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Mahantango - Mid Devonian

Geology 364 - Stratigraphy and Basin Analysis
Dept. of Geology and Environmental Studies
James Madison University
Lynn S. Fichter


     The Mahantango is exposed in this small quarry. If it were not for the quarry we would be hard pressed to see anything or make any interpretation. Just around the corner the normal outcrop is so badly weathered that it looks more like a thin bedded shale than a sandstone.
     But recall that the bedding was thick, and the sandstones amalgamated. Only a few rare thin shale beds can be found between the sandstones; other reactivation surfaces are scours. The beds tend to maintain thickness for long distance, except where they are scoured. This means the bottoms may undulate while the tops are deposited flat.
     Internally the beds are mostly massive, although sometimes towards the top are plane bed (HVL's). (And remember all the plumos structure we saw that was confusing). Scattered fossils are also present, and sometimes a concentration of fossils (mostly crinoids and brachiopods).
     This is the closest outcrop I know to a basin floor fan system; at least the well log signature's for basin floor fans I have seen would sure seem to translate into something looking like this.
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