An Extraterrestrial Pt Anomaly during the Late Glacial-Younger Dryas: Viso Massif (Italy and France)

Abstract

Paleosol evidence supporting the Younger Dryas Impact Hypothesis (YDIH) on the Viso Massif of France and Italy is expanded by a Pt anomaly at all sites investigated, accompanied by elevated Os, Ir, Ru, and Rh concentrations at several sites, thus affirming a cosmic driver to the YD climatic shift at 12.8 ka. Original, thin Allerød soils prevalent at the end of the Late Glacial comprise sediments affected by an airburst from a hypothesized secondary daughter fragment or fragments of the main 2P/Encke progenitor comet train that intersected Earth’s land surface and its alpine-continental ice sheets. This event has been previously postulated to have breached Lake Agassiz and other proglacial lakes in North America, released meltwater into the Atlantic Ocean through the St. Lawrence and into the Arctic through the Mackenzie River system, after which cold surface water shut down the thermohaline circulation of the Gulf Stream in the North Atlantic. This thermohaline event is the traditional explanation for YD cooling, but was it fast enough to match the pollen evidence, which confirms rapid temperature reversal? Or was an “impact winter” involved? Cosmic signatures reported here include elevated Pt/Pd ratios, Os, Ir, Ru, and Rh concentrations with orders of magnitude (OM) for Ir used to establish the main center of conflagrations that helped trigger an impact winter. While most sections show variable distributions of PGEs, some are fully affected by concentrations entirely through the unweathered substrate or parent material horizons (called “Cu” horizons). Peak distributions of platinum group elements (PGEs) provide new information on the dispersal patterns of grains that add the Western European Alps to the intercontinental array of sites containing the Younger Dryas boundary (YDB) layer, also sometimes called the black mat (BM). Previously, most age determinations for the Alps were derived from relative dating determinations (RD), but here, we report an AMS C14 date from one LG paleosol (G11-Bw) yielding an age of 12,816 ±44 cal yr BP age, coeval with the average 12.8 ka age of the BM.