In North America, what "fossils clues" in layers A and B indicate the kind of environment that existed when these rock layers were formed? How did the environment change in layer D?

The late Cretaceous period and environment changed due to changes in climate when the asteroid hit the planet and covered the sun rays.

Explanation:

As per the fossil records shown the layers A and B are the oldest and they have shells, ammonites, trilobites, and fish that shows it was underwater. The layer D is that formed by the dinosaurs and plants as in the Cretaceous period when plants on land were found.

Minecraft is the answer hehehhege