Hanagata, S. 2004. Miocene foraminifera from the Niigata oil and gas field region, northeastern Japan. In: Bubik, M.; Kaminski, M. (Editors), Proceedings of the Sixth International Workshop on Agglutinated Foraminifera, pp 151-166. Grzybowski Foundation Special Publication.

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https://www.researchgate.net/profile/Satoshi-Hanagata/publication/273144589

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Foraminiferal assemblages from the Miocene Teradomari Formation, which forms a major source rock in the Niigata oil and gas field region, back arc of northeastern Japan, are characterised by the occurrence of abundant agglutinated foraminifera. The scarcity of taxonomic studies on foraminifera from the Teradomari Formation has prevented discussion of the palaeoenvironment based on modern foraminiferal ecology. Therefore, the foraminiferal fauna of the Teradomari Formation in the type section of the formation is described in this study. Cluster analysis reveals five associations: the Trochammina nipponica-Veleroninoides akibae Association, Karrerulina coniformis Association, Cribrostomoides subglobosus Association, Karrerulina coniformis-C. subglobosus Association, and Gyroidina komatsui-Planocassidulina praehelenae Association. Their palaeoenvironmental implications were considered based on the abundance of calcareous foraminifera, diversities and the microhabitat preferences of benthic taxa. In addition, shallow marine and deep marine faunas were distinguished from turbidite facies. Trochammina nipponica-V. akibae Association indicates palaeoenvironment of brackish shallow marine. Karrerulina coniformis Association indicates calcium carbonate undersaturated and oxygen depleted condition. Cribrostomoides subglobosus Association indicates calcium carbonate undersaturation and high productivity. Karrerulina coniformis-C. subglobosus Association indicates calcium carbonate undersaturated, high productivity and oxygen depleted condition. Gyroidina komatsui-P. praehelenae Association indicates calcium carbonate saturated and oligotrophic condition which are possibly related to eustatic high sea level. Water stratification, possibly caused by fresh water input, together with high primary productivity and oxygen depletion, are inferred as primary factors for the deposition of source rock in the Niigata oil-gas field region. These factors were mainly controlled by the communication of seawater between the Sea of Japan and the Pacific Ocean. Veleroninoides akibae, which has been erroneously identified to Haplophragmoides compressum LeRoy in previous studies, is described as a new species.

Foraminifera

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