Magnetostratigraphy of Neogene rocks around the Himi area in Toyama Prefecture, Japan- Bull

摘要

Neogene rocks distributed in the Himi area adjacent to the Japan Sea have been subjected to a magnetostratigraphic study. The upper Neogene System is divided into the Ao and the Yabuta Formations in ascending order. The Ao Formation, which is 200 m thick, consists entirely of siltstone. The Yabuta Formation is more than 120 m in thickness and consists of calcareous sandy siltstone and sandstone. Both of the formations are intercalated with many tuff layers. Progressive demagnetization tests using thermal and alternating-field methods show that the tuff samples from 14 sites preserve reliable records of paleomagnetic directions. On the basis of magneto- and biostratigraphic data, the Ao and the Yabuta Formations are assigned to the Gilbert reversed polarity Chron and the Gauss normal polarity Chron on the standard geomagnetic polarity time scale.