The Kisoshisui Tokachi-Oki Well at a total depth of 4, 457.06m which is located offshore Tokachi in eastern Hokkaido, Japan was penetrated into the alternation of conglomerate, sandstone and mudstone, exceeding 2, 000m in thickness.
This paper is a study of the stratigraphy, the depositional environment and the distribution of the above sequence in this well.
The sequence is correlative with the Okoppezawa Formation of middle Miocene age. Numerous coarse grained sand beds are abundant in older sedimentary rock fragments and contain primary sedimentary structures such as graded bedding, lamination and rip-up clast. The formation in this well is characterized by a rapid sedimentation rate of about 1, 330m/Ma, a lack of microplanktonic fossils and a trace of arenaceous benthonic foraminifers.
The geological evidences indicate the Okoppezawa Formation in this well is typical turbidite facies in stagnant deep sea environment of deposition during middle Miocene age. The turbidite facies are distributed in a limited area along the western part of the Doto magnetic belt offshore Tokachi.
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