高知県西部中村市から宿毛市にかけて分布する最上部白亜系 : 始新統百笑層の層序と堆積場

概要

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The southwestern Shikoku is occupied by the upper Cretaceous Taisho Group of the Northern Shimanto Belt, the Henai Group ranging from latest Cretaceous to Middle Eocene time, and the Paleogene Hata Group of the Southern Shimanto Belt from north to south. The Taisho Group referred to as the melange facies of the Arioka Formation is defined as the Gudo Unit herein. The Henai Group consists of the Domeki, Hirata, Ishimiji, Ida, and Tanokuchi Formations and is recognized as a slope-basin sediment covering the Northern Shimanto Belt. The Domeki Formation of ca. 3000m thick is dominated by siliceous mudstone intercalated with thin tuff layers. The formation contains slump sheets including siliciclastic blocks, and interbeds a thick pile of olistostrome layers in the middle part. Based on lithology the Formation is further subdivided into the Kusushima, Daiyoji, Marunouchi, Kaba, Kurokawa, Iwasaki, Fuba, and Uyama Members. The formation is dated from Maastrichtian to Middle Eocene time by radiolarians and inoceramids. The slope-basin has deformed reflecting to the changes of the Kula and Pacific Plate motion, where the Domeki Formation deposited under the effect of the volcanic activities in the Chugoku and Shikoku provinces of Japan in latest Cretaceous and Paleogene time.
2003-12-25