Sandstone

1. 100 km 50 mi 15 m SEDIMENTOLOGY AND PALEOECOLOGY OF A NAMURIAN A TETRAPOD SITE, BUFFALO WALLOW FORMATION, WESTERN KENTUCKY CHESNUT, Donald R., Jr., Kentucky Geological Survey, 228 MMRB, University of Kentucky, Lexington, KY 40506-0107, drches01@pop.uky.edu, GREB, Stephen F., Kentucky Geological Survey, greb@kgs.mm.uky.edu, STORRS, Glenn W., Cincinnati Museum Center, 1301 Western Ave., Cincinnati, OH, 45203, storrsgw@EMAIL.uc.edu, GARCIA, William J., Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 wgarcia@hotmail.com, and BELLAN, Jack, Department of Earth Sciences, Eastern Kentucky University, Richmond, KY 40475-3102 Legend Measured section 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 are correlated to the Menard Limestone, and those at the top to the Kinkaid Limestone, making the tetrapods Namurian A (Elviran or upper Chesterian) in age. At this location, 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 toward the axis of the basin, suggesting decreased accommodation along the basin 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 found down basinal dip where complete Chester-style cyclothems are generally preserved. Illinois m Conglomerate Limestone Penn. 40 Caseyville Fm Indiana Sandstone Argillaceous limestone Kinkaid Ls Pennsylvanian strata Dolostone (Do= orange colored) Crossbedded Pyritized coal ball Upper Chesterian strata (above Menard Limestone) Ripple bedded Degonia and Clore Ls (?) undiff. Siderite nodule Deformed 30 Sandstone and shale Rooting or paleosol Vertical peds Shale (gray) Kentucky Shale (black) Slickensides ? Buffalo Wallow Fm. Shale (dark to maroon) Mudcracks 20 Upper Mississippian Study area Palestine Cross section Coaly shale Bioturbation Shale (calcareous) Algal laminations Do Western basin nomenclature Eastern basin nomenclature micrograbens Study Area L. Kinkaid Ls. Fossils Caseyville 10 Degonia Anthracosaur bones Fenestrate bryozoans Menard Buffalo Wallow Formation Clore Ls. ? Palestine Rhipsidian bones Blastoids Do Menard Ls. Lungfish burrows Compositid brachiopods Waltersburg road level Vienna Ls. Brachiopods clasts Spirifirid brachiopods Grain size Rough Creek Fault System Owensboro Graben Faults clay cslt fss fslt vfss cgl west east Palestine paleochannel Dark shale channel fill slump Lateral accreting coset paleosol small faults micrograbens Menard Ls The Menard Limestone consists of limestone and shale containing an abundant and diverse marine fauna including articulate brachiopods, crinoids, the blastoid Pentremites, bryozoa including Archimedes and rugose corals. Complex paleosol development in small graben-like structures at the top of the Menard indicate syndepositional structural movement, which also influenced sedimentation within the overlying Palestine Sandstone-equivalent paleochannel. The "Palestine" 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, placing the channel in an upper estuarine or fluvio-estuarine transitional position. Two dolostone beds within micrograben 1 cm 1 cm 1 cm Large clast Curvolithus 1 cm Conglomeratic lag with variable size clasts from different Chester horizons. Shale-draped foresets within laterally accreting cosets. Thick-thin foreset pairs occur in some crossbeds. Rhythmic lamination toward top of coset. Rooting is common at the top of the channel. Rare bioturbation in the channel. Anthracosaur bones pes Stephen Greb, 2000 A large semiarticulated embolomere (1.0-1.3m) was found near the toe of a slumped coset. It is unclear whether slumping killed and preserved the animal or whether it just transported the remains of a predeceased animal to the base of the channel. Additional embolomere, temnospondyl and to-be-named tetrapod remains were found in overlying lacustrine, floodplain and paleosol deposits developed on top of the paleochannel. These strata, in turn, were overlain and truncated by dark shale-filled scours, interpreted as abandoned, poorly oxygenated oxbows or chute-channel fills in a possible marsh setting. A localized thin coal and pyritic/calcareous lycopod coal balls found at the base of the scour indicate a vegetated setting prior to infilling with dark muds. Vertebrates preserved in dark shale-filled scours include Gyracanthus, xenacanths, palaeoniscoids, lungfish (in burrows), rhizodonts, a colosteid and an embolomere. Invertebrate fossils have not been noted. The fauna indicate largely fresh-water conditions. Deposition of the dark muds may reflect increased base level, probably laterally equivalent to the "Clore" marine transgression seen further down basinal dip. Allocyclic (eustatic cycles in this case) and autocyclic processes (such as channel switching), enhanced by limited accommodation space, appear to have controlled sediment preservation in this coastal setting and were probably important for the preservation of vertebrates at this site.