An exposure of the Buffalo Wallow Formation in western Kentucky has yielded a variety of Carbonifero

1
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_at_pop.uky.edu,
GREB, Stephen F., Kentucky Geological Survey,
greb_at_kgs.mm.uky.edu, STORRS, Glenn W.,
Cincinnati Museum Center, 1301 Western Ave.,
Cincinnati, OH, 45203, storrsgw_at_EMAIL.uc.edu,
GARCIA, William J., Department of Geology,
University of Cincinnati, Cincinnati, OH
45221-0013 wgarcia_at_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.
Mudcracks
Shale (dark to maroon)
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
Fossils
L. Kinkaid Ls.
Caseyville
10
Degonia
Fenestrate bryozoans
Anthracosaur bones
Menard
Buffalo Wallow Formation
Clore Ls.
?
Palestine
Blastoids
Rhipsidian bones
Do
Menard Ls.
Compositid brachiopods
Lungfish burrows
Waltersburg
road level
Vienna Ls.
Spirifirid brachiopods
Brachiopods clasts
Grain size
Owensboro Graben Faults
Rough Creek Fault System
clay
cslt
fss
cgl
fslt
vfss
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.