Period was previously thought to be ice-free
Arlington, Va.-Scientists using cores drilled from the
New Jersey coastal plain have found that ice sheets likely
caused massive sea level change during the Late Cretaceous
Period -an interval previously thought to be ice-free.
The scientists, who will publish their results in the
March-April issue of the Geological Society of America
(GSA) Bulletin, assert that either ice sheets grew and
decayed in that greenhouse world or our understanding
of sea level mechanisms is fundamentally flawed.
Led by Kenneth Miller of Rutgers University, the scientists
examined cores from Ocean Drilling Program Leg 174AX,
an onshore extension of an offshore expedition. They found
indications that sea level changes were large (more than
25 meters) and rapid (occurring on scales ranging from
thousands to less than a million years) during the Late
Cretaceous greenhouse world (99- 65 million years ago).
"The onshore-offshore drilling forms a important,
coordinated link to study the history of sedimentation
along this area of the U.S. continental margin,"
said Leonard Johnson, director of the National Science
Foundation (NSF)'s continental dynamics program, which
co-funded the research with NSF's ocean drilling program.
Analyses indicate minimal tectonic effects on the New
Jersey Coastal Plain at this time, the scientists say.
The other explanation for such large, rapid changes is
the waxing and waning of large continental ice sheets,
they maintain. What is perplexing, however, is that such
large and rapid sea-level changes occurred during an interval
thought to be ice free.
"Our studies of cores in New Jersey provide one
of the best- dated estimates of how fast and how much
sea level changed during the greenhouse world of the Late
Cretaceous," said Miller. "The Earth was certainly
much warmer at that time, probably due to high carbon
dioxide levels in the atmosphere. At the same time, our
estimates require that ice sheets grew and decayed on
Antarctica during this period of peak warmth, which has
been a previously heretical view."
The scientists propose that the ice sheets were restricted
in area to Antarctica and were ephemeral. The ice sheets
would not have reached the Antarctic coast, explaining
the relative warmth in Antarctica, but still could significantly
alter global sea level.