NEWS RELEASE: 4/22/99
New evidence links mass extinction with massive eruptions that split
Pangea supercontinent and created the Atlantic 200 million years ago
BERKELEY -- Hundreds of basalt outcroppings rimming the Atlantic Ocean
are actually the remnants of a single huge volcanic eruption some 200
million years ago that may have triggered a large extinction of life at
the end of the Triassic period, according to a report in this week's
issue of Science.
A team of researchers led by Paul R. Renne, director of the Berkeley
Geochronology Center and an adjunct associate professor of geology and
geophysics at the University of California, Berkeley, concluded that
these basalt dikes, sills and lavas, dispersed from the New Jersey
Palisades and the Brazilian Amazon to Spain and West Africa, resulted
from the most extensive pulse of magma eruptions known to date.
At the time these areas were near one another in the center of a
supercontinent known as Pangea. The eruptions began a process that
drove the land mass apart to create the Atlantic Ocean, at the same
time dispersing evidence of the eruption widely on the margins of four
The large flows of magma, which the researchers dubbed the Central
Atlantic Magmatic Province (CAMP), came from the Earth's upper mantle
and covered about seven million square kilometers over a geologically
short period of a few million years.
The beginning of the event matches within 20,000 years a global
extinction at the end of the Triassic period and the beginning of the
Jurassic. During this mass extinction, about half of all marine
species, mostly the ammonoid and bivalve mollusks, died out, while on
land several families of reptiles disappeared. Paleontologists regard
the extinction as one of the most deadly in the 600-million-year
history of multi-celled life. Many believe these changes set the stage
for the rise of dinosaurs in the Jurassic.
The close correspondence between the beginning of the CAMP eruptions
and the mass extinction suggests that the global disruption caused by a
long series of volcanic eruptions could have set off or at least
exacerbated the die-off.
"This is the best example of flood basalts associated with an
extinction," Renne said. "Some of the best stratigraphic evidence of
the mass extinction occurs in exactly the same site in which you find
the flood basalts -- they sit right smack on top of one another."
The likely scenario is that, as the magma surfaced in the form of
volcanoes over a large area of Pangea, noxious aerosols and greenhouse
gases disrupted the global climate and caused the extinction of a large
number of species. The basalts would have taken more than a million
years to cover the area and, thus, would overlay sedimentary evidence
of the extinction.
In 1995, a group led by Renne attributed another mass extinction, the
one that occurred at the end of the Permian and beginning of the
Triassic, to a similar magma flood in Siberia 250 million years ago. A
third mass extinction, the well-known event associated with the demise
of the dinosaurs at the boundary between the Cretaceous and Tertiary
periods, has been linked to a large volcanic flood that produced the
Deccan Traps in India.
"This is still one of the most intriguing issues in geology, the
relationship between extinctions and cataclysms such as magma floods or
asteroid impacts," he said. "What we now have is another piece of
evidence that shows there was a relationship between flood basalts and
The article detailing the extent of the CAMP basalts appears in the
April 23 issue of Science. Renne's coauthors include postdoctoral
fellow Andrea Marzoli, formerly of the Berkeley Geochronology Center
and now a research scientist at the University of Geneva, Switzerland;
Marcia Ernesto, a paleomagnetist at the University of São Paulo; and
geochemist Enzo M. Piccirillo of the University of Trieste, Italy.
Though many of these basalt outcrops, such as the well-studied
Palisades sill, had been dated to this general time period, until now
no one had realized the extent of the eruptions.
One reason the extent of the magma flow had not been recognized before
is that much of the evidence for the event is in temperate or tropical
forests, where outcroppings are obscured by vegetation and are heavily
eroded. However, recent field studies by French geologists in West
Africa and American geologists in the southeastern U.S. have provided
new information on the extent of basalt dikes and sills around the
Sills are what remain after magma intrudes into horizontal underground
fissures, then cools and is subsequently exposed. Dikes are the
remnants of magma that flowed into vertical fractures. Lava is magma
that broke through the Earth's crust and flowed on the surface before
The researchers in this study used the argon-argon (40Ar/39Ar) method
to date basalt lava flows, dikes and sills in Brazil, many of them
2,000 kilometers (1,300 miles) inland from the coast, and correlated
them with the ages of known formations up and down the East Coast of
the United States, in southwestern Spain, throughout West Africa, and
on the northern coast of South America. All proved to be from the same
era 200 million years ago, suggesting they have a common origin.
Paleomagnetic data from the Brazilian rocks confirmed the date.
While other episodes of flood basalts that have been correlated with
mass extinctions -- the Siberian Traps and the Deccan Traps, for
example -- are often several thousand feet thick, the preserved CAMP
lava flow piles are only about 1,000 feet thick. The researchers
estimate that in all the CAMP magmatism extended over 7 million square
kilometers in a period of a few million years, peaking about 200
million years ago. The total volume of magma is estimated at 2 million
cubic kilometers (500,000 cubic miles).
"While the volume is comparable to other flood basalt events, this one
spread over an area far larger than the others," Renne said. "This
system could have had many more volcanoes than the others."
As for the cause, Renne favors a theory put forward 10 years ago by
Berkeley geophysics professor and chair Mark Richards. Richards
ascribes flood basalts to a buoyant magma plume rising through the
viscous mantle from a spot near the boundary between the mantle and the
molten iron core, eventually cracking the surface in the middle of the
continent. The resultant rift zone pushes the land masses apart to
create an ocean, with an island chain forming over the hot spot and
recording the continual movement of the sea floor away from the rift
Though numerous hot spot island chains have been identified -- the
Hawaiian Islands in the Pacific, Iceland in the north Atlantic -- no
such chain has been associated with the break up of Pangea 200 million
years ago, Renne noted.
Two other coauthors of the paper are geochemist Giuliano Bellieni of
the University of Padova, Italy, and geochemical technician Angelo De
Min of the University of Trieste.
The research is supported by the National Science Foundation, several
Brazilian and Italian funding agencies and the Ann and Gordon Getty
Paul Renne can be reached at (510) 644-9200 or (510) 644-1350, or via
email at email@example.com.