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Gina
Gallo Abstract
The Minnesota River Valley, West
Central Minnesota |
GALLO,
Gina , Geology
Department, Augustana College, 639 38th Street, Rock Island, IL 61201,
gina-gallo@augustana.edu and COTTER, J.F.P, Geology Discipline, Univ of
Minnesota, Morris, Morris, MN 56267.
Boulder pavements are planar, single-stone thick
concentrations of glacially modified clasts which occur between or within
glacial units. An extensive boulder pavement occurs in the Minnesota River
valley in west central Minnesota. Different models of boulder pavement
formation have been suggested for this unique glacial deposit. Five sites
located in tributaries of the Minnesota River valley in Chippewa and
Yellow Medicine Counties were studied. Each site consisted of an outcrop
of till with at least one horizon of faceted and striated boulders. Till
stratigraphy and provenance was studied to determine if there were
multiple boulder pavements and relative age, source and origin.
Stratigraphic units were distinguished in the field on the basis of color,
texture and clast lithology. The sediment above, below and surrounding the
boulders was sampled and analyzed. Dry sieving and point counts were done
on each sample. Results of this study indicate that two distinct boulder
pavements are exposed in the Minnesota River valley. Till analyses
indicate the boulder pavements were deposited during different glacial
events. Because multiple horizons of boulder pavements occur in the
Minnesota River valley and elsewhere (e.g. Saskatchewan and Brazil),
depositional models for boulder pavements cannot call upon
"overly" unique glacial conditions. Research for this study was
funded by a grant from the N.F.S.- R.E.U. Program (NSR-EAR 9820249).
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