West Central Patagonia, a New Exploration Frontier

Carlos M. Urien

From Middle-late Paleozoic times, West Central Patagonia was a foreland platform where periglacial, fluvio-deltaic, shallow and deep neritic sequences were dispersed on an active continental margin. Acidic magmatism is present since Early Jurassic, due to subduction of the Pacific plate in a series of shifting west volcanic arcs until Late Tertiary, when the Andean orogeny was definitively emplaced, converting this region into a perisutural trend. The consecutive volcanic extrusions alternated with marine and continental sequences, rich in organic matter and reservoirs, generating potential and proven petroleum systems.

A Late Jurassic tectonic reactivation formed new depositional centers as the San Jorge-Rio Mayo embayment (resulting from a pull-apart setting), and the Austral and Malvinas basins. While in the west a marine flooding started, under euxinic conditions, the basal alluvial-deltaic plains and coastal lagoons moved eastward as staggered high-stand track sequences.

Thus, a Late Jurassic-Mid Cretaceous Petroleum System was formed, part of which is under exploitation in San Jorge and Austral basins. About Late Cretaceous, due to the rising of the Andean belt, a basin inversion took place in the west, sourcing predominant alluvial clastics and deltaic sequences offlapping eastward.

All these western Patagonia sequences were laid down on an internal sag realm, with suitable oil source and reservoir rocks, and sizable structures. This region is in consequence assigned a high rank of prospectability, thus opening a new exploration frontier.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995