The distributions of modern benthic foraminiferal assemblages were investigated in Ise and Mikawa bays, Japan, using surface sediments collected in September 2007. Forty seven species belonging to 40 genera were identified from Ise and Mikawa bays. Agglutinated species were dominant in the inner part of Ise and Mikawa bays, while calcareous species were dominant in the central part of Ise Bay. Significant shifts of assemblages were found in comparison with the distribution from surface sediments collected in 1940 from Ise Bay; calcareous species were replaced with agglutinated species in the inner part and the composition of calcareous species had changed completely in the central part. These results suggest that the present bottom environments are more eutrophic and anoxic than they were 67 years ago. Indicator species also suggested that Ise Bay is presently more eutrophic and anoxic than Mikawa Bay. A comparative study of distributions in Tokyo and Osaka bays demonstrated several similarities, while regional characteristic also were found there.

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岐阜県飛騨地方の高根地域に分布する安山岩質平行岩脈群と斑れい岩について地質と岩石磁気・古地磁気を調査した．前期中新世の安山岩質岩脈群からは「新しい岩脈法」によって2つの正断層型応力状態が推定された．安山岩の主要な強磁性鉱物は磁鉄鉱で，いくつかの岩脈には磁硫鉄鉱も含まれる．磁鉄鉱が担う磁化方位は東偏する．その方位は岩石磁気学的に高い信頼性を有するが，傾動の評価が難しい．方位の東偏は時計回り回転または北西への傾動を想定することで説明でき，前者の可能性が高い．この地域では岩脈群形成後に北中国地塊に対して約45°の時計回り回転が起こり，これは日本海拡大に関連した西南日本の時計回り回転を示すに違いない．高根と東海地方，北陸地方の間では大きな相対回転が起こっていない．伊豆弧衝突による回転の影響は高根までは及んでいないようだ．岩脈群形成時の応力状態は地磁気永年変化を平均化できるほどの期間継続していたと考えられる．

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Numerous paleomagnetic and chronological studies have contributed to the elucidation of the early Miocene (18-16 Ma) clockwise rotation of Southwest Japan associated with the major opening of back-arc basins in the Japan Sea. Paleomagnetic data have been reported previously from an andesitic parallel dike swarm in the Takane area, Takayama City, Gifu Prefecture, Central Japan, showing easterly deflection of the observed magnetization direction, in contrast to the expected paleomagnetic direction for the early Miocene. This must therefore represent clockwise rotation during the opening of the Japan Sea, providing the dike swarm was emplaced prior to its opening. Here we report new K-Ar hornblende ages from an andesite dike from the swarm. Two K-Ar ages of 22.1±1.2 and 21.2±1.2 Ma are statistically indistinguishable, and clearly pre-date the clockwise rotation.

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筆者らは三重県に分布する中新統一志層群の上部について浮遊性有孔虫・珪藻化石層序を検討した．大井層三ヶ野部層上部と片田層茶屋部層から得られた浮遊性有孔虫化石群集は亜熱帯的な性質を持ち，それらは今回調査した堆積岩セクションが浮遊性有孔虫化石層序のN.7帯～N.8帯下部に対比されることを示す．今回調査したセクションにおいて，N.7帯/N.8帯境界は大井層/片田層境界の約19m下位に位置することが判明した．N.7帯/N.8帯境界より下位の三ヶ野部層上部は珪藻化石層序のCrucidenticula sawamurae帯（NPD2B帯）に対比可能である．今後，N.7帯/N.8帯境界と磁気極性層序との対応関係およびその境界年代を今回調査したセクションで解明できる可能性があり，それが解明されれば17～15Maの古地磁気-微化石年代尺度の精度と確度が向上すると期待される．

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