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Geology and Previous HitHydrocarbonNext Hit Potential of the Argentine Atlantic Margin

Davison, Ian1
 Anderson, Lee1
 Gormly, Piers2
 Nutall, Peter2

1Earthmoves Ltd., Camberley, United Kingdom.
Houston, TX.

The Argentine Atlantic margin began rifting in Mid to Upper Jurassic times with a series of E-W ( San Julian, San Jorge, Colorado, Salado) and one N-S (Rawson) trending pull-apart basin developed. San Jorge and Colorado contain proven syn-rift lacustrine source rocks, but no syn-rift sources have been detected in other rifts yet. A pre-rift Paleozoic sequence of Silurian? to Permian age is imaged below the rift sections. Possible Permian age organic shales and coals are present onshore which are equivalent to the Springhill Formation in Africa. The flat-lying parallel-bedded Paleozoic strata reach up to 3 km thick but average less than 1 km and indicate they was laid down in a broad shallow intra-continental sag basin, which was not affected by subsequent folding and metamorphism, unlike the onshore area. The moveable oil in the Cruz del Sur-1 well in the Colorado Basin has been reportedly typed back to a Paleozoic source.

Salado and Colorado rifts extend out to the rifted margin of the south Atlantic and several Previous HitDirectNext Hit Previous HitHydrocarbonNext Hit Previous HitIndicatorsNext Hit (bright seismic amplitude anomalies) have been observed in the post-rift clastic reservoirs draped over rifted fault blocks. Anomalies are structurally conformable and large Cretaceous and Cenozoic reservoir plays are present where the syn-rift source rocks are buried in the oil window, and syn-rift faults are reactivated and break up to the Cenozoic. Large channel complexes with high amplitude seismic reflections suggest that large quantities of coarse clastics were transported out to the Atlantic rifted margin, and good sandstones reservoirs are expected out on the slope and abyssal plain.

New deep seismic indicates that the continental crust thinned to a β factor of 2 before thick seaward-dipping reflector complexes and ocean crust developed. The outer margin was stretched over a limited narrow zone of 20-50 km with shallow 1-3 km rifted half graben developed at the continental edge. We suggest that the Argentine margin was anomalously hot and much of the accommodation space created by crustal stretching was filled by magmas rather than subsidence of rifted blocks. Hence, early (140-130 Ma) Atlantic margin rifting was probably accompanied by high heat flow and early Previous HithydrocarbonTop migration.

No deepwater wells have been drilled on the Atlantic margin so far, but new seismic data indicates large viable targets for hydrocarbons in the post-rift section.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil