Middle Devonian bone beds of Ohio

Abstract

The Middle Devonian limestones of central Ohio consist of two formations, the Columbus (late Ulsterian) and the Delaware (early Erian). Within these are at least four thin bone beds: the First, 10 feet below the top of the Columbus in Franklin and southern Delaware counties, the Second, at the contact of the Columbus and the Delaware from Franklin county north to Lake Erie, the Third, 26 to 30 feet above the base of the Delaware in Franklin and Delaware counties, and the Fourth, 2 feet above the Third at Delaware. The Rocky Branch bone bed occurs in southeastern Indiana at the approximate horizon of the Second. These beds vary considerably in development, being absent at some localities and a foot or slightly thicker at others. They consist of clastic accumulations of crinoidal debris, innumerable scales, plates, teeth, and bones of fishes, conodonts, ostracods, and Foraminifera, relatively few macrofossils, mixed with rounded sand grains and a small amount of clay-size constituents, more or less thoroughly cemented by calcite. Another bone bed, the East Liberty, occurs between the Columbus formation and the Upper Devonian Ohio shale in the Bellefontaine Devonian outlier in Logan County, Ohio. It is mostly sand grains cemented by dolomite, with some fish material and a few phosphatic nodules, and is considered younger than the bone beds of central Ohio—perhaps of Olentangy age. The Kiddville layer in the lower part of the Boyle limestone of eastern Kentucky is similar to the East Liberty bone bed lithologically and faunally and probably represents approximately the same horizon. All these bone beds occur on the flanks of the Cincinnati arch, and none is now known in equivalent formations away from this structure. Most of the fish material is believed to have come from the fresh-water environments of the middle Paleozoic lowland area of Cincinnatia and is found not only concentrated in the bone beds but also thinly diffused throughout the enclosing limestones. These bone beds do not represent catastrophic annihilation of indigenous marine fish communities but are rather concentrates accumulated during diastems resulting from the fluctuations with respect to wave base of the very shallow sea bordering Cincinnatia. In places they represent lag concentrates, in others rapid subaqueous accumulations of coarser material transported from areas of lag concentrates with bypassing of finer particles, and in still others aeolian deposits derived from subaerial exposures of lag concentrates.