12. CUENCA DE ÑIRIHUAU

LUIS CAZAU; JORGE CORTIÑAS; SARA REINANTE; MARCOS ASENSIO; FLORENCIA BECHIS; DIEGO APREDA

FRONTERA EXPLORATORIA DE LA ARGENTINA

Instituto Argentino del Petróleo y del Gas

Lugar: Buenos Aires; Año: 2005; p. 251 - 273

Ñirihuau Basin. The fill of the Tertiary Ñirihuau Basin, which is located on the eastern Subandean flank of the Northern Patagonian Cordillera, is characterized by two major volcanic and sedimentary cycles. The Base Cycle (Late Paleocene - Early Oligocene) involves the Pilcaniyeu Volcanic Belt (Huitrera Formation) and the Cerro Bastión, ?Patagonian?, Río Foyel and Rincón de Cholila (?) formations. The Top Cycle (Early Oligocene - Pliocene) is represented by the Nahuel Huapi Group and consists, from base to top, of the El Maitén Volcanic Belt (Ventana Formation) and the Ñorquinco (?), Ñirihuau and Collón Cura formations. Structurally, the western part of the basin has been involved in the deformation process that gave rise to the Ñirihuau fold and thrust belt, whereas the eastern border accounts for the basin platform showing poor or no deformation with three distinct regions: North (Ñirihuau), South (Ñorquinco) and West (El Bolsón). The Petroleum Systems occurring in the basin are identified: a second system documented by gas recovered from drilling in Escuela N° 41 (Las Golondrinas) is added to the well-known immature petroleum system of Tertiary age which has been proven from wellbore and outcrop samples and oil from Arroyo de la Mina surface seepage. The high thermal maturity of this gas (~1.3 % VRE) would suggest a source rock that is different from the previous one. It is likely to have originated either from older rocks (Liassic ?) or from Tertiary rocks occurring deeper in the basin.