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Tomaru Formation Shikumi River Collaborative Research Group, 1991

Formerly included in Uonuma Group.

• Type locality: Tomaru, Tsunan city, Nakauonuma county, Niigata prefecture
• Volcanic rocks
• Pleistocene
• Contemporaneous heterotopic facies: Torikabuto volcano
• Correlation: Kusso Formation, middle Uonuma Formation

• Lithofacies: Andesite tuff breccia, Conglomerate
• Lithofacies (Minor): Interbedded sands and silt
• Sedimentary structures: Cross stratificaiton

• Thickness: 220 m or thicker
• Lower limit: Top of SK030
• Lower limit: Conformity

• Distribution: Tomaru - the left bank of Shinano river, Tsunan city, Nakauonuma county, Niigata pref.
• Tephra: Hi-TB, SK020

• Shimazu and Tateishi (1993) Geology of the Naebasan District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 5p.)