New belemnite records from the Mitarai Formation, Tetori Group, Japan: Delimitation of the Jurassic-Cretaceous boundary in the Japanese Islands

Abstract

Traditional faunal elements for zoning the uppermost Jurassic‒lowermost Cretaceous stratigraphic interval in Tethyan regions, i.e., ammonites and calpionellids, are either lacking in the boreal regions at that time, or are of generally low diversity and endemic compositions. Consequently, recognition of Jurassic-Cretaceous boundary interval sections has been hindered in many areas of the boreal regions, as well as some lower latitude intermediate areas, such as the Japanese Islands.Strata of the Mitarai Formation of the Tetori Group of central Japan have previously provided ammonites suggesting a broadly Tithonian–Berriasian age for the formation, but the Jurassic-Cretaceous boundary, nor the boundary interval, have never been precisely identified in it, due to the poorly preserved nature of the faunas and their endemic nature. We have recognized a fauna of belemnites from a locality of the Mitarai Formation, including Cylindroteuthis knoxvillensis Anderson, C. knoxvillensis?, C.? sp., Arctoteuthis tehamaensis (Stanton), A. cf. tehamaensis, A. cf. repentina Saks & Nal'nyaeva, and Acroteuthis? sp. Collectively, this belemnite assemblage of the Mitarai Fm indicates the interval of the Jurassic-Cretaceous boundary, as recognized at northern Siberia (Russia) and northern California (USA), and is thus the first certain identification of this boundary in the Japanese Islands. The Mitarai Fm belemnite assemblage can be used to establish the presence of the Jurassic-Cretaceous boundary interval in other areas of the Japanese Islands.