宮崎平野北部の鮮新統宮崎層群の地質と貝形虫化石群集

概要

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A total of 103 ostracode taxa were obtained from the upper Pliocene Sadowara and Takanabe Formations, Miyazaki Group, in the northern part of the Miyazaki Plain, Southwest Japan. Many of them live in sublittoral areas under the influence of the Kuroshio warm current. They have been also reported from upper Pliocene to lower Pleistocene deposits yielding the Kakegawa molluscan fauna. Three biofacies (U, M and L) were discriminated on the basis mainly of Q-mode cluster analysis. Biofacies U is dominated by Neonesidea spp., Loxoconcha ikeyai and Schizocythere kishinouyei, which live in sandy bottoms in upper to middle sublittoral zone. Biofacies M is characterized by Loxoconcha tamakazura, Loxoconcha tarda, Pontocythere cf. subjaponica and Cytheropteron uchioi which live in middle to lower sublittoral zone. Biofacies L contains such mud dwellers in lower sublittoral zone as Acanthocythereis munechikai, Bradleya albatrossia, Hirsutocythere? hanaii and Krithe spp. Spatio-temporal distribution of the ostracode biofacies and sedimentary facies show that 1) the sedimentary basin was deeper southward; 2) shallowing of the sea occurred during the deposition of the Sadowara Formation to the upper part of the Takanabe Formation; and 3) a rapid transgression occurred during the deposition of the uppermost part of the Takanabe Formation.
2008-10-01