Mathematics – Logic
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmpp41a..04d&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #PP41A-04
Mathematics
Logic
1817 Extreme Events, 3344 Paleoclimatology (0473, 4900), 4901 Abrupt/Rapid Climate Change (1605), 5421 Interactions With Particles And Fields, 6000 Planetary Sciences: Comets And Small Bodies
Scientific paper
We report mineralogical and noble gas evidence for an ET impact associated with the Younger Dryas (YD) event and the mass extinction of various megafauna throughout the Americas approximately 12,900 years ago. We examined numerous well established, 14C dated Clovis sites across the US including detailed sediment profile analyses at Daisy Cave, CA (DC), Murray Springs, AZ (MS), Topper, SC, and Blackwater Draw, NM (BWD). He, Ne, and Ar analysis of magnetic separates, bulk sediments, HF-acid treated residue, and fullerenes coupled with a detailed mineralogical and compositional analysis of magnetic separates by SEM suggest a marked increase in the accretion of extraterrestrial debris in sediments at the YD boundary layer. A preliminary characterization of the magnetic separates consistently observed across numerous sites indicates an extremely high abundance of relatively unoxidized, trace metal rich metallic grains with extremely unusual compositions (e.g. Pt (5-98%), Sn (25-28%) , Ni (1-11%), and Cu (12-90%). These compositions are not easily explained by ordinary terrestrial processes. A few examples include the YD layer at DC which contains numerous metallic grains including Fe-Ni, Cu-Ni, Fe-Sn-Ni, and Pt grains. Metallic iron grains are observed at BWD and Topper, while the Topper site also contains iron spherules, Fe-Ni metallic grains, and Fe-Ni oxides. At this point there is no evidence for a significant concentration of iron spherules, Fe-Ni oxides nor unusual metallic grains away from the proposed impact layer. The noble gas composition and isotopic ratios of fullerenes located at the YD layers contain trapped He with ET isotopic signatures (0.3-3.5 ncc/g 3He and 3He/4He 30- 220 Ra) while Argon ratios (40Ar/36Ar= 230-255) reflect a mixture of planetary and air components. Bulk sediments were treated with HF acid to remove silicates, leaving a carbonaceous residue. Acid treated residues from two boundary layers contained up to 5 ncc/g 3He and 3He/4He from 15- 374 Ra. The DC acid residue exhibits a significant galactic cosmic ray input with 3He/4He=374-800 Ra. Bulk and magnetic sediments away from the boundary layer contain only 1-10 pcc/g 3He in the bulk sediment with 3He/4He from 0.1 to 4.6 Ra. These are consistent with the background IDP flux. An increase in 3He concentrations (5-8 ncc/g) and 3He/4He (10-25Ra) of magnetic grains is observed near the YDB which likely reflects an increase in the flux of IDPs associated with the impactor. The results indicate that the noble gas carrier is concentrated in the carbonaceous phase. Specifically, helium remains trapped in fullerenes as has been seen in other impact events (e.g. PT). The metallic Fe phase is either relatively devoid of ET noble gases or has been degassed during atmospheric entry.
Becker Lee
Darrah Thomas H.
Elrandson J. M.
Kennett D. J.
Kennett James P.
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