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What types of rocks and sediments occur in the Great Lakes basin?

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Great Lakes Marquette Harbor Lighthouse on Lake Superior, Marquette, Michigan.

The Great Lakes basin features a diverse array of rock types and sediments, largely shaped by the region's glacial history and broad geographic extent.1

Bedrock Composition

The underlying geology of the basins consists of two primary types:
* Canadian Shield: Ancient rocks that cover portions of the Lake Superior and Lake Huron basins.1
* Paleozoic Sedimentary Rocks: These make up the remainder of the basins.1

Sediments and Deposits

The distribution of surface materials is heavily influenced by glacial activity and proximity to the shoreline:1
* Near-shore deposits: Large deposits of sand and gravel are commonly found near the lakeshores. Additionally, limestone outcrops are present in various areas.1
* Deep-basin deposits: The deeper areas of the lakes are characterized by the presence of glacial clays and organic sediments.1

These materials are part of a broader legacy of the Pleistocene Epoch, during which massive glaciers scoured the landscape, leaving behind fresh landforms and extensive glacial debris throughout the region.12