A quantitative paleoecological approach to high-resolution cyclic and event stratigraphy: the Upper Ordovician Miamitown Shale in the type Cincinnatian

Stratigraphic cycles form an underlying high-resolution chronostratigraphic structure for much of the sedimentary record. However, before their chronostratigraphic utility can be realized they must be reliably correlated. A new integrated cyclic, quantitative lithologic and faunal method of correlating meter-scale cycles has been developed for a 12 m interval of the Miami-town Shale in the Upper Ordovician of the Cincinnati, Ohio area. First, using lithologic criteria alone, six flooding-surface-bound (shale-on-limestone) shoaling-upward (shale-to-limestone) cycles were delineated and correlated between seven outcrop sections within a 30 km radius; many correlations were ambiguous. Unusual fossil occurrences constrain correlations of cycles 3 and 4, and the limited presence of a dalmanellid, Heterorthina fairmountensis , shows that the flooding surface above cycle 3 lies 10 cm below the lithologic limestone-shale contact. Cluster analysis of faunal abundance data constrained correlations between all cycles and showed a major transition at the top of cycle 2, again below the lithologic limestone-shale contact. Finally, faunal depth gradient fluctuations interpreted from ordination of faunal abundance data confirmed and clarified the nature of cycle correlations; the major transition at the top of cycle 2 is a transgressive surface, and the middle part of cycle 3 includes the interval of maximum water depth. These features delineate a larger, 10-m-scale, cyclicity. The smaller, meter-scale cycles, interpreted as averaging 40–100 ka in duration, demonstrate the potential of a ten-to twenty-fold increase in the resolution of the type Cincinnatian stratigraphic record. Ecostratigraphy, faunal cyclicity, cyclic stratigraphy, event stratigraphy epiboles, benthic paleoecology, Upper Ordovician, Maysvillian, Caradocian, Ashgillian, Cincinnati.