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   PNAS
   Proceedings of the National Academy of Sciences of the United States
   of America

Absence of geochemical evidence for an impact event at the
Bølling-Allerød/Younger Dryas transition

    1. François S. Paquay^a,^1,
    2. Steven Goderis^b,^c,
    3. Greg Ravizza^a,
    4. Frank Vanhaeck^c,
    5. Matthew Boyd^d,
    6. Todd A. Surovell^e,
    7. Vance T. Holliday^f,
    8. C. Vance Haynes Jr.^f and
    9. Philippe Claeys^b

    1. 


    ^aDepartment of Geology and Geophysics, University of Hawaii at
    Manoa, Honolulu, HI 96822;
    2. 


    ^bEarth System Sciences and Department of Geology, Vrije
    Universiteit Brussel, 1050 Elsene, Brussels, Belgium;
    3. 


    ^cDepartment of Analytical Chemistry, Universiteit Ghent, 9000
    Ghent, Belgium;
    4. 


    ^dDepartment of Anthropology, Lakehead University, Thunder Bay, ON,
    Canada P7B 5E1;
    5. 


    ^eDepartment of Anthropology, University of Wyoming, Laramie, WY
    82070; and
    6. 


    ^fDepartments of Anthropology and Geosciences, University of
    Arizona, Tucson, AZ 85721

    1. Edited by H. Jay Melosh, Purdue University, West Lafayette, IN,
       and approved October 27, 2009 (received for review August 6, 2009)

Abstract

   High concentrations of iridium have been reported in terrestrial
   sediments dated at 12.9 ka and are interpreted to support an
   extraterrestrial impact event as the cause of the observed extinction
   in the Rancholabrean fauna, changes in the Paleoindian cultures, and
   the onset of the Younger Dryas cooling [Firestone RB, et al. (2007)
   Proc Natl Acad Sci USA 104:16016-16021]. Here, we report platinum
   group element (PGE: Os, Ir, Ru, Rh, Pt, Pd), gold (Au) concentrations,
   and ^187Os/^188Os ratios in time-equivalent terrestrial, lacustrine,
   and marine sections to seek robust evidence of an extraterrestrial
   contribution. First, our results do not reproduce the previously
   reported elevated Ir concentrations. Second, ^187Os/^188Os isotopic
   ratios in the sediment layers investigated are similar to average
   crustal values, indicating the absence of a significant meteoritic Os
   contribution to these sediments. Third, no PGE anomalies distinct from
   crustal signatures are present in the marine record in either the Gulf
   of California (DSDP 480, Guaymas Basin) or the Cariaco Basin (ODP
   1002C). Our data show no evidence of an extraterrestrial (ET)-PGE
   enrichment anomaly in any of the investigated depositional settings
   investigated across North America and in one section in Belgium. The
   lack of a clear ET-PGE signature in this sample suite is inconsistent
   with the impact of a large chondritic projectile at the
   Bølling-Allerød/Younger Dryas transition.
     * Os isotopes
     * platinum group elements
     * Clovis
     * Pleistocene extinction
     * meteorite

Footnotes

     * ^1To whom correspondence should be addressed. E-mail:
       paquay{at}hawaii.edu
     * Author contributions: F.S.P. and S.G. designed research; F.S.P.
       and S.G. performed research; F.S.P., S.G., G.R., F.V., M.B.,
       T.A.S., V.T.H., C.V.H., and P.C. contributed new reagents/analytic
       tools; F.S.P. and S.G. analyzed data; and F.S.P. and S.G. wrote
       the paper.
     * The authors declare no conflict of interest.
     * This article is a PNAS Direct Submission.
     * This article contains supporting information online at
       www.pnas.org/cgi/content/full/0908874106/DCSupplemental.