[meteorite-list] Geologists Suggest Asteroid Created Coal-Rich Williston Basin

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun Nov 28 23:55:53 2004
Message-ID: <200411290455.UAA22487_at_zagami.jpl.nasa.gov>

http://www.billingsgazette.com/index.php?id=1&display=rednews/2004/11/28/build/state/60-asteroid-basin.inc

Geologists suggest asteroid created coal-rich Williston Basin
Associated Press
November 28, 2004

KALISPELL - The asteroid thought to have killed the dinosaurs when it
slammed into Earth 65 million years ago may also have created the
coal-rich Williston Basin, a group of geologists suggest.

The basin underlies most of northeastern Montana and western North
Dakota. It contains one of the largest lignite coal deposits in the
world at about 540 billion tons, according to U.S. Geological Survey
estimates.

The asteroid killed off most major predators, meaning plants in the
basin would have grown and died unimpeded for years, a team of
geologists from the University of Wisconsin-Milwaukee, the Milwaukee
Public Museum and the University of Rhode Island say in their research.

The uninhibited plant growth created substantial peat mires that
eventually turned into the coal fields that pepper the basin today, said
Peter Sheehan, curator of geology at the Milwaukee Public Museum.

The boundary between pre-impact and post-impact rock formations in the
basin is obvious, researchers said, with darker floodplain deposits
replaced by distinctive layers of lighter-colored sediments.

Just above the boundary, the first thin coal seam appears.

"We're suggesting that the impact caused these changes," Sheehan said.
"If not for that and the associated change in vegetation and animal
life, there would not have been a continuation of the (pre-impact)
formation."

Other theories on coal formation abound, however, and some colleagues
are already disputing the group's suggestion.

Kirk Johnson, chief curator at the Denver Museum of Nature and Science,
said the resurgence of a major inland sea may also have played a role in
coal.

"We think the coal formation could be related to the Cannonball Sea," he
said. "As sea levels rose, it may have raised groundwater levels and
created swamps."

The Cannonball Sea split off from a much larger waterway about 2 million
years before the asteroid impact, running from the Gulf of Mexico to
present-day North Dakota.

Johnson was somewhat skeptical of Sheehan's theory, saying he wanted to
see more data. More recent research shows that coal started forming in
the basin before the asteroid impact, he said.

"That's the real question for Peter," Johnson said. "Where's the data?"

Sheehan, who has studied the dinosaur extinction and other mass
extinctions for more than 20 years, said he knows proving the new theory
will be difficult.

"This is just a first attempt," he said. "We need to look at how fast
some of these changes occurred, and we need to look at the distribution
of the coal seams in relation to when herbivores returned. At this
point, what we're really saying is that this type of 'extraterrestrial'
event is something we need to be considering."
Received on Sun 28 Nov 2004 11:55:47 PM PST