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Glacigenic strata associated with the proto-Precordillera were deposited in the Calingasta-Uspallata and Río Blanco back-arc basins and the Paganzo foreland basin in west-central Argentina during the early Pennsylvanian (upper Namurian; Bashkirian). These basins were formed due to tectonic loading and later postcollisional extension in a convergent-margin setting along the western margin of Gondwana during the Chañic and Río Blanco tectonic events. Uplift of the proto-Precordillera fold-and-thrust belt during the latest Visean–earliest Namurian (Serpukhovian) resulted in the development of a widespread unconformity that formed the pre glacial basin floors. During the Namurian, alpine glaciers carved deep valleys into the upland, and ice drained radially away from the proto-Precordillera. Valley glaciers or an ice cap also occupied basement uplifts in the Sierras Pampeanas to the east. Ice was grounded below sea level in the Calingasta-Uspallata and Río Blanco Basins, where thick glaciomarine successions were deposited. In the Paganzo Basin, a thin glacial succession was deposited in both terrestrial and glaciomarine settings. Throughout the proto-Precordilleran region, deposition is interpreted to have occurred (1) subglacially, (2) in morainal banks, (3) as a result of settling from suspension out of meltwater plumes, (4) as rain-out from melting icebergs, and/or (5) from mass movement and sediment gravity flows. An abrupt upward transition from diamictites to marl-bearing, dropstone-free mudrocks marks glacial retreat and establishment of sediment-starved marine conditions. Above this, coarsening-upward successions and truncation surfaces signal either postglacial deltaic progradation during a forced regression or fluvial incision associated with a base-level fall. Although much is known about these strata, many questions remain, including the age of the deposits, environments of deposition, and the mechanisms responsible for the observed stratigraphic architecture.

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