1. Part 3: Cambrian and Ordovician History of Minnesota and Wisconsin
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

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

7. 1,000,000,000 Years Ago 500,000,000 Years Ago Minnesota becomes the
stable interior of the
North American Continent
500,000,000 Years Ago
Shallow seas begin to
periodically flood Minnesota

8. Laurentia Set Adrift from Rodinia

9. Early Paleozoic Epicontinental Seas

10. 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

11. Paleogeography of Middle Laurentia in the Early Paleozoic

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

14. Transgression of Depositional Environments

15. Regression  No Deposition/Erosion
The Jordan Unconformity

16. Transgressive - Regressive Cycles of the Hollandale Embayment

17. The Actual Picture Storms, Trans-Regress Mini-cycles
From A. Runkel (MGS)

18. 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

19. Fossil Hunting in the Twin Cities Lilydale Park (the Brickyards)

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

21. 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

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

23. 18 =1mm =.25mm =.15 mm

24. 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?

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