Posts Tagged ‘fault zone’

Horseshoe Upheaval

Southern Illinois definitley has an unique feature, known as the Horseshoe Upheaval.

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The rocks are about 350 million years old and were once some 3,500 feet below the surface. The tremendous power of the earth forced them upward. These upturned rocks are silca-rich limestone and chert of the Fort Payne Formation.

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The Fort Payne layer is the deep rust-colored layer in the above illustration. A line marks the location of the upheaval. The narrow wedge is sandwiched on both sides by younger rocks. This suggests the fault system went through two episodes of movement in opposite directions. First the rocks south of the fault zone were uplifted, bringing the Fort Payne rock to the surface. Then the southern block dropped back down. A wedge of the Fort Payne rock was sheared off and jammed in place within the fault zone.

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I left my truck in the picture for size comparison.

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Notice how the layered chert is turned almost vertical

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Walking isn’t the easiest at this site.

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Calcite veining occurs in a lot of the rock.

IMG_6019 redAgain, the layering was pushed vertically from its original positioning.

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Mosses, lichens and a few plants grow in the upheaval.

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Buffy and I climbed up the slope and

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into the bowl-like top of the upheaval. Obviously, the area is better seen before the trees leaf out.

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This shows limestone.

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We didn’t circle the whole top area. Walking wasn’t the easiest.

The Horseshow Upheaval is part of the Saline County Fish and Wildlife Area.

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