Argentina - Sierra de las Quijadas National Park

The Mesowic basins of the central western part of Argentina (Ischigualasto, Talampaya, Marayes, Guayaguas, Quijadas, among others) constituted depocentres that worked from the Triassic to the Cretaceous, generating the accumulation of continental sedimentary sequences under arid to semiarid climatic conditions. These sedimentary basins extend from the foothills of the Andes in La Rioja and Sierra de Valle Fertit in San Juan towards the south up to the Serranias Occidentales de San Luis and underground up to the Beazley Basin (Figure 3). All of them exhibit a rift structure of the hemigrabene type, characterized by an asymmetrical geometry with an active margin on the west and a passive margin on the east. They constitute the outcome of the extensive processes undergone by the South American plate during the Mesozoic, which led to the final collapse of the Gondwana supercontinent and the opening of the Atlantic Ocean. The lshigualasto and Talampaya basins exhibit a series of geological formations that portray the sedimentation of the entire Triassic Period. This can be inferred from the fossiliferous content of these layers as well as from radimetric dating of the volcanic rocks. However, the absence of fossiliferous sediments of the Jurassic and Cretaceous is remarkable, which would document the continuity of the environmental and biological evolution of the Upper Mesozoic. Geological formations of the Jurassic and Crztaceous Periods are found in different and distant areas of Argentina, including La Rioja, San Juan, San Luis, Mendoza and Neuqukn, and a sequence of basins located in the northwest and south of Argentina. The sedimentary outcrops in Sierra de las Quijadas are part of a chain of geological units the detailed study of which has enabled to complement part of the geohistorical and paleobiological information of the Upper Mesozoic in Argentina, which extends over 120 million years (the entire Jurassic and Cretaceous Periods) Sierra de las Quqadas is part of the Serranias Occiderniales Range in the northwest of the Province of San Luis and southwest of San Juan, which extends in the NNW-SSE direction along over 300 km, in discontinuous outcrops. This range exhibits a several-hundred meters-long sequence of sedimentary rocks of the red bed type, which includes several geological units of continental origin. These are known as Quehrada del Barn Formation, Los Riscos Formation, El Jume Formation, L a Cantera Formation, El Toscal Formation, La C m Formation (which includes volcanic rocks) and Largarcito Formation (Figure 4). As a whole, these units form the exposed stratigraphic column of the Mesozoic in San Luis province. From the paleoenvironmental point of view, these units represent a wide range of continental environments, including landslide, alluvial-fluvial, aeolian and lake deposits.