Irakawa Formation

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Irakawa Formation (Nishida and Chihara, 1966) Tamiya et al., 1973

Type locality: Iragawa - Azuchi, Yunohama - Kamo, Tsuruoka city, Yamagata prefecture
Coherent formation
Miocene

Lithofacies: Conglomerate, Tuffaceous sandstone, Mudstone
Lithofacies (Upper): Andesite lava, Acidic pyroclastic flow deposit

Thickness: 700 m
Upper limit: Unconformity (Zempoji Formation)
Lower limit: Unconformity (Yunohama Granite)

Atsumi Group
[ Upper ]
~~~~~~~~~~~~~~
Irakawa Formation
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Atsumidake Formation
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Aburato Formation
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Yamairagawa Formation
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Hitokasumi Formation
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[ Lower ]

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

Distribution: Iragawa - Azuchi - Yunohama - Kamo, Tsuruoka city, Yamagata pref.
Fossils (Aniai-type flora): Acer ezoanum, Acer subpictum, Aesculus majus, Alangium aequalifolium, Alangium iragawense, Betula sachalinensis, Betula sollennis, Fagus aburatoensis, Fagus antipofi, Fagus mulutinervis, Glyptostrobus europaeus, Metasequoia japonica, Quercus sp., Sorbus sp., Ulmus propinaqua, Zelkova ungeri

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.)