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Earth History GEOL 2110

Earth History GEOL 2110. The Paleozoic Era Part 3: Cambrian and Ordovician History of Minnesota and Wisconsin. Major Concepts.

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Earth History GEOL 2110

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  1. Earth History GEOL 2110 The Paleozoic Era Part 3: Cambrian and Ordovician History of Minnesota and Wisconsin

  2. 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.

  3. Geologic Timescale in Minnesota Today’s Lecture

  4. Evolution of the Penokean Mountains JAY COOKE St. CLOUD HIBBING

  5. 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

  6. Laurentia Set Adrift from Rodinia

  7. Early Paleozoic Epicontinental Seas

  8. 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

  9. Paleogeographyof Middle Laurentia in the Early Paleozoic

  10. Depositional Environments in Cambrian Epiric Seas From A. Runkel (MGS)

  11. Transgression of Depositional Environments

  12. Regression  No Deposition/Erosion The Jordan Unconformity

  13. Transgressive - Regressive Cycles of the Hollandale Embayment

  14. The Actual PictureStorms, Trans-Regress Mini-cycles From A. Runkel (MGS)

  15. Ordovician Rocks of the Mississippi River Bluffs P-Platteville Limestone G-Glenwood Shale S-St. Peter Sandstone P G-- S Indian Mounds Park P Minnehaha Falls G-- S P G-- S Ford Dam and Lock

  16. Fossil Hunting in the Twin CitiesLilydale Park (the Brickyards)

  17. Silica Sand Resources in SE Minnesota and SW Wisconsin Mined since the late 1800’s 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 silica-rich sandstone current and proposed sand mines

  18. 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

  19. High Purity Quartz Sandstone Formations >95% Qtz ~5mm

  20. 18 =1mm 60=.25mm 100=.15 mm

  21. 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-hydrofracdrilling 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?

  22. Next Lecture • The Paleozoic Era • Part 4: The Silurian and Devonian Periods

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