FACIES MOSAICS VS. SEQUENCE STRATIGRAPHY: USING FINE SCALE STRATIGRAPHIC CORRELATIONS TO DECODE SEDIMENTARY FACIES IN THE CINCINNATIAN, MAYSVILLIAN STAGE

Richly fossiliferous, shallow-marine Late Ordovician (Cincinnatian) strata of the Cincinnati area (SW Ohio, SE Indiana, N Kentucky) have a long history of research dating back over 150 years. A plethora of local stratigraphic terms, while reflecting minor local facies changes, has obscured some overarching patterns, including sedimentary sequences, sharp facies dislocations (discontinuities), and unique marker beds. These features provide a key to identifying a hierarchy of cycles and understanding of coeval facies and depositional environments in high resolution. A long-standing perception exists that the Maysvillian strata comprise a mosaic of local facies that cannot be subdivided and correlated in detail, with little small-scale cyclicity present. However, the results of an intense field investigation yield that this is not the case. The purpose of this research is to investigate high- order depositional sequences within the Cincinnatian, Maysvillian Stage in order to establish a well constrained sequence stratigraphic framework upon which further paleoecological and sedimentological investigations can be made. The Maysvillian Stage includes the Fairview (Calloway Creek) and Grant Lake (Ashlock) formations; these units have been divided into members (e.g., Miamitown, Bellevue, Coryville, and Mt. Auburn) in Ohio, but are left undifferentiated elsewhere, despite the fact that members and even submembers are recognizable throughout the study area. By tracing a series of single time planes and events, including seismite horizons, oncolite-rich zones, individual beds, and high-order cycles across depositional facies it has been possible to further resolve the Maysvillian strata occurring within the Grant Lake lithofacies. The use of these high order correlations can be used to test changes in depositional environment at a given time and increase understanding of the nature and proximality of sedimentation. High-resolution correlations have also revealed widespread disconformities at which units are regionally truncated. These fine scale stratigraphic correlations provide new, testable sedimentological models of deposition, gain a more detailed understanding of the broader Cincinnatian stratigraphy, and offer possible mechanisms for high order cyclicity on the Cincinnati arch.