http://www.innovations-report.de/html/berichte/geowissenschaften/bericht-39739.html

February Geology and GSA Today media highlights
Geological Society of America
February 2, 2005

The February issue of GEOLOGY covers a wide variety of potentially
newsworthy subjects. Topics include: earthquakes in the central Indian
Ocean and possible break-up of the Indo-Australian tectonic plate;
dynamics of the Chicxulub impact tsunami; sea-level rise and the future
of reef islands; evidence for abrupt climate change triggered by
meltwater from glacial Lake Iroquois; new evidence from the Late
Ordovician of CO2 as driver of climate change; and new support for a
causal relationship between changes in Earth's orbit and the end of
Earth's penultimate ice age.

Highlights are provided below. Representatives of the media may obtain
complimentary copies of articles by contacting Ann Cairns at
[EMAIL PROTECTED] Please discuss articles of interest with the
authors before publishing stories on their work, and please make
reference to GEOLOGY in articles published. Contact Ann Cairns for
additional information or other assistance.

Non-media requests for articles may be directed to GSA Sales and
Service, [EMAIL PROTECTED]

Geology

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La
Popa basin, northeastern Mexico, and its implications for distribution
of impact-related deposits flanking the Gulf of Mexico

Timothy F. Lawton, New Mexico State University, Las Cruces, Department
of Geological Sciences, Institute of Tectonic Studies, Las Cruces, NM
88003-8001, USA, et al. Pages 81-84.

The impact of a large extraterrestrial object on the Yucatan platform 65
million years ago created one or more large tsunami, or huge waves, that
displaced a large volume of the Gulf of Mexico onto the adjoining
continent. This water, rushing back toward the Gulf, would have
possessed tremendous erosive capacity and the ability to carry sediment
and fossils from the coast into deep water. Geologists working in
northeastern Mexico recently discovered evidence for this southward
backrush of water in the deposits of ancient valleys scoured into the
continental shelf. The valley-fill deposits, laid down at the end of the
Cretaceous period, contain abundant grains of formerly molten rock
(ejecta) thrown from the Chixculub impact crater. These grains evidently
arrived in northeastern Mexico before the tsunami, and the backwash of
Gulf-bound water eroded them from coastal regions and concentrated them
in the valleys as flow velocity slowed adjacent to the temporarily
lowered sea level of the Gulf. Also present in the valley-fill deposits
are fossils eroded from coastal settings; these organisms provide firm
evidence for the source of the flow. Although the duration of the
backflow is unknown, it is likely to have continued for hours or days
after the initial impact. These deposits therefore provide evidence for
an enormous sediment-recycling system set up by the run-up of tsunami
waves onto coastal North America shortly after the Yucatan impact. This
discovery confirms the grand scale of sediment and fossil recycling at
the end of the Cretaceous and helps to explain why the latest Cretaceous
fossils are commonly found above the impact rocks in the Gulf of Mexico
region.

[snip]

Geochemical signatures of Archean to Early Proterozoic Maria-scale
oceanic impact basins

Andrew Y. Glikson, Australian National University, Research School of
Earth Sciences, Canberra, Australia. Pages 125-128.

Until recently the nature of the early Earth crust was known mainly from
studies of small continental relics dominated by granite, whereas the
nature of the other ~90% of Earth crust remained unknown, except by
indirect methods. Glikson's paper examines the geochemical evidence
provided by ejecta fallout of large asteroid and comet impacts on the
early Earth (2.4-3.5 Ga), as preserved in sediments, which indicate that
the earth crust consisted largely of oceanic-type basaltic rocks, small
continental nuclei, and large transient impact basins (similar to the
lunar Maria). This model of early Earth is consistent with
considerations based on chemical and isotopic evidence from early
volcanic and plutonic terrains.

[snip]

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