[meteorite-list] Chinle

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:42:06 2004
Message-ID: <3A785A24.FA0E2EF8_at_lehrer1.rz.uni-karlsruhe.de>

Donald Blakeslee wrote:

> I have heard several passing references to some impact features found by
> Gene Shoemaker and others in Arizona, near Chinle. Can anyone point me
> to some written material on them and whether any meteorite fragments are
> associated?


Hi Don and List,

Here's what I've got.

Best wishes,

Bernd


E.M. Shoemaker et al. (1995) Impact crater identified on the
Navaho Nation near Chinle, Arizona (abs. Meteoritics 30, 578):

A small impact crater has been identified about 8 km north of Chinle,
Arizona, on the Navajo Nation. Preliminary studies show that the
crater is in a north-south dircection, measuring about 23 x 34 m in
diameter, with a depth of about 1.3 m. The impact origin of the crater
is identified by its shape, subsurface deformation, and an Fe-Ni oxide
fragment. We estimate the age to be about 150-250 yr. The impact site
is on the east side of the Chinle Valley at an altitude of 1685 m and
is about 2 km east of Chinle Wash. The crater formed on an alluvial
surface that slopes gently west toward the Wash. About 2 m of reddish
brown alluvial sand and silt of the Jeddito Formation of late
Pleistocene age rests on the Petrified Forest Member of the Chinle
Formation of late Triassic age. A moderately developed late Pleistocene
pedocal soil has developed on the Jeddito. Several thin discontinuous
caliche horizons occur at a depth of about 1 m. The caliche horizons
provided easily traced markers by which we could delimit the original
walls of the crater and recognize deformation along the crater walls.
Three trenches were excavated down to the top of the Chinle bedrock:
(1) an east-west trench 21 m long across the center of the crater,
(2) a north-south trench 13 m long in the north crater rim, and (3)
a north-south trench 12 m long in the south crater rim. Excavation
width was about 1 m and provided excellent exposures of the
subsurface stratigraphy and deformation. The trenches revealed
that the original crater was about 23 m wide and 27 m long. The original
rim crests have entirely eroded away so that no perceptible raised rim
remains. At the center of the crater, the original depth was about 3 m;
material washed from the rims now fills the crater floor to a depth of
1.5 m. The crater is symmetrical; however, the deepest part of the
original crater lies south of the center and was not reached in the
south trench.The east-west trench showed that the initial floor of the
crater was scoured down to the Jeddito-Chinle contact across the center
of the crater. Some of the Chinle was excavated by impact south of the
center, as seen in the trench in thre south wall. The original crater
walls slope inward about 30° on the east and west sides, about 20° on
the north, and about 45° on the south. Beds are dragged up along the
east, west, and south walls, but not along the north wall. The
deformation is restricted to within about 0.5 m of the wall. From the
asymetry of shape and deformation in the walls, we believe that the
impacting body struck at an oblique angle and was traveling from north
to south. A small, magnetic, FeO fragment, about 1 mm across, was
collected from material excavated from the south crater wall area.
Analyses of this fragment by electron microprobe detected a significant
Ni concentration of 5%. Two senior Navajo women (70-80 yr old)
independently remenber this crater as being much deeper during their
childhood, and both suggest that the impact was witnessed three to four
generations ago. Interestingly, many people in the Navajo community
thought that this crater was of impact origin. Additional work is
planned, including a broader aerial search for other possible impact
sites.
Received on Wed 31 Jan 2001 01:32:04 PM PST