The Coon Creek Formation or Coon Creek Tongue is a geologic unit and Konservat-Lagerstätte located in western Tennessee and extreme northeast Mississippi. It is a sedimentary sandy marl deposit, Late Cretaceous (Maastrichtian) in age, about 70 million years old. The formation is renowned for its pristine fossils of Late Cretaceous marine invertebrates, including gastropods, bivalves, decapod crustaceans, and ammonites, particularly at Coon Creek in McNairy County, Tennessee, which the formation is named for. It is also known for producing fosslis of marine vertebrates, such as mosasaurs and plesiosaurs. Notable fossils from this formation is the gastropod Turritella, the bivalve Pterotrigonia thoracica, as well as other fossils such as crabs.