Earth History
GEOL 2110
The Paleozoic Era
Cambrian and Ordovician History of
Minnesota and Wisconsin
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.
Geologic Timescale in Minnesota
Today’s
Lecture
Evolution of the Penokean Mountains
JAY COOKE
HIBBING
St. CLOUD
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
Laurentia Set Adrift from Rodinia
Early Paleozoic Epicontinental Seas
Distribution of Cambrian Sediments
over Laurentia
MCR
Warping of the Craton
• Broad horizontal
tectonic stresses
related to plate
motion
• Sediment loading
• Isostatic adjustments
due to different
densities within the
crust
Paleogeography of Middle Laurentia in
the Early Paleozoic
Depositional Environments
in Cambrian Epiric Seas
From A. Runkel (MGS)
Transgression of Depositional Environments
Regression  No Deposition/Erosion
The Jordan Unconformity
Transgressive - Regressive Cycles
of the Hollandale Embayment
The Actual Picture
Storms, Trans-Regress Mini-cycles
Greatly Vertically Exaggerated
From A. Runkel (MGS)
Ordovician Rocks of the Mississippi River Bluffs
P-Platteville Limestone
G-Glenwood Shale S-St. Peter Sandstone
G--
P
S
Indian Mounds Park
Minnehaha Falls
P
G--
S
P
G-S
Ford Dam and Lock
Fossil Hunting in the Twin Cities
Lilydale Park (the Brickyards)
Silica Sand Resources in SE Minnesota and SW Wisconsin
Mined since the late 1800’s
silica-rich sandstone
current and proposed sand mines
Currently 36 in WI, 7 in MN, 178 in US
In 2012,
70% of US
silica sand
goes to 
30% to
Hydrofracking
for Oil
and Gas
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
High Purity Quartz
Sandstone Formations
>95% Qtz
~5mm
18 =1mm
60=.25mm
100=.15 mm
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?
Next Lecture
The Paleozoic Era
The Silurian and Devonian Periods – Part 1
Quiz on Chapter 12 and MaG-Pz