Earth History GEOL 2110

Earth History GEOL 2110

The Paleozoic EraCambrian 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 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.

Geologic Timescale in Minnesota

Today’sLecture

Evolution of the Penokean Mountains

St. CLOUDJAY COOKE

HIBBING

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

Laurentia Set Adrift from Rodinia

Early Paleozoic Epicontinental Seas

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

Paleogeography of Middle Laurentia in the Early Paleozoic

From A. Runkel (MGS)

Depositional Environments in Cambrian Epiric Seas

Transgression of Depositional Environments

Regression No Deposition/ErosionThe Jordan Unconformity

Transgressive - Regressive Cycles of the Hollandale Embayment

The Actual PictureStorms, Trans-Regress Mini-cycles

From A. Runkel (MGS)

Greatly Vertically Exaggerated

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

Fossil Hunting in the Twin CitiesLilydale Park (the Brickyards)

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-

fracking for Oil

and GasCurrently 36 in WI, 7 in MN, 178 in US

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

High Purity Quartz Sandstone Formations

~5mm

>95% Qtz

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 EraThe Silurian and Devonian Periods – Part 1

Quiz on Chapter 12 and MaG-Pz