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Ohio's Ice Age

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Although difficult to imagine, Ohio has at vari- ous times in the recent geologic past (within the last 1.6 million years) had three-quarters of its surface covered by vast sheets of ice perhaps as much as 1 mile thick. This period of geologic history is referred to as the Pleistocene Epoch or, more commonly, the Ice Age, although there is abundant evidence that Earth has experienced numerous other “ice ages” throughout its 4.6 billion years of existence.
Ice Age glaciers invading Ohio formed in cen- tral Canada in response to climatic conditions that allowed massive buildups of ice. Because of their great thickness, these ice masses flowed under their own weight and ultimately moved south as far as northern Kentucky. Oxygen-isotope analysis …show more content…

When the entire ice sheet receded be- cause of melting, much of the ground-up rock mate- rial still held in the ice was deposited on the surface as ground moraine. The oldest morainic deposits in Ohio are of Illinoian and pre-Illinoian age. Ero- sion has significantly reduced these deposits along the glacial boundary, leaving only isolated rem- nants that have been mapped as dissected ground moraine and hummocky …show more content…

Lake deposits are primarily fine-grained clay- and silt-size sediments. The most extensive area of lake deposits is in north- ern Ohio bordering Lake Erie. These deposits, and adjacent areas of wave-planed ground moraine, are the result of sedimentation and erosion by large lakes that occupied the Erie basin as Wisconsinan-age ice retreated into Canada. Other lake deposits accumulated in stream valleys whose outlets were temporarily dammed by ice or outwash. Many outwash-dammed lake deposits are present in southeastern Ohio far beyond the glacial boundary. Peat deposits are associated with many lake deposits and formed through the accu- mulation of partially decayed aquatic vegetation in oxygen-depleted, stagnant water.
The term glacial drift commonly is used to re- fer to any material deposited directly (e.g., ground moraine) or indirectly (e.g., outwash) by a glacier. Because the ice that invaded Ohio came from Canada, it carried in many rock types not found in Ohio. Pebbles, cobbles, and boulders of these foreign rock types are called erratics. Rock collect- ing in areas of glacial drift may yield granite, gneiss, trace quantities of gold, and very rarely, diamonds. Most rocks found in glacial deposits, however, are types native to

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