Cleveland Shale

The Cleveland Shale, also referred to as the Cleveland Member of the Ohio Shale, is a Late Devonian shale geologic member in the eastern United States.

Identification and name

The Cleveland Shale was identified in 1870 and named for the city of Cleveland, Ohio. John Strong Newberry, director of the Ohio State Geological Survey, first identified the member in 1870. He called it the "Cleveland Shale" and designated its type locality at Doan Brook near Cleveland. Details of the type locality and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database.

Description

The primary minerals in the Cleveland Shale are chlorite, illite, pyrite, and quartz. Underground, the Cleveland Shale is black, dull grayish-black, bluish-black, or brownish-black in color. In exposed outcrops, it weathers to red, reddish-brown, or medium brown. Highly weathered rock turns gray. It is fairly fissile, breaking into thin, irregularly shaped sheets or flakes that occasionally display crystals of pickeringite. Relieved of stress once exposed, the Cleveland Shale is nonplastic and can appear as if fragmented into blocks due to jointing.

Pyrite basal boundary

There is a sharp and clear distinction between the Cleveland Shale and underlying Chagrin Shale. At the very bottom of the Cleveland Shale there is a thin, discontinuous layer of pyrite. This pyrite layer is discontinuous because after this rock was laid down, it was eroded. The erosion increases as one moves south along the valley of the Cuyahoga River and east to the Grand River. Portions of the pyrite layer, known as Skinner's Run Bed, contain fragments of petrified wood and fossilized fish bones worn smooth by the action of water. Above the pyrite layer, a limestone layer is found in west-central Ohio.
The remainder of the Cleveland Shale generally consists of a relatively hard, organic rich oil shale. It has both an upper and lower part.

Lower part

A clay shale, described as bluish or bluish-gray and as olive-black to brownish-black, forms the lower part. The lower part can be anywhere from a few inches to several feet in thickness. This layer is sometimes referred to as the Olmstead shale. This layer has been dated to between 362.6 and 361.0 million years old based on conodont biozones. Thin beds of gray or brown siltstone, lumps of pyrite, and layers of silica-heavy limestone with cone-in-cone structures are found in the lower part. In eastern Ohio, thin gray veins of siltstone appear. In western Ohio, the Cleveland Shale appears to interbed with the Chagrin Shale below it, erasing the clear boundary between the two rock units.

Upper part

The upper part of the Cleveland Shale is a black to brownish black silty shale with occasional thin beds of gray shale and siltstone. The upper part is much richer in petroleum and kerogen. When broken open, fresh samples smell like crude oil. Where the upper part is thick, and particularly in northeast Ohio, the shale has a distinctive "rippled" appearance. The upper of the Cleveland Shale contains abundant nodules of phosphate, nodules and bands of pyrite, bands of calcisiltite, and lamination. Almost no concretions are found in the upper part.

Geographic extent

The Cleveland Shale is a shale geologic member in Ohio in the United States.
The Cleveland Shale underlies much of northeast Ohio in beds of varying thickness.
In northeast Ohio, the member does not appear east of the Grand River.
Measurements taken in northeast Ohio show the Cleveland Shale to be to thick. It is thickest around the Rocky River north of Berea, Ohio, and thins to the east, west, and south.
The Cleveland Shale is found in east-central Kentucky. In east-central Kentucky, the Cleveland Shale is more uniform in thickness, ranging from, and increases in thickness toward the east.
The unit is also present in West Virginia and in southwest Virginia, where it is mapped as the Cleveland Member of the Ohio Shale.

Stratigraphic setting

The Cleveland Shale is a sub-unit of the Ohio Shale Formation. The Chagrin Shale underlies the Cleveland Shale. The Bedford Shale generally overlies the Cleveland Shale, with a sharp distinction between the two. In west-central Ohio, more than of Bedford Shale may lie above the Cleveland Shale. In places, red and grey shale may intertongue with the Cleveland Shale extensively. In far eastern Ohio, the Bedford Shale thins by more than. Where the Cussewago Shale is also present, the Bedford Shale is usually less than and may be locally absent. In some areas, the Cleveland Shale is described as overstepped or unconformably overlaid gradationally by Berea Siltstone and sharply by Berea Sandstone.
It is the regional equivalent of the Hangenberg Black Shale and the Bakken Shale.

Paleobiota

Exceptional marine animal fossils are found in the member. The Cleveland Shale is generally considered to be fossil-poor, but there are exceptions. The basal pyrite layer contains petrified wood and fossilized fish bones. The lower part is famous for its extensive and well-preserved fossil Chondrichthyans, Conodonts, Placodermi, and palaeoniscinoids ray-finned fishes. The giant predatory placoderms Dunkleosteus terrelli, Gorgonichthys clarki, Gymnotrachelus hydei, Heintzichthys gouldii, and five species of Titanichthys were all discovered in the Cleveland Shale. The Cleveland Shale is classified as a konservatte-lagerstatten, which means it often preserves complete body fossils. Typical early shark preservation includes soft tissue outlines and impressions, fin rays, gill musculature, cartilage, and stomach contents. Placoderms in the Cleveland Shale typically do not show any good soft-tissue preservation.
Faunal list follows Carr and Jackson and Carr.

Placodermi

All placoderms in the Cleveland Shale are arthrodires.

Genus	Species	Notes	Images
Bungartius	B. perissus	A medium-sized mylostomatid with a relatively low and narrow skull and a presumably durophagous diet.
Callognathus	C. regularis	A rare possible selenosteid based on small jaw plates.
"Coccosteus"	"C." cuyahogae	A rare coccosteomorph of uncertain affinities, based on a single jaw plate. Not necessarily a close relative of more complete and better-described species of Coccosteus.
Diplognathus	D. mirabilis	A somewhat large aspinothoracid with narrow serrated jaws.
Dunkleosteus	D. terrelli	A very large dunkleosteid with a massive bite force and an apex predator niche. The most famous placoderm in general, as well as one of the largest and most common fish in the Cleveland Shale. Previously considered a species of Dinichthys.
Glyptaspis	G. verrucosa	A rare arthrodire of uncertain affinities, known from a few roughly-textured belly plates.	-
Gorgonichthys	G. clarki	A very large aspinothoracid, similar in size and ecology to Dunkleosteus. Previously considered a species of Dinichthys.
Gymnotrachelus	G. hydei	A selenosteid with a low, broad skull and small tooth-like denticles along the jaw.
Heintzichthys	H. gouldii	An aspinothoracid with a boxy skull. Previously considered a species of Dinichthys.
Hlavinichthys	H. jacksoni	An aspinothoracid.
Holdenius	H. holdeni	An aspinothoracid similar to Heintzichthys, though with a deeper jaw.
Hussakofia	H. minor	A small dunkleosteid with a very short, deep jaw.
Mylostoma	M. eurhinus	A mylostomatid with a very broad skull.
Mylostoma	M. newberryi	A mylostomatid with a very broad skull.
Mylostoma	M. variabile	A mylostomatid with a very broad skull.
Paramylostoma	P. arcualis	A small selenosteid with a narrow skull.
Selenosteus	S. brevis	A small selenosteid with a broad skull.
Stenosteus	S. angustopectus	A small selenosteid similar to Selenosteus, with a broad skull.
Stenosteus	S. glaber	A small selenosteid similar to Selenosteus, with a broad skull.
Titanichthys	T. agassizi	A very large filter-feeding mylostomatid based on multiple species, some of which may be synonyms. The second most common placoderm in the Cleveland Shale after Dunkleosteus terrelli. Titanichthys hussakofi was formerly known as Brontichthys clarki.
Titanichthys	T. attenuatus	A very large filter-feeding mylostomatid based on multiple species, some of which may be synonyms. The second most common placoderm in the Cleveland Shale after Dunkleosteus terrelli. Titanichthys hussakofi was formerly known as Brontichthys clarki.
Titanichthys	T. clarkii	A very large filter-feeding mylostomatid based on multiple species, some of which may be synonyms. The second most common placoderm in the Cleveland Shale after Dunkleosteus terrelli. Titanichthys hussakofi was formerly known as Brontichthys clarki.
Titanichthys	T. hussakofi	A very large filter-feeding mylostomatid based on multiple species, some of which may be synonyms. The second most common placoderm in the Cleveland Shale after Dunkleosteus terrelli. Titanichthys hussakofi was formerly known as Brontichthys clarki.
Titanichthys	T. rectus	A very large filter-feeding mylostomatid based on multiple species, some of which may be synonyms. The second most common placoderm in the Cleveland Shale after Dunkleosteus terrelli. Titanichthys hussakofi was formerly known as Brontichthys clarki.
Trachosteus	T. clarki	A rare possible selenosteid known from a few armor fragments.