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

Paper No. 229-19
Presentation Time: 9:00 AM-6:30 PM


SPRY, Erin Katheryn1, ANDERSON FOLNAGY, Heidi2, BACCI, D.C.3, ROCHA-CAMPOS, A.C.3, JENNINGS, Carrie E.4 and COTTER, James F.P.1, (1)Geology Discipline, University of Minnesota, Morris, 600 East 4th Street, Morris, MN 56267, (2)University of Montana Western, Dillon, MT 59725, (3)Instituto des Geosciências, Universidade de São Paulo, Sao Paulo, 05450-001, Brazil, (4)Department of Earth Sciences, University of Minnesota, 100 Church Street, Minneapolis, MN 55455, Spryx015@morris.umn.edu

A new exposure of glacial diamictites in the Carboniferous Itararé Subgroup was found and analyzed in Witmarsum, Paraná State, Brazil. Multiple Carboniferous advances of the Gondwanan Ice Sheet dominate the stratigraphic record of the area (Trosdtorf, 2005); analysis of this new exposure appears to reveal a glaciomarine facies in this area that had not been previously recognized.

The exposure was studied in the field and samples were collected for laboratory analysis. Field analysis focused on the documentation of the clast orientation as well as characterization of facies. Clast lithologies were determined for provenance analysis and to reconstruct the depositional mechanism. Diamictite samples collected in the field were analyzed for grain size distribution and lithologies of the 1-phi size-fraction to further characterize the provenance. The outcrop was photographed and boulders of a 3:2 length/width ratio were outlined in Adobe Illustrator. Orientation of clasts were measured and plotted on a rose diagram.

Three distinct facies of diamictite were distinguished within the outcrop: one with a clear imbrication, another featuring no apparent orientation, and another showing a vague orientation. Three other facies containing no clasts were present in the outcrop: a laminated clay; a course grained, pebbly diamictite; and a non-laminated clay. Clear preferred orientation of clasts in the section displaying clear imbrication suggested that was formed as a subaqueous debris flow. The upper facies, also boulder-rich, displayed scattered orientation, which suggested it was deposited by rainout. Both of these depositional settings are recognized throughout the Parana Basin, but not previously in the Witmarsum area.

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