SEDIMENTOLOGY AND PALEOECOLOGY OF A CHESTERIAN TETRAPOD SITE, BUFFALO WALLOW GROUP, WESTERN KENTUCKY

An exposure of the Buffalo Wallow Formation in western Kentucky has yielded a variety of Carboniferous tetrapods, the oldest such fossils in the Illinois Basin. Limestones at the base of the exposure can be correlated to the Menard Limestone, and those at the top to the Kinkaid Limestone, making the tetrapods upper Chesterian (Elviran) in age. At this location, nonmarine clastic units in the Buffalo Wallow consist of heterolithic paleochannels and lateral floodplain facies; dark shale-filled scour fills; small, heterolithic scour fills; and numerous paleosols. Paleosols are more common at this location than farther west in the basin, suggesting decreased accommodation along its eastern margin, and possibly atop a local horst block. Decreased accommodation also resulted in complexes of laterally crosscutting paleochannels, and the loss of a Clore-equivalent limestone relative to the upper Chesterian series found down structural dip.

Complex paleosol development in small-graben-like structures at the top of the Menard Limestone may indicate syndepositional structural movement, which also influenced sedimentation within the overlying Palestine-equivalent paleochannel. The channel is interpreted to be a mixed-load, meandering channel, with pervasive paleoslumps. Thick-thin laminae alternations in some crossbeds, rhythmites, and abundant shale drapes on laminae are suggestive of tidal conditions. Lycopod rooting, and rhizodont and anthracosaur bones suggest dominantly fresh water conditions, perhaps placing the channel in an upper estuarine or fluvio-estuarine transitional position. A large semiarticulated embolomere was found toward the toe of a slumped coset. Additional embolomere remains were found in overlying lacustrine and floodplain deposits above a paleosol developed on top of the paleochannel. Rhizodont and lungfish remains were preserved in dark shale-filled scours, interpreted as abandoned, poorly oxygenated oxbows or chute-channel fills in a possible marsh setting. Limited accommodation and channel-filling processes may have been important in the preservation of vertebrate remains at this site.