Weathering rinds: Unlikely host clasts for evidence of an impact-induced event

Abstract

Interhemispheric evidence of a cosmic impact 12.9ka is known now from North to South America, Europe and Eurasia, all data supporting a cosmic event derived from cores and from geological sections. Most databases supporting the impact hypothesis at the Younger Dryas Boundary (YDB) rely on high-temperature microspherules, melted minerals, cracked clasts, presence of nanodiamond, high-temperature scoria, high Fe/Ni ratios, pdf's, shock melted quartz, high 10Be/9Be ratios and occasional presence of platinum metals. Controversy over the impact, the so-called Black Mat enigma, and its relation to the Younger Dryas readvance at the end of the last ice age, is fueled by arguments over whether a single extraterrestrial impact might sustain a 1kyr-long downturn in insolation engendering a substantial increase in worldwide ice volume. New evidence in the form of impact microfeatures – extreme breccia, high crack propagation, thick carbon encrustations and partial to full shock-melted/contorted grains – in weathering rinds from the Western Alps, France, as documented here, adds to the growing body of evidence that the event was truly widespread, if not worldwide in effect. Whereas evidence of cosmic impacts may be erased by glacial and fluvial erosion in high alpine areas, such events as demonstrated herein are recorded as punctuated time-stratigraphic events in microcosm, preserved in weathered clasts.