undifferentiated rock units

Paleontology and geology

During the Early Carboniferous (Mississippian), seas teeming with crinoids and brachiopods covered most of the state. Tectonic activity in the Late Carboniferous (Pennsylvanian) caused Gondwana to collide with the southern edge of Laurentia, forming the supercontinent of Pangea. This resulted in a mountain-building event (Alleghenian Orogeny) and the formation of the Southern Appalachian Mountains. Subsequent erosion of these mountains produced vast amounts of sediments that were swept into the sea, creating broad, coastal plains where forests of primitive trees and fern-like plants thrived. These forests are preserved today as the many coal seams and rocks rich with Coal Age fossils that are found throughout much of northern Alabama.