MICROPALEONTOLOGICAL BIOSTRATIGRAPHY AND ENVIRONMENTAL ANALYSIS OF THE COON CREEK FORMATION TYPE LOCALITY SECTION NEAR ENVILLE, TENNESSEE

The Coon Creek lagerstattäte consists of glauconitic, micaceous, sandy-clay, and clayey-sand in the partially enclosed early Mississippian embayment on the southern shore of Appalachia. Best known for pristine preservation of unaltered invertebrate fauna, preliminary biostratigraphic analyses of eight Campanian sediment samples from the Coon Creek section in Tennessee yielded a diverse assemblage of microfossils including calcareous nannofossils, benthic and planktonic foraminifera, dinoflagellate cysts, and terrestrial palynomorphs. Based on the co-occurrence of the calcareous nannofossil species Quadrum trifidum, Reinhardtites anthophorous, Reinhardtites levis and Eiffelithus eximius, the Coons Creek site can be placed in Zone CC22 (upper Zone UC15) and is late Campanian in age (~76.2-75.8 Ma). Foraminiferal Planktonic/benthic ratios fluctuate from interpreted near shore inner neritic water depths (4.7%) to outer inner neritic water depths (10.8%).

The presence of warm- and cold-water species of nannofossils and dinoflagellate cysts suggests that this site, located along the eastern edge of the Western Interior Seaway during the Late Cretaceous, was influenced by current flow from the south (Gulf of Mexico) and from the north (Arctic). Dinoflagellate cysts and terrestrial palynomorphs indicate an environmental shift towards shallow, more brackish conditions up-section in samples CC-12 through CC-15, as shown by the presence of Botryococcus and the increased abundance of heterotrophic dinoflagellates such as Andalusiella, Alterbidinium, Isabellidinium, and Spinidinium. Terrestrial palynomorph assemblages reveal a gymnosperm- and fern-dominated environment, although angiosperms replace gymnosperms in the middle part of the section in sample CC-12. Common benthic genera including Anomalinoides, Cibicides, and Bolivina and planktonic species include Rugoglobigerina rugosa and Planohedbergella prairiehillensis.