Neogene and Early Pleistocene diatom biostratigraphy and age synthesis of Site C9001/C0020, Northwest Pacific

• Prior to drilling, target coalbeds were estimated to be Eocene.
• New data are integrated with the overlying interval from Holes C9001C/D to produce a composite chronostratigraphic framework.
• New biostratigraphic results indicate the target coalbed is Early Miocene.
• The age of the deepest sediments recovered at Site C0020 is Late Oligocene.
• Sediment accumulation rates at Site C9001/C0020 are calculated to be ~ 120m/myr.

Integrated Ocean Drilling Program (IODP) Expedition 337 drilled a new core in 2012 that extended the coring depth of Hole C9001D at Site C9001 below the 647 meters below seafloor (mbsf) that was penetrated in 2006 during the Chikyu Shakedown Cruise CK06-06. Drilling operations at Site C0020 (formerly Site C9001), located 80 km off the Shimokita Peninsula of northeastern Honshu, Japan, penetrated Hole C0020A to a total depth of 2466 mbsf. IODP Exp. 337 sought to explore a deep hydrocarbon system and coalbeds that, prior to drilling, were estimated to be of Eocene age. Combined shipboard diatom and palynological analyses, however, revealed unexpectedly thick sections of Pliestocene and Miocene sediments, an approximately 12–15 million year hiatus at 1086.5 mud depth below sea floor (m MSF), and coalbeds younger than originally predicted. New biostratigraphic results from Hole C0020A indicate the target coalbed is Early Miocene. The age of the youngest sediments obtained in Hole C0020A is revised from Late Pliocene to Early Pleistocene, and the basal age of Hole C9001C is confirmed as Early Pleistocene. The age of the deepest sediments obtained at Site C0020 is Late Oligocene-Early Miocene. All new data are integrated with the overlying interval obtained from Holes C9001C and C9001D to produce a composite chronostratigraphic framework for Site C0020.