Wednesday, November 24, 2010

Watershed Geology

Captina Creek cuts through a section of the state known as the Little Switzerland plateau.  The plateau is part of the larger Western Allegheny plateau and occupies the extreme eastern end of the state, particularly Jefferson, Belmont and Monroe counties.  The upland ridgetops of these counties have horizontally deposited bedrock layers composed of lower Permian Period (~290 myo) sandstones, mudstones and siltstones.  The deeper valleys are composed of limestone rock layers that are slightly older from the upper Pennsylvanian Period (~310 myo).  When bedrock is exposed at the surface it can play a role in determining what types of vegetation become established on a land parcel.

Horizontal layering of shales, mudstones and siltstones.  The
underlying shale layer is much less resistant to weathering and
erodes quicker than the overlying layers of siltstone and mudstone.
The result is a rocky outcrop or overhang that adds diversity to an
ecosystem.  Rock formations like this can support unique plant
communities and provides habitat for reptiles, small mammals and
a diversity of invertebrates.  Siltstones and mudstones are similar
to sandstone but have a smaller grain size making them more brittle
and easier to fracture in some cases.

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