NSF PR 96-9 - March 14, 1996
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Scientists Report Surprising New Results from Caribbean
Sea Expedition
Crater fragments found more than 1,000 kilometers
away from the impact site, unexpected ancient volcanoes,
evidence of long-ago global warming, and clues to
recent climate change are just a few of the surprising
results of a recent National Science Foundation (NSF)
Ocean Drilling Program (ODP) research expedition.
Departing from Miami a few days before Christmas,
the research vessel JOIDES Resolution set out for
the Caribbean Sea on a two-month expedition to gather
new evidence of one of the greatest catastrophes in
Earth's history: the meteorite impact that caused
the extinction of the dinosaurs and other life forms
65 million years ago. Recent studies show that the
meteorite impact occurred on the north end of the
Yucatan Peninsula in Mexico, creating the 180-kilometer-wide
Chicxulub crater, which is now buried under younger
sedimentary rocks.
Says Robert Corell, NSF assistant director for geosciences,
"The global effects of this impact were so severe
that it closed one chapter in Earth history, and opened
another. The Caribbean Sea ODP research expedition
has led to new information about millions of years
of our planet's past."
By drilling deep into the ocean floor in the Caribbean
Sea, scientists on this expedition extracted valuable
materials blasted out of the Chicxulub crater at the
time of the great impact. These samples were recovered
in three drill cores, one from a kilometer-deep drill
hole north of Colombia, and two from half-kilometer-deep
drill holes near Jamaica. The lowermost parts of the
drill-core samples recovered in the Caribbean consist
mainly of altered glass spheres, or tektites. These
were formed when the explosive collision of the meteorite
with Earth generated very high temperatures that melted
the crustal rocks in the Yucatan Peninsula. The tektites
were deposited up to 1,000 kilometers from the crater,
a result of the impact.
Central American Volcanism Totally unexpected on this
expedition was the discovery that volcanic eruptions
in Central America have repeatedly spread volcanic
ash over the Caribbean in the past. Evidence from
new drill cores extracted from the ocean floor shows
that thousands of volcanic ash layers occur in Caribbean
sediments, with some individual layers up to 14 inches
thick.
These ash layers indicate that Central American volcanic
activity was particularly severe during two periods
in the geologic record, about 34 and 19 million years
ago. The sources of these volcanic ash layers lie
over 1,000 kilometers to the west, in the ancient
volcanoes of Guatemala, El Salvador, Nicaragua, and
Honduras, from which the Mayans quarried volcanic
rocks to build the great pyramid at Coban. The majority
of these volcanic eruptions were larger than any recent-history
volcanic event.
Ancient Global Warming, An Analogy to Today? Scientists
have been probing the Earth's geologic record for
past events that might help us understand the effects
of rapid climate changes. During the last few years,
geologists have found evidence, in sediment cored
from the deep ocean basins, for dramatic global warming
about 55 million years ago. This warming was coincident
with massive extinction of microscopic organisms living
on the sea floor, the most devastating event to strike
these microorganisms in the past 100 million years.
During the expedition, striking records of the dramatic
warming episode were brought up from the Caribbean's
depths at two sites, one Just north of Colombia and
the other south of Haiti. The finely layered sediments
show, for the first time, direct evidence of oxygen-poor
oceans. Sediments which are deposited under well-oxygenated
conditions are continuously stirred up by worms and
other deep-dwelling organisms. However, few organisms
can live in stagnant conditions. At the two Caribbean
sites, the sediments indicate that deep-dwelling organisms
either temporarily inhabited other areas, or in many
cases became extinct.
Clues to Recent Climate Change Bridging the gap between
ancient and modern climate is a quarter-million-year
record of tropical climate change preserved in Cariaco
Basin on the northern margin of Venezuela. Cariaco
Basin is the largest open-ocean example existing today
of anoxic, or totally oxygen-free, conditions. Here,
the stagnant waters and rapid accumulation of sediments
result in a record of past climate and oceanic conditions
of unparalleled resolution.
Scientists expect the Cariaco Basin sediments recovered
to produce an important record of how tropical climate
has varied on time scales of tens to thousands of
years over the recent geologic past. This will allow
for the first time a direct comparison of tropical
and polar climate change over the past 250,000 years.
The Cariaco Basin will also be studied as an analog
for how anoxic conditions in more ancient oceans may
have contributed to the formation of petroleum source
rocks.
[Note to editors and reporters: Photographs and video
of Ocean Drilling Program (ODP) research expeditions
are available from the ODP office at: (409) 845-9322.]
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