Middle to Upper Miocene and Pliocene sequences of southwest Sendai, as a standard referential stratigraphy in the Pacific side of NE Japan

藤原 治 鈴木紀毅 林 広樹 入月俊明 3 概 要 本巡検では,東北日本の太平洋側新第三系の標準地域としての宮城県仙 台市から名取市にかけて分布する新第三系を見学する.見学の要点は, シーケンス層序と奥羽山脈発達史などの研究成果を念頭においた観察にあ る.最下位の茂庭層では,同時期の地層では例の少ない岩礁性動物群化石 を見る.時間が許せば,茂庭層–旗立層境界に見られる海緑石層を見学し, 東北日本で同時期に海緑石層が形成されていた一端を紹介する.名取川下 流の露頭が本巡検の主要な見学地で,これまでの巡検で詳細には紹介され たことがない,旗立層と綱木層の不整合と堆積サイクルを見学する.この 見学地は,フィッション ・トラック年代の測定用試料を採集した露頭でも あるため,旗立層・綱木層の見学地としては模式地に匹敵する重要地点で ある.青葉山丘陵の見学地点では,綱木層と梨野層の境界を見学する.梨 野層は白沢カルデラの東縁を構成する地層とされるが,綱木層との層序関 係については不整合か整合か決着していない.最後に,仙台層群を観察す る.下位の名取層群とは対照的に水平層となっていることが分かるほか, 竜の口層から向山層への層相変化を見ることができる.

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