Abstract
The Lower Cretaceous strata exposed in the Sanchu Graben in the Kanto Mountains have been correlated with the Monobe-gawa Group in Shikoku on the basis of fossil evidence. It is well-known that they yield the bivalve assemblage which is called the Northern-Tethyan fauna. Recently, we obtained the abundant bivalve fossils from Nakanosawa and Hinatazawa at the eastern part of the Sanchu graben. These assemblages bear a close resemblance to the Tethyan fauna in Albian Age. On the other hand, they show little affinity to the Northern-tethyan fauna which was previously reported from the Sanchu Graben. Those lines of fossil evidence suggest that the Cretaceous System of the Sanchu Graben yields not only the Northern-tethyan fauna but also the Tethyan fauna in Albian Age. In addition, Inoceramus cf. hobetsensis was reported from Numa-sato located to southeast of Hinatazawa. The strata yielding Inoceramus hobetsensis (Turonian species) probably overlie those yielding the Albian Tethyan fauna.
