HR: 1330h
AN: B52B-1040    [PDF]
TI: Chondritic Meteoritic Fragments Associated With the Permian-Triassic (P-T) Boundary in Antarctica: Evidence for an end-Permian Bolide Impact.
AU: * Basu, A R
EM: abasu@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, 227Hutchison Hall University of Rochester, Rochester, NY 14627 United States
AU: Petaev, M I
EM: mpetaev@cfa.harvard.edu
AF: Department of Earth and Planetary Sciences, 20 Oxford Street Harvard University, Cambridge, MA 02138 United States
AU: Petaev, M I
EM: mpetaev@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AU: Poreda, R J
EM: poreda@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, 227Hutchison Hall University of Rochester, Rochester, NY 14627 United States
AU: Jacobsen, S B
EM: jacobsen@neodymium.harvard.edu
AF: Department of Earth and Planetary Sciences, 20 Oxford Street Harvard University, Cambridge, MA 02138 United States
AU: Becker, L
EM: lbecker@crustal.ucsb.edu
AF: Institute of Crustal Studies, University of California, Santa Barbara, CA 93106 United States
AB: We report the discovery of meteoritic fragments, as large as 400$\mu$m in size, in an end-Permian sedimentary bed in Graphite Peak, Central Transantarctic Mountains, Antarctica. Here, the P-T boundary is well constrained isotopically and paleontologically, and its lithology is well documented. The boundary at this site is also characterized by fullerenes containing extraterrestrial $^{3}$He and shocked quartz grains. We found meteoritic fragments in two samples of a claystone-breccia bed (separated stratigraphically by 23cm) that rests directly above the coal horizon with the last occurrence of {\it Glossopteris}. The meteoritic fragments display poikilitic or granular texture with euhedral-subhedral forsterite crystals enclosed in larger clinoenstatite grains showing polysynthetic twinning. Some silicate grains contain tiny inclusions of Fe, Ni-metal grains with chondritic Ni/Fe and Co/Ni ratios. Overall, Ni/Fe, Co/Ni and P/Fe ratios in the metal grains, Fe/Mg and Mn/Fe ratios in olivines and pyroxenes, and the chemistry of Fe, Ni, P, S-bearing oxides within the meteoritic fragments are typical of CM chondritic meteorites. The meteoritic grains found in magnetic separates of the sediments are accompanied by abundant metal nuggets, which are also found in an end-Permian bed from Meishan, south China. The common occurrence of these Fe-Ni-Si metal grains at Graphite Peak and at the Meishan P-T section provides further evidence that we sampled the P-T boundary at Graphite Peak. The association of metal grains with discrete meteoritic fragments at the Graphite Peak P-T boundary along with previous reports of such metal grains from other P-T localities leads us to support a catastrophic collision of a celestial body with the Earth at the end-Permian. We believe that this is what caused the global extinction event at the P-T boundary. Thus it appears that the two largest mass extinctions in Earth history at the K-T and P-T boundaries were both caused by catastrophic collisions with chondritic meteoroids.
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1630 Impact phenomena
DE: 2129 Interplanetary dust
DE: 3662 Meteorites
DE: 9614 Paleozoic
SC: Biogeosciences [B]
MN: 2003 Fall Meeting