[ Top ] [ Japanese ]

Iwaya Formation Sumi et al., 1962

Host of diatomite deposit

• Type locality: Iwaya, Takanosu, Kitaakita city, Akita prefecture
• Coherent formation
• Miocene
• Correlation: Ittori Formation, Yorinobezawa Formation, Otai Formation, Onnagawa Formation

• Sedimentary facies: Marine
• Lithofacies (East): Mudstone, Diatomaceous mudstone
• Lithofacies (West): Andesitic tuffaceous sandstone, Andesitic volcaniclastic rocks, Basaltic volcaniclastic rocks
• Lithofacies (Minor): Acidic tuff, Sandstone

• Thickness: 200 - 1,000 m
• Thickness (East): 300 - 500 m
• Thickness (West): 1,000 m
• Upper limit: Bottom of mudstone bed, Bottom of tuffaceous sandstone bed overlying shale
• Upper limit: Conformity (Fujikotogawa Formation), Transitional (Funakawa Formation), Interfingered (Himegatake Andesite), Unconformity (Maeyamagawa Formation)
• Lower limit (East): Bottom of hard shale bed or fine tuff bed
• Lower limit (West): Bottom of Subari Andesite and/or tuffaceous sandstone
• Lower limit: Conformity (Hayaguchigawa Formation, Osarubegawa Formation), Unconformity (Omata Formation)

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

• Distribution: Iwaya, Takanosu, Kitaakita city, Akita pref.; Takinosawa, Fujisato city, Yamamoto county, Akita pref.
• Fossils: Sponges (Makiyama chitanii)
• Fossils (Diatom): Actinocyclus ehrenbergii, Actinocyclus ehrenbergii var. tenella, Actinocyclus ingens, Actinocyclus tsugaruensis, Acitinoptychus senarius, Arachnoidiscus ehrenbergii, Asteromphalus moronensis, Cocconeis antiqua, Coscinodiscus argus, Coscinodiscus curvatulus var. odontodiscus, Coscinodiscus elegans, Coscinodiscus endoi, Coscinodiscus haradai, Coscinodiscus hirosakiensis, Coscinodiscus obscurus, Coscinodiscus oculus-iridis, Coscinodiscus radiatus, Coscinodiscus robustus, Coscinodiscus vetustissimus, Coscinodiscus yabei, Denticula lauta, Fragilaria hirosakiensis, Melosira sol, Melosira sulcata, Rhizosolenia spp., Rouxia peragalli, Rutilaria epsilon, Stephanogonia hanzawae, Stephanopyxis cfr. ferox, Stephanopyxis cfr. nipponica, Stephanopyxis schenckii, Stephanopyxis turris, Thalassiothrix longissima, Triceratium sp., Xanthiopyxis spp.

• Murakami et al. (2008) Jour. Geol. Soc. Japan, vol.114, Supplement, pp.111-120 DOI
• Sumi and Moritani (1973) Geology of the Yonaizawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 46p. (in Japanese with English abstract 4p.)
• Hirayama and Sumi (1963) Takanosu, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 7p.)
• Sumi et al. (1962) Dairakozan, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 51p. (in Japanese with English abstract 7p.)