Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS10] Paleoclimatology and paleoceanography

Wed. May 23, 2018 9:00 AM - 10:30 AM A08 (Tokyo Bay Makuhari Hall)

convener:Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Atsuhiko Isobe(Research Institute for Applied Mechanics, Kyushu University), Akihisa Kitamura(静岡大学理学部地球科学教室, 共同), Masaki Sano(Faculty of Human Sciences, Waseda University), Hitoshi Hasegawa(Faculty of Science and Technology, Kochi University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Michinobu Kuwae(Center for Marine Environmental Studies), Chairperson:Okazaki Yusuke

9:15 AM - 9:30 AM

[MIS10-02] Mid-Cretaceous Paleoceanographic change in Northwest Pacific based on benthic foraminiferal assemblage.

*Hiroshi Nishi1, Keita Omatsu2, Reishi Takashima1 (1.The Center for Academic Resources and Archives, The Tohoku Museum Tohoku University, 2.Energy Business Division, OYO Corporation )

Keywords:Middle Cretaceous, Oceanic Anoxic Events, benthic foraminifera

Mid-Cretaceous period is characterized by significant global warming and frequent occurrences of Oceanic Anoxic Events. Although numerous studies of the mid-Cretaceous paleoceanographic changes have been conducted in the sections of the Atlantic Ocean and Tethyan Sea, little is known in the Pacific Ocean. In order to understand paleoceanograhic changes during mid-Cretaceous in the Pacific Ocean, we studied benthic foraminiferal assemblages of the Yezo Group.

The Yezo Group is a coherent submarine sequences deposited in the Northwestern Pacific margin. The age of this strata is well constrained by macro-, micro-fossils as well as osmium- and carbon isotope stratigrahies (e.g., Du Vivier et al., 2015). We analyzed benthic foraminiferal assemblages of the Upper Albian–Lower Campanian intervals of the Yezo Group in order to detect the paleo-oceanograhic and paleo-environmental changes in the Northwest Pacific.

1) Establishment of benthic foraminiferal zones.

Based on benthic foraminiferal assemblages, we divided the Yezo Group into following seven benthic foraminiferal zones; Globorotalites sp. A assemblage zone, Textularia hikagezawaensisSilicosigmoilina futabaensis interval zone, S. futabaensisNuttalinella florealis interval zone, N. florealisStilostomella stephensoni interval zone, S. stephensoni interval zone and Karrerulina hokkaidoanaS. futabaensis assemblage zone. These zones are traceable throughout Hokkaido.

2) Paleo-depth changes

Based on paleodepth index species of the benthic foraminifera proposed by Sliter and Baker (1972) and Koutsoukos and Hart (1990), we inferred paleodepth changes in the Yezo Group. The depth of the Yezo Group ranges from about 150m to 1500m during the studied interval. The long term trend shows that the Yezo Basin deepened from Late Albian to Early Turonian, and then shallows toward Campanian. Short-term shallowing events were identified in the Albian/Cenomanian boundary, Mid-Cenomanian Event and around the Santonian/Campanian boundary.

3) Changes in dissolved oxygen level

According to oxygen index species of benthic foraminifera (Kaiho, 1994), we recognized change in dissolved oxygen in the studied interval. Low oxygen environment occurred around the OAE1d, Albian/Cenomanian boundary and Cenomanian/Turonian boundary in the Yezo Group. On the other hand, Late Cenomanian and Coniacian-Santonian interval is characterized by highly oxic environment.


Du Vivier A. D. C. et al., 2015. Earth and Planetary Science Letters, 428, 204–216.

Kaiho, K., 1994, Geology, 22, 719–722.

Koutsoukos, E. A. M. and Hart, M. B., 1990. Transactions of the Royal Society of Edinburgh: Earth Sciences, 81, 221–246.

Sliter, W. V. and Baker, R. A., 1972. Journal of Foraminiferal Research, 2, 167–183.