VoyForums
[ Show ]
Support VoyForums
[ Shrink ]
VoyForums Announcement: Programming and providing support for this service has been a labor of love since 1997. We are one of the few services online who values our users' privacy, and have never sold your information. We have even fought hard to defend your privacy in legal cases; however, we've done it with almost no financial support -- paying out of pocket to continue providing the service. Due to the issues imposed on us by advertisers, we also stopped hosting most ads on the forums many years ago. We hope you appreciate our efforts.

Show your support by donating any amount. (Note: We are still technically a for-profit company, so your contribution is not tax-deductible.) PayPal Acct: Feedback:

Donate to VoyForums (PayPal):

[ Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: [1] ]

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Date Posted: 06:08:18 03/13/03 Thu
Author: wally
Subject: Re: Attention: Slow and steady ( o k here)
In reply to: Felix Gregarious 's message, "Re: Attention: Slow and steady" on 21:22:52 03/11/03 Tue

>>sent email of stuff from jeeves to
>>slowandsteadywinstherace@ adbusters.org (did you get
>>it??????????)
>
>i did not get it because that e-mail address that i
>entered was fake. so is this one. why not post it on
>the board?
>
>peace,
>-=Felix=-

Three sites in Kentucky bear the scars of ancient
impacts by meteorites: the Jeptha Knob in Shelby
County, a site near Versailles in Woodford County, and
a site near Middlesboro in Bell County. A meteorite
impact usually forms a roughly circular crater, called
an astrobleme, and can crack the Earth's crust in a
characteristic circular pattern. Astroblemes may show
a "rebound structure" where a central core of rock has
been brought up from deeper underground by the impact.
The three Kentucky astroblemes represent the highly
eroded cores of the astroblemes that were situated
under the original craters; the crater walls eroded
long ago. Each of these structures is characterized by
a circular belt of arc-shaped faults cross cut by
faults radiating outward from the central core of
intensely broken rock. In the past, these structures
were referred to as "cryptoexplosive" because their
origin was uncertain.

A good example of an astrobleme is Jeptha Knob. Jeptha
Knob is located in Shelby County in north-central
Kentucky and can be observed on the Shelbyville and
Waddy geologic quadrangle maps (1:24,000 scale). This
nearly 3-mile-diameter group of hills is visible just
north of Interstate Highway 64. It contrasts sharply
with the surrounding rolling farm land. A paper by
Cressman (1981) describes the geology of the
astrobleme, shown on the map above. The colors on the
map represent different rock units. The black lines
(many dashed) are faults. The rock units shown in pink
in the center of the ring of faults have been uplifted
relative to the rocks outside of the ring.

The cross section across the Jeptha Knob astrobleme is
a representation of what the rocks beneath the surface
of Jeptha Knob look like. It dramatically illustrates
how the unit of rock shown in pink in the center of
the astrobleme has been pushed upward. This is the
geologic remnant of the uplifted rebound structure in
the center of the crater. Geologists think the
structure was formed around 425 million years ago,
during the Ordovician Period.

The following references may be helpful. They can be
ordered from the Publication Sales Office of the
Kentucky Geological Survey if they are not in your
library.

The Jeptha Knob astrobleme is shown on two maps (half
on each):

Cressman (1975) Geologic map of the Shelbyville
Quadrangle, Shelby County, Kentucky: U.S. Geological
Survey Geological Quadrangle Map, GQ-1258.

Cressman (1975) Geologic map of the Waddy Quadrangle,
central Kentucky: U.S. Geological Survey Geological
Quadrangle Map, GQ-1255.

The Jeptha Knob astrobleme is described in the
following technical report that contains a single map,
which combines the two geological quadrangles above.

Cressman, E. R., 1981, Surface geology of the Jeptha
Knob cryptoexplosion structure, Shelby County,
Kentucky: U.S. Geological Survey Professional Paper
1151-B, 16 p.

The Middlesboro astrobleme is shown on parts of three
maps:

Englund, K. G., 1964, Geology of the Middlesboro South
Quadrangle, Tennessee, Kentucky, Virginia: U.S.
Geological Survey Geological Quadrangle Map, GQ-301.

Rice, C.L., and Maughan, E.K., 1978, Geologic map of
the Kayjay and part of the Fork Ridge Quadrangle, Bell
and Knott Counties, Kentucky: U.S. Geological Survey
Geological Quadrangle Map, GQ-1505.

Rice, C.L., and Ping, R.G., 1989, Geology of the
Middlesboro North Quadrangle, Kentucky: U.S.
Geological Survey Geological Quadrangle Map, GQ-1663.

The Versailles astobleme is shown on one map:

Black, D.F.B., 1964, Geology of the Versailles
Quadrangle, Kentucky: U.S. Geological Survey
Geological Quadrangle Map, GQ-325.

Last modified Fri, 28 Jul 2000 19:49:58 GMT


JEPTHA KNOB, USA N36 6 W 85 6 4.8
452.0 Proven.(?) Ir anomaly.

VERSAILLES, USA N38 2 W 84 42 1.5
<400.0 Proven?

HOWELL, USA N35 14 W 86 36 1.6
~350.0 Proven? Shatter cones?

cryptoexplosive structures: Middlesboro, Versailles,
Jeptha Knob, and Muldraugh


CRYPTOEXPLOSIVE STRUCTURES
Three cryptoexplosive structures are shown on the
geologic map: Jeptha Knob, Versailles, and Middlesboro
(fig. 16). A fourth structure, the Muldraugh dome, is
unfaulted at the surface, but Silurian dolomite
apparently overlies brecciated Cambrian-Ordovician
Knox Dolomite in the subsurface (Freeman, 1951, p.
38).

Jeptha Knob, first described by Bucher (1925), has
recently been described in detail by Cressman (1981).
The structure, about midway between Louisville and
Lexington (sheet 2), is 14,000 ft in diameter. It is
characterized at the surface by concentric and radial
faults, an uplifted, brecciated, and partly
dolomitized central area, and a downdropped peripheral
belt. The age is closely constrained: disturbed beds
include rocks as young as latest Ordovician, which are
capped in the central part by undeformed earliest
Silurian strata. The origin of the Jeptha Knob
structure is uncertain, but meteoroid impact seems
most likely (Cressman, 1981, p. 14).

The Versailles cryptoexplosive structure was
discovered during the cooperative mapping project and
has been described by Black (1964). The feature is
about 5,000 ft in diameter and is in limestones and
shales of Middle and Late Ordovician age; no younger
beds are preserved in the area. At the surface it is
represented by a brecciated center within a belt of
concentric faults. The Versailles structure is about
10 mi west of Lexington (sheet 2 of the geologic map),
near the axis of the Cincinnati arch (fig. 16).

The town of Middlesboro, in far southeastern Kentucky
(sheet 3), is located in a topographic basin that is
the expression of a cryptoexplosive structure nearly 4
mi across in Lower and Middle Pennsylvanian rocks.
Englund and Roen (1963) suggested a meteor-impact
origin for the structure on the basis of the presence
of shatter cones and other features.

The origin of the Muldraugh dome is uncertain. It is a
domal structure, about 2 mi in diameter and unfaulted
at the surface, which has a structural relief of about
400 ft (Withington and Sable, 1969). This structure is
not labeled on the geologic map, but it appears as a
small, round outcrop area of the Muldraugh Member of
the Borden Formation (Mbf) at the east margin of sheet
3 about 4 mi south of the Ohio River. Freeman (1951,
p. 38) reported wells penetrating brecciated Knox
dolomites and cherts below coherent Silurian dolomite,
suggesting a "crypto-volcanic" nature. Cressman (1981)
suggested that Mississippian doming over a pre
Silurian deformational event argues against an impact
origin.

Sorry, I did no editing.................wally

[ Next Thread | Previous Thread | Next Message | Previous Message ]

Replies:

[ Contact Forum Admin ]

Forum timezone: GMT-8
VF Version: 3.00b, ConfDB:
Before posting please read our privacy policy.
VoyForums(tm) is a Free Service from Voyager Info-Systems.
Copyright © 1998-2019 Voyager Info-Systems. All Rights Reserved.