APPEARANCE OF A PALE BLUE GREEN FOSSILIFEROUS BED IN PREDOMINANTLY RED BEDS OF THE HINTON FORMATION IN SOUTHERN WEST VIRGINIA

Close inspection of a 20 cm thick, pale blue green, calcareous, argillaceous mudstone bed with a monoculture of myalinids sandwiched between red beds of mudstone and sandstone in the lower Hinton Formation of the Mauch Chunk Group (Upper Mississippian) along the Bluestone Lake in Summers County, West Virginia reveals a fairly sharp contact at the base of the bed and a more gradual contact at the top of the bed. The color and fossil content of the bed suggest the sediments of which the bed is comprised were deposited in a non-oxidizing, low energy environment with low organic carbon content, somewhere within the inner to outer shelf in shallow marine conditions. A microscopic examination of a crushed sample of the pale blue green bed did not reveal any indications of glauconite. The bed may reflect a rise in sea level and a concommitment reduction or hiatus in fluvial sediment input in the basin. The lower contact is sharp, underlain with dull red violet, fine-grained sandstone which fines up into a dull red violet mudstone. In some areas, however, the contact isn't as sharp, some of the dull red violet mudstone interpenetrating the pale blue green mudstone and vice versa over a vertical distance of 1-2 cm, possibly bioturbation at the interface. The base of the pale blue-green zone is a limey mud with calcium carbonate nodules (to 2 cm dia.). The entire pale blue green zone contains myalinids which appear to comprise a significant percentage (5 to 25 %) of the bed. The upper contact is a more gradual change from the pale blue green mudstone into a dark red maroon friable mudstone over a vertical distance of 4-7 cm. It is speculated that glacioeustatic events (or alternatively, subsidence or tectonoeustatic events) resulted in a rapid rise in sea level with a concommittment reduction in fluvial input, resulting in the deposition of the pale blue green mudstone bed. An alternative explanation giving rise to the pale blue green bed (with or without a rise in sea level) might have been a temporary reduction in atmospheric (and aqueous) oxygen content, providing a non-oxidizing environment for deposition.