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[MIS28-P02] Is the Jurassic-Cretaceous boundary recognized in the stratigraphic sequence of the Mitarai Formation of the Tetori Group in the Shokawa area, northern Central Japan?
Keywords:Jurassic-Cretaceous boundary, Belemnites, Mitarai Formation, Tetori Group, Central Japan
Stratigraphy of the Mitarai Formation of the Tetori Group in the Shokawa area, northern Central Japan recently attracts much attention because the Jurassic-Cretaceous boundary is supposed to be recognized in the stratigraphic sequence of this stratum (Sano, 2020; Haggart and Matsukawa, 2020). Furthermore, the occurrences both of the ammonoids of the Tethyan-Pacific affinity and Boreal belemnites in this formation probably contribute to discuss the molluscan paleobiogeography and its temporal change in the mid-latitudes of the Northwest Pacific. In this context, the detailed age of the Mitarai Formation is necessary for the further discussion.
In this paper, we studied all belemnite specimens deposited in the Hikaru Museum (Takayama City, Gifu Prefecture), which include the specimens described in Haggart and Matsukawa (2020). The belemnite fauna from the lowermost part of the Mitarai Formation is composed of four cylindroteuthidid belemnite species, namely Cylindroteuthis knoxvillensis, C. aff. knoxvillensis sensu Sano et al. (2015), Arctoteuthis tehamaensis and Simobelus cf. compactus. Although C. knoxvillensis and A. tehamaensis had been already described in Haggart and Matsukawa (2020), we revise the identification of some specimens, and reconfirm their occurrences in the Mitarai Formation based on our own observation.
In northern Siberia, C. knoxvillensis, A. tehamaensis and S. compactus occurs in the C. knoxvillensis Zone around the Volgian-Ryazanian boundary, which corresponds to the Middle to Late Berriasian (Dzyuba, 2013). Based on this information, the age of the lowermost part of the Mitarai Formation is possibly assigned to the Middle to Late Berriasian, and thus the Jurassic-Cretaceous boundary should be recognized in the strata below the Mitarai Formation, or maybe not present in the Tetori Group. However, since the identification of C. knoxvillensis and Simobelus cf. compactus are based on few, sometimes ill-preserved specimens, this age assignment should be reconfirmed based on the future studies of new belmnite specimens. Combination with other stratigraphic methods, such as calcareous nannoplankton biostratigraphy, Strontium isotope stratigraphy and paleomagnetic stratigraphy, are also requested to reveal the detailed age of the Mitarai Formation, and to recognize the Jurassic-Cretaceous boundary in the Tetori Group.
References
Dzyuba, O. S. 2013. Stratigraphy and Geological Correlation, 21(2), 189–214.
Haggart, J. W. and Matsukawa, M. 2020. Cretaceous Research, 111, 104281.
Sano, S. 2020. Paleontological Research, 24(2), 147–160.
Sano, S. et al. 2015. Journal of the Geological Society of Japan, 121(2), 71–79. (in Japanese)
In this paper, we studied all belemnite specimens deposited in the Hikaru Museum (Takayama City, Gifu Prefecture), which include the specimens described in Haggart and Matsukawa (2020). The belemnite fauna from the lowermost part of the Mitarai Formation is composed of four cylindroteuthidid belemnite species, namely Cylindroteuthis knoxvillensis, C. aff. knoxvillensis sensu Sano et al. (2015), Arctoteuthis tehamaensis and Simobelus cf. compactus. Although C. knoxvillensis and A. tehamaensis had been already described in Haggart and Matsukawa (2020), we revise the identification of some specimens, and reconfirm their occurrences in the Mitarai Formation based on our own observation.
In northern Siberia, C. knoxvillensis, A. tehamaensis and S. compactus occurs in the C. knoxvillensis Zone around the Volgian-Ryazanian boundary, which corresponds to the Middle to Late Berriasian (Dzyuba, 2013). Based on this information, the age of the lowermost part of the Mitarai Formation is possibly assigned to the Middle to Late Berriasian, and thus the Jurassic-Cretaceous boundary should be recognized in the strata below the Mitarai Formation, or maybe not present in the Tetori Group. However, since the identification of C. knoxvillensis and Simobelus cf. compactus are based on few, sometimes ill-preserved specimens, this age assignment should be reconfirmed based on the future studies of new belmnite specimens. Combination with other stratigraphic methods, such as calcareous nannoplankton biostratigraphy, Strontium isotope stratigraphy and paleomagnetic stratigraphy, are also requested to reveal the detailed age of the Mitarai Formation, and to recognize the Jurassic-Cretaceous boundary in the Tetori Group.
References
Dzyuba, O. S. 2013. Stratigraphy and Geological Correlation, 21(2), 189–214.
Haggart, J. W. and Matsukawa, M. 2020. Cretaceous Research, 111, 104281.
Sano, S. 2020. Paleontological Research, 24(2), 147–160.
Sano, S. et al. 2015. Journal of the Geological Society of Japan, 121(2), 71–79. (in Japanese)