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URIEN, CARLOS MARIA, Urien & Associates, Buenos Aires, Argentina

ABSTRACT: Tectonic Evolution of Western Patagonia and Hydrocarbon Habitats

In Devonian times, Western Patagonia was a Pericratonic Foreland basin. The rift-like, faulted platform underwent several marine transgressions-regressions related to tectonic episodes occurring mainly from Hercynian to Andean (Pyrenaic) times that modified the extension and nature of sedimentation in the region, due to the evolution of the Pacific Plate and Margin, and the accretion of successive acidic magmatic arcs. The marine sequences that flooded Patagonia, uneven in extension, shifted from North to South in accordance with differential subsidence in this margin, particularly in the three main sedimentary embayments: Neuquen, San Jorge and Magellan-Malvinas. Transversal ridges, following ancestral transtensional features, rejuvenated during the Atlantic opening, separate these e bayments. Marine sequences evolved into restricted circulation oxygen poor seas, whose organic matter rich sediments originated hydrocarbon source rocks, identified in the three most important basinal complexes of Patagonia. The beginning of the Andean Orogeny and the emplacement of the Andean Batholith, hindered the Pacific marine presence in western patagonian basins. Subsequently, an Eastern elongated region-wide subsidence allowed the accumulation of molasse-like sequences over most foredeep sediments in the region, creating several hydrocarbons habitats grouped as follows:

1. Neuquen: proven (Liassic to Aptian); Potential (Triassic).

2. San Jorge: proven: (Upper Jurassic to Lower Cretaceous), unproven (Lower Paleozoic to Lower Jurassic).

3. Magellan/Malvinas: proven (Lower Cretaceous), unproven (Jurassic to Upper Cretaceous).

During Laramic time, Atlantic highstand sea levels, flooded a great part of Extra Andean Patagonia, while the Andean Chain started rising with an active magmatic arc.

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