Volcanic origin for Younger Dryas geochemical anomalies ca. 12,900 cal B.P.

The Younger Dryas (YD) abrupt cooling event ca. 12.9 ± 0.1 ka is associated with substantial meltwater input into the North Atlantic Ocean, reversing deglacial warming. One controversial and prevailing hypothesis is that a bolide impact or airburst is responsible for these environmental changes. Here, highly siderophile element (HSE; Os, Ir, Ru, Pt, Pd, and Re) abundances and (187)Os/(188)Os ratios were obtained in a well-dated sediment section at Hall’s Cave, TX, USA to test this hypothesis. In Hall’s Cave, layers below, above, and in the YD have (187)Os/(188)Os ratios consistent with incorporation of extraterrestrial or mantle-derived material. The HSE abundances indicate that these layers contain volcanic gas aerosols and not extraterrestrial materials. The most likely explanation is that episodic, distant volcanic emissions were deposited in Hall’s Cave sediments. Coupled (187)Os/(188)Os ratios and HSE concentration data at close stratigraphic intervals are required to effectively differentiate between bolide and volcanic origins.