紀伊半島四万十帯, 音無川層群のタービダイト砂岩の化学組成  [in Japanese] Chemical characteristics of turbidite sandstones from the Otonashigawa Group in the Shimanto Belt, Kii Peninsula, Southwest Japan  [in Japanese]

古第三系音無川層群下部羽六累層のタービダイト砂岩の全岩化学組成をXRFで分析した.砂岩組成は, B.I.ダイアグラムで陸弧/開析島弧〜成熟島弧の後背地を示し, また, 化学組成に基づく他の識別ダイアグラムにおいても類似の造構場を示す.タービダイト砂岩内で粒度変化に対応した系統的な組成変化が認められるが, 砂岩部内においてはその変位幅はあまり大きくない.その上位のタービダイト泥岩では組成が大きく変わるが, 砂岩から泥岩までの一連のトレンドが認められ, hydraulic fractionationが確認された.タービダイト間に発達する半遠洋性泥岩はタービダイト泥岩とは異なる化学組成をもつ.

Chemical analysis by XRF was performed for the turbidites and their associated sediments of the Paleogene Lower Haroku Formation, the Shimanto Belt. The chemical features of sandstones show that the provenance of the basin was continental arc, dissected arc, evolved island arc or active continental margin, on the basis of the Basicity Index (B.I.) diagram and other discrimination diagram. The composition of sandstones varies a little within a single turbidite bed, but tubidite mudstones have considerablly different compositions. The data form a trend of hydraulic fractionation on the B.I. diagram, mainly due to grain size variation. The turbidite black mudstones have defferent chemical features from the interbedded hemipelagic greenish mudstones.