GEOLOGY AND GEOMORPHOLOGY OF OWL CAVE (SIPHON NO. 1 CAVE) IN THE SILURIAN-DEVONIAN KEYSER LIMESTONE, HIGHLAND COUNTY, VIRGINIA

Owl Cave is located in Silurian-Devonian strata on the west flank of Chestnut Ridge in Highland County, Virginia. The cave has two levels, and total known passage length of 959 m. The westernmost part of Owl Cave is located near the axis of the northeast-trending Chestnut Ridge anticline, and strata in the cave dip away from the anticline axis at angles of <6°.

The following eight beds are visible in Owl Cave (from top to base):

(8) 1.5 m thick bed of packstone-grainstone with chert nodules at base;

(7) 0.6 m thick bed of green shale with laminations;

(6) 2.0 m thick bed of packstone-grainstone with wavy laminations, mm-thick shale laminations, crinoid and brachiopod fragments;

(5) 4.0 m thick bed of packstone-grainstone with wavy laminations, ribbon chert, bryozoan and brachiopod fragments;

(4) 2.0 m thick bed of packstone-grainstone with wavy laminations, crinoid and brachiopod fragments;

(3) 2.6 m thick bed of packstone-grainstone with fragments of stromatoporoids, Favosites, and algal mats;

(2) 0.6 m thick bed of packstone-grainstone with fragments of stromatoporoids and Favosites at main entrance of cave, grading north into wackestone-packstone with black ribbon chert;

(1) 0.5 m thick bed of wackestone to packstone.

The lower level of the cave is mostly within Beds 1-6, which are mapped as the Jersey Shore Member of the Keyser Limestone. Most of the lower level consists of keyhole-shaped passages at the contact between two beds (e.g., Beds 3 and 4). Most of the upper level is within Bed 6-8. Bed 7 is mapped as the La Vale Member of the Keyser Limestone. Bed 8 is mapped as the New Creek Limestone. Most of the upper level consists of narrow passages that follow joints primarily within one bed (e.g., Bed 6). Shale (Bed 7) forms the ceiling of much of the upper level.

The upper level of Owl Cave is interpreted as having formed within the phreatic zone with water confined below the shale (Bed 7) and horizontal passage enlargement occurring along joints. This setting is similar in nearby caves (Butler Cave, Breathing Cave) where a sandstone bed forms the cave ceiling and is thought to have been a barrier to water movement during cave formation. In contrast, the lower level is interpreted as having formed later as the water table fell and passage enlargement occurred preferentially along bedding planes at the top of the water table (top of phreatic zone).