Print this pageTectonic and Structural Controls of Basin Evolution in Argentina: The Mesozoic Austral and Neuquen Basins
TANKARD, ANTHONY
The Mesozoic basins of Argentina developed along pre-existing crustal fabrics. Their tectonic evolution involved several episodes of extensional subsidence and structural inversion. Triassic-Early Jurassic extension was characterized by basement-involved faulting which formed discrete half grabens which were structurally linked. In contrast, Late Jurassic-Cretaceous extension was controlled by NW-diverging shear zones related to opening of the Atlantic Ocean. The five petroleum producing basins in Argentina are intimately linked to this system of mid-Mesozoic shear zones. Prospectivity reflects the amount of inversion and structural trap formation in each basin. Optimal amounts of structural inversion occur in the Neuquen basin which produces more than 40% of Argentina's oil. The climax of Andean orogenesis in the late Cenozoic overprinted and reactivated many of these earlier trends.
The Neuquen basin of west-central Argentina contains a sedimentary fill which is punctuated by several unconformities reflecting intermittent subsidence and periods of structural inversion. Triassic extension initially created a suite of isolated rift segments and discrete source-rock depocenters. Since the Callovian onward, the Neuquen basin was subjected to periodic inversion of earlier extensional structures. The most conspicuous inversion trend is the Huincul arch which formed along the restraining bend of an intracrustal shear zone. Neuquen basin contains multiple source rock and reservoir intervals. In contrast, the Austral basin of southern Argentina has the least amount of structural inversion. The Austral basin is characterized by a single source rock - reservoir couplet. However, the tectonic framework suggests that the Austral basin may contain Jurassic and Cretaceous source rocks and several reservoir units.