2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 229-12
Presentation Time: 9:00 AM-6:30 PM


STRANGE, Bobbi G., Department of Geology and Geological Engineering, South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57701, ANDERSON FOLNAGY, Heidi, University of Montana Western, Dillon, MT 59725, ROCHA-CAMPOS, A.C., Instituto des Geosciências, Universidade de São Paulo, Sao Paulo, 05450-001, Brazil and COTTER, James F.P., Geology Discipline, University of Minnesota, Morris, 600 East 4th Street, Morris, MN 56267, bobbi.strange5@gmail.com

A cryptocrystalline siliceous unit was first discovered by Trosdtorf (2005) while mapping the Late Paleozoic glacial units of the Itararé Subgroup in the southeastern Paraná Basin near Witmarsum, Paraná State, Brazil. Three locations, in the Witmarsum area, have deposits comprised of this cryptocrystalline unit. Although these lithologies have previously been compared to Novaculite, a metamorphosed chert, they are not Novaculite sensu stricto. Other studies have hypothesized a volcanic origin for the unit. Additionally, a fourth location near the city of Palmeira contains a previously undescribed unit with similar characteristics. To determine the origin and geochemical composition of these units, samples were analyzed in thin sections using: X-ray Diffraction (XRD), optical microscopy, and other instrumentation. Whole rock chemistry and the chemical analysis of these rocks will also be used to determine if this lithology is the result of a single or multiple depositional events.

The cryptocrystalline siliceous unit occurs at a distinct stratigraphic horizon and is interbedded with lenses of (presumed) glaciogenic sands. Further examination of the contact between the cryptocrystalline siliceous unit and the sand lenses will provide better insight on these glacial deposits. Illustrator images display the contact between the interbedded lenses of fine grained microcrystalline quartzite and quartz rich sand inclusions showing possible syndepositional soft-sediment deformation.

The fourth location contains a new amorphous shale unit discovered near the city of Palmeira, Paraná State, Brazil 20 km east of Witmarsum. This new unit occurs lower in the stratigraphic record (at the base of the Itararé Subgroup) but has characteristics that are similar to the cryptocrystalline siliceous unit described above.

Research for this study was funded by a grant from the N.S.F.-R.E.U Program (NSF-EAR 1262945)