Answer:
Pierre shale
Step-by-step explanation:
The area was covered by an inland sea between 75 and 70 million years ago, and the Pierre shale is the sedimentary rock that formed on the seabed. These were the dinosaur era years, however as they were land animals, no dinosaur remains have been discovered in the shale. Ammonites and mosasaurs are two fossil species that are frequently discovered in Pierre shale.