Late Miocene ostracodes from the Kubota Formation, Higashi-Tanagura Group, Northeast Japan, and their implications for bottom environments

概要

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Sixty-seven ostracode species including those in open nomenclature are identified in thirty-six samples from the upper Miocene Kubota Formation, Higashi-Tanagura Group, distributed in Fukushima Prefecture, northeastern Japan. The lower part of the Kubota Formation yields Spinileberis sp. dominantly. In the middle to upper part of the formation, dominant species are Schizocythere kishinouyei (Kajiyama), Kotoracythere abnorma Ishizaki, Hanaiborchella triangularis (Hanai), Cytheropteron miurense Hanai, Paracytheridea neolongicaudata Ishizaki and Finmarchinella japonica (Ishizaki). Most of these species live off southwestern Japan under a subtropical to warm marine climate regime, but cryophilic and circumpolar species also occur sparsely in the middle to upper part. The ostracode assemblages indicate that the lower and the middle to upper parts of the Kubota Formation were deposited in an enclosed inner bay influenced by warm water and a warm shallow sea, respectively. Principal component analysis reveals that the influence of open sea water became strong in the upward sequence of the middle part. Analyses of ostracode faunas indicate that the Shiobara fauna from the Kubota Formation flourished in warm-water conditions.
日本古生物学会の論文
2001-12-31