Lost Interval

From Ohio History Central

After deposition of Upper Pennsylvanian-Lower Permian rocks, the preserved record of the geologic history of the state ended. For the next 295 million years, until the glaciers of the Pleistocene Ice Age covered much of the state beginning about 1.8 million years ago, no rocks or sediments that were deposited have survived in Ohio. During this long hiatus, which has been called the Lost Interval, Ohio was above sea level and erosion removed significant amounts of rock that was deposited throughout much of the Paleozoic. This interval encompassed most of the Permian Period, all of the Mesozoic Era, and almost all of the Cenozoic Era. During this time, the Appalachian Mountains reached their final height and were worn down and the supercontinent of Pangea split apart as the Atlantic Ocean began to form. The end of the Permian witnessed the greatest extinction of life, when 90 percent of species disappeared. The Mesozoic saw the rise and diversification of dinosaurs, and their extinction at the end of the Era, and the appearance of birds and mammals. The Cenozoic saw the rise and dominance of mammals. However, no rock record is preserved in Ohio to record these significant events.

Nevertheless, without question, dinosaurs lived in Ohio during the Mesozoic, as did mammals during the Cenozoic. It would be unreasonable to think that the extensive lowlands of Ohio were not occupied by terrestrial species of dinosaurs that lived along the river systems in a warm climate. However, conclusive proof, in the form of dinosaur fossils, has never, and will never, be found in Ohio. Even though dinosaur skeletons would have been entombed in river sediments, erosion has removed every trace of evidence. Thus, no Mesozoic sediments, and fossils, are present in the state.

Such a circumstance would apply to most of the Cenozoic, formerly divided into the Tertiary and Quaternary but now called the Paleogene and Neogene. Most certainly, Ohio has an extensive, well-preserved record of events, and life, during portions of the very last part of the Cenozoic, the Pleistocene and Holocene. However, more than 60 million years of Cenozoic history is missing, along with the hordes of mammals that must have roamed the state. However, a tantalizing discovery in an ancient sinkhole exposed in a limestone quarry in neighboring Indiana provides proof of the presence of mammals such as camel, rhino, and other extinct species that roamed the region during the late Pliocene Epoch. These animals fell into the sinkhole and were preserved as it filled with sediment and was protected from the grinding and plucking destruction as continental glaciers advanced across the area. Perhaps a similar sinkhole deposit will one day be discovered in Ohio.

It would be difficult to calculate the exact amount of rock record removed from Ohio during the Lost Interval, but it had to be enormous. Middle to Upper Paleozoic rocks, deposited during the Devonian, Mississippian, Pennsylvanian-Permian, undoubtedly were deposited west of their present area of outcrop in central and eastern Ohio. A bit of evidence supports this conclusion because the Upper Devonian Ohio Shale is preserved more than 30 miles west of its present contiguous outcrop in central Ohio on an elevated upland in Logan County. This upland is known to geologists as the Bellefontaine Outlier and is the site of Campbell Hill, Ohio’s highest point at an elevation of 1,549 feet.

It is not unreasonable, therefore, to assume that Devonian, Mississippian, and Pennsylvanian-Permian rocks once were present in much of the western half of the state. Periods of uplift during the Mesozoic and Cenozoic rejuvenated rivers and streams and further downcutting and rock removal occurred. The final sculpting of the landscape was accomplished by several major advances of continental glaciers during the Pleistocene Ice Age.

See Also