A time gap at the Permian-Triassic boundary in the South Kitakami Belt, Northeast Japan
was examined on the basis of ammonoid biostratigraphy.  The occurrence of the
Wuchiapingian ammonoids have been known from the lower-middle part of the Upper Permian
Toyoman Series and recently the Changhsingian one was discovered from the upper part of the
same series.  Glyptophiceras cf. gracile, the only known ammonoid specimen from the Lower
Triassic Hiraiso Formation unconformably overlying the Toyoman formations and which has
provided the basis for correlating the Hiraiso Formation with the Griesbachian, is now consid-
ered to be a Smithian or Spathian species.  The Osawa Formation, lying conformably over the
Hiraiso Formation, yields abundant Spathian ammonoids from its lowermost to uppermost part.
Based on these data it is considered that a stratigraphic interval spanning from the Griesbachian
to lower Smithian (or Smithian) is missing in the South Kitakami Belt.