Abstract This field guide focuses on key outcrops that highlight recent nomenclatorial changes of Early Silurian strata in western Ohio (e.g., Dayton Formation, Osgood Formation, Laurel Formation, Lewisburg Formation, Massie Formation, Euphemia Dolomite), as well as the Brassfield Formation and Springfield Dolomite. The field trip begins near the apex of the Cincinnati/Findlay Arch at a quarry in Ludlow Falls, Ohio, and ends at a more offshore position to the southeast, near Clifton, Ohio. Recent conodont biostratigraphic and δ 13 C carb chemostratigraphic data for many of those formations at the field trip localities clearly demonstrate coeval stratigraphic patterns present throughout western Ohio that were previously obscured due to prior inconsistent lithostratigraphic terminology and correlation. Those data also help to show important differences in stratigraphic patterns in western Ohio. Strata correlative to the Lee Creek Formation are recognized for the first time near the apex of the Cincinnati/Findlay Arch in western Ohio in West Milton, Ohio, and are tentatively identified as that formation. At the same locality the Dayton is shown to be completely absent, and the Osgood Formation overlies a thin unit tentatively identified as the Lee Creek Formation and underlying Brassfield Formation. The Springfield Dolomite at the Barrett Paving Materials Ludlow Quarry in Ludlow Falls, Ohio, contains trilobites of the Gravicalymene celebra Association, one of the most taxonomi-cally diverse and geographically widespread trilobite associations in the Silurian of North America. Pentamerid brachiopods occur with molts of Gravicalymene celebra in the Springfield there, suggesting an environmental complexity not seen elsewhere; pentamerids are not found in strata containing the Gravicalymene celebra Association in most other areas of the Midwest.

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.

Abstract Graphic correlation of 12 previously uncompiled stratigraphic sections wiih the Silurian composite standard of KJeffner (1989) results in a revised Silurian composite standard (CS) that has Worldwide applicability as a high-resolution chronostraligraphy. The additional range-data on 52 graptolite species, 39 conodont species, 10 events, and one boundary stratotype make it possible to graphically correlate virtually any stratigraphic section (which meets the data requirements of the graphic correlation method) containing representatives of diagnostic conodont and/or graptolite species with the newly revised Silurian CS. The nonannular absolute chronology based on the Silurian CS divides with confidence into 92 standard time units (STUs), a resolution that is a minimum of twice that of any previously proposed Silurian chronostraligraphy. Most sections graphically correlate with the Silurian CS by fitting a straight line of correlation, indicating that the standard reference section (Cellon, Austria) consists of rock which accumulated at a relatively constant rate. The absolute chronology based on the Silurian CS is thereby consonant (or nearly so) with an annular scale, and the 92 STUs it divides into are of equal annular length. Conodont and graptolite chronozones are defined in the Silurian CS according to international rules of stratigraphy and, if they contain at least one STU, can be recognized with confidence in any section that is a part of the Silurian CS or that can be added to it by the graphic correlation method. The conodont and graptolite chronozones defined in the Silurian CS are based on zones proposed by Walliser (1964), Barrick and Klapper (1976), Jeppsson (1988), Aldridge and Schönlaub (1989), Kleffner (1989), and Cocks and Nowlan (1993, for a proposed standard left-hand column for international Silurian correlation Charts). All post-Aeronian Silurian series and stage boundaries can be recognized with confidence in any section that is already or can become a part of the Silurian CS. Three of the series boundaries, the Llandovery/Wenlock, Ludlow/Pridoli, and Pridoli/Lochkovian (Silurian/Devonian), are recognized in the Silurian CS based on the position of the “golden spike” in their boundary stratotypes. Lower boundaries of the graptolite zones that are at the same or approximate leveis as the other Silurian boundaries are used to recognize the positions of those boundaries in the Silurian CS. The Silurian chronostratic scale, based on the range-data on conodont species, graptolite species, events, and boundary stratotypes represented in the Silurian CS, is calibrated by using the Wenlock/Ludlow and Silurian/Devonian tie-points of Harland and others (1989) and STUs as chrons of equal duration to interpolate between and below those tie-points. The Silurian time scale developed by this method provides the best means at present for estimating the durations of the Wenlock, Ludlow, and Pridoli Epochs, and all of the ages that comprise them (except perhaps for the Sheinwoodian and Homerian). The Pridoli was the longest epoch with a duration of 8.4 Ma, compared to 7.1 Ma for the Ludlow and 2.6 Ma for the Wenlock.