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

[Ron Baalke]

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."