EXCEPTIONAL BEDDING-SURFACE EXPOSURE OF SHALLOW-MARINE CARBONATE SAND WAVES (DUNES) IN THE CEDARVILLE DOLOMITE, SILURIAN, WEST-CENTRAL OHIO, USA: NEW INSIGHTS INTO MID-CONTINENT DEPOSITION DURING THE SILURIAN

The Cedarville Dolomite was deposited in a shallow epicontinental sea during the Middle-Late Silurian. The Cedarville is generally 30 m thick and typically massive to poorly bedded. Other than large-scale bedding, depositional sedimentary structures are generally lacking, likely the result of extensive recrystallization. Hence, few studies of the Cedarville have addressed sedimentary processes associated with its deposition. Most studies have treated its faunal assemblage which includes brachiopods, crinoids, blastoids, and corals.

An exceptional bedding-surface exposure of sand waves within the Cedarville provides new insights into sedimentary processes associated with its deposition and characteristics of its depositional environment. The exposure is the floor of a quarry located ~1 mile southeast of Cedarville, Ohio. Areal exposure of the quarry floor is approximately 100 m x 240 m. The sand waves are exposed as four consecutive, slightly sinuous, symmetric ridges whose crestlines trend east-northeast. Bedform heights (H) are typically 0.5-1.4 m and vary along the lengths of the bedforms. Wavelengths (L) are on the order of 21-34 m. Crests are convex upward, whereas the sides are planar to concave upward with inclinations on the order of 6^o-17^o. Bedform troughs are concave upward. The internal structure of the bedforms has not yet been studied in detail, but appears to be concordant with their surface form. Much of the bedding surface exhibits evidence of extensive burrowing.

Characteristics of the sand waves are comparable to many tidal sand waves on modern continental shelves. Orientations of the Cedarville sand waves are oblique to the paleoshoreline and indicate sediment transport directions and, hence, tidal currents oriented north-northwest and south-southeast. The H/L ratios of the Cedarville sand waves are consistent with those of dunes. Empirical relationships between dune height and wavelength, and flow depth suggest that the Cedarville dunes were deposited in water depths on the order of 3-8 m, but possibly up to 10-30 m. These estimates span water depths from above to below fair weather wave base. Bedform symmetry and inclinations of their sides less than the angle of repose may reflect nearly symmetric tidal-current velocities and possibly modification by wind-driven waves.