Quaternary radiolarian biostratigraphy in the subarctic northeastern Pacific (IODP Expedition 341, Site U1417) and synchroneity of bioevents across the North Pacific

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. In order to clarify the relationship between tectonic and climate changes during the Neogene, refinements to existing biostratigraphy are necessary. 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 theNW Pacific; for example, the three biozones in the NW 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 Ma, respectively. Based on the age model that we used in this study and the shipboard palaeomagnetic reversal events, the first occurrences (FOs) of Amphimelissa setosa and Schizodiscus japonicus in the NE 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 NW 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, for the first time identified in the NE Pacific, are significantly older than what is found elsewhere at 1.48 and 1.30 Ma, respectively.