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] ______________________________________________ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
