房総半島中部,上総層群最下部の第三紀・第四紀境界付近の火山灰層 "Kd38"

概要

論文の詳細を見る
The "Kd38" tuff in the central part of the Boso Peninsula occurs near the boundary between Tertiary and Quaternary. Two types of "Kd38" tuffs had been described by many authors. Stratigraphic relationships of the "Kd38" tuffs were studied at four routes from the lowest part of the Kazusa Group. One of Kd38 tuffs is characterized by presence of Fe-rich orthopyroxene with X_<Mg>=26. It occurs in the middle zone of the Yoro route, whereas the other one is characterized by abundance of cummingtonite and is observed in the lower zone. The former one is recognized in the four routes, but the latter is found only in Yoro and Minato routes which are located at the eastern and western ends of the studied area, respectively. It suggests that a small rise was present in the central part where the cummingtonite tuff had been eroded out soon after deposition.
国立科学博物館の論文
2000-12-22