An air-fall ash layer in the Grotta dei Baffoni cave in the Frasassi Gorge (Marche Apennine, Italy): Relevance to the Younger Dryas debate

A thin tephra layer was discovered in a section of cave sediments in the Grotta dei Baffoni Cave (GDB), in the Marche Apennine of central Italy, immediately underlying a clayey layer containing charcoal fragments dated at 12,843 ± 122 years before present. This date indicated that humans were occupying the cave at the very beginning of the Younger Dryas cooling event. Petrographic and geochemical analysis of the volcanic glass contained in the tephra layer suggests that this deposit represents a distal air-fall ash erupted from a volcano in the Campi Flegrei caldera, which produced the Neapolitan Yellow Tuff (NYT). Radiocarbon AMS dating of charcoal particles from this GDB tephra layer yielded an age around 14.4 ± 0.4 ka, which is consistent with the chronology of the NYT eruption, which occurred some 14.1 ± 1.4 thousand years ago. Nevertheless, the sediment succession in this cave deposit actually covers a time interval across the sudden and drastic Younger Dryas cooling event, which occurred around 12.9 ka. There is an ongoing debate about the causes of the Younger Dryas event, which divides the scientific community into a faction sustaining that the Younger Dryas cooling event was triggered by an elusive meteorite impact, and an opposing one that advocates volcanic eruptions, such as the eruption of the Laacher See volcano in central Germany, which was precisely dated at 13 ka. A detailed trace element and 187Os/188Os analysis through the sedimentary succession in the Grotta dei Baffoni Cave did not reveal evidence of any platinum-group element anomalies or an osmium isotope signature that would support an extraterrestrial impact event around the time of the Younger Dryas event. The Grotta dei Baffoni tephra layer turned out to be derived from a large eruption in the Campi Flegrei of southern Italy, which produced the huge Neapolitan Yellow Tuff around 14.1 thousand years ago. This catastrophic event appears to be synchronous with the minor Older Dryas cooling event, which preceded the Younger Dryas by some 1300 years.