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

Paper No. 229-17
Presentation Time: 9:00 AM-6:30 PM


PEASE, Emily Camille, Jackson School of Geosciences, The University of Texas at Austin, 101 East 27th Street, Austin, TX 78712, ANDERSON FOLNAGY, Heidi, University of Montana Western, Dillon, MT 59725, JENNINGS, Carrie E., Department of Earth Sciences, University of Minnesota, 100 Church Street, Minneapolis, MN 55455, 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, emkaypease@aol.com

A previously undescribed, massive, boulder-rich diamictite with large, sub-angular to sub-rounded clasts occurs in a newly discovered outcrop of the Carboniferous Itararé Subgroup in Witmarsum, Paraná State, Brazil. These appear to be glaciogenic diamictites deposited during one of the many advance-retreat phases of the Paraná lobe of the Gondwanan Ice Sheet.

The goal of this study is to determine the depositional environment and provenance of this diamictite unit. Images of the outcrop were analyzed to determine the apparent orientation of the boulders with a 3:2 length/width ratio in order to determine mode of transport. Sediment analyses of inter-clast diamictite samples from the outcrop were conducted to determine sand grain lithology and provenance, grain size, roundness, and sphericity.

Results of this research were compared to the results of the analysis of a nearby, presumably correlative, unit (4 m away). Analysis of boulders (greater than 0.2 m in diameter) in this outcrop showed the same orientation as that of the nearby exposure. However, differences were observed. Although the clasts of all sizes in the outcrop studied show no apparent preferred orientation, clasts of all sizes in the nearby exposure do exhibit a preferred orientation that indicates flow. Additionally, sediment analyses show differences in both grain size distribution and provenance between the two exposures. Thus, correlation of the boulder-rich unit between the two exposures is tentative. However, if this unit is the result of a subaqueous debris flow, variations in sedimentary characteristics over a small distance would be expected.

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