Abstract This article is aimed at providing an overview of the geology of the Dayton region to those who seek an introduction to Dayton’s geological story. The oldest rocks exposed in the area are Ordovician (Katian Stage, Cincinnatian Series in local North American usage) in age, and are world famous for the quantity and quality of their fossils. Unconformably overlying the Ordovician strata are Silurian (Llandovery–Wenlock Series) dolomites, limestones, and shales, which represent tropical seas that were at times rich in crinoids, corals, brachiopods, and other invertebrates. A large time gap (unconformity) in the rock record of some 420+ million years occurs between the Silurian and the Pleistocene “Ice Age” deposits of the area. Significant changes to the natural environment in the Dayton area have occurred during the Anthropocene. A number of localities that can be reached within about 30–40 minutes from downtown Dayton are described. This is effectively Montgomery County and adjacent counties. As such this treatment is brief and not meant as a compendium but as an introduction and outline of Dayton’s geology and geological history. The localities selected illustrate Dayton’s geological heritage, from the Ordovician to the Pleistocene, while several of the area’s distinctive natural landmarks are discussed. A number of the landforms are expressions of the Niagara Escarpment, where resistant Silurian limestones and dolomites overlie less resistant older rocks.

Abstract The Silurian rocks of the Cincinnati Arch in Ohio, Kentucky, and Indiana have been studied for nearly two centuries. Compilation of data from these studies, combined with detailed analysis of nearly 20 continuous drill cores and remeasuring and resampling of more than 60 major outcrops, is the basis for a high-resolution sequence stratigraphic framework. Seven depositional sequences are assigned on the basis of through-going unconformities, which mirror those already recognized in the early Llandovery to early Ludlow of the northern Appalachian Basin. Revision of the conodont biostratigraphy for the Cincinnati Arch has produced results that both agree and disagree with the other lines of data implemented in the sequence stratigraphic depositional model. Biostratigraphic correlations between southern Ohio and the Niagara Falls area are largely in agreement with correlations based on other lines of data, as are correlations between west-central and western Ohio, southeastern Indiana, and northern Kentucky. However, correlations between southern and west-central Ohio show major areas of disagreement. Preliminary whole rock carbonate carbon isotope analyses in western-central Ohio show patterns roughly comparable to those documented in the Niagara region, Gotland, and elsewhere. Chemostratigraphic data that might resolve inconsistencies in the correlations between southern and west-central Ohio were not yet available at the time of publication.