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The Cañadón Asfalto basin, central Chubut, Argentina, comprises a volcano-sedimentary sequence related to the opening of the Atlantic Ocean during Mesozoic times. The Lonco Trapial, Cañadón Asfalto and Cañadón Calcáreo formations are the main units related to the evolution of this basin. The Las Chacritas and Puesto Almada members are distinguished in the Cañadón Asfalto Formation. LA-HR-ICP-MS U-Pb and Lu-Hf data on zircon were obtained on these units. The Lonco Trapial Formation gave a weighted average age of 172.3±1.8 Ma. A pyroclastic level from the Las Chacritas Member gave a weighted average age of 168.2±2.2 Ma. Two U-Pb concordant ages of 160.3±1.7 Ma on a laminated tuffite and 158.3±1.3 Ma on a pyroclastic level were obtained for the Puesto Almada Member. Two maximum depositional ages constrain the sedimentary provenance areas for the basin: 1) A sample from the Sierra de la Manea range, where a

Central Patagonia is traversed by a belt of Early to Middle Jurassic calc-alkaline intermediate volcanic rocks interspersed with more felsic volcanic rocks which are associated with the widespread magmatism that took place during Gondwana break-up times. This work uses K-Ar and Ar-Ar dating and whole-rock and phenocryst (plagioclase, amphibole, clinopyroxene and titanomagnetite) compositional data to refine the age, geochemical signature and reservoir conditions of these volcanic rocks, which are known as Lonco Trapial Formation. The andesites, dacites and trachydacites which were the object of this study have either amphibole or clinopyroxene as the main

The carbonate-evaporitic sequence of the Caaeadón Asfalto Formation that crops out in Caaeadón Carrizal (Chubut province, Argentina) is characterized by a lacustrine facies association. This sequence includes an extensive biohermal belt, flood facies with high lake-level and low lake-level stages, and desiccation-evaporation facies. The biohermal belt shows three growth-stages of microbial communities. This belt controlled sedimentation in nearby areas, favoring the formation of the pan lake of Caaeadón Carrizal. High lake-level flood facies represent sedimentation during periods of great water input to the pan lake. Low lake-level flood facies are characterized by low-energy conditions and by the development of a shallow lake with marginal zones and palustrine subenvironments. Desiccation facies represent a dry mudflat that borders the saline lake. Evaporation facies are related to the shrinkage of the water body and to the migration of the shallower facies towards the center of the ephemeral lake.