[meteorite-list] Crater Makes an Impact on Three Sessions at GSA

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:47:09 2004
Message-ID: <200111071708.JAA12373_at_zagami.jpl.nasa.gov>

http://www.usgs.gov/public/press/public_affairs/press_releases/pr1521m.html

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 News Release
                                             Address
 U.S. Department of the Interior 953 National Center
 U.S. Geological Survey Reston, VA 20192
 Release Contact Phone Fax
 November 6, 2001 Diane Noserale 703-648-4333 703-648-6859
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Crater Makes an Impact on Three Sessions at GSA

Note to Editors: Interviews with the scientists during the Geological
Society of America (GSA) Annual Meeting can be arranged by contacting
Carolyn Bell (USGS) or Ann Cairns (GSA) in the GSA newsroom in Boston at
617-954-3214.

What happens when a rock from space that's more than a mile wide slams into
the Earth at supersonic speed? Scientists from the U.S. Geological Survey
(USGS) and its partners are learning as they analyze evidence they are
recovering from cores drilled during the past two summers into the
Chesapeake Bay impact crater and surrounding structures. USGS scientists
David Powars, C. Wylie Poag, and J. Wright Horton, Jr. will present new
evidence obtained from cores and seismic surveys, on the devastating effects
this event had on the Earth 35 million years ago, during three separate
sessions at the Annual Meeting of the Geological Society of America,
scheduled for Nov. 4-8 in Boston, Massachusetts.

It's bigger and deeper than we imagined: "This comet or asteroid shot
through the Earth's atmosphere, leaving a vacuum in its wake. Then it hit,
splashing through several hundred feet of ocean and slicing through several
thousand feet of coastal plain sediments," says Powars. "It fractured the
crystalline bedrock below to at least a depth of seven miles and a width of
85 miles. Billions of tons of ocean water were vaporized and millions of
tons of debris were ejected into the atmosphere within minutes. Marine life
was decimated, and a train of giant waves of seawater inundated the land,"
explains Powers, whose talk "Structure and Composition of the Southwestern
Margin of the Buried Chesapeake Bay Impact Structure, Virginia" is scheduled
for 4:45 pm Tues, Nov. 6, Hynes Convention Center Room 202.

What's written in stone: USGS scientists are looking for clues left in the
bedrock from this extraordinary event in the deep past, to deal with an
ordinary modern-day issue: finding ground water suitable to support a
rapidly-developing region. Studies are underway to understand the impact
structure and its influence on ground water.

"We are examining the composition, age, and structure of crystalline
basement rocks beneath the Coastal Plain sediments. We are beginning to
learn more about these rocks and how they were affected by the impact
event," Horton explains.

"Crystalline rocks hidden under the blanket of Coastal Plain sediments make
up one of the most poorly understood areas of geology in the U.S., and
drilling in the impact structure has provided rare samples from as deep as
2083 feet." "Crystalline Rocks from the First Corehole to Basement in the
Chesapeake Bay Impact Structure, Hampton, Virginia" is scheduled for 2:45 pm
Thurs., Nov. 8, Hynes Convention Center Room 200.

Not a creature was stirring: USGS scientists have recently identified a zone
of silt above the post-impact fallout that is devoid of signs of indigenous
life. Wylie Poag points out that the heat from this impact must have
instantly incinerated every living thing within hundreds of miles. Poag will
review evidence -- such as fractures and deformation features in crystals,
melted rock, and tiny glass spheres -- that indicate shock pressures at
ground zero that could only have come from an impact. "From Shocked Basement
to Fallout Spherules: The Coring Record at the Chesapeake Bay Crater" is
scheduled for 4:15 pm Thurs, Nov. 8, Hynes Convention Center Room 304.

The USGS serves the nation by providing reliable scientific information to:
describe and understand the Earth; minimize loss of life and property from
natural disasters; manage water, biological, energy, and mineral resources;
and enhance and protect our quality of life.

                                *** USGS ***
Received on Wed 07 Nov 2001 12:08:16 PM PST