| Summary: | 新潟県北蒲原郡中条附近の6つの断面から得た合計86個の試料中の化石放散虫を検討した。その結果を要約すれば次のようである。1)本地域においては,下位からP.R-N.R Zone,Thecosphaera antarctica Zonule,Thecosphaera japonica Zonuleの3帯の化石放散虫層序が設定できる。P.R-N.R Zoneは鍬杭層および下関層の大部分,Thecosphaera antarctica Zonuleは下関層の上部と内須川層の下部Thecosphaera japonica Zonuleは内須川層上部と鍬江層にそれぞれ当る。2)内須川層の上部は,Thecosphaera japonicaを特徴種とするTj型群集がみられ,Thecosphaera japonica Zonuleが設定されるが,下部はArchipiliicaeの種が多く,Tj-Ar型群集で椎谷層に対比される。また鍬江層はArchipiliicaeの種が殆んどなくThecosphaera japonicaに占められ西山層に対比される。3)Ta-Ar型群集は,その主要種を検討した結果浮遊性有孔虫との関係や最近のRiedelの研究からみて,Middle Miocene～Upper Mioceneのlowerを示す。またTj型群集の出現はUpper Mioceneのupperと思われる。 The whole 86 samples collected from six sections of the Kitakanbara Area in the Niigata sedimentary basin were under examination. Radiolarian fossils are generally well-preserved in the Neogene formations of this area, except in the Kamagui and the lower Shimoseki formations. We divided them into two zonules: one is the Thecosphaera antarctica zonule characterized by Thecosphaera antarctica together with the species such as Thecosphaera miocenica, Cyrtocapsa spp., Theocapsa himiensis, Eucyrtidium delmontense, Lycinocanium nipponicum, Sethocyrtis japonica, Antkocorys akitaensis, etc., the other is the Thecosphaera japonica zonule represented by Thecosphaera japonica together with the species such as Thecosohaera tochigiensis, T. akitaensis, Stylatractus yatsuoensis, Spireuma? circularis etc. The Thecosphaera antarctica zonule corresponds to the upper Shimoseki and lower Uchisugawa formations, while the Thecosphaera japonica zonule is equal to the upper Uchisugawa and the Kuwae formations. In the Kamagui and the lower Shimoseki formations, no assemblage is recognized owing to the poor occurrence of Radioiarian but Globorotalia peripheroronda-G. praescitula zone by Shimbo and Maiya is found. Judging from the present results, the relation between the planktonic foraminiferal zonation and the radiolarian stratigraphy in the oil-bearing field of Japan is shown in Table 7.
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