Exploration Opportunities in Western South Atlantic Continental Margin Sedimentary Basins
Carlos Urien1 and Craig Schiefelbein2
1 Urien & Associates, Buenos Aires, Argentina
2 Geochemical Solutions International, Inc, Houston, TX
Focused efforts and the presence of oil-prone source rocks within the pre-salt (Early Cretaceous) lacustrine rift sequences and Middle to Late Cretaceous deep marine sequences have resulted in exploration success in both shallow and deep waters of the Equatorial and mid-Atlantic regions of Africa and Brazil. Similar efforts in the South African Orange Basin have also yielded positive results, all of which should encourage focus on the heretofore under-explored southwestern basins of Southern Brazil and Argentina.
After break-up and continental drifting, intracratonic basins that developed during the formation of Gondwana were partially preserved in South America, Africa, Antarctica and Australia. Subsequent transtensional forces produced transform fractures resulting in the formation of the Salado, Colorado, Rawson and North Malvinas aulacogens that, together with the Luderitz and Orange basins, formed the initial triple-junction, where the first syn-rift continental sequences were deposited. This initial rift propagated northward to the zone of equatorial fractures. Grabens and half-grabens evolved into “marginal basins” that are preserved in the Continental Margin of Eastern South America and its conjugate, Western Africa.
The present study summarizes the basic paleoclimatic, paleoenvironmental and paleogeographic evidence that supports the existence of proven and possible Petroleum Systems in this region. Geochemical data from crude oils and potential source rocks obtained from DSDP sites, outcrops, and exploration wells indicate favourable conditions for the accumulation and preservation of oil-prone organic matter of diverse origin (fresh water lacustrine, brackish lacustrine, marine, hypersaline and deltaic marine) and age that varies from Jurassic to Tertiary. These data also support adequate thermal evolution and the presence of migration paths, reservoirs and seals.