三郡-中国帯に分布する錦層群からのペルム紀放散虫

筆者らは,島根県六日市町付近に分布する錦層群の生層序学的研究を行なった.本地域の錦層群は下位より,Na層(チャート相),Nb層(泥岩相),Nc層(砂岩相)からなる.Na層はAlbaillella sinuata帯およびPseudoalbaillella sp. C群集帯(今回新たに設定)を含んでおり,一方,Nb層はPseudoalbaillella sp. C帯,Ps. globosa群集帯およびFollicucullus monacanthus群集帯により特徴付けられる.Nc層とNb層の一部はFo. scholasticus群集帯の下部を含んでいる.六日市地域の錦層群の年代はこのような放散虫化石層序にもとづけば,北米のLeonardianおよびGuadalupianもしくは中国の茅口統(Maokouan)に相当する.また,本論文では,ここに述べた5化石帯のうち下部の3帯を再定義した.筆者のうち石賀と渡瀬は,Albaillella sp. Dの古生物学的検討から1新種(A. siunata)を提唱し,合わせてAlbaillellariaに属する3種の記載を行なった.

Biostratigraphical study of the Nishiki Group was done in the Muikaichi area, Shimane Prefecture, Southwest Japan. The Nishiki Group in the area consists of three formations, namely, the Na, the Nb and the Nc formations, in ascending order. The Na formation (chert facies) includes the upper part of the Albaillella sp. D Assemblage-zone and the Pseudoalbaillella sp. C A-zone (newly denned), while the Nb formation (mudstone facies) is represented mainly by the Pseudoalbaillella sp. C, the Ps. globosa and the Follicucullus monacanthus A-zones. The Nc formation (sandstone facies) and some part of the Nb formation include the lower part of the Fo. scholasticus A-zone. The Nishiki Group in the Muikaichi area is regarded to include the Leonardian and Guadalupian equivalents or the Maokouan based on the radiolarian biostratigraphy. The lower three of these five zones are redefined. A new species is proposed on the basis of paleontologic study of Albaillella sp. D with description of additional three species of Albaillellaria.