始新世-漸新世前期四万十累層群の堆積岩岩石区  [in Japanese] Petroprovinces of the Eocene-early Oligocene Shimanto Supergroup  [in Japanese]

始新世-漸新世前期四万十累層群について, 既存の文献による砂岩組成と今回新たに加えた岩片組成に基づき, 琉球区, 日向区, 室戸区, 駿河-相模区の4つの堆積岩岩石区を認定した。琉球区(沖縄から種子島までの範囲)の砂岩は長石質ないし石英質アレナイトからなり, 日向区(九州と四国西部地域)の砂岩はおもに石質ないし長石質ワッケで, 一部のものはカリ長石を含まない。室戸区(四国東部と紀伊半島地域)の砂岩は長石質アレナイト, 一部ワッケからなり, 駿河-相模区(赤石山地と関東山地地域)の砂岩は石質から長石質のワッケないしアレナイトで一部カリ長石を含まない。各堆積岩岩石区からの古流向と砂岩組成は, 砕屑物はそれぞれの堆積岩岩石区に隣接した後背地から供給されたことを示す。日向・駿河-相模の両区の後背地はあまり開析されていない火山弧であり, 一方, 室戸・琉球の両区の後背地は, 著しく開析された火山弧で広く花崗岩類・堆積岩・変成岩が露出していた。

The Eocene-early Oligocene Shimanto Supergroup, extending for approximately 1400 km along the outer part of Southwest Japan and the Nansei Islands, consists of trench-fill and forearc basin-fill deposits, which represent as a whole accretionary complexes. Sandstone compositions from previous literature and this study allow us to propose four petroprovinces: from SW to NE, the Ryukyu, Hyuga, Muroto, and Suruga-Sagami Petroprovinces. The Ryukyu Petroprovince is characterized by quartz-rich feldspathic and quartz osearenite, the Hyuga Petroprovince by lithic and feldspathic wacke including potash feldspar-free sandstones, the Muroto Petroprovince by feldspathic arenite including wacke, and the Suruga-Sagami Petroprovince by lithic and feldspathic sandstones including potash feldspar-free sandstones. Paleocurrent directions and sandstone compositions from the four petroprovinces indicate that trench sedimentaion is characterized by dominant axial transport along the trench, although transport did not pass through the boundaries between the four petroprovinces, and that clastic material was derived from an adjacent dissected areas sociated with each petroprovince.