The Coon Creek Formation is a geologic formation located in western Tennessee and extreme northeast Mississippi. It is a sedimentary sandy marl deposit, Late Cretaceous (Maastrichtian) in age, about 73 million years old. The formation is known for producing mosasaurs and plesiosaurs, particularly at Coon Creek in McNairy County, Tennessee which the formation is named for. Additionally, the formation produces many other underwater invertebrates such as Turritella and the state fossil of Tennessee, the bivalve Pterotrigonia thoracica, as well as other fossils such as crabs.