Unmixing detrital zircon U-Pb ages reveals tectonic and climatic depositional influences on the Carboniferous Ansilta Formation, Calingasta-Uspallata Basin, Western Argentina

The Late Paleozoic Ice Age (LPIA) was a principal control of sedimentation across Gondwana from the late Devonian through early Permian. We assess the hypothesis that glacial to interglacial transitions in western Argentina were the primary control influencing sediment routing patterns among the various Carboniferous-Permian basins in western Argentina. The Carboniferous Ansilta Formation consists of glaciomarine, nearshore, and fluvial systems deposited during the LPIA along the eastern margin of the Calingasta-Uspallata Basin in Argentina. The lower, glacially influenced succession of the Ansilta Formation records at least five glacial advances; the upper succession of consists of progradational shallow marine, deltaic, and fluvial strata. We combine 1225 new U–Pb zircon ages from six samples of the Carboniferous Ansilta Formation in the Calingasta-Uspallata Basin with 5864 U–Pb ages from 147 published samples in the detritalPy-mix forward mixture model to characterize provenance shifts. For the glacially influenced lower Ansilta Formation, sediment was derived locally from the Protoprecordillera, which was a prominent highland with alpine glaciers flowing west and east into the Calingasta-Uspallata and Paganzo basins, respectively. Thus, there was little or no connection between these two basins during Serpukhovian-Bashkirian glaciation. The fluvial/deltaic upper Ansilta had distal sediment sources in the Sierras Pampeanas. Furthermore, our results support the collapse of the Protoprecordillera topographic barrier, enabling drainage patterns connecting the Paganzo and Calingasta-Uspallata basins by late Pennsylvanian-early Permian time.