Paleontology and geology
The Precambrian and Early and Middle Paleozoic: Precambrian and Cambrian rocks are only represented by material brought up in drill cores; however, early to middle Paleozoic rocks are well-represented at the surface in Kentucky Ordovician, Silurian, and early Devonian rocks contain abundant fossils, indicating the presence of warm, shallow seas teeming with trilobites, brachiopods, corals, bryozoans, and other invertebrates. By the Late Devonian, the seas over Kentucky had become depleted in oxygen, and black muds rich in organic material began to accumulate on the sea bottom. The Carboniferous was a time of fluctuating sea levels and the formation of huge river delta systems with extensive swamps. With the exception of the far western region and the Nashville Dome, most of Kentucky is covered by these Carboniferous rocks, the source of Kentucky’s vast coal deposits.
The Late Paleozoic and Mesozoic: The retreat of the extensive shallow seas of the Paleozoic left much of Kentucky exposed during the late Paleozoic (Permian) and Mesozoic; however, fossils from a few Permian rocks brought up in drill cores indicate that the shallow sea persisted in the far western part of the state. The Mesozoic is represented only by a small area of Cretaceous rock in the far western Jackson Purchase area. These rocks are mainly nearshore marine gravels and sands, deposited from rivers flowing from the north and east. Few fossils are known from this time.
The Cenozoic: Cenozoic fossils are well-preserved and fairly abundant in Kentucky. The Tertiary is represented by plant fossils, including leaves, wood, and pollen. Though not shown on this map, Quaternary glacial deposits are present in the northern part of the state, and fossils of mastodons, mammoths, giant ground sloths, bison, elk, the short-faced bear, lions, and other mammals are found in mineral springs and salt licks, as well as in caves, sinkholes, ponds, and river gravel deposits in several places around Kentucky.