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PLATINUM GROUP ELEMENTS DO NOT SUPPORT A METEORITE IMPACT AT THE YOUNGER DRYAS.

Session: Myths and Misrepresentations surrounding Cosmic Impact claims in Paleoclimatology, Paleontology, Paleoecology, Geoarchaeology, and Quaternary Research

Presenting Author:

Philippe Claeys

Authors:

Claeys, Philippe¹, Goderis, Steven²

(1) Archaeology, Environmental Changes & Geo-Chemistry,, Vrije Universiteit Brussel, Brussels, Belgium; Pacific Centre for Isotope and Geochemical Research, Dept. of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada, (2) Archaeology, Environmental Changes & Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium,

Abstract:

The onset of the Younger Dryas (YD) at approximately 12.9 ka has been associated with elevated concentrations of platinum-group elements (PGEs), including platinum (Pt), iridium (Ir), palladium (Pd), osmium (Os), and ruthenium (Ru), in a range of terrestrial and ice-core archives primarily in North America, Europe, and the Middle East. These elevated anomalies constitute one of the most central lines of evidence for the Younger Dryas Impact Hypothesis (YDIH), which proposes that an extraterrestrial impact or airburst contributed to abrupt climatic cooling, megafaunal extinctions, and cultural changes near the Pleistocene–Holocene transition. However, several laboratories have failed to reproduce the Ir positive anomalies, using samples from various Yuounger Dryas sites, including the very same sections (Blackwater Draw, NM, Topper SC, and Lommel, Belgium) where elevated Ir was originally reported. Indeed, most YD boundary sections analyzed exhibit no Ir or PGE enrichment. Furthermore, the initially reported Younger Dryas positive Ir anomalies correlate negatively with nickel (Ni) concentrations, which seems highly unusual for two siderophile elements, both abundant in meteorites that normally share the same geochemical behaviour. This is also contradictory to analyses reported at other stratigraphic levels marked by a major meteorite impact such as the K-Pg boundary, or within the impactite, enriched in meteoritic component from several craters, such as Popigai, Morokweng, or Lapparjärvi, where Ni and Ir are clearly positively correlated. Elevated Pt concentrations have been reported from the Greenland Ice Sheet Project 2 (GISP2) that seem to slightly post-date the Younger Dryas. However, this Pt peak is not coupled with an enrichment in any of the other PGEs. This decoupling renders a mantle or meteoritic source for the Pt highly unlikely. Terrestrial and marine Osmium isotopic data have generally not provided unequivocal evidence for a dominant extraterrestrial source, either. This presentation examines the current status of the distribution and origin of highly siderophile elements within the Younger Dryas sequence, argues that there is limited support for a meteorite impact occurring approximately 12,9 ka ago, and discusses different explanations to account for the observed geochemical signatures.