Lost River - Karst Information Portal

Regional Physiography and Stratigraphy
The Ohio River Fringe and South-Central Karst Areas of
Indiana: An Introduction
By Dr Arthur N. Palmer
(edited and updated from the 1973 and 1992 NSS Convention Guidebooks by Kevin Strunk).
Of the nation’s many cave areas, few can
rival south-central Indiana in the perfection
of its karst features. Located in a northwardextending
arm of the Interior Low Plateaus,
a sequence of Paleozoic age limestones,
sandstones, and shales has been spared the
cover of glacial drift which masks the bedrock
in five-sixths of Indiana (Figures 1 and 2).
Differential erosion of these exposed
rocks has produced a distinctive physiography
consisting of a broad limestone plateau,
called the Mitchell Plain, bordered on the
east and west by highlands of more resistant
rocks. These Mississippian-age rocks include
the limestone units of the Ramp Creek,
Harrodsburg, and Salem (Sanders Group),
and the St. Louis, Ste. Genevieve, and Paoli
Limestones (Blue River Group), with a total
thickness of about 500 feet. This sequence is
underlain by interbedded siltstones and shales
of the Borden Group, which are exposed to the
east of the Mitchell Plain to form the Norman
Upland. The limestone sequence is overlain
by interbedded sandstones, limestones, and
shales of the Chester Series which form the
Crawford Upland to the west of the Mitchell
Plain (Figure 3). These geologic relationships
extend southward into Kentucky, where karst
development is even more striking (Figure 4).
Most of Indiana’s caverns and associated
karst phenomena are located in the Mitchell
Plain and in limestone ridges capped by
sandstone in the Crawford Upland (Figures 5A
and 5B). Four factors combine to make this a
classic karst region: (1) Erosion has exposed the
limestones over a large, continuous area because
of the low regional dip (30 feet per mile to the
south-southwest) and lack of glacial cover; (2)
The humid climate of southern Indiana favors
solutional processes; (3) Most of the limestones
are dense and compact so that solution is
concentrated along joints and bedding plains
rather than dispersed throughout intergranular
spaces; and (4) Master (base-level) streams are
incised deeply into the limestones, creating
local hydraulic gradients sufficient for karst
development over an extensive area.
Physiography and Development of the Ohio River Fringe and
South-Central Indiana Karst
By Dr Richard L. Powell
(edited and updated from the 1973 and 1992 NSS Convention Guidebooks,
and numerous Powell, Palmer, and related references by Kevin Strunk).
The karst area of south-central Indiana is
developed on or within the carbonate rocks of
Mississippian age that lie within the Norman
Upland, the Mitchell Plain, and the Crawford
Upland physiographic subunits of the Highland
Rim Section of the Interior Low Plateaus
Province (Figures 5 and 6; Fenneman, 1938,
pp 425–427; and Malott, 1922). Therefore,
by definition, the area was not glaciated, but
is bounded on the north, east, and west by
the maximum extent of mappable Pleistocene
glacial drift deposits. The southern boundary,
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