A revised Barremian-Aptian age for the Mitarai Formation (lower Tetori Group, Makito area of central Japan), previously considered Middle Jurassic-earliest Cretaceous

Abstract

The Tetori Group of central Japan, dated in the past as Middle Jurassic-Early Cretaceous, has been widely used in correlation and even for dating Asian non-marine Late Mesozoic strata, because it is composed of marine and non-marine deposits, containing marine molluscs and various non-marine fossils. However, when comparing the marine bivalve faunas, four out of 11 species previously recorded from the Mitarai Formation (a critical formation in determining the age of the Tetori Group) of the lower Tetori Group in the Makito/Shokawa area of northern Gifu Prefecture, central Japan (i.e., Palaeonucula makitoensis (Hayami) Entolium inequivalve Hayami, Thracia shokawensis Hayami, and Pleuromya hidensis Hayami) could be recognized from the Barremian-Aptian Qihulin and Yunshan formations of the Longzhaogou Group in the Yunshan area of eastern Heilongjiang, NE China. These formations yield Barremian ammonites and the global late Barremianmiddle Albian (mainly Aptian) index Aucellina caucasica-Aucellina aptiensis assemblage, suggesting that the Japanese Mitarai Formation is late Early Cretaceous (Barremian-Aptian, mainly Barremian) rather than Middle Jurassic or Late Jurassic-earliest Cretaceous in age, and implying that the basal formation of the Tetori Group, the Ushimaru Formation, conformably overlain by the Mitarai Formation, is likely to be no older than Hauterivian.