earth history geol 2110 the paleozoic era part 3: cambrian and ordovician history of minnesota and...
TRANSCRIPT
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Earth History GEOL 2110
The Paleozoic EraPart 3: 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 sandstoneshalelimestone 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 Minnesota
Today’sLecture
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Evolution of the Penokean Mountains
St. CLOUDJAY COOKE
HIBBING
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1,000,000,000 Years AgoMinnesota becomes the
stable interior of the North American Continent
500,000,000 Years AgoShallow 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 PictureStorms, Trans-Regress Mini-cycles
From A. Runkel (MGS)
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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--
G--
G--
S
S
S
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Fossil Hunting in the Twin CitiesLilydale Park (the Brickyards)
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Silica Sand Resources in SE Minnesota and SW WisconsinMined since the late 1800’s
silica-rich sandstonecurrent and proposed sand mines
In 2012, 70% of US silica sand goes to
30% to Hydro-
fracing 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 DrillingIdeal 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 EraPart 4: The Silurian and Devonian Periods