THE STRATIGRAPHIC DISTRIBUTION OF THE LATE ORDOVICIAN ‘BUTTER SHALE’ LAGERSTäTTEN IN THE CINCINNATI ARCH REGION
The change from brachiopod-bryozoan dominated fauna of the surrounding Cincinnatian to the mollusk-trilobite rich fauna of the butter shales indicates an increased rate in sedimentation allowing for mobile organisms to dominate where sessile fauna no longer can. This environment was episodically overwhelmed due to storm events and submarine mud flows, rapidly smothering even the mobile organisms providing the exceptional preservation. The butter shales are also punctuated with lenses of limestone and siltstone, allowing for the return of brachiopods and bryozoans. In contrast, the Moranburg shale of the Maysvillian aged Grant Lake Formation, is dominated by articulated Glyptocrinus and likely represents a time of low sedimentation rate punctuated by rapid sedimentation. The differences in these lagerstätten may be explainable in terms of sequence stratigraphy. Here we present a preliminary comparison of butter shale stratigraphy, paleontology, sedimentology and taphonomy.