Extraterrestrial Nanoparticle Signatures at the Younger Dryas Boundary (~12,800 years ago) from Wonderkrater, South Africa

Abstract

<ns5:p>Background Previous work identified a platinum anomaly at Wonderkrater, South Africa, within sediments modeled to the onset of the Younger Dryas (~12,800 cal BP). To investigate the nature of this anomaly, we analyzed sedimentary nanoparticles using single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS). Methods Nanoparticles were extracted from peat sediments spanning the modeled Younger Dryas Boundary (YDB) interval and analyzed for particle number concentrations, elemental compositions, elemental ratios, and multi-element nanoparticle clusters. Results from the YDB interval were compared with sediments above and below the anomaly. Results A pronounced geochemical anomaly is confined to a narrow interval between 357.5 and 362.5 cm depth. Total nanoparticle number concentrations increase by a factor of 4.6 relative to surrounding sediments (p &lt; 0.01), accompanied by reduced average particle mass. The anomalous interval contains two distinct nanoparticle populations: one enriched in platinum-group and siderophile elements, and a second enriched in lithophile and rare earth elements. Eight elemental ratios exhibit elevated values relative to background sediments, including Au/Ir (3.80), Cr/Ni (3.75), and Au/Pt (1.16), each exceeding background values by more than a factor of two. Systematic fractionation among noble and siderophile elements is also evident, with Au, Pt, and Pd exhibiting greater enrichments than Os, Ir, and Ru, consistent with elemental fractionation during high-temperature vaporization, condensation, and atmospheric transport processes. Several multi-element nanoparticle clusters occur predominantly within the YDB interval. Conclusions The YDB layer at Wonderkrater contains a compositionally distinct nanoparticle assemblage characterized by elevated platinum-group elements, siderophile-element enrichments, unique elemental ratios, and changes in terrestrial dust-related signatures. The elemental ratio patterns and nanoparticle populations are consistent with a compositionally heterogeneous, volatile-bearing extraterrestrial component modified by high-temperature processes, together with enhanced terrestrial dust input. These observations are consistent with the introduction of geochemically distinct nanoparticle populations coincident with the onset of the Younger Dryas.</ns5:p>