IDENTIFYING CYCLICITY IN THE LITHOLOGICALLY MONOTONOUS UPPER ORDOVICIAN (CINCINNATIAN) BELLEVUE FORMATION: A TEST OF THE UTILITY OF TAPHONOMIC AND PALEOECOLOGICAL ANALYSES FOR CYCLE RECOGNITION

Interpreting monotonous sections in the rock record presents a challenge because of the lack of lithological features typically used to diagnose environmental and temporal change at the outcrop scale. This study uses the taphonomy and paleoecology of fossil assemblages collected from the Bellevue Formation (Cincinnatian, Maysvillian, C-2 Sequence) to test three hypotheses related to the identification of sedimentary cycles. First, that color variation of brachiopod fossils can be meaningfully related to degree of time-averaging, with dark coloration positively correlated with other taphonomic features such as fragmentation and corrosion. Second, variations in taphonomy accurately reflect changes in environment as indicated by independent evidence such as fossil assemblages. Third, that taphonomy and paleoecology can be used to recognize cyclicity in an otherwise monotonous section.

Field observations of lithology, taphonomy, and paleoecology were made within a high-resolution stratigraphic framework. Multiple brachiopod specimens from each bed were examined in the lab and detailed taphonomic data were recorded, including: corrosion, articulation, color alteration, location of the brachiopod in the bed, orientation of the valve, fragmentation, encrustation, boring, and breaching of the valves. Numerical scores were assigned to the taphonomic data, allowing for multivariate analysis to be applied to all the data. In addition, taxon presence/absence and abundance data were collected for all beds throughout the section, and beds were described lithologically. Statistical analysis suggests that coloration is a meaningful taphonomic indicator. Additionally, analysis also shows correspondence between many of the taphonomic characters studied. Comparison of taphonomic indicators with the results of paleoecological ordination analysis suggests a relationship and underscores the utility of a combined taphonomic and paleoecological approach in recognizing cyclicity.