Quaternary radiolarian biostratigraphy of IODP Site 341-U1417A@en

Expedition 341 of the Integrated Ocean Drilling Program (IODP) retrieved sediment cores spanning the time interval between the Pleistocene and Miocene from the southern Gulf of Alaska. Onboard Pleistocene radiolarian biostratigraphy is hereby refined by increasing the sampling resolution. The 178 core samples from the upper 190 m CCSF-B of Site U1417 contained faunal elements similar to the Northwest Pacific; for example, the three biozones in the Northwest Pacific (i.e., Eucyrtidium matuyamai, Stylatractus universus and Botryostrobus aquilonaris) were also recognized in the Gulf of Alaska, spanning 1.80-1.13 Ma, 1.13-0.45 Ma, and the last 0.45 Myr, respectively. Based on the age model that we used in this study and the shipboard paleomagnetic reversal events, the first occurrences (FOs) of Amphimelissa setosa and Schizodiscus japonicus in the Northeast Pacific were preliminarily determined to be 1.48 and 1.30 Ma, respectively. The last occurrence (LO) of Eucyrtidium matuyamai and the FO of Lychnocanoma sakaii, both well-established bioevents in the Northwest Pacific, were dated at 0.80 Ma and 1.13 Ma, respectively. The LO of E. matuyamai is a synchronous event at 1.05±0.1 Ma in the North Pacific, while the FOs of A. setosa and S. japonicus are significantly older than what found elsewhere at 1.48 Ma and 1.30 Ma, respectively.综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）第341次科考航次从阿拉斯加湾南部采集了覆盖更新世至中新世时段的沉积岩芯。本研究通过提升采样分辨率，优化了航次现场已开展的更新世放射虫生物地层学研究。U1417站位190米以浅的CCSF-B层段的178个岩芯样品，其放射虫动物群组合与西北太平洋海域相似；例如西北太平洋的三个放射虫生物带——松村真锥虫（Eucyrtidium matuyamai）、环球拟管虫（Stylatractus universus）与北极葡萄星虫（Botryostrobus aquilonaris），在阿拉斯加湾也被识别，对应时限分别为1.80~1.13 Ma、1.13~0.45 Ma以及0.45 Ma至今。基于本研究采用的年代模型及航次现场获取的古地磁倒转事件数据，东北太平洋海域的刚毛双筛虫（Amphimelissa setosa）与日本裂盘虫（Schizodiscus japonicus）的首次出现（First Occurrences, FOs）初步确定为1.48 Ma和1.30 Ma。西北太平洋中已被广泛确认的两个生物地层事件——松村真锥虫的末次出现（Last Occurrence, LO）以及酒井亮壳虫（Lychnocanoma sakaii）的首次出现，其年代分别被限定为0.80 Ma和1.13 Ma。松村真锥虫的末次出现事件在北太平洋全域同步发生于1.05±0.1 Ma，而刚毛双筛虫与日本裂盘虫的首次出现时间则显著早于其他海域的已有报道，分别为1.48 Ma和1.30 Ma。