群馬県邑楽郡明和町に掘削された温泉井より産出した浮遊性有孔虫化石

Planktonic foraminiferal fossils of 24 species belonging to 11 genera were obtained in seven Miocene mudstone samples from a hot spring well(drilling depth 1,500 m) in Meiwa Town, Ora-gun, Gunma Prefecture, Japan. The genus Praeorbulina, which is effective for age determination, is included. Its suggests that the 870 to 820 m depth mudstone corresponds to the N.8 zone(Blow, 1969). From the composition of the occupying species, it is presumed that this area was strongly affected by warm currents. The N.8 zone sediments were found in the Meiwa hot spring well, revealing a structural and age gap between the Tatebayashi observation well and the Meiwa hot spring well. As a result, the data supported the indication that a large fault(Tonegawa Tectonic Line) lies between the two wells. [ABSTRACT FROM AUTHOR]

群馬県邑楽郡明和町において掘削された温泉井（掘進長1,500 m）から得られた中新統泥岩7試料か ら,11属24種の浮遊性有孔虫化石が産出した.これらの中に,地層の時代決定に有効なPraeorbulina属が 含まれ,870〜820皿はN.8帯（Blow, 1969）に相当すること示唆された.また,占有種の構成から本地域 は暖流の影響を強く受けていたことが推定された.明和温泉井中にN.8帯に相当する地層が認められたこ とから,館林観測井と明和温泉井の間に構造的・時間的ギャップが明らかとなった.その結果,両井の間 に断層（利根川構造線）が伏在するという指摘を裏付けるデータとなった. [ABSTRACT FROM AUTHOR]