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

Proceedings of the National Academy of Sciences, published online before print December 10, 2009; doi: 10.1073/pnas.0908874106

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

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

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.

Link:  http://www.pnas.org/content/early/2009/12/09/0908874106.abstract