PRELIMINARY INTERPRETATIONS OF GLACIOMARINE FACIES, THEIR DISTRIBUTION, AND IMPORTANCE IN THE SOUTHERN PARANÁ BASIN, BRAZIL

The Paraná Basin of southern Brazil contains one of the most complete and detailed glacial and post-glacial records of the late Paleozoic ice age (LPIA; 346-259 Ma) during the Carboniferous and Permian. Despite this, there is little consensus on the character and timing of the glacial intervals. One hypothesis describes numerous small ice sheets extending into the basin from locally elevated areas (Rocha-Campos et al., 2008). A competing hypothesis describes a massive ice sheet that originates in Africa and extends across the entire basin (Holz et al., 2008). Therefore, the goal of this project is to test these hypotheses by describing the glaciomarine facies and their distribution. A preliminary analysis (Summer 2014) of the Itararé Group (Carboniferous-Permian) in the southern portion of the Paraná Basin exhibits a number of possible glacial and proximal glaciomarine features related to advance and retreat cycles of a dynamic ice front. Outcrops and core data were described and depositional environments were interpreted from the region around Caçapava do Sul in Rio Grande do Sul State to Porto Amazonas in Paraná State. Characteristic glaciomarine features encountered include: rythmites, rythmites with outsized clasts (including diamictite clasts), massive and stratified diamictites, striated and bullet-shaped clasts, deformed blocks, striated and grooved pavements and clasts ploughed into the substrate. Interpretations of depositional environments include: basin margin, subglacially grooved and ploughed surfaces (traction till), morainal bank deposits, distal glaciomarine cyclosams and cyclopels, slides, slumps, and debris flows, ice-rafted debris, and iceberg keel marks. Future work will be done to interpret the timing, location and nature of glaciation via a detailed sedimentological and geochemical approach. Reconstructions of ice volume are needed to constrain climate models and explore how Earths current climate may evolve under increased atmospheric CO₂.