Eruption of the Old Crow tephra deposited ~200 km³ of volcanic ash throughout Alaska and the northwestern Yukon (eastern Beringia), providing an isochronous marker across the region on a scale unique in the Pleistocene. The Old Crow tephra represents a critical temporal piercing point used extensively to link geographically disparate stratigraphic sections and the paleo-environmental records they contain. Although the canonical age of the Old Crow suggests eruption during the transition between the glacial and interglacial periods of Marine Isotope Stages (MIS) 5 and 6 at ~125 ka, recent U–Th–Pb and (U–Th)/He zircon dating of the tephra suggests eruption at ~200 ka, within MIS 7. If accurate, this revised eruption age begets significant change to existing models describing the geologic and biotic evolution of Beringia in the Pleistocene. Thus, confidently knowing the age of the tephra is critical to its time-stratigraphic utility and for past and future work in the region where the tephra has been found. With this contribution, we review existing Old Crow age constraints and present an eruption age for the tephra determined via high spatial resolution ion microprobe U–Pb surface analysis on zircon crystals isolated from source-proximal (<500 km from plausible source) pumiceous pyroclasts of the tephra. By dating only glass-mantled crystals isolated from discrete pumice clasts, we limit the potential for sample contamination from exotic crystals and resulting age bias. The young population of dates from this dataset corroborate previous radiometric dates and confirm Old Crow eruption within late MIS 7 at 207 ± 13 ka.

Old Crow 火山喷发沉积约 200 公里³整个阿拉斯加和育空地区西北部（白令基东部）的火山灰，以更新世独特的规模提供了整个地区的等时标记。Old Crow tephra 代表了一个关键的时间穿刺点，广泛用于连接地理上不同的地层剖面及其包含的古环境记录。尽管 Old Crow 的典型年龄表明在海洋同位素阶段 (MIS) 5 和 6 的冰期和间冰期之间的过渡期间喷发了约 125 ka，但最近的 U-Th-Pb 和 (U-Th)/He 锆石测年火山灰表明在 MIS 7 内大约 200 ka 喷发。如果准确的话，这个修订的喷发年龄会对现有描述更新世白令旗地质和生物演化的模型产生重大变化。因此，自信地了解 tephra 的年龄对于其时间地层学实用性以及在发现 tephra 的地区的过去和未来工作至关重要。凭借这一贡献，我们回顾了现有的 Old Crow 年龄限制，并提出了通过高空间分辨率离子微探针 U-Pb 表面分析对从近源（距可能源 <500 公里）的火山碎屑中分离的锆石晶体确定的火山喷发年龄。火山灰。通过仅对从离散的浮石碎屑中分离的玻璃披覆晶体进行测年，我们限制了来自奇异晶体的样品污染和由此产生的年龄偏差的可能性。来自该数据集的年轻人群证实了以前的辐射测量日期，并确认了 MIS 7 晚期 207 ± 13 ka 内的 Old Crow 喷发。