Jan Cannon spent years studying the striking features of meteor
He now pursues the impact of those craters on the
oil and gas industry. And for petroleum geologists, Cannon has two
basic messages about terrestrial meteor craters:
"The mechanics involved in forming an impact crater create brecciated
rock that makes an excellent reservoir."
"More than one part of an impact crater has potential to produce
Cannon will present his views at the AAPG Annual
Meeting in Houston, in his paper "Hydrocarbon Potential of Buried
The association of meteor craters and hydrocarbons
gives his work more than theoretical interest. Cannon now targets
impact structures to help generate crater-prospects.
"The production potential is so fabulous, people
would like one," he said. "It's difficult because geologists haven't
been schooled to recognize them. There are a lot of circular things
out there, but not all of them are impact craters."
Cannon is president of Planetary Data in Tecumseh,
His paper will be part of the March 11 morning session
"NASA: Human Exploration of Earth, Moon and Mars," chaired by Bill
Muehlberger, a University of Texas emeritus professor.
Muehlberger has his own story about the need for
geologists to be better schooled in recognizing impact craters.
He recalled taking students on field trips through
East Texas, where he would point out the edge of the Marquez Dome
as an excellent example of a salt dome rim.
Study and analysis later revealed that the Marquez
feature is part of a meteor impact structure.
"You talk about feeling dumb," Muehlberger said.
'You Have a Crater Here'
craters and their potential seized the attention of the Oklahoma
oil industry in the early 1990s. Several new, deep wells in the
Sooner Trend produced exceptional amounts of oil and gas.
Why, no one knew for sure.
Rick Carlson, an independent petroleum geologist
in Edmond, Okla., put together some of the first prospects in the
deeper play. At that time he worked for DLB Oil and Gas.
"In the Sooner Trend in that area there's a lot of
well control," he said. "There's Mississippi Hunton penetrations
— you can map structural closure."
The new wells produced from the Arbuckle formation,
just above the Cambrian. One of Carlson's wells showed over 300
feet of gross pay on logs.
Great — but why?
"I couldn't map a structure that large," Carlson
recalled. "Up to then, there had been only four wells drilled to
the Arbuckle in Major County."
Some 2-D seismic existed, but its quality was too
poor to help, he said. Computer simulations that aided later analysis
weren't available at the time.
In 1991, the 1-20 Gregory in the new play targeted
Arbuckle at about 8,800 feet. DBL and Continental Resources partnered
with operator D&J Oil.
"We kept waiting for the Arbuckle to come up and
it wouldn't come up," Carlson said. "We kept drilling shale and
going lower. And lower. And lower."
Penetration rates suddenly increased. Cuttings included
brecciated granite with good shows, as well as shattered quartz
and feldspar with cleavage faces.
As it turned out, the Gregory had encountered a rich
reservoir on a high near the center of an astrobleme.
"Nobody at the time knew this was an impact crater,"
Carlson said. "Dr. Cannon was the first one who said emphatically
to me, 'You have a crater here.'"
Today, the structure is famous as the Ames Hole (May,
1992 EXPLORER). Carlson believes a meteor or asteroid the size of
a football field shattered 1,000 feet of Arbuckle and another 1,000
feet of basement rock, producing a crater more than 10 kilometers
Subsequent research indicated that the Ames crater
began to fill with fine sediments, ultimately producing a thick,
"Impacts will create their own reservoir rock," Carlson
noted. "They can create their own source rock. They create their
own faulting and closure."
Overlooking the Obvious
Impact craters may go unnoticed because they are
subtle, buried structures and geologists tend to have little training
in identifying them, according to Cannon.
"It's like the Ames Hole," he said. "Most everybody
at first accepted the theory that it was a buried caldera.
"In the conterminous United States, we should find
about 105 craters (similar to the Ames Hole). So far, we've only
found five to seven of them."
Craters offer clues to their true origin, Cannon
One of the clinching proofs for the origin of the
Ames Hole came from the presence of coesite and maskelynite, minerals
associated with meteor impacts.
Craters display morphological changes that occur
as certain thresholds of impact energy are crossed, Cannon said.
Larger craters show the effects of backward reflection of the original
"The brecciated center actually rebounds — this
is what causes the porosity," he said. "The shockwave comes back
and pulls up the rock in the middle."
In strictly scientific terms, Cannon calls the result
"an incredible, fractured mess."
"The morphology is a real key," he said. "On Earth
you start to see that effect at about three kilometers. But on the
moon, you don't start to see it until 23 kilometers."
Looking Up, Looking Down
Oddly, Cannon's introduction to impact craters had
nothing to do with Earth, much less oil and gas.
He earned his doctorate in geology at the University
of Arizona and went to work at the U.S. Geological Survey Astrogeology
Center in Flagstaff, Ariz. Cannon became a member of the NASA Remote
Sensing Applications Program and later mapped lunar landing sites
for Apollo missions.
"We mapped impact craters, because that's the primary
feature on the moon," he said. "They're the most common landform
in the universe."
Later, while teaching at the University of Alaska,
he used satellite images to identify an impact crater in central
"The water draining out of this lake had a high nickel
content," he said. "The USGS had found a high nickel anomaly in
"People didn't really know what to look for," Cannon
explained, but he knew the nickel anomaly could indicate a meteor
The Alaska discovery began his use of remote imaging
as a tool for crater hunting.
"I find them in satellite imagery because there's
an overprinting on the surface," he said. "We feel the mechanism
driving that overprinting is gravity tides."
His work with NASA helped him understand the results
of impact events. In analyzing the geology of Earth craters, he
noted that "we're still on the learning side.
"Our studies of the moon tell us that there were
a whole lot more of them in the Precambrian than there are now."
Buried impact craters can develop reservoir rock
in the brecciated central uplift, brecciated floor materials, fractured
rim materials and unconsolidated ejecta piles, Cannon said.
Those come from enormous force. Cannon said meteors
travel at 22 kilometers per second or faster, and typically gain
speed when they enter a planet's gravity well.
"That's because 22 kilometers per second is the cut-off
point for orbital velocity," he explained. "It turns out to be very
simple. Anything moving slower, hundreds of millions of years ago
would have fallen into the sun."
The force of a large meteor impact produces pressures
that exceed the Hugoniot elastic limit (HEL) for crustal rocks and
minerals. Permanent deformation of rock occurs from stress waves
beyond that point.
features in the geology at an impact site can affect the nature
of, and effect the shape of, the resulting crater, according to
Cannon. For instance, at Meteor Crater, Ariz., the crater appears
to be square.
"The fracture sets actually controlled the polygonality
of the impact crater," he said.
Successful development of a crater structure depends
on recognition of its morphology and degree of preservation, Cannon
said. Deeply buried craters, however, are not simple to discover
Carlson said the subtlety of impact crater geology
appeals to him, and keeps him interested in discovering a structure
similar to the Ames Hole.
"They're kind of stealth-like. The Ames Hole was
in the backyard of the Sooner Trend, where 1,000 wells had been
drilled," he said. "There it was sitting on the Anadarko shelf for
a long, long time, and nobody found it."
But evidence existed — for geologists trained to
Carlson said the Ames crater can be discerned in
Permian formations draped over the structure.
He recalled an earlier well drilled at the crater
Conventional thinking led the operator to abandon
the attempt after encountering wet sands.
"It was the driest dry hole you can imagine," he
said. "If they had drilled 500 feet deeper, they would have found
the Gregory well reservoir."
Cannon believes much more scientific study is needed
to understand how meteor impacts have affected the present crustal
structure of Earth.
"Just like Chicxulub, we can no longer ignore the
importance of impact craters on the history of our planet," he said.
Examining craters as potential hydrocarbon reservoirs
adds to their geological significance, although Cannon never expected
to see that kind of exploration on his resume.
"When I was mapping the Apollo landing sites," he
said, "hydrocarbons were the furthest thing from my mind."