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.

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

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.

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.

Sandstone

Crossbedded

Ripple bedded

Conglomerate

Deformed

Sandstone and shale

Shale (gray)

Shale (black)

Coaly shale

Shale (calcareous)

Limestone

Argillaceous limestone

Dolostone (Do= orange colored)

Pyritized coal ball

Siderite nodule

Rooting or paleosol

Vertical peds

Slickensides

Mudcracks

Bioturbation

Algal laminations

Fenestrate bryozoans

Blastoids

Compositid brachiopods

Spirifirid brachiopods

Fossils

Legend

Shale (dark to maroon)

Brachiopods clasts

Rhipsidian bones

Anthracosaur bones

Lungfish burrows

Do

10

20

30

40

m

Caseyville Fm

Kinkaid Ls

Degonia and Clore Ls (?) undiff.

Palestine

?

Pe

nn

.

Bu

ffa

lo W

all

ow

Fm

.

Up

pe

r M

iss

iss

ipp

ian

road level

Measured section

Do

Menard

cglclay

fsltcslt

vfssfss

Grain size

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.

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.

L. Kinkaid Ls.

Clore Ls.

Degonia

Menard Ls.

Vienna Ls.

Caseyville Study Area

Owensboro Graben Faults

Palestine

Waltersburg

Buffalo Wallow Formation

Rough Creek Fault System

15 m

Western basin nomenclature Eastern basin nomenclature

Pennsylvanian strata

Upper Chesterian strata (above Menard Limestone)

Illinois

Indiana

Kentucky

Study areaCross section

100 km

50 mi

?

Palestine paleochannel

Menard Ls micrograbens

paleosol

slump Lateral accreting coset

eastwest

Dark shale channel fill

small faults

pes

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.

Curvolithus

Rooting is common at the top of the channel. Anthracosaur bones

Large clast

1 cm1 cm

1 cm

1 cm

micrograbens

Two dolostone beds within micrograben

Rare bioturbation in the channel.

Stephen Greb, 2000