Chronostratigraphy of 1505 m long hot spring well drilled in the central Kanto Plain, central Japan

Abstract

The chronostratigraphy of a 1505 m deep hot spring well drilled in Otone town, Saitama Prefecture, in the central Kanto Plain of Japan, was determined by tephrostratigraphy, and calcareous nannofossil and diatom biostratigraphy and is correlated with Neogene and Quaternary sequences that outcrop within the Kanto Plain area. Units A (depth 1434–1505 m), B–E (depth 773–1434 m), and F (depth 0–773 m) correlate with the Middle Miocene Hiki Group of the Hiki Hills, the Middle–Late Miocene Tokigawa Group of the Hiki and Iwadono hills and the Late Pliocene–Pleistocene Kazusa and Shimosa groups of the Boso Peninsula, respectively. The Niwaya unconformity is thought to separate Units A and B, and the Kurotaki unconformity correlates with the base of Unit F. The base of the Kazusa Group has also been identified in the Kazo1–Shobu1 Line seismic section and reaches a maximum depth of ca. 1000 m at Shobu town.