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We studied the northern tip of the Austral-Magallanes basin in the Southern Patagonian Andes, between the Buenos Aires Lake and the Mayer River at 46º35' SL and 48º35' SL, respectively. Proposed objectives were: i′ to differentiate Mesozoic-Cenozoic tectonostratigraphic units and, ii′ to characterize the different deformational events that took place in the area linked to a variable regional geodynamic context. Sandstones provenance analysis was performed on the Aptian -Albian compressive retroarc deposits and Cenozoic foreland deposits. Studied samples were classified using tectonic discrimination diagrams which show: i′ for Cretaceous rocks a dominant sediment source from a recycled orogen and, to a lesser extent, a dissected to transitional arc whereas ii′ the Cenozoic rocks show a magmatic arc provenance. According to the performed analyses, the evolution of the northern sector of the Austral-Magallanes basin is proposed to include four tectonostratigraphic units related to: i′ a Late Jurassic rift stage; ii′ a Berriasian Barremian thermal subsidence stage; iii′ an Aptian Albian compressive retroarc stage; and iv′ a Miocene foreland stage s.s. The Late Cretaceous-Paleocene was