AN ABSOLUTE TIME TABLE FOR THE LOWER TO MIDDLE PENNSYLVANIAN BREATHITT GROUP OF KENTUCKY

The Breathitt Group (Lower to Middle Pennsylvanian) of Kentucky consists of stream-deposited angular-grained sandstone bodies, extensive shale and siltstone complexes, abundant coal beds and a few widespread marine limestone and shale beds; a heterogeneous assemblage, similar throughout, that in bulk is distinctly different from the formations above and the Lee and New River Formations below. It also contains tonsteins (kaolinized volcanic ash beds), two of which have been dated using standard U-Pb single crystal zircon methods. The lower tonstein, in the Upper Banner coal bed, is dated at 316.1±0.8 Ma and the upper, in the Fire Clay coal bed, is dated at 314.6±0.9 Ma. Linear interpolation between these ages produces estimate ages for the marine Betsie Shale Member (315.5 Ma) and the marine Kendrick Shale Member (314.9 Ma). Using this extrapolation, an age for the Kennedy - Douglas coal bed at the base of the Breathitt Group is estimated at 316.3 Ma. It is underlain by the marine barrier bar sandstones of the Lee Formation and the fluvial deposits of the New River Formation. Extrapolation upward from the Fire Clay coal bed suggests that the marine Magoffin Member and the marine Stoney Fork Member are 314.4 Ma and 313.6 Ma respectively. Ages for beds above the Stoney Fork member were not extrapolated because of an upward change in lithologic style and inferred sedimentation rate. These ages suggest that the beds below the Stoney Fork Member were deposited between 316.3 Ma and continued to 313.6 Ma, if these dates are confirmed by future analyses.