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Geology and Petroleum Resources of Argentina

H. Douglas Klemme

Argentina occupies the southern portion of the Brazilian craton in an extensively accreted zone. The plate tectonics setting of Argentina involves a Gondwana reentrant (South America, Africa, and Antarctica) whose evolution as yet is uncertain. Along the east flank of the Andes, late Paleozoic and early Mesozoic taphrogenic (rift) basins of apparent wrench-rift origin contain 85% of the discovered oil and gas in Argentina. Movement and docking of the Patagonian and Deseado-Falkland massifs (microplates?) were accompanied by intense late Paleozoic-early Mesozoic volcanic activity and the development of intracraton and interplate rifts where restricted lacustrine or shallow marine source rocks were deposited. Subsequent late Tertiary foredeep folding on the semicratonic acc eted zone developed on the western margin of the rift basins, but did not affect the undisturbed portion of the basins.

Source rocks include marine bituminous shales of Devonian, Jurassic, and Cretaceous ages, and lacustrine bituminous shales of Triassic and Jurassic ages. Reservoir rocks are predominately clastics, generally interbedded with the source sequence. Reservoir rocks of the wrench-rift basins are considerably downgraded due to high tuffaceous content. Cap rocks are predominately interbedded and overlying shales, although in the Nuequen basin a semi-regional evaporite cap is present. Trap types are dominantly: (1) tilted fault blocks and faults in the wrench-rift basins; (2) geomorphic arches and fault blocks in the Magallanes basin; and (3) compressional folds in the Torija-Chaco basin. The undiscovered oil and gas resources are assessed at 60 to 70% of the amount already discovered, divide equally between producing and nonproducing basins.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.