Lost River - Karst Information Portal

2007 NSS Convention Guidebook
specific type section was not designated.
The Sanders Group consists of a variety of
carbonate rocks in complex facies relationships.
The Ramp Creek and Muldraugh Formations at
the base of the group are dominantly a mixture
of fine-grained dolomite and of limestone that
in places contains abundant echinodermal
and bryozoan fragments. Cherty and siliceous
intervals are common, and minor amounts
of siltstone and shale are present. Above that
interval in the Harrodsburg Limestone wellcemented
bioclastic calcarenites and calcirudites
are dominant over argillaceous limestone,
dolosiltites, and shale. The abundance of geodes
and chert decreases upward in the group. The
Salem Limestone except for the Somerset Shale
Member at its base is dominated by porous
calcarenite, although it contains a wide variety of
other kinds of limestone.
The group crops out along the margin of the
Illinois Basin in an irregular arc from Fountain
County to southern Harrison County. It is
present throughout the subsurface west and
south of the outcrop belt. Along the central and
southern parts of the belt the Sanders generally
ranges between 120 and 150 feet in thickness, but
it is thinner toward the north. It thickens abruptly
off the margin of the Borden delta deposits
(see “Borden Group”), principally because of
thickening of the Muldraugh Formation within
the resulting topographic basin, and it reaches
a maximum thickness of about 510 feet (150
meters) in the subsurface in Posey County in the
extreme southwest toe of Indiana.
The Sanders Group overlies rocks of the
Borden Group with a depositional hiatus
marked by a sharp lithologic break and in
most places by a zone of glauconite at the top
of the Borden. Throughout most of its extent
it is overlain conformably by the St. Louis
Limestone, although local hiatuses are possible.
Along its northern margin, however, the group
is truncated by pre-Pennsylvanian erosion and
is unconformably overlain by the Mansfield
Formation (Morrowan). The Sanders Group
is middle Valmeyeran in age. The names Ramp
Creek, Harrodsburg, and Salem are used in
Illinois, although the first two are considered
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to be members of the Ullin Formation and
“Muldraugh” is considered to be a junior
synonym of “Ramp Creek.” The units are not
precisely isochronous throughout, however.
In the Kentucky part of the Illinois Basin
the name Salem is also used, but the Warsaw
Limestone of Kentucky use approximates the
Harrodsburg and all but the lower part of the
Ramp Creek-Muldraugh section in Indiana.
The latter two formations are equivalent to the
Fort Payne Formation in adjacent Illinois and
Kentucky. The oldest part of the Sanders Group
is in the Gnathodus texanus-Taphrognathus
Assemblage Zone (conodonts), and the rest
is in the Taphrognathus varians-Apatognathus
Assemblage Zone .
The Ramp Creek, Harrodsburg, Salem, and
St. Louis formations are part of a thick sequence
of platform carbonate deposits that exemplify
the style of deposition that occurred within the
Illinois Basin during the Middle Mississippian
(Valmeyeran). On the eastern margin of
the basin, the Salem and other Valmeyeran
rocks are exposed in a northwestward to
south-southeastward-trending outcrop belt
that extends from west-central Indiana into
Kentucky. At the surface, the Salem ranges from
60 to 90 feet thick and thickens considerably
westward into the basin. Outcrop studies of the
Salem in Indiana indicate that individual facies
(distinguishable lithologic variations within
a larger unit) within the formation define a
shallowing-upward progradational sequence
conformable (gradational) with the uppermost
Harrodsburg and the basal St. Louis limestones.
Upper shore-face facies of the Harrodsburg are
overlain conformably by extensive cross-bedded
fossiliferous grainstones deposited in a highenergy
environment. Individual shoal deposits
are separated by foraminifera-rich grainstones
deposited in intershoal environment. Shoal and
intershoal deposits constitute the majority of
the Salem, and are the source of the commercial
building stone. These deposits are overlain
successively by sand flat, open lagoonal, and
restricted lagoonal deposits. The basal St. Louis
was deposited in an intertidal-flat environment
that marks the termination of the shallowing-