Sequence Outcrop Photos

Sequence Boundaries in Devonian Black Shales, Tennessee, Kentucky, and Ohio

A geologic outcrop in DeKalb County, Tennessee, shows the contact between the Chattanooga Shale (Lower Gassaway and Dowelltown members) and the underlying Leipers Limestone (Ordovician), with three people standing at the base for scale.

The red arrow points to the boundary between the Dowelltown and Gassaway members of the Chattanooga Shale. This surface coincides with the Frasnian/Famennian boundary, but the uppermost Frasnian has been removed by erosion.

A geologic outcrop near Coumbus, Ohio, shows the contact between the overlying Lower Huron shale and the underlying Upper Olentangy shale, with a geologic hammer marking the boundary.

The red arrow points out the erosive boundary between the Olentangy Shale (Frasnian) and the Ohio Shale (Famennian, above hammer). The lowermost portion of the Famennian is missing here. It was either eroded or never deposited.

A geologic outcrop in southern Tennessee shows a rock with prominent, labeled horizontal layers and a scale bar of 50 cm, with white dashed lines and arrows indicating subtle truncation surfaces.

Two erosion surfaces in the Gassaway member of the Chattanooga Shale. Both surfaces can be traced over large distances.The upper surface marks the base of the Middle Gassaway member, a lateral equivalent of the Camp Run Member of the New Albany Shale in Kentucky and Indiana.

A large geologic outcrop along a highway in Kentucky shows distinct horizontal layers of Camp Run/Mid-Gassaway and Trousdale shale formations.

The red arrows mark the base of mid-Famennian shales (above) in east-central Kentucky. The package above the arrows is essentially the same as in the picture above. However, the shales below the arrows are Givetian to early Frasnian in age. Contrary to the Tennesse outcrops (above), most of the Frasnian and the lower to mid-Famennian are missing.

A rock outcrop near Sligo Bridge, DeKalb County, Tennessee, shows a heavily fractured and weathered shale section with a person at the base for scale and a red arrow highlighting a potential erosion surface.

The red arrows mark the erosive base of the Upper Gassaway member of the Chattanooga Shale. The shale package below the arrows is the Middle Gassaway member. This surface also marks the base of the Clegg Creek member (New Albany Shale) in Indiana.

A rock outcrop along an interstate in Kentucky shows the contact between the Upper Gassaway/Camp Run and the overlying Upper Huron formations, with a small waterfall and red arrows highlighting specific features.

The red arrows in this image point to the same surface as those in the previous image. The contact is equivalent to the base of the Clegg Creek (Indiana) and Upper Gassaway (Tennessee).

A geological outcrop at Stebbins Gulch, northeast Ohio, shows the contact between the lighter-colored Cleveland Shale and the darker Chagrin Shale, with two red arrows highlighting the boundary.

The red arrows mark the erosive contact between the Cleveland Shale (above) and the Chagrin Shale (below). There are scours and lenses of pebbles (sandstone/siltstone from underlying Chagrin) and sand at the contact. This surface traces all the way into Tennessee.

A rock outcrop in Smith County, Tennessee, shows a well-defined boundary between the Phosphatic Member and the underlying Foerstia beds, with a geologic hammer at the base for scale.

The red arrows point to an erosion surface that juxtapose a Cleveland Shale equivalent (phosphatic member) and shales of the Upper Gassaway member the Chattanooga Shale. The fact that we find the fossil alga Foerstia in the shales just beneath this surface indicates substantial erosion. In eastern Kentucky and Ohio the missing interval would amount to several hundred meters of shale.