Personal Blurb
I was born and raised in Michigan. The Great Lakes and the geology that can be found there, particularly in the Upper Peninsula will forever hold a place in my heart.
I was born and raised in Michigan. The Great Lakes and the geology that can be found there, particularly in the Upper Peninsula will forever hold a place in my heart.
The Geology of Michigan: an Overview
To an untrained observer, the geology of Michigan resembles a "bulls-eye" pattern, with the youngest rocks painting the core of the state (Fig. 1). This is reflective of the structural geology of Michigan, a large basin, which likely formed due to some combination of rebound from uplift generated during plume magmatism ~1 billion years ago (see "The Mid-Continent Rift") and depression of the crust during widespread glaciation. Most of the bedrock in the Lower Peninsula is covered by glacial materials and soil, however rare outcrops of Pennsylvanian sandstone can be found in the center of the state and excellent outcrops of Devonian shallow marine fossils, particularly reef building organisms can be found in the northern part of the Lower Peninsula, spanning an arc along the lake shore from near Traverse City to Alpena. These Devonian reefs are also the source of the state stone, the Petoskey Stone, which is the fossilized coral Hexagonaria. Unlike the lower peninsula, the Upper Peninsula (U. P.) is rich in bedrock exposure with exquisite outcrops like Pictured Rocks and Jasper Knob, a beautiful exposure of banded iron formation. Beyond the visual appeal of some of the upper peninsula's geology, it also hosts fascinating finds like the ~2 billiion year old stromatolites in the Kona Dolomite and tsunami deposits related to the Sudbury impact. |
Fig. 1 Geologic map of the Michigan basin. Image credit: michigan.gov
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Michigan's Geologic Resources
The Lower Peninsula The Lower Peninsula is home to a wide array of natural resources. Historically, coal was mined in the interior of the state along narrow seems in Pennsylvanian limestone and was used for heating homes and furnaces in factories, some of these seems can still be found at Fitzgerald Park near Lansing. Additionally, if you've ever been on a road trip through the lower peninsula you have likely seen pump heads for natural gas wells in fields and forests along the highway. From a materials and construction perspective, Grand Rapids used to be home to a large gypsum mine, which has since been converted to storage for Founders Brewing (Fig. 2), and deep below Detroit is a large, potentially economic deposit of salt. Michigan is also fortunate in that it boasts large outcrops of limestone which can be used for construction, such as the quarries in Alpena, and it has abundant sand and gravel. The Upper Peninsula The U. P. is widely known as "Copper Country" due to the abundant native copper that can be found along the shores of Lake Superior (Fig. 3). In addition to copper, other precious metals such as silver and gold were historically mined in small deposits. Currently, Eagle Mine is in operation and extracts a high grade Ni and Cu ore from an unexposed massive sulfide deposit. There are also several historic and operating iron mines in the U. P. Beyond metals, the U. P. also hosts the Jacobsville Sandstone, a burnt red sandstone, along the shores of Lake Superior. This important historic building stone can be found throughout the U. P. as well as in many buildings in the lower peninsula, such as throughout the campus of Michigan State University. |
Fig. 2 Barrels of beer stored in the former gypsum mine beneath Grand Rapids. Image credit: Detroit Free Press
Fig. 3 Nineteen ton piece of native copper named "Lake Copper" that was extracted from Great Sand Bay and is on display at Michigan Technological University. Image credit: Michigan Technological University
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The Mid-Continent Rift
Approximately 1 billion years ago, a section of Earth's crust spanning from Oklahoma through Michigan and to Alabama in an arc began pulling apart (Fig. 4). This structure, known as the Mid-Continent Rift, is thought to be a hybrid structure generated both by plate movements and interaction with a mantle plume. Interaction with the mantle plume resulted in a large quantity of magma being erupted, now known as the Keweenawan Large Igneous Province (KLIP). KLIP lava flows can be found at several locations throughout the U.P. and along the shores of Lake Superior. Outcrops of these lava flows can be found at Interstate Park and Porcupine Mountains State Park in addition to parks throughout Wisconsin, Minnesota, and Canada. More information on the Mid-Continent Rift can be found in articles from the NPS, EOS, and national geographic. |
Fig. 4 Map showing structural extent of the Mid-Continent Rift in North America. Figure credit: Stein et al. (2018)
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