[ Top ] [ Japanese ]

Yokoo Formation (Yamagishi, 1964)

Some researchers treated as a member of Uchimura Formation.

Invalid synonym: Yokoo Member

• Type locality: Seba river, Soehi - Hatayama, Sanada town, Ueda city, Nagano prefecture
• Coherent formation
• middle Miocene (? - 15 Ma, Foraminifera)
• Intruded by: Quartz porphyry, Hornblende porphyry, Diorite porphyry

• Sedimentary facies: Marine
• Sedimentary facies: Reductive circumstance
• Sedimentary facies: Continental slope
• Depth of water (Top): 700 - 1,500 m
• Lithofacies (Upper): Shale
• Lithofacies (Upper, Minor): Sandy mudstone, Glauconite sandstone
• Lithofacies (Middle): Interbedded tuff and shale
• Lithofacies (Middle, Minor): Tuff breccia
• Lithofacies (Lower): Tuff
• Lithofacies (Lower, Minor): Tuffaceous sandstone
• Sedimentary structures (Top): Clastic dikes
• Sedimentary structures: Current ripples, Slump structures

• Thickness: 400 - 900 m or thicker
• Upper limit (Mori Member): Bottom of t1 Dacite Tuff
• Upper limit: Conformity (Iseyama Formation, Mori Member, Toyosaka Member)
• Lower limit: Conformity (Taroyama Formation)

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

• Distribution: Kangawa river, Motohara, Sanada town, Ueda city, Nagano pref.; Seba river, Soehi - Hatayama, Sanada town, Ueda city, Nagano pref.; Numairi - Mount Takato, Sanada town, Ueda city, Nagano pref.; Kamishiojiri, Ueda city, Nagano pref.; Wadaira - Hirasawa - Nasawa river - Mido river - Yagawa river, Sakaki city, Hanishina county, Nagano pref.
• Fossils: Shark (Centrophorus sp., Teeth), Fish (Eosardinella sp., Bones), Shell-bearing Polychaeta (Yokoia sp.), Foraminifera (Cyclammina sp.), Plants (Sequoia sp., Lindera sp.)
• Fossils (Fish scale): family Clupeidae, family Macrouridae, family Myctophidae, family Sparidae
• Fossils (Shellfishes): Acharax tokunagai, Cyclammina sp., Palliolum peckhami, Uvigerina sp.

• Suzuki (2008) Jour. Geol. Soc. Japan, vol.114, no.10, pp.536-539 DOI
• Suzuki (2008) Jour. Geol. Soc. Japan, vol.114, no.1, pp.43-46 DOI
• Suzuki (2007) Jour. Geol. Soc. Japan, vol.113, no.1, pp.23-26 DOI
• Kato and Akahane (1986) Geology of the Nagano District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 120p. (in Japanese with English abstract 5p.)
• Kato (1980) Geology of the Sakaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 57p. (in Japanese with English abstract 5p.)