Japan Geoscience Union Meeting 2023

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-GL Geology

[S-GL22] Frontier research on chronostratigraphic unit boundaries

Fri. May 26, 2023 9:00 AM - 10:15 AM International Conference Room (IC) (International Conference Hall, Makuhari Messe)

convener:Hiroyuki Hoshi(Department of Earth Sciences, Aichi University of Education), Reishi Takashima(Tohoku University Museum, Tohoku University), Junichiro Kuroda(Department of Ocean Floor Geoscience, Atmosphere and Ocean Research Institute, the University of Tokyo), Makoto Okada(Department of Earth Sciences, College of Science, Ibaraki University), Chairperson:Hiroyuki Hoshi(Department of Earth Sciences, Aichi University of Education), Reishi Takashima(Tohoku University Museum, Tohoku University), Junichiro Kuroda(Department of Ocean Floor Geoscience, Atmosphere and Ocean Research Institute, the University of Tokyo), Makoto Okada(Department of Earth Sciences, College of Science, Ibaraki University), Tetsuji Onoue(Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University)

9:30 AM - 9:45 AM

[SGL22-03] The Weissert Event record and radiometric ages of Soma Nakamura Group

*Taiga Tomaru1, Reishi Takashima2, Yuji Orihashi3, Toshiro Yamanaka4, Hiroshi Nishi5, Azumi Kuroyanagi2, Yoshihiro Asahara6 (1.Department of Earth Science, Graduate School of Science, Tohoku University, 2.The Center for Academic Resources and Archives Tohoku University Museum , 3.Global Environment and Disaster Prevention Sciences, Graduate School of Science and Technology, Hirosaki University, 4. School of Marine Resource and Environment, Tokyo University of Marine Science and Technology, 5.Institute of Dinosaur Research , Fukui Prefectural University, 6.Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University)

Keywords:Early Cretaceous, Somanakamura Group, Carbon-isotope stratigraphy

The Oceanic Anoxic Events (OAEs), frequently occurred during Cretaceous, are characterized by widespread distribution of black shale and positive δ13C excursion in the stratigraphic record. Major OAEs were accompanied with emplacement of Large Igneous Provinces (LIPs) before the onset of events. The Weissert Event, occurred Late Valanginian-Early Hauterivian, is represented by a prolonged δ13C positive excursion, and LIPs of Panana-Etendeka flood basalt erupted contemporaneously with the event. Consequently, Weissert Event was previously regarded as one of the global OAEs. However, due to limited distribution of black shale, there are no consensus about the trigger of perturbation of carbon cycle and environmental change during the Weissert Event.
Global biostratigraphic correlation of Lower Cretaceous is problematic because strengthened faunal and floral provincialism during Early Cretaceous. On the other hand, a distinct positive isotope peak in δ13C of the Weissert Event is useful chemostratigraphic marker for international stratigraphic correlation. The positive δ13C peak of Weissert Event have been reported from various sections in Europe while few studies were performed for the Weissert Event in circum-Pacific sections. In order to discover positive δ13C excursion of the Weissert Event in the northwest Pacific and to estimate the numerical age of the event based on radiometric dating of the tuffs, we studied stable carbon isotope stratigraphy and U-Pb dating of tuffs in the Upper Jurassic-Lower Cretaceous Somanakamura Group, exposed eastern Fukushima prefecture, Japan. We identified a prominent positive carbon isotope excursion from the uppermost formation (Koyamada Formation) of the Somanakamura Group. U-Pb zircon ages of the tuffs exhibit 135.59±0.77, 133.9±1.2, 133.22±0.60 Ma. The former age was obtained from the horizon below the positive δ13C peak while the latter two were from above the positive δ13C peak. These line of evidence suggests that the positive δ13C peak in the uppermost Somanakamura Group corresponds to the Weissert Event, and radiometric age of the Weissert Event accord well with the calculated astronomical age by Martinez et al., 2015.