[meteorite-list] Geologist Says Santa Fe May Sit in Meteorite Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 11 Aug 2013 21:04:08 -0700 (PDT)
Message-ID: <201308120404.r7C448Qb023564_at_zagami.jpl.nasa.gov>

http://www.santafenewmexican.com/news/health_and_science/article_7c9de31e-2cdd-5be1-98ef-db2e915637de.html

Science matters: Geologist says city may sit in meteorite crater
By Roger Snodgrass
The New Mexican
August 9, 2013

Santa Fe is built over what might well be the remains of a large meteorite
crater. Those who know this already should raise their hands and pat themselves
on the head.

"Judging by satellite imagery and aerial photos, Santa Fe appears very
close to the middle of it," Thornton "Tim" McElvain, a retired petroleum
geologist who has been looking into the crater for more than a decade,
said this week. "I really don't know the size of the crater. It could
be up to 50 miles in diameter."

Thinking of Chicxulub, the monumental crater underneath the Yucatan Peninsula,
where an asteroid strike ended the era of dinosaurs, McElvain said, "It
could have caused an extinction event."

Despite the uncertainties, there is a lot to learn in this grand puzzle.

The dating is still up in the air - somewhere between 20 million and more
than a billion years ago. The younger date is when the Rocky Mountains
stood up over a very brief time span, under circumstances that await a
fuller explanation. Needless to say, the upward thrusts and tilt thoroughly
mixed things up. The older date is associated with a geological period
dubbed "the great unconformity," a vacant space in the stratigraphy of
the Southwestern United States, when hundreds of millions of years of
the geological record were expunged.

Here's the story of the Santa Fe Impact Crater in progress:

While visiting Rochechouart, a village in west-central France, in 1998,
McElvain, who has lived in the Santa Fe area for more than 50 years, saw
a peculiar formation of grooved, cone-shaped rocks that reminded him of
similar features he had seen at home. As it happens, Rochechouart shares
its name with a meteor crater in which the village partly sits.

Throughout the world, as McElvain discovered, the kinds of rocks that
geologists call "shatter cones" are associated with impact craters. When
the cones are connected with another signature clue, called shocked quartz,
the combination is nearly enough to ascertain the existence of a genuine
impact crater. Impact craters on Earth are caused by a celestial collision
with an asteroid or comet that penetrates the atmosphere and crashes to
the surface. Depending on size, these events can cause a very large explosion
and shockwaves strong enough to melt and deform stone.

After returning to the Santa Fe area, McElvain was like a detective at
the scene of the crime, trying to put the pieces together. Not surprising
for a case that encompasses eons, this one turned out to be rather messy.
Much of the evidence was destroyed, what was left was well hidden, and
the cops (or academic gatekeepers) were too busy with other important
matters to lend much of a hand.

In 2004 and 2005, McElvain found credible shatter cones and shocked quartz
in the southern Sangre de Cristo Mountains along Hyde Park Road, a few
miles northeast of Santa Fe. The discovery was written up in a peer-reviewed
paper in Earth and Planetary Science Letters in 2008, with McElvain as
a co-author. The paper included detailed mapping, measurement and petrographic
analysis of the shatter cones that strongly supported the existence of
a "previously unrecognized but highly eroded or tectonically dismembered
terrestrial impact structure."

The Planetary Impact Data Base in the Planetary and Space Science Centre
lists the Santa Fe Impact Structure as having originated 1.2 billion years
ago and measuring 3.7 to 8 miles in diameter.

Beginning with investigating an isolated impact crater in Pecos, McElvain
went on to investigate the Santa Fe crater and eight other structures
in the Southwest. He is exploring an even more complex hypothesis - that
the Santa Fe crater is one of many formed by a string of meteor pieces
that hit the Earth at about the same time. McElvain has self-published
and updated papers on these subjects from time to time on the digital
documents library Scribd
(www.scribd.com/doc/93445091/southern-rocky-mountain-and-colorado-mid-tertiary-impact-event).

'"The bombardment of the Earth is going on and has not stopped," McElvain
said, when asked if he thought meteors and asteroids should be an ongoing
concern. "Stephen Jay Gould [an American paleontologist who died in 2002]
identified a pattern that he called 'punctuated equilibrium,' which said
that roughly every 30 million years there is an extinction event.' Meteor
impacts are a big thing in the history of Earth and of life on Earth."
Received on Mon 12 Aug 2013 12:04:08 AM PDT