Abstract
Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. 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. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.
Highlights
In 2013, Petaev et al.[1] discovered an anomalously large platinum (Pt) peak in ice core samples from the Greenland Ice Sheet Project 2 (GISP2), providing the most compelling evidence to date for a catastrophic extraterrestrial event coincident with the onset of the Younger Dryas (YD) climate episode
We evaluate evidence of platinum group elements (PGE) enrichment from archaeologically-stratified sedimentary sequences across North America that date to the Younger Dryas boundary (YDB) in order to test the implications of Petaev et al.[1] who suggested the likelihood of a global Pt anomaly
Testing was limited at first to four North American sedimentary sequences (Arlington Canyon, California; Murray Springs, Arizona; Blackwater Draw, New Mexico; and Sheriden Cave, Ohio; Fig. 1) with well-defined and well-dated YDB age sediments containing peaks in YDB impact-related proxies. These analyses revealed a large above-background Pt anomaly at each site in the identical sample previously identified as the YD boundary layer (Fig. 2) containing abundance peaks in YDB proxies, including micro-spherules, meltglass, and nanodiamonds
Summary
In 2013, Petaev et al.[1] discovered an anomalously large platinum (Pt) peak in ice core samples from the Greenland Ice Sheet Project 2 (GISP2), providing the most compelling evidence to date for a catastrophic extraterrestrial event coincident with the onset of the Younger Dryas (YD) climate episode. The Younger Dryas impact hypothesis proposed a causal link between a cosmic impact event and a) the onset of the YD climate cooling episode at ~12,800 calendar years BP, b) a peak in continental-scale biomass burning, c) extinction of more than 35 genera of North American Pleistocene megafauna, and d) the demise of the Paleoindian Clovis technocomplex[3] In support of those links, several studies[3,4,5,6,7] have reported an exotic assemblage of impact-related proxies in a widely-distributed layer at the YDB, dating to 12,800 ± 150 Cal B.P. Impact proxies reported for YDB sites include but are not limited to high-temperature iron and silica-rich magnetic spherules, nanodiamonds, aciniform carbon (soot), high-temperature melt-glass, and elevated, above-background concentrations of nickel, osmium, and iridium[3,4,5,6,7]. Even though their Pt anomalies are small, their results are consistent with the independent impact-related Pt study by Petaev et al.[1]
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