[B-PT25_2PM2] Biotic history and its relation to the Earth history

[BPT25-07] Upper Oligocene to Lower Miocene radiolarian biostratigraphy in the Northwest Pacific

*Isao MOTOYAMA¹, Taiki SAWADA² (1.Yamagata University, 2.Japan Petroleum Exploration Co.,Ltd.)

Keywords:Radiolaria, biozone, Site 884, North Pacific

Ocean Drilling Program Leg 145 Hole 884B core provides the most continuous Neogene sequence of pelagic sediments in the northwest Pacific. We examined radiolarians from the Upper Miocene to Lower Miocene sediment of the core to establish subdivided radiolarian biozones. The Upper Oligocene sequence can be divided into three zones, Actinomma sp. A, Hexacontium sp. B and Cyrtolagena laguncula Zones, in ascending order. The Lower Miocene sequence can be divided into four zones, Botryopyle sp. B, Pentactinosphaera hokurikuensis, Stichocorys subligata and Dendrospyris sakaii Zones, in ascending order. Each of Botryopyle sp. B Zone and P. hokurikuensis Zone has been subdivided into subzones a, b and c. Some episodes of significant faunal changes of radiolarians are identified within the studied interval. They seem not to reflect global cooling events but to reflect some regional events.