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For comparison, they analyzed six YDB magnetite and ilmenite grains, which showed undetectable Ir in grains compared to an average of 2.2 ppb in YDB spherules, undetectable Os versus 4 ppb, and an average of 16.2 ppb of Pt in non-YDB grains compared to 145 ppb in the YDB.
Such large compositional differences between grains and spherules suggest that PGE enrichments in the YDB spherules are real and that the spherules did not derive from the melting of local magnetic and/or ilmenite grains, but rather are of non-local origin.
Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B. 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.
These include linear sand ridges of mixed aeolian and fluvial origin, aeolian sand-sheets and dunes, levee and alluvial terrace deposits, slopewash deposits, and lacustrine and aeolian Carolina bay sand rims.
None of the eastern sites are associated with the black mat or any measurable increase in organic matter (see Supplementary Information, “Study Sites”).
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Sawlowicz notes that PGE anomalies may result from multiple processes of enrichment, including: a) cometary or meteoritic influx [Supplementary Table 7]; b) impactites from an extraterrestrial impact event [Supplementary Table 7]; c) volcanoes [Supplementary Table 10]; d) mantle material, e.g., from tectonic motion or in cratons [Supplementary Table 7]; e) exhalative-hydrothermal processes; f) precipitation from seawater; g) post-depositional transport and precipitation at redox boundaries; and h) reduction from intermediate and low-temperature solutions.
Results are discussed below and in Supplementary Information.
