Geological Cross Section of Ohio

Geological Cross Section of Ohio. . A geologic cross section depicts the distribution of rock layers in Ohio as being like the layers of a cake. This cross section traverses from the Ohio-West Virginia boundary at Belpre, Ohio, to Bellefontaine, then to the Michigan-Indiana-Ohio boundary intersection., Beginning at the Ohio-West Virginia border, rock layers present thousands of feet below the surface rise in elevation westward until they reach the surface in west-central Ohio. Traversing northwest from the Bellefontaine area, rock layers lie generally flat but then gently descend into the Michigan Basin., Rock units at great depths (tan and brown on the cross section) can be sedimentary, igneous, or metamorphic rocks older than 542 million years. These rocks are deeply buried and poorly understood because of limited sampling., Beginning about 2.6 million years ago (mya), sheets of ice up to a mile thick repeatedly advanced from and melted back to Canada. Those glaciers flattened the landscape by shaving off hills and filling in valleys, which is why western Ohio is so flat., During later stages of the Ice Age, Lake Erie covered much more of northern Ohio than it does now. Lake-bottom sediments formed the Black Swamp that covered much of northwestern Ohio, incredibly rich farmland that couldn't be used until drainage systems were put in place., Thick layers of limestone and dolomite of the Silurian Period (440-416 mya) formed beneath tropical ocean waters. These rocks are responsible for the scenery at Clifton Gorge State Nature Preserve and John Bryan State Park. Silurian rocks are a major source of aggregate used in construction., Near Bellefontaine is a feature geologists call the Bellefontaine Outlier. Here, resistant bedrock deflected the advancing glaciers, leaving behind Ohio's highest elevation point at 1,549 ft above sea rocks between Bellefontaine and Columbus have been stripped away by erosion., Beneath the Fairgrounds, about 165 ft of glacial debris (called drift) sit on rocks from the Devonian Period (416-359 mya). Those rocks formed from sediment deposited in a shallow sea when Ohio was south of the equator. The change from white Columbus Limestone (the stone used to build the Ohio State Capitol) to the dark shale at Highbanks Metro Park marks the uplift and erosion of the ancestral Appalachian Mountains, the source of the sediment., The Hocking Hills, in Hocking County, owe their scenic beauty largely to the Black Hand Sandstone, a resistant rock unit formed during the Mississippian Period (359-318 mya) by streams carrying tremendous quantities of sand and gravel eroded from ancestral Appalachian Mountains as they were rising to the southeast., Coal from rocks of the Pennsylvanian Period (318-299 mya) powered the industrial revolution in Ohio. Those rocks also supplied clay and shale that made Ohio the brick and clay capitol of the world. Ohio was a major producer of iron in the nation at the time of the Civil War (1861-1865) and supplied the iron used in the Union iron-clad ship Monitor.