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Ogawa Formation (Morishima, 1941) Saito et al., 1962

Invalid synonym: Sekiya Formation, Oyakawa Sandstone and Conglomerate Formation, Doro Formation, Kamitaru Formation, Furumi Formation

• Type locality: Sara river, Ogawa - Io, Iiyama city, Nagano prefecture
• Coherent formation, Volcanic rocks
• Basin-fill deposit
• late Pliocene - early Pleistocene (ca. 2.3 - 1.1 Ma; 2.41, 2.2, 1.82, 1.48, 1.2 Ma, FT)
• Correlation: Uonuma Formation, Naradate Formation, Sarumaru Formation
• Intruded by: Hypersthene augite andesite dikes

• Sedimentary facies: Regression deposit
• Sedimentary facies (Upper): Terrestrial
• Sedimentary facies (Main part): Fluvial
• Sedimentary facies (Main part, Minor): Lacustrine
• Sedimentary facies (Lower): Marine, Fluvial
• Sedimentary facies (Main part): Meandering river, Braided river
• Sedimentary facies (Lower): Inner bay, Foreshore, Shoreface, Fluvial
• Lithofacies (Western part, Top): Hypersthene augite andesite tuff breccia, Conglomerate
• Lithofacies (Main part): Conglomerate, Sandstone Mudstone
• Lithofacies (Main part, Minor): Lignite, Plant roots, Volcanic mudflow deposit
• Lithofacies (Lower): Sandstone, Mudstone, Conglomerate
• Sedimentary structures (Main part): Trough cross stratification, Imbrication
• Sedimentary structures (Lower): Trough cross stratification, Bioturbation

• Thickness: ca. 500 - 1,700 m
• Thickness (Western part, Top): 250 - 300 m
• Thickness (Main part): ca. 250 - 1,600 m
• Thickness (Lower): ca. 100 - 250 m
• Upper limit: Conformity (Minochi Formation), Unconformity (Konigori Formation, Yashiki Formation, Madaraokogen Pyroclastic Rocks, Mure Debris Avalanche Deposit), Abut unconformity (Terao Pyroclastic Flow Deposit)
• Lower limit: Bottom of the horizon intercalating gravelly sandstone and non-marine mudstone beds
• Lower limit: Conformity (Seguchi Formation, Nigoriike Formation)

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

• Distribution: Hiramaru river - Nagasawa river - Doro river - Sekikawa river - Okemi - Mount Takatoko, Myoko city, Niigata pref.; Sara river, Ogawa - Io, Iiyama city, Nagano pref.; Tomikura pass - Mount Kuroiwa - Mount Nabekura - Yanaikubo, Iiyama city, Nagano pref.; Fukoji, Iizuna city, Kamiminochi county, Nagano pref.; Kamiyamakokusaimura, Shinano city, Kamiminochi county, Nagano pref.; Madara river, Kitanagae - Oyakawa, Nakano city, Nagano pref.; Yoshizawa - Hinatazawa - Kaesa - Kamiimai - Futatsuishi - Komeyama, Nakano city, Nagano pref.; Imokawa river - Mount Hanamijo - Kamiakashio, Iizuna city, Kamiminochi county, Nagano pref.
• Fossils (Main part, Plants): Metasequoia japonica (Stocks, Branches, Leaves, Cones)
• Fossils (Main part, Lacustrine): Diatoms (Stephanodiscus sp.)
• Fossils (Main part, Shellfishes): Acila insignis, Astarte cf. hakodatensis, Clinocardium ciliatum, Lucinoma acutilineata, Macoma incongrua, Siphonalia fusoides, Turritella nipponica
• Fossils (Lower, Shellfishes): Corbicula sp., Ostrea gigas
• Tephra: Drg, Nwp, Dlp, Sk, T4

• Nagamori et al. (2003) Geology of the Togakushi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 109p. (in Japanese with English abstract 3p.)
• Yanagisawa et al. (2000) Geology of the Iiyama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 144p. (in Japanese with English abstract 6p.)
• Akahane et al. (1992) Geology of the Nakano District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 106p. (in Japanese with English abstract 4p.)