Lost River - Karst Information Portal

2007 NSS Convention Guidebook
importance, but where the Bethel Formation is
thin, large cave passages may have their ceilings in
the Beaver Bend (for example, Wildcat, Sexton
Spring, Quimby, and Stephen Quarry Caves).
Sample Formation, Reelsville Limestone,
Elwren Formation – The Sample Formation
in Indiana contains 24 to 42 feet of varicolored
shale and thin-bedded, cross-bedded sandstone.
Shales dominate north of Orange County but
sandstones become more conspicuous southward
to the Ohio River (Shaver, et al, 1986 p 136). The
Sample is overlain by gray, somewhat ferruginous,
biomicritic limestone of the Reelsville. The
Reelsville Limestone may be as much as 10 feet
thick, but is missing in many places due to nondeposition
(Shaver, et al, 1986, p 122). In some
instances the limestone may have been removed
by solution. It is not important as a cave-bearing
unit. The Reelsville is overlain by the Elwren
(Cypress) Formation which includes thinbedded
fine-grained sandstone, cross bedded
sandstone, and green-gray and red-brown shale
and mudstone and ranges from 20 to 60 feet in
thickness (Shaver, et al, 1986, pp 43–44). The
Elwren is called the Cypress in the subsurface by
the oil and gas industry and along with the Ste.
Genevieve is one of the most prolific oil and gas
producers in the Illinois Basin.
Stephensport Group
The name Stephensport, though having
some earlier mention (see Swann, 1963, p 83),
was formally proposed in a group sense by
Gray, Jenkins, and Weidman (1960, p 37), who
redefined it to consist in descending order of
the Glen Dean Limestone, the Hardinsburg
Formation, the Golconda (now Haney)
Limestone, the Big Clifty Formation, and the
Beech Creek Limestone. The group, named for
Stephensport, Breckinridge County, Kentucky,
consists of about equal parts of limestone, shale,
and cliff-forming sandstone (Gray, 1962, table 2
and fig. 4).
The total thickness of the Stephensport
Group is 130 to 230 feet (40 to 70 meters).
The Stephensport conformably overlies the
West Baden Group (Chesterian) and is overlain
conformably by the Buffalo Wallow Group
102
(Chesterian) or disconformably by the Mansfield
Formation (Morrowan). It is recognized on the
outcrop from central Owen County southward
to the Ohio River. In the subsurface it extends
from Clay County southwestward .
The Stephensport Group is exactly correlative
with the Okaw Group of southwestern Illinois
(Swann, 1963, p 53) but is distinct in usage by
including prominent clastic formations the
Okaw is dominantly limestone (Swann, 1963, pp
45–46). On the basis of their conodont faunas,
formations of the group represent the Gnathodus
bilineatus-Cavusgnathus altus and Gnathodus
bilineatus-Kladognathus mehli Assemblage
Zones of the North American standard
(Collinson, Rexroad, and Thompson, 1971). The
group spans the Visean-Namurian boundary of
European usage and correlates with rocks within
North American foraminiferal Zones 16s and 17
of Mamet and Skipp (1971).
Beech Creek Limestone – The Beech
Creek Limestone of the Stephensport Group
is the most speleologically important unit of
the Chester Series. It ranges in thickness from
8 to 33 feet and can be divided lithologically
into three members (Shaver, et al, 1986, p 11).
The lowermost member is a dark gray to gray,
sparry, biomicritic limestone which sometimes
is oolitic. It is 0 to 12 feet thick on the outcrop.
The middle member is a massive, cross-bedded
biocalcarenite. The upper member is thinnerbedded
and in places is laminated although it is
cross-bedded near the top. The Beech Creek is
characterized by the presence of countless crinoid
columnals as much as 25 millimeters in diameter.
It also has abundant brachiopods and bryozoans.
Many areas of subterranean drainage have
formed in the Beech Creek in the western part of
the Crawford Upland, and caves including twomile
long Jim Rays Cave (the type section) are
typical. [Because the Beech Creek outcrop is in
the rugged Crawford Upland several miles west
of the Mitchell Plain with its larger and more
obvious karst, the Beech Creek outcrop has not
been systematically hill hopped for caves. The
known caves such as Jim Rays Cave in Greene
County are typically large (walking) spring caves
1,000 feet to 2 miles long. The Beech Creek