El depocentro Alto Atuel: primeras descripciones de las unidades del Jurásico Inferior aflorantes en las nacientes del río Atuel

Abstract

The Alto Atuel depocenter is located on the northwestern margin of the Neuquén Basin. This study focuses on the Jurassic volcano-sedimentary successions cropping out at the headwaters of the Atuel River, which have been scarcely studied over time. This depocenter, located at 34°35’S and 70°10’W in southern Mendoza Province, is of interest due to its position within the basin, which can provide information about the interaction between marine sedimentation and volcanic arc activity during the Early Jurassic. Lithological and biostratigraphic analyses were conducted on a stratigraphic log more than 450 meters thick, allowing the recognition of three sections based on their lithological characteristics. The basal section exhibits high-energy volcaniclastic and pyroclastic deposits. The middle section is dominated by pyroclastic deposits and lava flows interbedded with calcareous sandstones and marls containing marine invertebrate fossils. The upper section reflects a shift towards lower energy marine environments, where interbedded black shales, tuffs, and calcarenites with sparse fossil remains are predominant. The fossil content allowed dating the marine successions as late Pliensbachian–early Toarcian. On the other hand, the lithological analysis of the successions suggests that the Alto Atuel depocenter evolved in isolation, at least during the Early Jurassic, as indicated by the presence of a significant volcanic input, which is not evident in depocenters located immediately to the east, such as Atuel and La Valenciana depocenters.