[ Top ] [ Japanese ]

Ishido Formation (Naruse et al., 1951) Suzuki et al., 1990

Invalid synonym: Ishido Siltstone Formation, Ishido Group

• Type locality: Nenkami, Minamiboso city, Chiba prefecture
• Coherent formation
• middle - late Miocene
• Correlation (Upper): lower Kiyosumi Formation
• Correlation: Amatsu Formation, Nishizaki Formation

• Sedimentary facies: Marine, Surface deposits of landward slope of trench
• Lithofacies: Mudstone, Siltstone-dominant interbedded sandstone and siltstone
• Lithofacies (Minor): Scoriaceous sandstone, Sandstone-dominant interbedded sandstone and mudstone, Gravel-bearing mudstone
• Sedimentary structures: Slump structures

• Thickness: ca. 400 - 1,050 m
• Upper limit: Transitional (Kagamigaura Formation), Unconformity (Sagashi Formation)
• Lower limit: Unconformity (Hota Group)

------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown

• Distribution: Nenkami - Ishido - Kuroiwa - Shimomihara - Mikogami - Fukuzawa - Haraoka - Cape Namuya - Senkimori - Anbaya - Wada, Minamiboso city, Chiba pref.; Ichiihara, Kamogawa city, Chiba pref.
• Fossils: Sharks (Isurus sp.), Sponges (Makiyama chitanii), Foraminifera, Radiolarians, Diatoms, Calcareous nannofossils

• Takahashi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.8, pp.375-395, DOI
• Kawakami and Shishikura (2006) Geology of the Tateyama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 82p. (in Japanese with English abstract 5p.)
• Suzuki et al. (1990) Geology of the Nago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 48p. (in Japanese with English abstract 3p.)
• Nakajima et al. (1981) Geology of the Kamogawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 107p. (in Japanese with English abstract 7p.)