Lost River - Karst Information Portal

2007 NSS Convention Guidebook
base level. The magnetostratigraphy suggests
that the upper level of Wyandotte Cave was
abandoned in the early to middle Pleistocene,
following a drop in the regional base level
that occurred no later than 0.78 Ma ago and
accompanied the expansion of the Ohio River
drainage system. Commensurate with the time
taken for the effects of a drop in base level to
propagate up-basin, it is likely the upper level
in Marengo Cave was abandoned after the
upper level in Wyandotte Cave was vacated
(that is, < 0.78 Ma ago). The smaller (7-meter)
separation between the upper and lower levels
in Marengo Cave reflects the diminished
influence that a drop in base level commonly
has in locales relatively far removed from a
The erosional history of Blue River is the
key to understanding the history of cavern
development in the Harrison Crawford State
Forest area. The topography and caverns have
developed contemporaneously as Blue River
has established new and deeper channels in
progressive stages. Perhaps as many as five
stages will eventually be recognized and proved
to exist along Blue River, and each stage may
be reflected in cavern development in adjacent
tributary areas.
The earliest stage to be recognized is the late
Tertiary peneplain. This erosion surface can be
visualized by looking out from one of several
high vantage points in the area, principally
the Overlook at Leavenworth, the cemetery
south of Frenchtown, along the ridge road
south-west of Corydon, and in the vicinity
of Pilot Knob near Corydon. Peneplains
have long been a misunderstood feature. The
concept of a peneplain intended here is that of
a gently sloping land surface with slight relief
in respect to a large area. Streams upon this
surface meandered slowly in a southwesterly
direction, separated from each other by low,
rolling ridges. Small hills may have risen sharply
from the plain in some places. By no means is it
114
Erosional History of Blue River
basin outlet. Greater stability of the landscape
in the vicinity of Marengo Cave implies that
there the subsurface and surface landforms are
more mature than caves and drainage basins
in close proximity to the Ohio River. Stability
also facilitates the development of an extensive,
integrated drainage system in basins buffered
by distance from the full impact of base level
lowering. In these basins, a further drop in base
level will likely be absorbed by the subsurface
portion of the drainage network. Therefore, in
the Crawford Upland, evolution toward a karst
plain will progress more rapidly in tributary
drainage basins that are relatively far removed
from the Ohio River. (See Figures 17 & 20.)
By Richard L. Powell, BIG Newsletter, Vol 5 No. 2, August 1963
inferred that this surface was flat. [Note KLS:
many geomorphic workers discount the notion
of the peneplain, but it does seem to have some
context on a regional scale to explain similar
surfaces which appear to correlate. Many
workers promote pedimentation, but can a
regional scale feature be called a pediment?
(See the Lost River discussion of localized
pedimentation.)
Eventually this peneplain or erosion surface
was uplifted with respect to sea level or base
level (the level to which streams will erode their
channels). The meandering streams began to
deepen their channels, first in the downstream
portions, and eventually eroded headward into
the area of the present Crawford Upland and
Mitchell Plain. Blue River, Indian Creek, Buck
Creek, and an ancestral Ohio River, which may
have headed within the Norman Upland at this
time, eroded their channels to a depth of about
350 feet below the peneplain surface of the late
Tertiary, or slightly below the present elevation
of the Mitchell Plain. A temporary base level
occurred, and the streams attempted to erode
the adjacent land to the level of the streams (the
process of peneplanation). During this period
of constant base level the soluble limestones