[meteorite-list] Scientists Study Virginia Land For Clues On Chesapeake Bay Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:11 2004
Message-ID: <200106121537.IAA12377_at_zagami.jpl.nasa.gov>

http://www.kcstar.com/item/pages/printer.pat,fyi/3accbc10.608,.html

CRATER OF CIVILIZATION
Scientists study Virginia land for more clues on how the world was

By TINA MCCLOUD
Newport News Daily Press (Virginia)
June 11, 2001

A 10-foot-long tube of mud, brought up from hundreds of feet below the
Earth's surface, shares secrets from 35 million years ago.

That's when an asteroid or comet a mile or two wide crashed into what later
became the Chesapeake Bay. The impact left a crater about 56 miles wide and
one mile deep.

Chunks of debris were blown into the air, some settling back into the crater
in a jumble, the rest forming two concentric ridges like a bull's-eye.
Scientists describe it as looking like an upside-down sombrero.

Below the surface, the natural layers of rock and sediment were fractured.
That meant the aquifers -- underground water supplies -- no longer traced a
predictable path, and some became saltier than seawater.

Studying the big hole, identified only around 1994 as the Chesapeake Bay
Impact Crater, is important to understanding those aquifers, which supply
water to thousands of people and businesses in southeast Virginia, said
Scott Bruce, a groundwater geologist with the Virginia Department of
Environmental Quality.

That's why Bruce and Jean Self-Trail, a paleontologist with the U.S.
Geological Survey, are at work in a commuter parking lot in Mathews, Va.

The gravel-covered, county-owned lot seems an unlikely spot for exploring
the crater, which lies under hundreds of feet of sediment that were
deposited through the eons as the sea waters ebbed and flowed.

However, Mathews is a prime study site because it lies within the crater's
outer rim, which is about 28 miles from its center at Cape Charles on the
eastern shore.

Normally, the oldest things are buried the deepest. In the crater they're
all mixed up. Self-Trail, who studies ancient environments, helps date the
material by determining which microfossils are in the sediment. She knows
their time period and the type of water they lived in.

Each 10-foot section is videotaped and a written description is made. The
scientists use standard color samples, similar to those that show different
shades of house paint, to guide their decisions on which type of sediment
and rocks are present. That makes the description less subjective, Bruce
said.

The breakthrough to the crater fill material came at 738.8 feet below
ground. That degree of precision is important as the information gathered in
Mathews is added to data from five previous sites.

Last year, a hole 2,083 feet deep was drilled inside the crater at NASA
Langley Research Center in Hampton, Va.

Joel Levine, who studies atmospheric sciences there, is eager to test the
cores for trapped gases and analyze what the atmosphere was like millions of
years ago.

More than two dozen cores, frozen in liquid nitrogen to prevent
contamination, are awaiting study, he said.

"This has never been done before," said Levine, so he and a small team have
designed and built equipment to do the testing. If successful, this would be
a "very exciting tool" to learn more about Earth's history, said Levine, who
hopes testing will get under way within a month.

The NASA Langley and Mathews studies are part of a five-year project in
which the Hampton Roads Planning District Commission and the College of
William and Mary also are participating.

Cores were previously excavated in Newport News Park, Exmore and Kiptopeke
on the eastern shore, and Windmill Point on the Rappahannock River. The next
core may be drilled in Norfolk next year, said Bruce.

Bruce said the agencies hope to drill a 6,000-foot core hole at Cape
Charles, the center of the impact area.

What caused the giant crater?

Q. What hit us?

A. Whatever it was vaporized on impact. No one knows for sure. It was either
a comet (ice mixed with rock and organic material) or an asteroid (made of
either iron-rich silicates, carbon-containing materials or metals like iron
and nickel). Scientists use the generic word "bolide."

Q. When and where?

A. About 35 million years ago, in the ocean near the mouth of what would
become the Chesapeake Bay.

Q. How big was the bolide?

A. Probably one to two miles in diameter.

Q. How fast was it going?

A. About 50,000 mph.

Q. A big boom?

A. Energy equal to 10 trillion tons of TNT, or more than 100 times the
explosive yield of the world's entire nuclear arsenal.

Q. How big a hole did it make?

A. The "impact area" is about 56 miles wide and about one mile deep at the
center, which is near Cape Charles on the eastern shore.

Q. Is that big?

A. It's the largest impact crater in the United States and the sixth largest
on Earth (of about 160 known).

Q. Can I see it?

A. No. Through the eons, it has been buried under hundreds of feet of
sediment and the water of the Chesapeake Bay.

Q. Where can I read more?

On the Web at geology.er.usgs.gov/eespteam/crater/ or observe.ivv.nasa.gov.

--Sources: NASA, Scott Bruce (Department of Environmental Quality), U.S.
Geological Survey, Virginia Explorer magazine
Received on Tue 12 Jun 2001 11:37:44 AM PDT