Coon Creek Formation

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 70 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 marine invertebrates such as Turritella and the state fossil of Tennessee, the bivalve Pterotrigonia thoracica, as well as other fossils such as crabs.

The story of Coon Creek began near the end of the Cretaceous Period, around 71 million years ago. At that time western Tennessee, eastern Arkansas, western Kentucky, and southeast Missouri were submerged beneath the Mississippi Embayment, a bay of the Gulf of Mexico. Coon Creek was formed in shallow coastal water probably less than 100 feet deep (Russell and Parks 1975). The sea floor was heavily populated with shellfish, crabs, and lobsters. Huge plesiosaurs, marine crocodiles, sea turtles, and mosasaurs shared the waters with sharks and fierce fanged-tooth fishes. The climate was warmer than today. Coon Creek was semi-tropical, like present-day southern Florida (Wade 1926). Heavy waves from severe tropical storms constantly churned up shallower parts of the sea floor.

...
Wikipedia