WIDESPREAD PLATINUM ANOMALY DOCUMENTED AT THE YOUNGER DRYAS ONSET IN NORTH AMERICAN SEDIMENTARY SEQUENCES CONSISTENT WITH GREENLAND ICE CORE DATA

In 2013, Petaev et al. reported a large extraterrestrial platinum (Pt) anomaly in the Greenland ice sheet (GISP2) at the Younger Dryas onset (YD boundary layer, or YDB). In this study, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on bulk sediments from stratified archaeological sites to evaluate evidence of a corresponding platinum (Pt) anomaly. Here we document discovery of a distinct Pt anomaly horizon in 11 archaeological sedimentary sequences across North America that date to the YD onset. The widespread, apparent synchronicity of a Pt anomaly at the YDB is consistent with GISP2 data and suggests the atmospheric input of platinum-rich dust. Another anomaly involves the Pt/Pd ratios for the YDB layer, which are typically very different from the background Pt/Pd ratios above and below the YDB layer. Because there is no known geochemical reason that Pt/Pd ratios should differ locally only in the YDB, Pt/Pd anomalies suggest the influx of non-local Pt 12,800 years ago.

Petaev et al. (2013) suggested a likely extraterrestrial source of Pt from the impact of a sub-kilometer iron meteorite with an unusual fractionated core highly enriched in Pt. Although this study finds no evidence to contradict the conclusions of Petaev et al. that the Greenland Pt enrichment most likely resulted from an extraterrestrial source, there is some question about the type of impactor and whether the Pt originated from the impactor and/or from target rocks. In addition, our findings show no contradiction with the Younger Dryas impact hypothesis (YDIH), although detailed evidence for such an impact or airburst is beyond the scope of this research. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. Furthermore, this Pt datum will likely prove valuable in dating and correlating archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.