Quaternary radiolarian biostratigraphy of IODP Site 341-U1417A

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.