Middle Devonian faunas of the Michigan and Appalachian Basins: Comparing patterns of biotic stability and turnover between two paleobiogeographic subprovinces

The hypothesis of Coordinated Stasis, developed from observations of extended periods of faunal stability in Middle Devonian sediments of the Appalachian Basin, has been the topic of intense research in recent years in the field of paleoecology. Investigations into patterns of faunal persistence have been conducted on various sedimentary basins throughout the rock record; however no study has yet attempted to document concurrent faunal patterns in separate paleobiogeographic regions. The Middle Devonian Appalachian and Michigan basins provide a perfect test case for an examination of coeval patterns of faunal change as they were separate paleobiogeographic subprovinces at this time. Patterns of faunal turnover were examined in the Michigan Basin and compared to the well-documented record the coeval Appalachian Basin. In order to compare patterns at a fine scale, correlations between the Appalachian and Michigan Basins were refined using sequence stratigraphic criteria resulting in a high-resolution stratigraphic framework between the basins. It was possible to correlate both large- and small-scale sequences between the basins indicating the primary control on deposition across much of eastern North America was eustatic sea level oscillation. It was also possible to constrain the timing of tectonic activity between the basins as well as refine the biostratigraphy of the interval. Three separate faunal intervals were identified as having existed in the Middle Devonian in the Michigan Basin and were determined to be analogous to the Evolutionary Ecological (EE) Subunits of the Appalachian Basin Middle Devonian; the timing of faunal turnover between the EE Subunits was coeval between the basins. The degree of taxonomic mixing between the basins was also examined at the level of 3rd-order depositional sequence through the duration of the Hamilton-Traverse EE subunit using the Jaccard similarity coefficient indicating greater amounts of mixing between the basins at the beginning and end of the interval with more restricted mixing in the middle of the interval. Comparison of biofacies replacement through time was examined at a fine scale through a single 3rd-order sequence in the Appalachian Basin, the Michigan Basin, and an intermediate region using Detrended Correspondence Analysis yielding similar patterns through time in all areas.