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GL / GL Land / Bedrock

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Last updated in September, 2000

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	This page presents the geologic characteristics of the Great Lakes, especially their bedrock. The geologic setting of the Great Lakes basins began far earlier, with the formation of the bedrock in which these basins occur. The foundation for the present Great Lakes basin was set about 3 billion years ago, during the Precambrian Era. Most bedrocks are composed of sedimentary rock of Paleozoic age (roughly 200 to 600 million years old), but the rock surrounding Lake Superior, the northernmost and deepest of the Great Lakes, is much older igneous and metamorphic rock, Pre-Cambrian in age (one to two billion years old). These igneous and metamorphic rocks were formed by mountain-making processes-volcanoes, intrusions and metamorphism-that were active through much of Pre-Cambrian time. Igneous and metamorphic rocks are the most resistant rocks of all in the Great Lakes region, so the land around the Lake Superior basin is especially high and hilly. These very old rocks actually occur down below the younger, Paleozoic sedimentary rock in the south, forming the so-called Pre-Cambrian "basement" rocks there. Northwards they rise nearer the surface until they occur at the surface, forming a broad Pre-Cambrian upland around the Lake Superior basin and throughout much of Canada, called the "Canadian Shield." Granitic rocks of the shield extend southward beneath the Paleozoic, sedimentary rocks where they form the 'basement' structure of the southern and eastern portions of the basin (Forsyth, 1996; The Great Lakes: An Environmental Atlas and Resource Book, 1995).

	1. What type of bedrocks were composed in the Great Lakes basin? 2. What was Earth's environment like when the rocks of the Great Lakes basin were formed?

	GS-006 The fossil fauna of the islands region of western Lake Erie. GS-017 Kelley's Island glacial grooves. GS-018 Guide to Put-in-Bay (South Bass Island, Ohio): Historical places, natural features, and island ecology. EP-079 The Great Lake Erie. - Chapter 2. The Geological Setting of the Great Lakes EP-014 Geography of The Great Lakes To request these materials, please visit OSG website.

	1. Earth Systems - Education Activities for Great Lakes Schools Land & Water Interactions in the Great Lakes When did the rocks in the Great Lakes basin form? How were sedimentary rocks in the Great Lakes basin formed? How did rocks and rivers shape the Great Lakes? What evidence of glaciation exits in the Great Lakes region? What evidence of glaciation and geologic processes can be found on Great Lakes beaches?

	Geology and Mineral Resources source: The Great Lakes: An Environmental Atlas and Resource Book (1995)
	Geologic Time Chart. The Great Lakes basin is a relatively young ecosystem having formed during the last 10,000 years. Its foundation was laid through many millions of years and several geologic eras. This chart gives a relative idea of the age of the eras. source The Great Lakes: An Environmental Atlas and Resource Book (1995)
	Lake Erie Bathymetry From Great Lakes Forecasting System (GLFS)
	1. Natural Process in the Great Lakes: Geology http://www.epa.gov/glnpo/atlas/glat-ch2.html#1 2. Lake Erie Facts and Figures http://www.great-lakes.net/refdesk/almanac/lakes/eriefact.html 3. History of Lake Erie http://www.dnr.state.oh.us/odnr/geo_survey/lakeerie/lefact1.htm 4. Great Lakes Science Center - USGS http://www.glsc.usgs.gov/ 5. Digital geologic map and mineral deposits of the Lake Superior region http://minerals.usgs.gov/pubs/of97-455/superior.html 6. Great Lakes Environmental Research Laboratory (GLERL) http://www.glerl.noaa.gov/pr/about/mission.html 7. Great Lakes Forecasting System (GLFS) http://superior.eng.ohio-state.edu/nf-index.html

Copyright 1999. Ohio Sea Grant College Program and Earth Systems Education Program of The Ohio State University

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