Geochemical re-evaluation supports cosmic impact rather than volcanism at Younger Dryas onset, Hall’s Cave, Texas: Reply to Sun et al. 2020

Hall’s Cave, situated on the Edwards Plateau of central Texas, contains a well-dated latest Quaternary sedimentary sequence containing a high-resolution record of faunal, climatic, and geochemical changes. In a recent study, Sun et al. (2020) examined trace element concentrations and osmium isotope compositions from this sequence and concluded that a peak in platinum group elements (PGEs) and a negative excursion in 187 Os/ 188 Os values near 151 cm depth were best interpreted as being more consistent with volcanic emissions from the Laacher See eruption in Germany (~12.9 ka) than with an extraterrestrial impact. Here, we re-examine their geochemical dataset from Hall’s Cave, including previously unreported data from a sample at 153 cm depth that exhibits the highest measured platinum concentration (1807 ppb) in the sequence. This critical sample aligns stratigraphically with the onset of the Younger Dryas cooling event, dated to approximately 12,800 cal yr BP and not with the timing of the Laacher See volcanic eruption in Germany. We assess the implications of these results in the context of both cosmic impact and volcanic hypotheses and highlight the importance of comprehensive data inclusion, high-resolution sampling, and stratigraphic consistency in evaluating proposed causal mechanisms for abrupt climate events and associated geochemical anomalies.