HR: 0830h
AN: OS51C-0868    [PDF]
TI: Biostratigraphic age of the Sediments From Southern Hydrate Ridge, ODP LEG 204
AU: * Watanabe, M
EM: mht.watanabe@aist.go.jp
AF: Geoscience Institute, Geological Survey of Japan, AIST, Central 7, 1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Su, X
EM: xsu@cugb.edu.cn
AF: Center of Marine Geology, China University of Geosciences, 29 Xuanyuan Road, Beijing, 100083 China
AB: ODP Leg 204 drilled 9 sites on the southern Hydrate Ridge, and 4 of them penetrated the top of the accretionary complex of the Cascadia subduction zone. Diatoms and calcareous nannofossils from sediments recovered were studied to assign ages for these sediments. 13 late Pliocene to Pleistocene microfossil events, 5 diatom and 8 calcareous nannofossil events, were recognized. We determined precise ages of the sediments using these bioevents. Highly-deformed sediments of the accretionary complex recovered at Site 1244, 1251 and 1252 were assigned to late Pliocene to earliest Pleistocene (ca. 2.5-1.6 Ma). Fine-grained hemipelagic sediments with turbidite layers which uncomformably overlies Accretionary complex were assigned to early Pleistocene to Holocene (ca 1.6 Ma to present). The unconformity between deformed accretionary complex and slope basin sediments found at the eastern flank of Hydrate Ridge and the eastern slope basin (Site 1244, 1251 and 1252) was assigned to early Pleistocene (ca. 1.0-1.5 Ma). At the western flank of Hydrate Ridge thick sediment (more than 350 m) deposited at the same time. This difference in sedimentation pattern must have resulted from topographic change and movement of depocenter at around 1 Ma. Sedimentation rates at Leg 204 sites ranges from 2 cm/k.y. to 163 cm/k.y. and varies by sites and periods. In the eastern slope basin (at Site 1251 and Site 1252), the sedimentation rate has increased significantly at about 300 ka or younger.
DE: 1744 Tectonophysics
DE: 3022 Marine sediments--processes and transport
DE: 3030 Micropaleontology
DE: 9350 North America
DE: 9604 Cenozoic
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting