Provenance of late Paleozoic glacial/post-glacial deposits in the eastern Chaco-Paraná Basin, Uruguay and southernmost Paraná Basin, Brazil

Abstract The Parana Basin, Brazil and the Chaco-Parana Basin, Uruguay both contain sedimentary records that are critical to reconstructing late Paleozoic ice centers in central Gondwana. The orientations of subglacial landforms and glaciotectonic structures suggest that late Paleozoic glacial deposits in the eastern Chaco-Parana Basin and the southernmost Parana Basin are genetically related, as they were likely glaciated by the same ice center. However, the location and extent of the ice center responsible for depositing these sediments are unclear. Furthermore, changes in sediment dispersal patterns between glacial, inter-glacial, and post-glacial intervals are not understood for this region of Gondwana. Therefore, this study utilized U–Pb detrital zircon geochronology to assess the provenance of glacial and post-glacial sediments from the eastern Chaco-Parana Basin (San Gregorio, Cerro Pelado, Tres Islas Formations) and the southernmost Parana Basin (Itarare Group). Results show dominant age peaks at ∼520–555 Ma, ∼625 Ma, 750–780 Ma, and 900–1000 Ma in all samples from the eastern Chaco-Parana Basin. These zircons are interpreted to have been derived from sources in the Cuchilla Dionisio Terrane and Punta del Este Terrane in southeastern Uruguay, and possibly the Namaqua Belt in southern Namibia. Another important source was likely Devonian sedimentary rocks of the Durazno Group in central/eastern Uruguay. Meanwhile, a sample of the glaciogenic Itarare Group from the southernmost Parana Basin contains a different detrital zircon signature with peaks at ∼580 Ma, ∼780 Ma, ∼2110 Ma, and ∼2500 Ma that closely resembles underlying sedimentary and meta-sedimentary rocks of the Precambrian/Cambrian Camaqua Basin. Detrital zircon ages in the glacial and post-glacial sediments indicate that local sources were dominant. In contrast, zircon ages from relatively ice-distal glaciomarine intervals in the Chaco-Parana Basin reflect more distal sources to the east and southeast, which indicates a larger drainage catchment opened when glaciers retreated and/or the zone of maximum subglacial erosion shifted. Although most zircon ages in the Chaco-Parana Basin can be attributed to Uruguayan sources, results support the hypothesis that glaciers emanated from southern Namibia and southeast Uruguay into the Chaco-Parana Basin. From there, ice flowed northwest into the Parana Basin and then receded back towards Africa as the paleoclimate warmed. The detrital zircon inventory in our study region is distinct from the eastern Parana Basin, suggesting at least two unique African source regions for glaciers that deposited sediments in the Parana and Chaco-Parana Basins.