Lost River - Karst Information Portal

closely this apparent relationship between
structure, rock type, and physiography when
investigating the south-central Indiana karst.
In more recent years, oil company geophysical
data has also detailed the geology of the Ohio
River Fringe area where a series of deep-seated
faults and broad folds has been delineated. The
relationship of these structures to local karst
development is unclear (KS)].
The east-facing Knobstone Escarpment and
its dip slope component, the Norman Upland,
were formed by stream erosion on thick
siltstones, thin shales, and thin limestones of
early Mississippian age (Borden Group, Figure
3). These rocks underlie carbonate rocks of
middle Mississippian age (Sanders and Blue
River Groups, Figure 5B and 6) that floor the
western margins of the eastern-most valleys.
This westward thickening wedge of
sedimentary rocks, upon which is developed
Regional Physiography and Stratigraphy
the karst topography of the Mitchell Plain, is
due to planation by surface streams that had
gradients less steep than the dip of the bedrock.
Those streams which maintain their flow across
the Mitchell Plain have eroded through an eastfacing
escarpment into the Crawford Upland,
which is developed upon and into a series of
interbedded shales, limestones, and sandstones
of late Mississippian age (Stephensport and
West Baden Groups, Figure 3). The escarpment
is known as the Chester Escarpment and is
in part equivalent to the Dripping Springs
Escarpment southwest of Mammoth Cave
(Weller, 1927, p 179), but is significantly
different lithologically and structurally.
The modern streams which drain the karst
areas are commonly deeply incised meandering
streams that head just west of the Knobstone
Escarpment, although the East Fork and West
Fork of the White River head considerably
Figure 2. Map of Indiana showing two major karst areas ( from Powell, 1961).
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