Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmgc41b1055c&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #GC41B-1055
Mathematics
Logic
0325 Evolution Of The Atmosphere (1610, 8125), 0468 Natural Hazards, 3344 Paleoclimatology (0473, 4900), 3672 Planetary Mineralogy And Petrology (5410), 6022 Impact Phenomena (5420, 8136)
Scientific paper
The 4 kyr BP impact event has been identified from deep-sea, soil and archaeological records as the worldwide pulverisation of a volatile-rich debris jet(1). High resolution sequences show two stages of ejecta fallout linked to the impact-triggered doublet gaseous regime(2): scattered solid debris at the ground surface and spray of the vaporized hot fireball with thermal blast and local ignition. Ejecta debris consist of flow- textured impact glass, impact breccia and incompletely melted marine clasts: volcano-clastic sandy mudstone, calcareous mud, granite-gneiss, schists, volcanic breccia, kerogen and algal mud. Marine microfossils, organo-mineral markers, and the debris-fallout spatial pattern indicate two potential impact craters: an Antarctic source with an admixture of volcanic glass and ice rafted debris, from the vicinity of Heard Island and the Kerguelen plateau; a low latitude, shallow water one with hydrocarbons possibly from the Gulf of Mexico. Fine mixing of target materials from far distant source craters emphasizes a unique impact-ejecta. This matches the theoretical view of a debris jet channelled along the corridor cut through the atmosphere by the incoming projectile, raised upward, and dispersed widely(3). The isotopic anomaly of the sulphur phase in the kerogen volatile-component, indicating mass independent fractionation due to photolytic transformation, suggests launching at great heights, beyond the O2-O3 UV shield, responsible for climate disturbances. The incomplete melting of target rocks and global dispersion of impact breccia out of the craters would result from splash of small-sized projectile at rather great water depth and a low angle impact (10-15 degrees) into porous, highly compressible marine sediments. The spatially variable distribution of the organo-mineral and melt components, and the wide range of phase transformation reflect nonequilibrium shock-melting and micro-scale thermal processes in the heterogeneous vapor plume ejected from the impact sites. The 4 kyr BP event provides the first opportunity to compare on a variety of scales the environmental effects of globally dispersed ejecta from a multiple-site oceanic impact and the complex responses of human societies to frightening manifestations. [1] Courty, M.-A. et al., 2006. Geoph. Res. Abs., vol. 8, A-01812 [2] Alvarez, W., Claeys, P. and Kieffer, S., 1995. Science, 69, 930-936 [3] Kring, D.A., and Durda, D.D., 2002. J. Geoph. Res., 107E8: 1029
Abbott Dallas H.
Cortese Gennaro
Courty M. M.
Crisci Alfonso
Crosta Xavier
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