GEOLOGY AND GEOMORPHOLOGY OF PARSONAGE CAVE AND MUSTOE-ULCER CAVE IN THE SILURIAN-DEVONIAN HELDERBERG GROUP, HIGHLAND COUNTY, VIRGINIA

Parsonage Cave and Mustoe-Ulcer Cave are located near the community of Mustoe, Highland County, Virginia. Parsonage Cave is above Mustoe-Ulcer Cave, and the two caves have air-flow connection but no human-size connection. Parsonage Cave has a total known passage length of 256 m and the entrance is 32.3 m above the Jackson River, whereas Mustoe-Ulcer Cave has a total known passage length of 188 m and the entrance is 18.3 m above the river. Both caves are maze caves in the Silurian-Devonian Helderberg Group near the axis of a NE-trending anticline. Strata in both caves dip ~5° SE. Parsonage Cave is in cherty beds of the Licking Creek Limestone. In Mustoe-Ulcer Cave, the following 4 stratigraphic units are visible (from top to base):

(4) 2.3 m thick packstone-grainstone of crinoid stems and mm-size fossil debris (New Creek Limestone); exposed in the Bat Room (back of cave);

(3) 1.0-2.1 m thick wackestone with 5-10 cm thick beds and 1 cm thick silty beds (LaVale Member of the Keyser Limestone); forms the entrance passage and most passage ceilings;

(2) 2.4-6.1 m thick packstone with 5-10 cm thick beds and much stromatoporoid debris (Jersey Shore Member of the Keyser Limestone); most of the cave has formed in this unit, which thickens westward within the cave;

(1) >2.1 m thick in-situ stromatoporoid reef boundstone (Jersey Shore Member of the Keyser Limestone); base not seen in the cave.

Passages in Units 3 and 4 are bounded by bedding planes and have rectangular or square profiles. Passages in Units 1 and 2 follow NW or NE trending vertical joints with tall, narrow profiles and prominent vertical fluting on passage walls. Some ~3 m long intervals of passages are nearly filled by clay, with larger clay-free passages on either side.

Mustoe-Ulcer Cave is interpreted as having developed initially near the water table under a low hydrologic gradient where the water had no free surface in contact with air. The location near an anticline crest (greatest flexure) likely facilitated joint enlargement, leading to nearly equal horizontal dissolution along joints during initial cave development. Later, the water table dropped below the cave and the cave filled with mud. Subsequently, surface water entered the cave along ceiling joints (moving vertically down to the lower water table), and removed much of the mud from the cave and created vertical fluting.