Late Triassic bivalves from Sambosan accretionary complex, southwest Japan, and their biogeographic implications

This paper records eight species of Late Triassic Tethyan bivalves from the oceanic limestone and associated basaltic volcaniclastic rocks which belong to the Sambosan accretionary complex in southwest Japan. The bivalve-bearing succession consists of basaltic volcaniclastic rocks (ca. 60 m thick) conformably succeeded by dark gray bedded limestone (ca. 10 m thick), which is, in turn, overlain by massive limestone (ca. 50 m thick). The succession is dated as Carnian to Norian by means of conodonts and bivalves. Upper Triassic bivalves, including Gruenewaldia decussata, G. woehrmanni and Costatoria goldfussi, are recorded from the examined succession. Their occurrence implies a Tethyan affinity for the examined Sambosan oceanic rocks. No bivalve species characteristic of a high latitudinal zone occurs in this succession.