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Iwaya Formation (Shikama, 1936) Ikebe, 1961

• Type locality: Eshima island, Iwaya, Awaji city, Hyogo prefecture
• Coherent formation
• Eocene - Oligocene
• Correlation: Taihata Formation

• Sedimentary facies (Upper): Shallow marine
• Sedimentary facies (MIddle): Fluvial, Coastal
• Sedimentary facies (Lower): Freshwater
• Sedimentary facies (Upper): Open sea
• Depth of water (Upper): Subtidal zone
• Lithofacies (Upper): Mudstone, Sandstone
• Lithofacies (Upper, Minor): Shell limestone
• Lithofacies (Middle): Sandstone, Conglomerate
• Lithofacies (Lower): Breccia
• Lithofacies (Lower, Minor): Mudstone, Breccia, Lignite, Tuff
• Sedimentary structures (Upper): Pipe rocks
• Sedimentary structures (Middle): Pipe rocks

• Thickness: ca. 100 m
• Thickness (Upper): 40 m or thicker
• Thickness (Middle): ca. 20 - 40 m
• Thickness (Lower): 10 - 50 m
• Upper limit: Unconformity (Osaka Group)
• Upper limit: Unconformity (Tosanji Granite)

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

• Distribution: Eshima island - Iwaya - Tokiwa - Nakamochi, Awaji city, Hyogo pref.
• Fossils: Barnacles (Balanus sp.), Brachiopods, Calcareous algae, Silicified woods
• Fossils (Shellfishes): Acila sp., Arcopsis sp., Babylonia toyamaensis, Barbatia (Abarbatia) sp., Callista sp., Calyptraea tubura, Chlamys cf. igeniosa, Cyclocardia cf. siogamaensis, Dentalium sp., Diodora minoensis, Homalopoma sp., Lima sp., Macoma izurensis, Mactra sp., Meretrix sp., Minolia sp., Musashia yanagidaniensis, Naticarius minoensis, Onustus sp., Ostrea sp., Oxyperas sp., Phos sp., Protorotella togariensis, Saccella misensis, Siphonalia sukuhoraensis, Solen sp., Turritella (Hataiella) sagai, Turritella kiiensis, Varicorbula sp., Zeuxis sp.
• Fossils (Foraminifera): Miogypsina sp., Operculina sp.

• Ozaki and Harayama (2003) Geology of the Takasago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 87p. (in Japanese with English abstract 3p.)
• Mizuno et al. (1990) Geology of the Akashi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 5p.)
• Huzita and Maeda (1984) Geology of the Suma District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 101p. (in Japanese with English abstract 7p.)