Silurian rocks in Kentucky are exposed on the eastern and western flanks of the
Cincinnati Arch, a large wavelength cratonic structure separating the Appalachian
foreland basin from the intracratonic Illinois Basin. The arch experienced uplift during
latest Ordovician-Early Silurian time, so that the exposed Silurian section is relatively
thin due to onlap and post-Silurian erosional truncation on the arch. On both flanks of the
arch, dolomitic carbonates predominate, but the section on the eastern side reflects a
more shale-rich ramp that faced eastern Appalachian source areas. In the Silurian section
on the western side of the arch, protected behind the arch barrier, shales are rare except
during the highest sea levels, and rocks in the area reflect deposition across a broad, lowgradient shelf area, interrupted by structurally controlled topographic breaks. Using the
progression of interpreted depositional environments and nearshore faunal communities,
a relative sea-level curve, which parallels those of previous workers, was generated for
the section in Kentucky. While the curve clearly shows the influence of glacial eustasy,
distinct indications of the far-field, flexural influence of Taconian and Salinic tectonism
are also present. In fact, at times regional tectonic subsidence seems to have
overwhelmed the effects of glacio-eustasy. Moreover, a regional angular truncation in the
section, as well as overlying, bentonitic shales and a dysaerobic fauna in the deepestwater part of the section (Estill Shale), are best explained in terms of far-field tectonic
subsidence accompanying the first tectophase of the Salinic orogeny in the Appalachian
area.