Odale-Articles-Barringer

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IMPACT CRATER EXPLORATIONS

by: Charles O'Dale

BARRINGER IMPACT CRATER

The Barringer Crater from a distance of approximately 10km, and an altitude of 4000' above ground.
  • Age (ma): 0.049 ± 0.003a
  • Diameter: 1.19 km
  • Location: Arizona, U.S.A. N 35° 2' W 111° 1'
  • Shock Metamorphism: Shatter cones & rare PDF in quartz grains.
  • The 50 meter diameter 300,000 ton impacting meteorite impacted at approximately 15 km/sec and vaporized on impact. From siderophile elements detected in a meteorite fragment - siderophile elements (PGE, Ni, Au), it was determined the impactor was a IA iron (Tangle, Hecht 2006). The meteorite was a coarse octahedrite, average composition: 92% Fe, 7% Ni with Co, P and other trace elements (Buchwald, 1975). Meteorites from this fall are named “Canyon Diablo” after the canyon near where the first identified meteorite from this impact event was found.

a Three different dating techniques, taking advantage of the natural decay of naturally radioactive elements, have been used to determine the age of the impact crater. All three techniques are in agreement:

  • Sutton (1985) used thermoluminescence techniques to determine an age of 49000 +/- 3000 years;
  • Phillips et al (1991) used cosmogenic 36-chlorine techniques to determine an age of 49700 +/- 850 years, and;
  • Nishiizumi et al. (1991) used in situ production of 10-berilyum and 26-aluminum to determine a minimum age of 49200 +/- 1700 years.

General Area: This best known of all impact craters is 60 km ESE of Flagstaff, AZ on a flat plain south of the Little Colorado River. Although the crater is 1.19 km wide, it is very conspicuous because its bright rim contrasts with the darker plain of sedimentary rocks.

Specific Features: Meteor Crater is the type example of simple, bowl-shaped impact craters. It has slightly polygonal sides and a rim that rises nearly 50 m above the surrounding plain. Beyond the rim are low mounds of material thrown out by the impact. This impact happened when the Neanderthals were still in Europe and Homo sapiens were just emerging and entering Europe. The North American Ice Age would not end for another 30,000 years!
Superimposed on this space shuttle image of the crater area are the effects of the impact with its accompanying fireball on the local environment (with permission from NASA/Univ. AZ Space Imagery Center). Any animal within 25 km of the impact probably would not have survived the blast.
The Barringer Crater, approximately 150 km south east of the Grand Canyon, is classified as a simple meteorite crater (Kring 2007). Before the Barringer Crater was identified as an impact crater it was called Coon Mountain or Coon Butte. It was then called Meteor Crater after the nearest (now defunct) post office, “Meteor”. Barringer, who first postulated that the feature was the result of a meteorite impact, had established this post office at the Sunshine flag stop on the nearby railroad.
Odale-barringer-Barringer geology.jpg

D. Barringer assembled evidence to support an impact origin for the Barringer Crater. He then presented the following arguments for the impact origin of the crater to the Academy of Natural Sciences in Philadelphia in 1906, and again in 1909:

  • The presence of millions of tons of finely pulverized silica, which could only have been created by enormous pressure.
  • The large quantities of meteoritic iron, in the form of globular "shale balls", scattered around the rim and surrounding plain.
  • The random mixture of meteoritic material and ejected rocks.
  • The fact that the different types of rocks in the rim and on the surrounding plain appeared to have been deposited in the opposite order from their order in the underlying rock beds.
  • The absence of any naturally occurring volcanic rock in the vicinity of the crater.

These conclusions were championed by geologist George P. Merrill. Merrill analyzed a new type of rock discovered by Barringer at the crater, which Barringer called "Variety B". He concluded that it was a type of quartz glass which could only be produced by intense heat, similar to the heat generated by a lightning strike on sand. Merrill also pointed to the undisturbed rock beds below the crater, which proved that the force which created the crater did not come from below (Merrill 1908).

It was in 1920 that the structure was finally recognized to be an impact crater, the first feature on Earth to be so recognized.

Odale-barringer-Crater wall.jpg
One of the striking features of the crater is that its cross section clearly matches the geology of walls of the nearby Grand Canyon. The image of the crater wall (right) illustrates, from the bottom;

-the 260 million year old Coconino sandstone (Permian Age),

-the yellowish Toroweap formation, a Permian sandstone,

-the cream coloured 250 million year old Kaibab formation sandstone,

-the Kaibab 10 million year unconformity (the contact between older rocks and younger sedimentary rocks in which at least some erosion has removed some of the older rocks before deposition of the younger), and

-the 240 million year old reddish brown Moenkopi sandstone top layer of the crater wall (over the unconformity).


TOP: The shocked Coconino Sandstone is weakly shocked sandstone (<10 GPa) that lacks remnant porosity and contains abundant grain comminution and fracturing. Note the "rock flour" on the shocked sample. BOTTOM: The unshocked Coconino Sandstone consists of a fine to medium-grained, moderately well-sorted, rounded quartz arenite with ~ 20 vol% porosity. Coconino sandstone layers are typically buff to white in color. It consists primarily of sand deposited by eolian processes (wind-deposited) approximately 260 million years ago.
Barringer Crater is one of the few craters on this planet with a remaining crater rim.
Over seventy drill holes have been completed in the rim of the crater as part of a continuing research program of impact craters by the U.S. geological Survey. The drilling has shown that the overturned flap with its inverted stratigraphy is generally continuous out to about 400 m beyond the rim crest. The overturned flap is thickest on the southern side of the crater. Correlations between drill holes show rim uplift of at least 16 m at a distance of 30 m from the crater walls. The interpretation of the drill data suggests that relatively little erosion has occurred since the formation of the crater.

The rim of the 1.19 kilometre diameter Barringer Crater is still well defined, even after approximately 49 thousand years of erosion. It has been estimated that the first two stages of the cratering process (time from initial contact of the impactor until the end of the excavation stage) here at Barringer took approximately 6 seconds! Almost 63 million cubic metres were evacuated from this area in that time to form the crater. The height of the rim over the surrounding plain is 36 - 61 metres. Investigations around this rim confirmed an "overturned rim sequence".


Examples of fractured bedrock are scattered randomly around rim of the Barringer Crater.
The Barringer Crater is one of the youngest impact sites on this planet and the effects of the impact still remain in situ. On the rim of the crater I noted fracturing of this country rock by the impact shock wave. Note that the country rock at this point was uplifted approximately 45 metres from its original position over the surrounding plain. Erosion has not yet exposed the fractured rocks buried outside of the crater.

An overturned rim sequence is also present at the rim of the Barringer Crater and is now recognized as one of the hallmarks of an impact crater.

Barringer Crater imaged in infra red by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) part of NASA's Earth Observing System - Image courtesy of IVIS Laboratory, Univ. of Pittsburgh
On our planet, erosion will quickly remove an ejecta blanket and destroy any surviving meteorite fragments with the result that crater ejecta remains in only the youngest and best-preserved impact crater. This ASTER Infra Red image documents the pattern of the ejecta blanket around the relatively young Barringer Crater. The pattern of the ejecta blanket, although it has been modified by 49K years of erosion, implies an impact from the south west. The majority of the ejecta blanket forms in the north east, downrange, direction.

Aerial Exploration

Barringer ejecta.jpg
The light coloured north east flowing ejecta blanket of the Barringer Crater is visible from left centre to bottom centre of the image (image looking southwesterly).

Some of the Barringer Crater ejecta curtain can been seen here in visible light as illustrated in this image. I took this image of the crater from about 1000' above the ground. The "lighter" coloured sand is the remnants of the ejecta curtain. The pattern of the ejecta implies that the direction of the impactor was from the upper left of this image. If I was flying here at the time of impact, 49 thousand years ago, I would not know what hit me!!

We did a complete orbit of the crater in order to document it from each direction. Note the “square” shape of the crater, technically called a jointed crater. This shape is determined by the faults in the geology of country rock at the impact site.

In the "east view" image, if you look at the crater floor at the 5 o’clock position you will see a small white dot. Apparently that is the remains of a small aircraft. The pilot flew into the crater but with the tight turning radius required to stay away from the crater wall, he could not climb to exit the crater. It is a lesson in density altitude VS climb rate in steep turns. The altitude of the crater rim is over 5500’. The pilot and passenger survived albeit in a slightly “bent up” condition.

An excellent documentation of an exploration trip to the bottom of the Barringer Crater can be viewed at: www.meteorite.com


References

Barringer, D. M., 1906, Coon Mountain and its crater: Proceedings of the Academy of Natural Sciences of Philadelphia, v. 57, p. 861-886.

Buchwald, V.F. (1975) Handbook of iron meteorites. University of California Press, Berkeley, v. 3, pp. 937-942.

Kring David A., Guidebook to the Geology of Barringer Meteorite Crater, Arizona (a k a Meteor Crater), The 70th Annual Meeting of the Meteoritical Society, August 2007

Merrill, G.P. (1908) The Meteor Crater of Canyon Diablo, Arizona; its history, origin, and associated meteoric irons. Smithsonian Miscellaneous Collections, v. L, no. 1789, pp. 461-498 (with muliple plates).

TAGLE, R. and HECHT, L., Geochemical identification of projectiles in impact rocks. Meteoritics & Planetary Science Volume 41, 26 JAN 2010.

University of New Brunswick


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