Earth History GEOL 2110 The Paleozoic Era Cambrian and
Ordovician History of Minnesota and Wisconsin
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Major Concepts When sea-level rose in the Cambrian and
Ordovician (Sauk and Tippecanoe Trangressions), the mid-continent
of Laurentia was low lying, but with some broad topographic highs
(Wisc. Dome, Transcontinental Arch, Sioux Highland, Taylors Falls
Volcanic Islands) and lows (Hollandale Embayment). Four major
transgressive cycles are represented by stratigraphic sequences of
sandstone shale limestone in Minnesota and Wisconsin. Regressions
are marked by regressive sands capped by unconformities. The purity
and coarseness of the Cambrian and Ordovian quartz sandstone
formations have made them important sources for glass making and
other industrial uses over the decades. However, they are currently
highly sought after as sources of natural proppants for use in
hydrofracing extraction of oil and gas.
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Geologic Timescale in MinnesotaTodaysLecture
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Evolution of the Penokean Mountains St. CLOUD JAY COOKE
HIBBING
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1,000,000,000 Years Ago Minnesota becomes the stable interior
of the North American Continent 500,000,000 Years Ago Shallow seas
begin to periodically flood Minnesota
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Laurentia Set Adrift from Rodinia
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Early Paleozoic Epicontinental Seas
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Distribution of Cambrian Sediments over Laurentia Warping of
the Craton Broad horizontal tectonic stresses related to plate
motion Sediment loading Isostatic adjustments due to different
densities within the crust MCR
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Paleogeography of Middle Laurentia in the Early Paleozoic
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From A. Runkel (MGS) Depositional Environments in Cambrian
Epiric Seas
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Transgression of Depositional Environments
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Regression No Deposition/Erosion The Jordan Unconformity
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Transgressive - Regressive Cycles of the Hollandale
Embayment
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The Actual Picture Storms, Trans-Regress Mini-cycles From A.
Runkel (MGS) Greatly Vertically Exaggerated
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Ordovician Rocks of the Mississippi River Bluffs Indian Mounds
Park Minnehaha Falls Ford Dam and Lock P-Platteville Limestone
G-Glenwood Shale S-St. Peter Sandstone P P P G-- S S S
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Lilydale Park (the Brickyards) Fossil Hunting in the Twin
Cities Lilydale Park (the Brickyards)
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Silica Sand Resources in SE Minnesota and SW Wisconsin Mined
since the late 1800s silica-rich sandstone current and proposed
sand mines In 2012, 70% of US silica sand goes to 30% to Hydro-
fracking for Oil and Gas Currently 36 in WI, 7 in MN, 178 in
US
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Use Silica Sand in Hydrofracing for Oil and Gas Drilling Ideal
Proppant Characteristics Strong - crush resistant Med-crs sand size
(16-70 mesh) Rounded and well sorted Homogeneous physical
properties Low specific gravity Low cost and accessible
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High Purity Quartz Sandstone Formations ~5mm >95% Qtz
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18 =1mm 60=.25mm 100=.15 mm
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OPPOSITION TO EXPANSION OF SILICA SAND MINING Concerns: -
Transportation (truck traffic, road degradation, noise, safety,
dust) high road use taxes, noise and dust abatement - Air quality,
silicosis? wetting, minimal crushing - Water quality and quantity
issues recycling -Landscape alterations reclamation plans up front
- Opposition to end use-hydrofrac drilling for oil and gas Most
operations are currently regulated to varying degrees by State and
County level ordinances. Key questions How does SS mining differ
from aggregate mining that has been practiced and regulated for
decades? What is the magnitude and duration of the expansion?
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Next Lecture The Paleozoic Era The Silurian and Devonian
Periods Part 1 Quiz on Chapter 12 and MaG-Pz