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Yabuzuka Formation (Kawai and Yamada, 1960) Iijima and Yoshikawa, 1994

Invalid synonym (Bottom): Kuroishi Intrusive Rock

• Type locality (Upper): Nishiyama Tumulus - Snake center, Yabuzuka town, Ota city, Gunma prefecture
• Type locality (Middle): Yabuzuka hot spring, Yabuzuka town - Mount Raiden, Ota city, Gunma prefecture
• Type locality (Lower): Yunoiri, Yabuzuka town, Ota city, Gunma prefecture
• Type locality (Bottom): Kuroishi pass, Kiryu city - Ota city, Gunma prefecture
• Volcanic rocks
• early Miocene (17.5 - 15.1 FT)

• Sedimentary facies: Lacustrine
• Sedimentary facies (Bottom): Dry terrestrial
• Lithofacies (Upper): Pumice lapilli tuff, Reworked volcaniclastic rocks, Welded tuff
• Lithofacies (Middle): Reworked volcaniclastic rocks, Volcanic conglomerate, Tuffaceous conglomerate, Tuffaceous sandstone, Tuffaceous mudstone
• Lithofacies (Lower): Pumice lapilli tuff
• Lithofacies (Bottom): Basalt - Basaltic andesite lava
• Sedimentary structures (Bottom): Clinker

• Thickness: ca. 150 - 200 m
• Thickness (Upper): ca. 80 m
• Thickness (Middle): ca. 40 m
• Thickness (Lower): 20 - 50 m
• Thickness (Bottom): 30 - 60 m
• Upper limit: Unconformity (Godo Formation)
• Lower limit: Unconformity (Kanayama Welded Tuff, Gyodosan Complex)

• Distribution: Nishiyama Tumulus - Snake center - Yabuzuka hot spring - Yunoiri, Yabuzuka town, Ota city, Gunma pref.; Mount Raiden, Ota city, Gunma pref.; Kuroishi pass, Kiryu city - Ota city, Gunma pref.

• Ito et al. (2022) Geology of the Kiryu and Ashikaga District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 101p. (in Japanese with English abstract 4p.)