The geologic history which follows is based almost entirely on Gary Kihn’s master’s thesis, which he completed in December 1988, and a paper based on Kihn’s thesis authored by Dr. Lon C Ruedisili, Gary Kihn and Richard C Bell published in The Ohio Journal of Science Volume 90, Number 4, September, 1990.
Several short studies had been completed on Seneca Caverns prior to Kihn’s study. Short and Bell (1970) presented a brief description of the cavern in a geologic report for Woodward-Clyde Consultants and theorized that Seneca Caverns is a collapse or breakdown-type cavern due to deep-seated solution activity. The Seneca Cavern fracture system is developed in rock strata deposited during the Devonian period of geologic time and probably extends downward into rock of Silurian period age.
The cavern is a solution collapse or break-down type cavern at the confluence of two (2) major fractures in the middle Devonian Columbus and Lucas Formations and possibly the underlying Silurian strata.
Evidence for this collapse is visible in the southern wall or block, which has moved or slipped downward approximately eight feet (2.5 meters) and is highly shattered and jumbled. In many rooms the floor appears to fit into the ceiling much like a jigsaw puzzle. This collapse process seems similar to that proposed by geologists Verber and Stansberry (1953) for the caves on South Bass Island (Put-In-Bay). The collapse was probably initiated by the conversion of anhydrite to gypsum in the underlying Bass Island Group. The expansion process during the conversion may have led to a 33%-62% (White 1926) increase in volume which would be instrumental in deforming overlying stratified rock, resulting in vertical as well as lateral fracturing. The gypsum (CaSO4●2H2O), being very soluble, was then dissolved by ground water moving vertically through joints and fractures in the rock.
Level one (1) and two (2) and the upper portion of level three (3) in Seneca Caverns are composed of the middle member of the Columbus Formations which is a light-gray, medium to massively bedded limestone about 30 feet (11 meters) in thickness. A distinct horizon containing abundant fossil specimens of the brachiopod Brevispirifer gregarious is found in the ceiling of level one while Muscrospirifer mucronatus is found in the ceiling of level two. Other fossils present in this member included the brachiopods Leptorhynchus sp., Schizophora proinpa, Chonetes sp; the horn corals Heliophyllum halli, Zaphrentis corniculum, and the Gastropod (snail) Tentaculites scalariformis.
Located about mid-way through Tin Pan Alley (upper third level), is the Juan Vicente’ fossilized armored fish. Discovered in 1991 by Seneca Caverns’ tour guide Juan Vicente’, it is the largest and most significant fossil feature in the caverns. Although the existence of the armored fish in Devonian strata is well known to paleontologists, they are not common nor are they frequently found.
The fossil is embedded I the Middle Devonian Columbus limestone and therefore lived about 385 million years ago. Michael Hanson, Paleontologist with the Ohio Division of Geological Survey, has tentatively identified it from photographs as Macropetalichthys (macro-petal-ithees) sullivani (sull-i-vani).
Level four (4) and the upper portion of level five (5) are composed of the lower- most member of the Columbus formation. It is massive, light-gray limestone six feet (2 meters) thick, contains gray to white layers and nodules of chert. No fossils have been found in this member.
Level four (4) and the upper portion of level five (5) are composed of the lower-most member of the Columbus Formation which is light brown, massive dolomitic limestone or dolostone which is 25 feet (8 meters) thick. It does not contain many fossils but the horn coral Zaphrentis corniculum is present in the upper 3 feet (1-meter).
The lower half of level five (5) exhibits a drastic and abrupt color change in the bedrock. It changes from light gray to light brown and has been determined to be highly dolomitic limestone or dolostone.
Levels six (6) and seven (7) contain an appreciable amount of chert and abundant coral fossils both of which are indicative of the upper portion of the Lucas Formation. The contact between the Columbus Formation and the underlying Lucas Formation probably exists in Seneca Caverns.
An in-depth study of aerial photography, satellite photography, topographic maps, published scientific articles (Kihn 1988) (Stith 1997) and a professional survey of the caverns to established vertical and horizontal control (Kihn, Gallagher, Bell 1987), revealed that Seneca Caverns formed at the intersection of two (2) major fractures (Stith 1997) in the Columbus Limestone.
The fracture containing Seneca Caverns trends NE/SW while the intersecting fracture trends NW/SE. The dip or slant of the NE/SW while the intersecting fracture as, measured in the cavern, and is 40˚NW.
The total vertical extent (depth) of the fracture has not yet been determined because of the presence of the water in the lower portion of the cavern.
The rooms in Seneca Caverns are generally rectangular in shape and are controlled by the joint patterns in association with natural cleavage controlled fracturing.
The study confirmed the existence of a very distinct nearly right angle fracture pattern within the study area. The dominant trend of this pattern is NE/SW. The less dominant trend is NW/SE. Armstrong (1976) theorizes that this fracture pattern has resulted from stress generated in the Findlay Arch region, about 40 miles (52 kilometers) west of the caverns. This stress probably developed as the rock in the Appalachian Basin, to the East, and Michigan Basin, to the NW settled at different rates.