Fossil Foraminifera from the Miyata Formation, Miura Peninsula, Kanagawa Prefecture

Abstract

The Miyata formation occurs in the southern part of the Miura peninsula, Kanagawa prefecture, Japan., Since previous publications on this formation have described chiefly its Foraminifera and Mollusca, the principal purpose of this paper is to describe the environmental conditions under which the formation was deposited as determined from a study of foraminiferal assemblages., The Miyata formation consists of conglomerate and cross-bedded sandstone containing shells, which are overlain in succession by sandstone, an alternation of sandstone, and siltstone, and fossiliferous sandstone., The Miyata formation overlies the Hayama and Hayashi formations unconformably and the Kwanto volcanic ash overlies the Miyata formation unconformably., The Miyata formation is about 20 meters thick at the cliff at Okine (locs., 1, 2)., It is bounded on the north and south by vertical faults., Forminifera were collected from 19 different localities in the Miyata formation, but in all cases from the same stratigraphic horizon., These collections were compared with Recent Foraminifera from the tidal zone and inter-tidal region in the vicinity of the Miura peninsula to aid in the determination of the paleo-environment of the Miyata foraminiferal assemblages., The following conclusions were reached : 1) The foraminiferal assemblages of the Miyata formation comprise species flourishing in shallow water., The east and central parts of the Miyata formation are deeper than the western part in depositional facies, as inferred from the bathymetrical distribution of the Foraminifera., 2) The distribution of the Foraminifera within the Miyata formation shows an intimate relationship with the litho-facies, particularly with the grain size distribution of the rocks., 3) The temperature of the sea water at the time of deposition of the formation, as inferred from the Foraminifera, was somewhat lower than or nearly the same as the present sea water adjacent to the peninsula., 4) The fossil Foraminifera comprise an assemblage which lived near the shore of the open-sea.,