Modes of fossil barnacle occurrences reflecting transgression in the Miocene Natori Group of the Moniwa-Goishi area, northeast Japan

Abstract

Modes of occurrence of fossil barnacle reflecting transgression are discovered from the basal part of the Miocene Natori Group in the Moniwa-Goishi area. The group exhibits the transgressive sequence from subaerial lavas and volcaniclastics to shoreface-shelf deposits in ascending order. Fossil barnacles show autochthonous (in situ individuals on gravel surface) to allochthonous (disarticulated fragments) occurrences. Autochthonous barnacle species, Balanus bisulcatus and Concavus sendaicus are found from bay deposits of the early transgressive stage, and the overlying ravinement deposits formed during marine flooding, respectively. Discoveries of autochthonous barnacles make possible reconstruction of depositional environments and paleoecolgy of extinct barnacles.