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Shimazushima Formation Chiba et al., 2000

• Type locality: Shimazushima island, Chibu city, Oki county, Shimaneprefecture
• Coherent formation
• late Miocene (5.4 Ma, K-Ar)
• Intruded by: Trachybasalt dike, Basaltic andesite dike, Trachyte dike
• Correlation: lower Somma, Tsuma Formation (Nakazato Member)

• Sedimentary facies: Shallow marine
• Lithofacies: Tuffaceous sandstone
• Lithofacies: Tuffaceous siltstone, Tuffaceous mudstone, Tuffaceous conglomerate
• Sedimentary structures: Wavy stratification, Parallel stratification, Trough cross-stratification

• Thickness: ca. 30 m
• Upper limit: Unconformity (Trachybasalt lava, Basaltic andesite lava)

• Distribution: Shimazushima island - Usuge (Watashigami), Chiburijima island, Chibu city, Oki county, Shimane pref.
• Fossils (Trace fossils): aff. Ophiomorpha isp.

• Chiba et al. (2000) Geology of the Urago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 74p. (in Japanese with English abstract 3p.)