2000 Volume 52 Issue 52 Pages 53-62
The Middle Pleistocene Tanabu Formation is exposed in seacliffs along the northern coast of the Shimokita Peninsula in Northeast Japan. The formation was divided into two members by Kuwano (1957) as follows: the upper part of the formation (the Ishimochinaya Member) and the lower part of the formation (the Shiosaki Member). This paper investigated the Ishimochinaya Member at Inasaki on the coast from the sedimentological point of view. Estuarine and Barrier island depositional systems are recognized in the formation at Inasaki. The Barrier island depositional system consists of foreshore-shoreface, tidal channel-fill and lagoonal sedimentary fades. The foreshore-shoreface sedimentary facies are repeatedly incised by tidal channel-fill sedimentary facies in the surveyed section. Therefore barriers in the formation correspond to a wave-dominated barrier in microtidal environments. The temporal and spatial distribution of these fades associations suggests that the barrier island depositional system of the formation was formed under transgrssive conditions during a relative sea-level rise in the Middle Pleistocene.