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Onnagawa Formation (Ohasi ex Toyama, 1925) Chitani, 1930

Invalid synonym: Sannai Formation (Regional name of Yokote area, Akita pref.)

• Type locality: Onnagawa, Oga city, Akita prefecture
• Coherent formation
• middle - late Miocene (13;1 - 6.7 Ma)
• Contemporaneous heterotopic facies: Kusanagi Formation
• Contemporaneous heterotopic facies (Lower): Innai Tuff Member
• Correlation: Odoji Formation, Iwaya Formation, Maekawa Formation, Otaki Formation, Yugoya Formation
• Intruded by: Olivine dolerite, Olivine basalt, Dacite, Rhyolite, Moyasan Rhyolite, Nibetsu Granite, Babame Dolerite, Soyakyo Andesite, Zentoku Quartz Diorites, Koshikiyama Dacite, Daiyama Quartz Diorites

• Sedimentary facies: Marine
• Sedimentary facies: Still water (Foraminifera)
• Sedimentary facies: Turbidite
• Water temperature: Cold current, Reductive (Foraminifera)
• Depth of water: Shallow marine - Barhyapelagic (Foraminifera)
• Lithofacies (Upper): Diatom-originated siliceous stone (Chert), Interbedded sliceous stone and siltstone
• Lithofacies (Lower): Interbedded siliceous stone and sandstone
• Lithofacies (Minor): Porcelanite, Diatomite, Acidic tuff, Basaltic pyroclastic rocks, Glauconite sandstone
• Paleocurrent: North to South

• Thickness: 10 - 160 m
• Same age as Noshirooki Andesite
• Upper limit: Bottom of the glauconite concentrated zone at the lower part of diatomaceous siltstone (6.6 Ma, Kano, 2018)
• Upper limit: Bottom of the thick acidic tuff (Ozawa et al., 1979)
• Upper limit: Transitional (Funakawa Formation), Conformity (Subari Andesite, Osanai Tuff Member, Kurosawa Formation), Unconformity (High I Terrace Deposit, Katanishi Formation, Ishikurayama Formation, Chokai volcanic products, Fukizawa Formation)
• Lower limit: Top of glauconite sandstone bed (Nishikurosawa Formation, Kano et al., 2011)
• Lower limit: Bottom of hard shale overlying acidic tuff or mudstone beds (Koyanosawa Formation, Ozawa et al., 1985)
• Lower limit: Transitional (Nishikurosawa Formation, Kitanomatasawa Formation), Interfingered (Manaitayama Volcanic Rocks), Conformity (Hachiwari Formation, Hayaguchigawa Formation, Koyanosawa Formation, Koani Formation, Gongenyama Formation, Sugota Formation, Kotsunagizawa Formation, Aosawa Formation, Okawa Formation), Unconformity (Monzen Formation, Nomuragawa Formation, Daijima Formation)

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

• Distribution: Onnagawa, Oga city, Akita pref.; Nishikurosawa - Shimoshinzan - Nomura river, Oga city, Akita pref.; Aniai, Kitaakita city, Akita pref.; Tokusawa - Takinosawa - Miyazawa, Yurihonjo city, Akita pref.; Futatsui town, Noshiro city - Lake Subari, Fujisato city, Yamamoto county, Akita pref.; Kariwano, Senboku city, Akita pref.; Tomari river - Mizusawa river, Minehama, Hachimori, Happo city, Yamamoto county, Akita pref.; Tsurugata - Hiyama - Omori - Hadachi, Noshiro city, Akita pref.: Komata river, Ochiai - Moritake hot spring - Nagaomote - Koikawa, Mitane city, Yamamoto county, Akita pref.; Asaminai, Gojome city, Minamiakita county, Akita pref.; Kisoishi, Taiheihatta, Akita city, Akita pref.; Saraminai creek, Akita city, Akita pref.; Koide creek - Taihei river - Uyashinai, Kawabe, Akita city, Akita pref.; Funaoka - Shonai, Kyowa, Daisen city, Akita pref.; Kokoroyari, Tsuchikawa, Daisen city, Akita pref.; Matsukura, Omagari, Daisen city, Akita pref.; Kimigano river, Iwaki, Yurihonjo city, Akita pref.; Iwanomezawa - Agenoue - Mount Takashiro - Shimohebita - Miyata - Kamihebita - Shobuno - Tokuzawa - Shinsawa - Nozoki - Okurasawa - Futamata - Mount Nagane - Noshinai - Imonozawa - Toritame - Mount Shibakura - Osuna river, Yurihonjo city, Akita pref.; Koyoshi river, Yashima town - Chokai town, Yurihonjo city, Akita pref.; Honai - Tateai - Oikata - Otashiro, Higashiyuri, Yurihonjo city, Akita pref.; Niiyama - Yagami - Joboji, Omonogawa town, Yokote city, Akita pref.; Mount Shichiko - Chojamori, Ugo city, Ogachi county, Akita pref.; Iwasaki, Yuzawa city, Akita pref.; Kogawa - Kamihitane - Kamijinego - Cho river - Momoyake-Omori - Itabira - Sunago, Chokai town, Yurihonjo city, Akita pref.; Innai, Ugo city, Okachi county, Akita pref.
• Fossils: Sponges (Makiyama chitanii), Fish (Bones, Scales), Fish (family Clupeidae), Shark (Teeth), Echinoids, Trace fossils, Plants (Liquidambar sp., Pollen)
• Fossils (Shellfishes): Cryptonatica sp., Cultellus? sp., Macoma sp., Nassarius sp., Paliollum peckhami, Paphia euglypta
• Fossils (Foraminifera): Ammobaculiles spp., Ammodiscus incertus, Anormalina glabrata, Bathysiphon nipponica magnacornuta, Bolivina cf. pacifica, Buccella sp., Bulimina nipponica, Bulimina cf. pupoides, Cassidulina lobatulus, Cassidulina cf. norcrossi, Cassidulina subcarinata, Cassidulina cf. sublinbata, Cassidulina yabei, Cassidulinoides sp., Cibicides aknerianus, Cibicides pseudoungerianus, Cribrostomoides renzi, Cribrostomoides subglobosum, Cyclammina cancellata, Cyclammina cf. ezoensis, Cyclammina japonica, Cyclammina pusilla, Dentalina subsoluta, Dorothia sp., Epistominella aff. bradyana, Epistominella pulchella, Fissurina sp., Fursenkoina sp., Glandulina laevigata, Globigerina bulloides, Globigerina pachyderma, Goëssella schenki, Globobulimina auricalate, Globobulimina pupoides, Gyroidina sordanii, Gyroidinoides cf. soldanii, Haplophragmoides cf. emaciatum, Haplophragmoides renzi, Haplophragmoides cf. subglobosum, Hopkinsina morimachiensis, Hopkinsina sinboi, Hormosina globulifera, Lagena sp., Larnacantha? elliptica, Larnacantha? polycantha, Lenticulina lucida, Martinottiella communis, Massilina sp., Melonis nicobarense, Melonis pacificum, Melonis pompilioides, Nodosaria sp., Nonionellina cf. labradorica, Oridorsalis umbonatus, Plectofrondicularia sp., Praeglobobulimina kamedaensis, Praeglobobulimina pacifica, Praeglobobulimina pupolides, Praeglobobulimina pyrula, Pseudononion grateloupi, Pullenia bulloides, Pullenia elegans, Pullenia salisburyi, Rosalina sp., Saccammina sphaerica, Sigmoilina schlumbergeri, Sigmoilopsis schlumbergeri, Sphaeroidina bulloides, Sphaeroidina compacta, Spirosigmoilinella compressa, Spongodiscus spp., Textularia spp., Trifarina sp., Triloculina sp., Uvigerina yabei (or akitaensis), Uvigerina proboscidea, Valvulineria glabya, Valvulineria cf. sadonica
• Fossils (Diatoms): Actinocyclus ingens, Actinoptyclus ingens f. ingens, Actinoptychus senarius, Aulacoseira spp., Azpeitia vetustissima, Caritatus jouseanus, Cavitatus miocenicus, Cocconeis costata, Cocconeis curviritunda, Coscinodiscus argus, Coscinodiscus endoi, Coscinodiscus marginatus, Coscinodiscus stelleris, Coscinodiscus temperis, Coscinodiscus yabei, Delphineis surirella, Denticula hustedtii, Denticulopsis hyalina, Denticulopsis katayamae, Denticulopsis simonsenii, Denticulopsis vulgaris, Diploneis smithii, Hyalodiscus obsoletus, Ikebea tenuis, Melosira sol, Melosira sulcata, Nitzschia grunowii, Nitzschia heteropolica, Nitzschia pliocena, Paralia sulcata, Proboscia barboi, Rhizosolenia barboi, Rhizosolenia hebetata, Rhizosolenia styliformis, Rouxia californica, Rouxia yabei, Simonseniella barboi, Stellarima microtrias, Stephanogonia hanzawae, Stephanopyxis spp., Stephanogonia hanzawae, Synedra jouseana, Thalassionema hirosakiensis, Thalassionema nitzschioides, Thalassionema schraderi, Thalassiosira temperei, Thalassiothrix longissima
• Fossils (Radiolarians): family Acanthodesmiidae, Anthocyrlidium ehrenbergi, Artostrobiidae, Botryostobus bramlettei, Calocycletta virginis, Cannartus petterssoni, Carpocaniidae, Cenoshaera spp., Collosphaera spp., Cromyodruppa concentrica, Cycladophora akitaensis, Cyrtocapsella japonica, Cyrtocapsella tetrapera, Diarlus didynus, Diarlus hughesi, Diartus petterssoni, Didymocyrtis laticonus, Didymocyrtis penultima, Druppatractus irregularis, Eucyrtidium calvertense, Eucyrtidium cienkowskii, Eucyrtidium inflatum, Gondwanaria sp., Lamprocyrtis hannai, Larcopyle sp., Larcospira sp., Larnacantha? elliptica, Larnacantha? polyacantha, Lipmanella spp., Lithatractus tochigiensis, Lithocarpium spp., Lithopera renzae, Lophophaena sp., Lychnocanoma nipponica magnacornuta, Lychnocanoma nipponica nipponica, Lychnocanoma nipponica magnacornuta, Ommatartus sp., Periphaena spp., Porodiscus spp., Pyloniidae spp., Pylospira sp., Rhopalodictyum spp., Sethocyrtis japonica, Spongocore spp., Spongodiscus spp., Spumellaria sp., Stichocorys delmontensis, Stychocorys peregrina, Stylacontarium aff. bispiculum, Stylatraclus sp., Stylodictya sp., Theocalyptra davisiana cornutoides, Theoconus nipponicus, Theocorys japonica, Theocorys redondoensis, Theocorythium sp., Theocyritis redondoensis, Xiphospira spp.

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