ジュラ紀・白亜紀境界付近における放散虫化石群の変化 (予察) : とくに多節 Nassellaria について

概要

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Nine radiolarian assemblage-zones (A-z) are recognized in the Jurassic and the lowermost Cretaceous sequences of Japan, namely, in ascending order, the Parahsuum simplum A-z (early Early Jurassic); the Parahsuum sp. D A-z (middle Early Jurassic), the Hsuum sp. B A-z (late Early Jurassic), the Unuma echinatus A-z (Bajocian-early Bathonian), the Guexella nudata A-z (late Bathonian-Callovian), the Gongylothorax sakawaensis-Stichocapsa naradaniensis A-z (Oxfordian), the Tricolocapsa sp. O A-z (Kimmeridgian), the Pseudodictyomitra primitiva-Pseudodictyomitra sp. A A-z (Tithonian) and the Pseudodictyomitra cf. carpatica A-z (Berriasian). In this radiolarian biostratigraphic framework, the stratigraphic range of four multi-segmented nassellarian genera (Parahsuum, Hsuum, Archaeodictyomitra and Pseudodictyomitra) is investigated. Hsuum with discontinuous costae and Parahsuum disappeared in the P. primitiva-P. sp. A A-z and in the T. sp. O A-z, respectively. A certain group of Archaeodictyomitra, which occurs abundantly in the Lower Cretaceous, first appeared in the T. sp. O A-z. Pseudodictyomitra made the first appearance at the base of the P. primitiva-P. sp. A A-z. Judging from the stratigraphic range of the above-mentioned four genera, it is pointed out that a remarkable faunal change took place in the T. sp. O A-z and/or the P. primitiva-P. sp. A A-z, which are assigned to Kimmeridgian-Tithonian in age.
日本古生物学会の論文
1986-06-20