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Maruyama Formation Kujiraoka, 1953

• Type locality: Maruyama, Kitamata, Sakata city, Yamagata prefecture
• Coherent formation
• late Pliocene (Foraminifera)
• Correlation: Upper Tentokuji Formation, Sakekawa Formation

• Lithofacies: Siltstone
• Lithofacies (Minor): Mudstone, Sandstone, Acidic tuff

• Thickness: 100 - 650 m
• Upper limit: Transitional (Kannonji Formation), Unconformity (Shonai Group, Horaisan Volcanic Rocks, Owarabi Debris Avalanche Deposit, Kusatsugawa Debris Avalanche Deposit, Chokai volcano products)
• Lower limit: Transitional (Tateyama Formation)

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

• Distribution: Maruyama - Minaminomaeda - Tateyama, Kitamata, Sakata city, Yamagata pref.; Odaino, Masuda, Sakata city, Yamagata pref.; Shikanomata river - Mount Horai, Sakata city, Yamagata pref.; Arase river, Kannonji, Sakata city, Yamagata pref.; Komasuda - Ushiroyama - Washioyama - Yamaya - Kamimochiyama, Sakata city, Yamagata pref.; Takenokozawa hot spring, Tsuruoka city, Yamagata pref.; Onumashinden Sakata city, Yamagata pref.
• Fossils: Shellfishes
• Fossils (Foraminifera): Ammonia cf. beccarii, Ammonia japonica, Brizarina robusta, Buccella frigida, Buliminella elegantissima, Cassidulina norcrossi, Cassidulina yabei, Cibicides lobatulus, Cibicides pseudoungerianus, Cibicides ungerianus, Cribroelphidium yabei, Cribrononion clavatum, Cribrostomoides cf. evoluta, Cribrostomoides subglobosum, Cyclammina cancellata, Cyclammina japonica, Cyclammina pusilla, Epistominella pulchella, Fissulina sp., Gaudryina arenaria, Globigerina bulloides, Globigerina pachyderma, Globigerina quinqueloba, Globobuliminina sp., Globocassidulina subglobosa, Globorotalia inflata inflata, Globorotalia inflata praeinflata, Globorotalia orientalis, Guttulina spp., Haplophragmoides sp., Islandiella japonica, Islandiella margareta, Lagena acticosta, Loxostmum limbatum, Marginulina grobra, Martinottiella communis, Melonis nicobarense, Melonis pompilioides, Miliammina echigoensis, Nonioneuina labradorica, Orbulina universa, Praeglobobulimina pupoides, Pullenia apertula, Quinqueloculina spp., Sphaeroidina bulloides, Trifarina hughesi, Trifarina kokozuraensis, Uvigerina akitaensis, Uvigerina yabei, Volvulineria sadonica
• Fossils (Radiolarians): Cenosphaera sp., Cromyodruppa concentrica, Cyrtocapsella sp., Flustrella camerina, Flustrella cf. flustrella, Larnacantha polyacantha?, Lychnocanium nippoicum, Melittosphaera sp., Sethacyrtis japonica, Spireuma circularis, Spongodiscus spp., Stylosphaera sp., Thecosphaera japonica, Theocyrtis redondoensis

• Nakano and Tsuchiya (1992) Geology of the Chokaisan and Fukura District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 138p. (in Japanese with English abstract 7p.)
• Tsuchiya (1989) Geology of the Osawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 85p. (in Japanese with English abstract 6p.)
• Tsuchiya et al. (1984) Geology of the Tsuruoka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 77p. (in Japanese with English abstract 5p.)
• Ikebe et al. (1979) Geology of the Sakata District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 42p. (in Japanese with English abstract 3p.)