INTEGRATION OF SEQUENCE STRATIGRAPHY AND TRILOBITE PALEOECOLOGICAL PATTERNS: AN EXAMPLE FROM THE UPPER ORDOVICIAN OF OKLAHOMA

Paleoecological studies have shown that certain groups of trilobites demonstrate consistent responses to environmental gradients in a variety of stratigraphic and depositional settings. These associations (biofacies) have recently undergone intense study in the Upper Ordovician, a time period when the Taconic Orogeny was underway in eastern Laurentia. A quantitative study (QxR mode cluster analysis, non-metric multidimensional scaling, rarefaction analysis) of the paleoecological patterns of 1,561 trilobite individuals in 19 Oklahoma collections show that systems tract identity has a strong effect on rarified diversity. Statistically significant differences in diversity are also present across depth gradients in Oklahoma, but comparison with bathymetrically similar deposits in the Taconic Foreland Basin showed similar diversity until the regional extirpation of some trilobite faunas in the late Mohawkian. These data also support several predictions of biofacies/sequence integration, such as rapid shifts in biofacies composition across sequence boundaries. However, TST deposits do not show more rapid vertical shifts in biofacies composition relative to HST deposits as would be expected, likely because of taphonomic effects obscuring the signal. The generally poor preservation of condensed TST grainstone and packestone allowed for the preservation of only robust, convex trilobites (e.g., Failleana, Isotelus).