CONICET | Buscador de Institutos y Recursos Humanos

In the southern Central Andes of Argentina, between 34° and 41°S, the Neuquén Group records Upper Cretaceousnonmarine deposits that provide direct evidence of synorogenic sedimentation associated with the developmentof an early foreland basin. The configuration of this basin and its relation to the Malargüe fold and thrust belt areanalyzed in this article using sedimentological analyses, U-Pb dating of detrital zircons and seismic and surfacestructural data. The remnant wedge-top depozone preserved in the Argentinian Andean slope exposes sedimentologicalinformation that indicates that braided fluvial systems, which may have formed part of broaderfluvial fans, transported and deposited the sediments from an extensive relief area located in the present westernAndean slope to the Chilean Coastal Range zones. The eastern border of this depositional system was defined bya basement uplift, interpreted either as a forebulge or an incipient broken foreland system, from where gravelsandybraided river systems fed the foredeep depozone transporting and depositing sediments from the exposedcratonic area in the east. Consequently, an initial underfilled foreland basin was configured. The evolution of thisearly basin and the areas of sediment supply were controlled by the eastern expansion of the Malargüe fold andthrust belt, through the development of thick-skinned anticlines, which progressively fragmented the wedge-topzone. The evidence collected suggests that the Late Cretaceous uplift was a major tectonic event that exposed theentire Mesozoic column of the Neuquén basin up to the Permian-Triassic basement, which implies more than2,500 m of denudation at that time. U-Pb determinations yielded a maximum depositional age of ca. 91±2 Ma(Late Turonian), which suggests either non-deposition or cannibalization of a sedimentary interval of ca. 10 Myat 36°S, when compared to the age of the basal sections of the Neuquén Group at other latitudes.

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