MIDDLE-UPPER DEVONIAN (GIVETIAN-FAMENNIAN) BONE/CONODONT BEDS FROM CENTRAL KENTUCKY: REWORKING AND EVENT CONDENSATION IN THE DISTAL ACADIAN FORELAND BASIN

A roughly 5m long exposure of Ohio Shale along Little Hardwick Creek southeast of Clay City, Kentucky comprises a complexly condensed interval that spans the late Givetian to the middle Famennian. This section features three thin, but distinctive conodont and bone-rich sandstone beds. The lowest Portwood black shale (~70 cm) yields conodonts diagnostic of the latest Givetian disparilis Zone. This shale is crosscut by neptunian dikes filled with phosphatic sandstone that is continuous with the 0.5-1 cm bone bed A; the latter yields fragmentary early Frasnian conodonts. Bone bed B, about 40 cm higher, is thin sandy, and also yields fragmentary Frasnian conodonts. The thickest bed (bed C; 0-10 cm) occurs above a 16 cm thick interval of burrowed black shale and is at the base of the Selmier Formation. Bed C yields reworked highest Frasnian and lower Famennian conodonts. This bone-bed appears to coincide with Conkin’s bone-bed 17. The bed is lenticular and amalgamated with a lower portion of calcareous sandstone and gray shale containing abundant coalified/calcified wood and well preserved conodonts. The uppermost 2-5 cm is a sharply based, crudely graded Zoophycos-bioturbated bed with abundant clasts of reworked, phosphatized bone, coalified, calcified, and pyritized wood, reworked pyrite nodules, as well as rare crinoid ossicles and quartz pebbles. The upper surface displays well preserved, disarticulated arthrodire plates and coalified logs. An excavated slab >5m² yielded seven large, coalified logs (up to 1 m long) and many small wood fragments with a vaguely preferred, nearly N-S, orientation. The well-preserved dermal bones (superognathals, inferognathals, nuchal plate) are possibly derived from a single individual of Dinichthys sp. Additional elements include an inferognathal of cf. Eastmanosteus, acanthodian spines, cladoselachid teeth, and scales of actinopterygian fish. The bones appear to be concentrated on the western (leeward) sides of flow-perpendicular logjams. This remarkably preserved bone bed shows evidence for long-term condensation, erosional concentration, bioturbation, and final physical reworking, possibly by storm generated currents.