--> Tectonic Evolution of Western Patagonia and Hydrocarbon Habitats, by C. M. Urien; #90986 (1994).

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Abstract: Tectonic Evolution of Western Patagonia and Hydrocarbon Habitats

Carlos Maria Urien

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 embayments. 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 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 sediment in the region, creating several hydrocarbons habitats grouped as follows:

1. Neuquen: proven zones, Liassic, and Aptian; potential zones, Triassic.

2. San Jorge: proven zones, Upper Jurassic, Lower Cretaceous; unproven zones, Lower Paleozoic, Lower Jurassic.

3. Magellan/Malvinas: proven zones, 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 #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994