CAN CARBON ISOTOPES CONSTRAIN HIGH-RESOLUTION STRATIGRAPHY OF ORDOVICIAN SHALLOW WATER FACIES IN THE CINCINNATI, OHIO REGION?
The Ordovician Maysvillian transect from Cincinnati, OH to Central Kentucky displays a transition from subtidal to peritidal facies. The sub-Bellvue unconformity is a major feature of the section in Cincinnati where erosion truncates several beds within the Miamitown Shale. Generally the Fairview–Bellevue section in Cincinnati is correlated to the Calloway Creek Formation (subtidal), and Tate (peritidal) and Gilbert (subtidal) members of the Ashlock Formation in Kentucky. While there are theoretical sequence stratigraphic considerations in making such a correlation, the precise position of the sub-Bellevue unconformity has proven difficult to pinpoint within this succession. There are particularly few clues to correlation in the relatively monotonous, fossil-poor peritidal lithologies of the Tate.
Bergström et al. (2010) established some potentially useful carbon isotope excursions in this interval based on a composite Cincinnatian section, with the Maysvillian section sampled near Maysville, Kentucky. The recovery following the Fairview excursion particularly appears to mark the location of the sub-Bellevue unconformity in the Bergström section. We refined the isotope curve for the upper Kope–Mt. Auburn Member in the Maysville area.
To test the ability to correlate from deep subtidal into more shallow water facies, we sampled four other sections along a subtidal to peritidal transect. The Fairview excursion can be tracked into the deep subtidal near Cincinnati, OH, but to the south an extended positive to negative trend through the Tate may indicate that it correlates to a similar but more abrupt recovery associated with the Bellevue. This finding may be evidence of an expanded peritidal section deposited during a time when sediment starvation was occurring in the more distal part of the basin.