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LIGHT, MALCOLM P. R., M. L. KEELEY, and M. P. MASLANYJ, Intera, United Kingdom, CARLOS M. URIEN, Urien & Associates, B.A., and S. L. HOGGS, Cullen Valdez Rojas y Asociados, B.A.

ABSTRACT: Hydrocarbon Prospectivity of the Argentine Continental Slope

A rift basin containing stratigraphic and structural closures is developed along the Argentine slope over a distance of some l000 km and area of 50,000 sq km in potentially exploitable water depths of 200 to 1500 m. The post rift sequences which formed during subsequent thermal subsidence may also contain stratigraphic closures. A sequence stratigraphic interpretation was made on a set of widely spaced regional seismic lines linking major unconformities with those recognized in the San Jorge Basin and offshore Namibia. No wells exist on this part of the continental margin. Rifting is interpreted to have began during the Late Triassic/Jurassic, and terminated in Early Cretaceous. The first marine seaways flooded the Rift alluvial plains and lake establishing predominantly brackish cond tions. This narrow body of marine water seems to have passed over the Falkland Plateau and Magellan Basin in Oxfordian time onto a transitional crust but not yet oceanic. In Hauterian-Barrenian time, low circulation marine conditions with oxygen deficiency prevailed in the area up to Rio Grande/Walvis Ridge flooding in part the coastal pull-apart basins. A major marine transgression in the Maastrichtian formed a widespread seal over the entire shelf and slope area. Four play types are identified on the Argentine slope. Play Type I is a major north-east trending elongate delta system sourced inland from the San Julien (N. Malvinas) Basin and deposited on the southern Patagonian shelf and rise. Play Type II consists of reworked deltaic barrier sands that accumulated along the crest of the uter Basement Ridge. The Outer Basement Ridge forms Play Type m: a major structural closure 400 km long that has potential for structural and stratigraphic traps. Play Type IV comprises a series of margin-parallel rift systems situated in the offshore region between the 200 m and 1500 m isobaths. Regional seismic data and geological correlations suggest that oil prone source rocks are likely in the Middle and Upper Jurassic and Cretaceous formations. Source rocks are probably mature to the east and west of the Outer Basement Ridge and in the eastern depocenter of the Colorado Basin. Eastward directed migration from Jurassic age lacustrine source rocks in the Colorado Basin may have charged traps along the crest of the Outer Basement Ridge. Westward directed migration from deeply buried A tian age marine source rocks in the Atlantic basins has probably charged prospective stratigraphic and structural traps in a suite of coast-parallel grabens developed on the Argentine continental shelf and slope. The northeast orientated Cretaceous-Tertiary age elongate deltaic system reworked barrier complex forms a play east and north east of the San Julien Basin. The Argentine offshore region, therefore, despite being virtually completely untested, offers significant encouragement as a productive hydrocarbon province.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.