas (500,000 sq km) and Colorado-Salado (300,000 sq km) basins, continental - marine reservoir intervals have been identified. Three plays were selected for further analysis according to their proven, probable and possible petroleum systems:
Colorado-Salado Type: NW-SE-trending basins with Paleozoic structural control roughly orthogonal to the coast and superimposed coast-parallel structuring related to later opening of the South Atlantic. Structural trends containing organic-rich intervals include pre-rift Permian and possible syn-rift lacustrine, Tithonian to Barremian facies, buried and sealed by marine Cretaceous high-stand systems tract units.
Patagonian Margin toe: Elongate depocenters of Early Cretaceous lacustrine and Valanginian marine intervals tapering to thin condensed sections beneath the shelf from more than 6 km of sediments below the lower slope and rise.
Malvinas/Austral: Proven oil sourced in Late Jurassic rifts and Neocomian shallow marine sequences. Similar transgressive Oxfordian age sequences were observed in DSDP-330/Ewing Bank and Tithonian-aged facies have been drilled in the Malvinas basin.
We tested these hypotheses with improved mapping of basin outlines, prominent structural features and sediment thicknesses. A super-regional review of oil geochemistries extends inferences about hydrocarbon kitchens from better-known Brazilian basins down to the Patagonian Toe. Higher-potential areas meriting greater exploration efforts are illustrated.