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Indiana Geologic Map

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Indiana's bedrock, mostly hidden, is a grand procession through Paleozoic time raised up by two arches between two basins. (more below)
Indiana's rocks

Created by Andrew Alden from the U.S. Geological Survey's Geologic Map of the United States, 1974, by Philip King and Helen Beikman (fair use policy)

Click the map for a larger version
Bedrock in Indiana is at or near the surface only in the central south end of the state. Elsewhere it's buried by much younger sediment carried down by the glaciers during the ice ages. The thick green lines show the southern limits of two of those glaciations.

This map shows the sedimentary rocks, all of Paleozoic age, that lie between the glacial deposits and the extremely old (Precambrian) basement rocks making up the heart of the North American continent. They are mostly known from boreholes, mines and excavations rather than outcrops.

The Paleozoic rocks are draped over four underlying tectonic structures: the Illinois Basin to the southwest, the Michigan Basin to the northeast, and an arch running northwest to southeast that is called the Kankakee Arch on the north and the Cincinnati Arch on the south. The arches have lifted the layer-cake of rocks so that the younger beds have eroded away to reveal the older rocks beneath: Ordovician (about 440 million years old) in the Cincinnati Arch and Silurian, not quite so old, in the Kankakee Arch. The two basins preserve rocks as young as Mississippian in the Michigan Basin and Pennsylvanian, youngest of all at about 290 million years, in the Illinois Basin. All of these rocks represent shallow seas and, in the youngest rocks, coal swamps.

Indiana produces coal, petroleum, gypsum and huge amounts of stone. Indiana limestone is widely used in buildings, for instance in Washington DC's landmarks. Its limestone is also used in cement production and its dolostone (dolomite rock) for crushed stone. See a gallery of Indiana geological attractions.

More about Indiana Geology

More Indiana resources on About.com:
About Indianapolis
Indiana Maps
Indiana Geography, State Symbols & Facts
Indiana National Parks
Best Indiana State Parks in the Spring
Best Indiana State Parks in the Winter
Indiana Campgrounds
Indiana Campground Reviews

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