OOLITIC LIMESTONE BED WITHIN APPALACHIAN ACADIAN FLYSCH (MIDDLE DEVONIAN MAHANTANGO FORMATION), NE WEST VIRGINIA- INFLUENCE OF A FOREBULGE?

In northeastern West Virginia, near Wardensville (Hardy County), a 30 to 50 cm thick bed of oolitic limestone occurs within the Middle Devonian Mahantango Formation. The Mahantango at this locality is well exposed, is about 280 m thick, is an overall somewhat progradational sequence of marine flysch facies shale and siltstone, and is very fossiliferous. The Mahantango deposits were derived from an easterly source area during one of the early phases of the Acadian orogeny. The oolitic limestone is massive and contains abundant crinoid debris and very little siliciclastic contamination. It occurs near the middle of the Mahantango, about 10 m beneath the base of an unnamed massive siltstone. An outcrop gamma ray log of a portion of the exposure has been correlated with subsurface gamma ray logs from as close as 10 km away (the oolitic limestone appears on logs as a distinct, unique, low radiation spike). The oolitic limestone bed has been identified in the subsurface over an area extending 80 km north and 50 km west of Wardensville, but only its western limit has been defined at this time. The occurrence of this unique lithology within flysch implies cessation of transport into the area of siliciclastic material, as well as shallow water depths, during the time of its deposition. Deposition may have taken place in a bathymetrically positive area at shoal depths remote from shores as a result of uplift of a tectonic forebulge. It should be noted that recent work has suggested that a Late Devonian early Famennian forebulge was located in a similar geographic position.