Paleontology and geology

In the Early and Middle Devonian, a shallow sea covered much of Indiana, depositing limy sediments that have preserved a diversity of marine invertebrate fossils, particularly rugose and tabulate corals. The corals constructed a great expanse of patch reefs that are now exposed in the southeastern part of the state at the Falls of the Ohio and extend all the way to New York State. Although Indiana remained covered by a widespread inland sea in the Late Devonian, conditions changed and black and gray muds were deposited instead of limy sediments. These sediments were carried into the sea from the eroding Acadian Mountains to the east. The shales formed from these sediments are characterized by high amounts of organic matter (from decayed algae and plant material), abundant pyrite, some fossils, and signs of bioturbation. This map shows a broad band of Devonian rocks across the northern section of the state, with exposures extending from the west to the southeast.