Type Geological formation Country United States Primary Chalk Overlies Ripley Formation | Unit of Selma Group Region Alabama Named for Prairie Bluff, Alabama | |
 | ||
The Prairie Bluff Chalk Formation is a geological formation in North America, within the U.S. state of Alabama. The chalk was formed by marine sediments deposited along the eastern edge of the Mississippi embayment during the Maastrichtian stage of the Late Cretaceous. It is a unit of the Selma Group and marks the end of the Cretaceous in Alabama. Evidence has been found within the formation at Braggs, Moscow, and Millers Ferry in Alabama indicating an instantaneous to brief erosional event, most likely a tsunami, at the Cretaceous–Paleogene boundary (K–T boundary). It is hypothesized that this event, along with faulting and liquification of the Prairie Bluff Chalk, is related to the meteorite impact at the Chicxulub crater site, directly south, across the Gulf of Mexico, from the formation.