Geology of the Illinois Basin.
The Illinois Basin is a large geological feature that underlies the land surface of most of Illinois, significant parts of Indiana and Kentucky, and small parts of Iowa and Missouri. The Basin initially formed near the beginning of the Cambrian Period (542 million years ago) as a shallow, open-ended depression that opened to the seas to the south-southeast. By the time of the Early Pennsylvanian, the Basin's areal extent continued southward into eastern Arkansas, northern Mississippi, and northwestern Alabama. During the very end of the Pennsylvanian Period (299 m.y.a.) and into the Permian Period (299-251 m.y.a.), the southern end of the Basin was uplifted, forming the present-day, spoon-shaped Basin.
Rocks and Fossils Through Time
Geology of Deep Saline Sequestration