UNMIXING SEDIMENT SOURCES OF THE CARBONIFEROUS ANSILTA FORMATION OF THE CALINGASTA-USPALLATA BASIN, WESTERN ARGENTINA

The response of sediment routing patterns between glacial and interglacial intervals are not well constrained past the Cenozoic record. Western Argentina hosts one of the most complete and laterally continuous records of the Late Paleozoic Ice Age. The Ansilta Formation consists of glaciomarine, nearshore, and fluvial systems deposited during the Late Paleozoic Ice Age (LPIA) along the eastern margin of the Calingasta-Uspallata Basin in Argentina. The lower glacially influenced succession (0–427 m) records at least five glacial advances; the upper succession of the Ansilta Formation (427–700 m) consists of progradational shallow marine shelf, deltaic, and fluvial strata. This study tests 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. We combine 1225 new U-Pb ages from 6 samples of the Pennsylvanian Ansilta Formation in the Calingasta-Uspallata Basin and with 5,990 U-Pb ages from 183 published samples in a forward mixture model in order characterize provenance shifts in glaciogenic strata between glacial and interglacial intervals. For the glacially influenced lower Ansilta succession, sediment sourced locally from the Protoprecordillera, which was a prominent highland with alpine glaciers flowing east and west into the Calingasta-Uspallata and Paganzo basins, respectively. Thus, there was little or no connection between these two basins during Episode 2 LPIA glaciations. The upper fluvial/deltaic succession has distal sediment sources in the eastern Sierra Pampeanas and Famatinian Belt. Furthermore, our results support the collapse of the Protoprecordillera topographic barrier, enabling drainage patterns connecting the Paganzo and Calingasta-Uspallata basins during the late Pennsylvanian-early Permian time.