Systematics and paleoecology of Devonian stromatoporoids from the Cou Falls, Iowa City, and Osage Springs Members, east-central Iowa

The ultimate goal of this research is to study the systematics and biodiversity of stromatoporoid species exquisitely preserved in Givetian exposures throughout east-central Iowa. The goal of this study is not only to identify these stromatoporoids using qualitative descriptions, but also to utilize a set of simple quantitative morphometric methods to delineate morphological differences among these stromatoporoid species. In this present study, over 100 specimens of stromatoporoids were collected from exposures of the Cou Falls and Iowa City Members of the Coralville Formation and the Osage Springs Member of the Lithograph City Formation. All specimens were thin sectioned and ten species were identified using both qualitative characteristics and a new set of morphometric methods. A discriminant analysis was performed to differentiate among taxa using the 72 best preserved specimens. Statistically significant differences in several micromorphological characters measured on the longitudinal thin sections clearly separate these species. Formal systematic descriptions were prepared based on the results. Chi-square analyses were used to determine a relationship between stromatoporoid growth form and lithology, providing clues to the depositional environments of sampled horizons of these Members. The species composition of this sample set was also examined in conjunction with other samples sets to determine faunal changes before, during, and after the Taghanic Onlap. R and Q mode hierarchical cluster analyses clearly show that distinctly different faunas thrived on either side of the Transcontinental Arch (TCA), in both the Eastern American and Old World Realm. This provincialism abruptly ended during the Taghanic Onlap when the Transcontinental Arch was breached by a shallow sea. New stromatoporoid faunas, possibly more tolerant of these environmental variations thrived during this period. Although distinctly different stromatoporoid faunas were present on either side of the TCA before the Onlap, cosmopolitan faunas which became established in the early Frasnian thrived throughout the set of transgressive-regressive pulses of the Onlap. The results of these analyses are vital to future understanding of the faunal changes that occurred directly before the Frasnian-Fammenian extinction event.