HR: 0800h
AN: P41A-0202    [Abstracts]
TI: Clasts of Bladed Serpentine in a K/T Boundary Layer From the Central North Pacific: Implications for Catastrophic Impact by a Chondritic Projectile
AU: * Leung, I S
EM: irene.leung@lehman.cuny.edu
AF: Department of Geology, Lehman College, CUNY, 250 Bedford Park Blvd. West, Bronx, NY 10468/1589, United States
AU: Hagstrum, J T
EM: jhag@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 937, Menlo Park, CA 94052, United States
AB: A 24-m long piston core (LL44-GPC3) retrieved marine sediments from the central North Pacific. At a depth of 2055-2056 cm downcore, a thin layer having an Ir anomaly of 10 ng/g was identified as the 65 m.y. old K/T boundary layer by Kyte et al.,1995. We studied 6 samples of clay selected from 2042-2060 cm by Jim Broda (Woods Hole Oceanographic Institution), and found that only the 1 cm-thick Ir layer contains many microtektites (impact glass), 4 crystals of silicon carbide (SiC), about 20 clasts of serpentine, usually associated with several grains of magnetite. We believe that this sharply defined Ir layer might have been deposited by a catastrophic event of relatively short duration, perhaps triggered by an impactor. Serpentine crystals in the clasts are blade-like, but may also be foliated or granular. Bladed crystals are reminiscent of barred textures, or excentroradial groups of olivine and/or pyroxene, commonly found in chondrules. We also found a fine-grained, white substance which forms veins between serpentine crystals, resembling "Saponite" reported in an interplanetary dust particle (IDP) which was also composed of serpentine, by Keller et al., 1992, who believed that the IDP had links to hydrated CI chondrites. Thus, the precursor of serpentine clasts found in the GPC3 core, might have been a CI, or a carbonaceous chondrite (carrier of SiC) whose collision with Earth might have set off a fireball capable of transporting serpentinized chondritic particles and grains of SiC to our core site in the North Pacific.
DE: 6015 Dust
DE: 6022 Impact phenomena (5420, 8136)
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting