OBSERVATIONS on DISTAL SEQUENCES IN FAMENNIAN BLACK SHALES OF CENTRAL KENTUCKY AND THEIR IMPLICATIONS FOR RECONSTRUCTING DEPOSITIONAL SETTINGS

Famennian black shales in central Kentucky, deposited near the crest of the Cincinnati Arch, show closely spaced truncation surfaces in a stratigraphic interval that is correlative with the Camp Run Member of the New Albany Shale of Indiana. A total of four erosion bounded packages, ranging in thickness from 0.5 to 1 m, are exposed. Truncation surfaces are undulose-inclined and display angular contact of juxtaposed packages. Typically truncation surfaces are shale-on-shale, erosion occurred into a firm substrate, and there is no or only minimal development of boundary lags.

The basal portion of each package contains discontinuous sandy beds with load casts. Dolomite cemented sandy beds consists predominantly of rounded carbonate (now dolomite) grains with an admixture of fossil debris, rounded quartz grains, and glauconite. Grains of this type do not occur in underlying Devonian black shales and must have been derived from older carbonate strata (Ordovician through mid-Devonian age) that form the core of the Cincinnati Arch.

Collectively, the truncation surfaces and their associated features attest to repeated sea-level drop (erosion) and rise (shale accumulation), as well as erosion and exposure of older units on the crest of the Cincinnati Arch during sea level drops. Our observations also imply that the Camp Run Member of the New Albany Shale in Indiana should consist of at least four sequences. None have been documented so far, and this probably reflects the greater distance between the crest of the Cincinnati Arch and Indiana locations (greater water depth). What are clear sequence boundaries in central Kentucky tends to become less pronounced as we go east or west of the crest of the Cincinnati Arch, and will over a distance turn into a "correlative conformity" that is easily missed in core or outcrop. How to recognize these surfaces in distal locations is a subject of ongoing investigations.