2000 Volume 52 Issue 52 Pages 63-74
The middle Pleistocene Yabu Formation, Shimosa Group distributed in the Shimosa Plateau is deposits of Paleo Tokyo-Bay. The investigation area, Kisarazu Plateau is located at the most southern part of the Shimosa Plateau and also the southern margin of Paleo Tokyo-Bay. The Yabu Formation is mainly composed of sands, and alternation of sands and muds, We exhibit the distribution of Yabu Formation at the Kisarazu Plateau, using intercalated volcanic ashes and examining a depositional system by fades analysis.
As a result, spit-bay depositional system was reconstructed at the heads of Paleo Tokyo-Bay from the shape of basin and facies distribution of the formation. In addition, the change of depositional system in the Yabu Formation was considered. Consequently, the depositional sequence corresponding to a glacio-eustatic sea-level change was recognized in the formation, and it became clear that the spit developed dung taransgression associated with interglacial period and the bay was filled and diminished during subsequent sea-level lowering.
