LIFE BEFORE THE RICHMONDIAN INVASION: STRATIGRAPHICALLY RESTRICTED FOSSIL OCCURRENCES IN THE TYPE MAYSVILLIAN OF THE CINCINNATI AREA AND THEIR IMPLICATIONS FOR PRE-RICHMONDIAN ECOLOGICAL STABILITY

While the Upper Ordovician (Cincinnatian: Edenian) Kope Formation has been well studied using a host of high-resolution stratigraphic techniques, the remainder of the Cincinnatian is relatively poorly resolved. On the other hand the Richmondian strata of Cincinnati have long been noted for multiple incursions of brachiopods and other fauna, leading to a well studied varied and diverse fauna. Between the Kope and the Richmondian strata lie the Maysvillian strata that are neither as well resolved as the Kope nor as faunally diverse as the Richmondian. Building from the Kope, high-resolution stratigraphic study of the Maysvillian is currently underway, and has resulted in highlighting that this interval contains some interesting faunal incursions of its own. The base of the Maysvillian is marked by the Fairview Formation and, in much of Kentucky, by an interval of abundant Strophomena and Constellaria. Higher up, base of the Fairmount Member of the Fairview Formation is marked by an incursion of Orthorhyncula,  which becomes more abundant to the south. Above that level Heterorthina fairmountensis appears near the base of the Miamitown Shale and becomes more abundant to the northwest. The Miamitown Shale is also associated with a gastropod-rich packstone bed and more than one horizon of edrioasteroid-encrusted shell pavements.

While the Bellevue Member is often associated with Vinlandostrophia ponderosa, this species also occurs in lower strata if they are of sufficiently shallow-water facies. The Corryville Member is marked by a distinctive form of the common brachiopod Rafinesquina, R. nasuta. The Mt Auburn Member contains a unique form of Vinlandostrophia, V. ponderosa auburnensis.

Near the top of the Maysvillian in Kentucky is horizon yielding an otherwise rare sponge, Dystactospongia. It is  extremely abundant, and covers a single bedding plane wherever found. Finally, the end of the Maysvillian is marked by the disappearance of Vinlandostrophia ponderosa, while the brachiopod  Hebertella comes in very strongly.These faunal incursions and local extinctions show promise in helping to make high-resolution correlations, at least within the Cincinnati Arch region.