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2023 Vol.132 No.3

Phoenix Fold on the Southern Coast of the Kii Peninsula

The Samotogawa Formation of the Paleogene to Neogene Muro Group at the southern Kii Peninsula is composed of sandstone/mudstone alternation, which forms part of the Muro Accretionary Complex of the Southern Shimanto Belt. It has fold structures of various sizes formed in partially consolidated sediments. The photograph shows a good example of these fold structures observed on the coast near Kuchiwabuka, Susami Town, Nishimuro County, Wakayama Prefecture. Once speculated to be gravitational slump folds on the sea floor, they are now considered to have deformed under high pore pressure during accretion, because the direction of fold axis overturning is opposed at some locations. The fold at the middle of the image is called the Phoenix fold, after the name of the nearby village of Amadori, which means bird of heaven. The horizontal top part of the fold is about 5 m in length and provides an impressive landscape. Visitors can sign up for a guided tour through the Nanki Kumano Geopark Center.

(Photograph & Explanation: Junko KOMATSUBARA; March 28, 2023)