Stratigraphy of the Miura and Kazusa Groups in the Miura Peninsula, Japan

The Miura Peninsula consists of the late Cenozoic sedimentary sequence that is divided into the Hayama, Miura, Kazusa and Sagami Groups and Alluvial sediments. The respective units display an unconformable relationship, namely, a marked clino-unconformity between the Hayama and Miura Groups and a parallel unconformity between the Miura and Kazusa Group are characteristics in the peninsula. There are several sedimentary basins in which the Miura, Kazusa and Sagami Groups are distributed surrounding the Hayama Upheaval Belt around the peninsula. The succesive sequence of all the Miura, Kazusa and Sagami Groups is distributed trending east-west and dipping north, it constitutes the southern west wing of the Kanto Structural Basin in the northern part of the peninsula. The middle and southern parts of the peninsula are characterized by the folds of the Miura Group. The present study has as its objective to describe the stratigraphy and lithology of the Miura and Kazusa Groups and some units of the Sagami Group in the middle and northern parts of the peninsula. This study forms a link in the chain of the researches on the Cenozoic tectonics of the Miura Peninsula. The Miura Group, ranging in age from Late Miocene to Late Pliocene, is divided into two formations: the Zushi and Ikego Formations. The Zushi Formation includes Tagoegawa Sandstone and Conglomerate Member in the northern part, Shimoyamaguchi Sandstone and Conglomerate Member in the southern part, the respective members constitute a basal part of the formation. The Ikego Formation contains Takatoriyama Pyroclastics Member at the lower part. This member is newly named by the author in this study. It is pointed out that the pyroclastic materials were possibly derived from autochthonous materials exploded from a submarine volcano at the bathyal floor. The stratigraphic relation between the Zushi and Ikego Formations is wholly conformable but disconformable in a part, the later relation was caused by submarine erosion on the top of a small dome of the Zushi Formation. The Late Pliocene to Early Pleistocene Kazusa Group is divided into six formations which in ascending order are the Uragō, Nojima, Ōfuna, Koshiba, Nakazato and Tomioka Formations. The Nojima Formation contains Imaizumi Sandstone and Conglomerate Member at the lower to middle parts