File:Blocher Member-Morgan Trail Member boundary (New Albany Shale, Upper Devonian; Interstate 65 entrance ramp roadcut, Bullitt County, Kentucky, USA) 1.jpg

English: Weathered shales in the Devonian of Kentucky, USA.

These are weathered shales in the New Albany Shale, a Devonian-aged formation in Kentucky, Indiana, Illinois, and eastern Missouri. The unit is dominated by dark-colored marine mudshales of Late Devonian age. These black shales were deposited in a moderately deep, anoxic seafloor environment. This was a widespread lithofacies during the Late Devonian's Global Anoxia Event. The New Albany Shale is equivalent to the Ohio Shale, the Antrim Shale, and the Chattanooga Shale in surrounding states.

The New Albany Shale's member terminology varies from region to region. In southern Indiana and adjacent areas of Kentucky, the New Albany consists of (from the base upward): Blocher Member, Selmier Member, Morgan Trail Member, Camp Run Member, and Clegg Creek Member.

The rocks in the lower part of the photo are the Blocher Member, which consists of dolomitic black shales (dolosiltites, actually). The fissile nature of Blocher rocks is due to post-depositional compaction. Blocher beds are rich in organic carbon and have been homogenized by bioturbation.

The two recessive-weathering, soft, gray shale horizons in the ~middle of the picture are the basal beds of the Morgan Trail Member. The actual lowermost Morgan Trail beds are absent here, as is the entire Selmier Member. So at this site, the Blocher-Morgan Trail contact is an unconformity, and also represents the Frasnian-Famennian boundary. In conformable sections, the Selmier Member-Morgan Trail Member contact is the Frasnian-Famennian boundary.

Unconformities are surfaces of erosion and/or nondeposition of sediments. If the beds above and below the contact have the same orientation (in this case, ~horizontal), the surface is a disconformity or paraconformity. Disconformities have obvious paleotopography along the contact. Paraconformities lack obvious paleotopography, and are often difficult to recognize initially.

The Morgan Trail Member here has black shales with sharp bases, overlain by gray shales. The interbedded gray shale-black shale interval is relatively shallow water. Bedding in the upper Morgan Trail is more massive. Marcasite nodules (FeS2 - iron sulfide; "fool's gold") are present in the upper Morgan Trail Member.

Stratigraphy: Morgan Trail Member unconformably overlying the Blocher Member, New Albany Shale, upper Frasnian Stage to lower Famennian Stage, middle Upper Devonian

Locality: roadcut along the western side of the south-bound entrance ramp to Interstate 65 at the Route 245-Interstate 65 interchange, north-northeast of Belmont & south of Sherpherdsville, south-central Bullitt County, north-central Kentucky, USA (37° 55' 24.45" North latitude, 85° 41' 18.33" West longitude)