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For a century and a half, isolated sandstone bodies scattered in a belt across the central part of Missouri have been interpreted as Pennsylvanian age filled sink hole deposits, based on their geometry, distribution, and that they appeared to be the first significant sandstone above the Ordovician carbonate units. However sedimentary facies and facies associations indicate that these sandstones were deposited by running water, possibly as valley-fills over paleokarst surfaces. Additionally, the units are often overlain by Ordovician through Mississippian strata and residuum, suggesting they range in age. The purpose of this study is to map these bodies using modern GIS techniques and to more fully document and describe their physical characteristics in order to better understand their origin and timing.
Citation preview
A REEXAMINATION OF PENNSYLVANIAN “FILLED-SINK” DEPOSITS IN EAST-CENTRAL MISSOURI: ARE THEY PENNSYLVANIAN AND
ARE THEY FILLED SINKS?
William W. Little
Missouri Department of
Natural ResourcesGeological Survey and Resource Assessment Division
Small circular outcrops
DickiteDisturbed bedding
Stratigraphic position
Evidence Supporting Pennsylvanian Sink and Cave Fill Features
Oc
Oc“Psf”
“Psf” (rimrock)
Oc
Oc
Mc
“Psf”
“Psf” (rimrock)
Oc
Oc
Mc
“Psf”
Mc
“Psf” (rimrock)
“Psf”
A B
C D
B
D
Mc
Oc
Paleokarst unconformity
Mb?
Mc
Oc
Paleokarst unconformity
Mb? B
A
Mc
Oc
Mc
Mb?
Oc
“Psf” (rimrock)
Remnant paleokarst hills
Oc
“Psf” (rimrock)
Remnant paleokarst hills
Oc
Oc
Mb
Mc
ds
Interbeddedss, ms, & ds}
PaleokarstHill on Oc
ds
Interbeddedss, ms, & ds}
PaleokarstHill on Oc
ds
ds
ds
ss & ms
Middle O Everton Fm on I-55
“P sink-fill” on Hwy 50
Outcrop pattern and measured sections for Middle Ordovician strata
GeneralizedSection
MeasuredSections
Cave Hill RdExposure
“Psf” (rimrock)
Mr
“Psf” (rimrock)
Mr
“Psf” (rimrock)
Mr
Versailles
Mr
“Pss”
Goerlisch Ridge
Mr
“Pss”
Vichy
Mr
“Pss”
Otterville East
Mr
“Psf”
Oc
Morrison
Mr“Pss”
Fredricksburg
Mr“Pss”
New Melle
Mr
“Pss”
Washington East
Mr“Pss”
“Pss”
Mr
“Pms”
Mississippian Residuum from atop a Pennsylvanian sandstone
Modern stream gravel from same area
Mississippian Residuum from atop a Pennsylvanian sandstone
Glacial erratics from the Troy area
Oc
“Psf”
“Psf” (rimrock)
Oc
“Psf”
“Psf” (rimrock)A
B
Oc
“Psf”“Psf” (rimrock)
ss
ms
South side of hwy North side of hwy
Differential Compaction
Oc“Pss” Oc
.• In some places, these deposits are interbedded with carbonates of Ordovician age.
• In other localities, they underlie Mississippian-age limestones.
• As shown on the state geologic map, small remnants of Devonian and Mississippian-age strata locally overlie these deposits.
• Cobbles and small boulders of fossiliferous Mississippian-age chert are found on the surface above these deposits throughout their mapped extent.
Evidence Supporting a Pre-Pennsylvanian Age
Most deposits are flat-lying with disturbed strata being restricted to lateral margins.
The regional distribution pattern of sandstone resembles that of an integrated drainage system and commonly forms a sheet.
Internal structures of sandstones indicate deposition by moving water.
Sandstone bodies are often flanked by stratified successions of interbedded claystone, siltstone, and thinner sandstones.
Evidence Supporting a Paleovalley Origin