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Isodayama Formation Iizuka, 1930

Invalid synonym: Shiratakibashi Formation (east of Tsugaru fault), Rokumaebashi Formation (east of Tsugaru fault), Uchimanbe Formation, Daishaka Formation, Aizawa Formation, Yunosawa Formation, Tsukushimoriyama Formation, Chushi Formation

• Type locality: Otaki creek, Aomori city, Aomori prefecture
• Coherent formation
• late Pliocene - early Pleistocene
• Contemporaneous heterotopic facies (Upper): Hongogawa Pumiceous Volcaniclastic Rocks
• Contemporaneous heterotopic facies (Middle): Takazumoriyama Scoriaceous Volcaniclastic Rocks
• Contemporaneous heterotopic facies (Lower): Otakizawa Pumiceous Volcaniclastic Rocks, Shoheizugawa Pumiceous Volcaniclastic Rocks
• Correlation: Misogasawa Formation, Fudotaki Formation
• Intruded by: Hosono Andesite

• Sedimentary facies (Upper): Shallow marine
• Depth of water: Upper - Lower sublittoral
• Lithofacies: Tuffaceous sandstone
• Lithofacies (Minor): Muddy sandstone, Sandy mudstone, Pumiceous tuff breccia
• Sedimentary structures: Trough cross-stratification, Herringbone cross-stratification, Graded bedding
• Paleocurrent: Northeast - North-northwest

• Thickness: 60 - 1,500 m or thicker
• Upper limit: Unconformity (Tazawamoriyama Formation, Hakkoda 1st-stage Pyroclastic Flow Deposit, Hakkoda 2nd-stage Pyroclastic Flow Deposit)
• Lower limit: Unconformity (Nyunai Formation, Genpachimori Formation, Fudotaki Formation)

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

• Distribution: Maedanome - Wakayama, Goshogawara city, Aomori pref.; Magonai river - Mekuraishi, Aomori city, Aomori pref.; Rokumaibashi river, Rokumaibashi, Ushirogata, Aomori city, Aomori pref.; Shirataki bridge, Uchimanbe river - Sunagawa creek, Uchimanbe, Aomori city, Aomori pref.; Sekinemata creek - Yomogida river - Nagashina river, Yomogida city, Higashitsugaru county, Aomori pref.; Okunai river, Maeda, Aomori city, Aomori pref.
• Fossils (Omma-Manganji fauna): Swiftpecten swiftii, Chlamys cosibensis, Acesta goliath, Glycymeris yessoensis, Mizuhopecten yessoensis yokoyamae, Patinopecten yessoensis, Chlamys tanassevitschi, Yoldia notabilis, Crenella sp., Venericardia ferruginea, Nemocardium samarange, Nemocardium sp., Entodesma sp., Thracia sp., Teconatica sp.
• Fossils: Fish scales, Trace fossils (Rosselia isp., Rholadidae), Makiyama chitanii, Pipe rocks
• Fossils (Upper, Foraminifera): Discorbinella bradyi, Globocassidulina subglobosa, Lagena acuticosta, Lagena glacilis, Melonis pacificum, Oolina hexagons, Pullenia apertula, Trifarina kokozuraensis, Uvigerina akitaensis, Globigerina bulloides, Globigerina imcompta
• Fossils (Diatoms): Neodenticula seminae, Nitzschia reinholdii, Neodenticula aff. koizumii, Proboscia curvirostris
• Tephra: Obirakiyama Pyroclastic Flow Deposit

• Nagamori et al. (2013) Geology of the Aomori-Seibu District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 67p. (in Japanese with English abstract 4p.)
• Fujii (1981) Geology of the Aburakawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 38p. (in Japanese with English abstract 3p.)