The Sedimentology and Petrology of the Upper Cambrian Mt. Simon, Eau Claire, and Galesville Formations in Southeastern Minnesota
1993-06
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The Sedimentology and Petrology of the Upper Cambrian Mt. Simon, Eau Claire, and Galesville Formations in Southeastern Minnesota
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1993-06
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Abstract
The Mt. Simon Sandstone, Eau Claire Formation, and the
Galesville Sandstone comprise the Upper Cambrian
Dresbachian Stage, and are found as subsurface strata in
southeastern Minnesota with scattered small outcrops along
the Mississippi and St. Croix Rivers. The formations are
relatively flat-lying units located in a structural lowland
termed the Hollandale Embayment. The Mt. Simon has an
unconformable contact with the underlying Precambrian
basement. The Eau Claire is conformable with the underlying
Mt. Simon and the overlying Galesville. The Galesville has
an unconformable contact with the overlying Ironton
Sandstone of the Franconian Stage. The Dresbachian
formations thicken from northwest to southeast direction
across the state, cross-bedding has a south-southwest
direction of dip.
The Mt. Simon is primarily a medium- to coarse grained,
moderately sorted, thick bedded orthoquartzitic sandstone
with some feldspathic sandstone and shale laminae. The Eau
Claire contains fine-grained, well-sorted, thin bedded
orthoquartzites, arkoses, and quartzose arkoses, and
laminated shales. The formation is very fossiliferous and
glauconitic. The Galesville consists of medium-grained,
well-sorted, thick bedded orthoquartzitic and feldspathic-quartzose
sandstones.
Petrology of the three formations is simple. The mineralogy
is dominated by quartz with secondary feldspars. Mic, clay
matrix, carbonate, pyrite, and feldspar cement, glauconite,
and fossils are accessory components. Heavy minerals
include zircon (dominant in most samples), tourmaline,
garnet, rutile, apatite, and opaques, and are well-rounded
for the most part. Fossils include trilobites, brachiopods,
mollusca, and worm burrows.
The Mt. Simon Sandstone, on the basis of lithology, grain
size and sorting, bedding and cross-bedding, is a
nearshore, highly turbulent, shallow water deposit. The Eau
Claire Formation, on the basis of lithology, grain size and
sorting, bedding and cross-bedding, and fossils and
glauconite, is probably an offshore shelf deposit of quiet,
relatively deep water. Characteristics, however, also
resemble tidal flat deposits, which the formation may be in
part. The Galesville Sandstone, on the basis of lithology,
grain size and sorting, bedding and cross-bedding, is a
nearshore deposit of turbulent, shallow waters.
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University of Minnesota M.S. thesis. June 1993. Major: Geology. Advisor: Richard Ojakangas. 1 computer file (PDF); xi, 167 pages. This degree was awarded posthumously on January 31, 2024.
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Churchill, Richard. (1993). The Sedimentology and Petrology of the Upper Cambrian Mt. Simon, Eau Claire, and Galesville Formations in Southeastern Minnesota. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/262506.
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