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Subject: Ancient Cataclysm off U.S. Pinpointed;Meteorite Impact Tore Up Midatlantic
Date: Wed, 28 Oct 92 04:28:31 EST
Message-ID: <44.1992Oct28.042831@AmeriCast.com>

Ancient Cataclysm off U.S. Pinpointed;Meteorite Impact Tore Up
Midatlantic Coast 35 Million Years Ago<By Boyce
Rensberger=Washington Post Staff Writer= A gigantic wall of water
- a wave that may have been a thousand feet high and 360 miles
long - crashed against the east coast of North America. It tore
up the land from New Jersey to North Carolina, churning it so
deeply that when the wave subsided, the layered deposits of seven
previous geologic ages were scrambled for miles inland.

That, according to a report yesterday by scientists with the U.S.
Geological Survey, is what happened about 35 million years ago
when a half-mile-wide meteorite slammed into the ocean 80 miles
east of what is now Atlantic City.

A year ago, the same geologists reported finding the zone of de-
vastation in Virginia and Maryland and estimated that a meteorite
must have plunged into the Atlantic about 40 million years ago.
Now they have established that the cataclysm happened more re-
cently and that the effects reached farther up and down the
coast. In addition, they think they have found the underwater
crater made by the impact. It is an oval 9 by 15 miles and meas-
ures 1,500 feet deep from the bottom to the rim.

The impact launched a monster ripple "hundreds or thousands of
feet high," the scientists said, that widened until it crashed
ashore at a speed as high as 500 mph.  Along the way, the roiling
water excavated ancient deposits hundreds of feet down and mixed
them into one muddy mess that settled as the wave subsided.  "The
enormous wave gouged out a 200-foot-deep, Connecticut-sized area
along Virginia's coast and filled it with a spectacular assort-
ment of large boulders and shock-altered minerals wrenched from
beds of seven geologic ages and mixed together like plums in a
pudding," C. Wylie Poag, leader of the group that made the
discoveries, told a Cincinnati meeting of the Geological Society
of America. Poag is based at the Geological Survey's Woods Hole,
Mass., research center.

The impact was similar in principle to one that occurred 65 mil-
lion or 66 million years ago and which is blamed for the extinc-
tion of the dinosaurs, but very different in scale. The older ob-
ject has been estimated at six miles in diameter, or about 1,700
times more massive than the half-mile meteorite. No mass extinc-
tions are associated with the 35 million-year-old impact.

Poag said that additional research over the last year has shown
that the same churned-up deposits extend from northern New Jersey
south to Cape Hatteras, N.C. The area of destruction is a band
reaching inland from the present shoreline from 18 miles to 60
miles. The disruption extended inland the farthest in Virginia,
reaching across southern Chesapeake Bay almost to Richmond.

Poag said signs of the cataclysm are no longer evident on the
land surface because they have been buried by 1,200 feet of sedi-
ments deposited since the meteorite fell. The crater lies beneath
3,000 feet of ocean sediments and 120 feet of water.

Hints of the ancient cataclysm emerged in 1983 when the National
Science Foundation's Deep Sea Drilling Project found that within
the Atlantic floor lay a two-inch layer of shock-altered minerals
and pieces of glassy material. Minerals are altered in these ways
by powerful explosions such as atom bombs. When large meteorites
hit the Earth, they release enough energy to melt or vaporize
large amounts of material. The molten material hardens into
glassy form and falls back to ground.

 Poag and his colleagues extracted cores of Earth's crust at
sites along the coast and found that the normally neat layer-cake
of ancient deposits had been churned up. Deposits known from oth-
er sites to be 110 million to 35 million years old were jumbled
together. Boulders of a kind that lay in the same layer in adja-
cent areas are strewn through a 200-foot-thick zone.

More recently, Poag has made the geologist's equivalent of CT
scans of the sea floor. These images, called seismic profiles,
are made by sending shock waves into the Earth's crust and
recording the waves that return to sensors as they bounce off
hidden layers. The result is comparable to what one would see by
digging deep into the ground and looking at the wall of the hole.

Seismic profiles of most of the coastal region revealed the
long-buried crater, a blanket of blasted-out material around it,
and, along the coast, chaos where there should be neat
layers.<02:34 10-28C9999-----

Copyright 1992, The Washington Post.  This story is from the
Washington Post's Capitol Edition On-Line and is not to be ar-
chived or redistributed.

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