UPPER CRETACEOUS (OWL CREEK FORMATION) INVERTEBRATE FOSSILS FROM A NEW SITE IN STODDARD COUNTY, MISSOURI

Recent mining operations in Stoddard County, Missouri have exposed a fresh section of Upper Cretaceous Owl Creek and Lower Paleocene Clayton formations. The Owl Creek is the youngest and stratigraphically highest Upper Cretaceous formation present in the eastern Gulf region. The new Missouri deposit is composed of approximately 185cm of sediment, distributed in four distinct zones; a lower, hard carbonate coquina (30cm) overlain by a glauconitic, sandy clay (70cm) overlain by a gray clay (65cm) and topped by an indurated gray clay (20cm). Zonal contacts appear slightly wavy and tend to grade into one another. The deposit has been reworked and constitutes the entire Clayton formation at this location.

Well-preserved invertebrate fossils, mainly mollusks, are found within the deposit in great abundance, particularly within the carbonate coquina and the lower glauconitic clay. Fifty-one species have been identified and are represented by sixteen gastropods, Twenty-seven pelecypods, Five cephalopods, one scaphapod, one chaetopod, one bryozoan and one echinoid. Also present are the remains of mosasaur, shark and turtle as well as carbonized wood and trace fossils such as glauconitic/phosphatic burrows.

In Missouri, Upper Cretaceous invertebrate fossils have been documented exclusively by poorly detailed internal casts and external molds and imprints in soft matrix. Existing literature is heavily supplemented with descriptions and illustrations of well-preserved specimens from the type section of the Owl Creek formation in Tippah County, Mississippi. These new Missouri specimens are of the highest quality and preserve excellent detail. Some specimens have both valves intact while others show evidence of predation. Within the glauconitic clay, several species of pelecypods retain their original shell and cephalopods still have their bright iridescence.

The well-preserved fauna recovered from the Stoddard County site represent an opportunity to describe the characteristic features of Upper Cretaceous invertebrates from Missouri more clearly. A number of specimens have not been previously described in state literature and others, as yet unidentified, may represent new genera or species.