Microfossils and biostratigraphy of the Upper Cretaceous Coon Creek Formation Lagerstätte, Mississippi Embayment, USA

The Upper Cretaceous Coon Creek Formation type-locality in McNairy County, Tennessee, is an exceptional marine invertebrate Lagerstätte that was deposited in a nearshore reentrant into the ancestral continent of Appalachia. Extensive taxonomic analysis of the macrofauna has been done for over 100 years. However, documentation of the microfossil component at the type-locality has largely been ignored. This paper provides analysis of calcareous microfossils (benthic and planktonic foraminifera, calcareous nannofossils and ostracods) and palynomorphs (pollen, spores, algal remains and dinoflagellates) for detailed age control and information regarding environment of deposition. The Coon Creek type-locality is late Campanian (76.8–76.0 Ma) in age and was deposited in 35–60 m water depths. Calcareous nannofossil assemblages suggest that there was an influence of colder water through time, possibly by a connection to the northern Western Interior Seaway. The complex interplay between currents of the Gulf of Mexico and the Western Interior Seaway, upwelling and runoff influenced the palaeoenvironment. Increased influx of freshwater palynomorphs near the top of the section suggests placement proximal to the palaeoshoreline and that weathering increased through time. Changes in the dinoflagellate assemblage may be linked to a mosasaur mass mortality event and the presence of a harmful algal bloom.