Japan Geoscience Union Meeting 2015

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS23] Geopark

Mon. May 25, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Takayuki Ogata(Faculty of Education, University of the Ryukyus), Mahito Watanabe(Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology), Takayuki Arima(Department of Tourism Management, Faculty of Economics, Teikyo University), Yoshihiro Hiramatsu(Faculty of Natural System, Institute of Science and Engineering, Kanazawa University), Marekazu Ohno(Unzen Volcanic Area Geopark Promotion Council), Tetsuya Waragai(Graduate School of Science and Engineering, Nihon University), Takeyuki Ueki(Faculty of Risk and Crisis Management, Chiba Institute of Science)

6:15 PM - 7:30 PM

[MIS23-P01] Japanese continental drift theory mentioned over 1200 years ago, before the Wegener's theory

*Ritsuo NOMURA1, Hiroyuki TAKATA2, Akira TAKASU1, Toshiaki IRIZUKI1, Hiroki HAYASHI1, Akira TSUJIMOTO1 (1.Shimane University, 2.Pusan National University)

Keywords:Izumo Province fudoki, Kunibiki myths, Shimane peninsula, early Miocene, Continental drift theory

Geology of the Shimane Peninsula has been known as having the most deformed strata among the Miocene series of the Japanese Islands. Otsuka (1939) named it as "Shinji folded zone." Tai (1952) mapped the northwestern part of Matsue City and first discussed the stratigraphy of the Miocene formations. Large-scaled investigations carried out by the governmental institution (1967-1971),and subsequently Yamauchi et al. (1980) and Nomura (1986), respectively, discussed the stratigraphy and biostratigraphy of the eastern and middle part of the peninsula. Kano et al. integrated the areal geology into 1/50,000 scaled map such as Taisha, Izumoimaichi, Etomo , Sakaiminato and Matsue.
Izumo-no-kuni-fudoki (The Izumo Province fudoki) was compiled in 733, which was 1282 years ago. A very stimulated story, the Shimane Peninsula was formed as added the land pulled part from the peninsula, somewhere of Shiragi, old name of Korean country (A.D. 6~10 century). This story is very popular in Japan, known as "the Kunibiki myths." The physicist and essayist, Torahiko Terada, took up this story just like the Wegener's "Continental Drift Theory" in his essay of "Geophysicist and mythology." Up to the present, no one discussed the place where is the peninsula of Shiragi. However, the place is clearly located in Korea.
One more stimulated concern on this story is the paleomagnetic reconstruction of early Miocene Honshu Island. Clock-wise rotation of southwest Honshu Island has been well studied, and the geographic location of southwest Honshu Island in the early Miocene is clarified as being very near Korea.
We investigated the geology of the Pohang basin and its neighboring area. The early Miocene series of the Guryompo Peninsula are mainly composed of the Beomgogni Group and Janggi Group, both of which are characterized by volcaniclastic rocks such as dacite and andesite. Lithology of shale in the Janggi Group is similar to that of the Koura Formation distributed in the Shimane Peninsula, which yields brackish fossil Corbicula. The geologic ages of the Beomgogni Group and Janggi Group are ranged in 22~17Ma, earlier ages of which are also similar to those of the Koura Formation.
Surprisingly enough, the story of the "Kunibiki myths" suggests the people 1300-years ago figured out geographic nature of the earth that is unchanged with the present view of the earth. The "Kunibiki myths" never mentioned the geological reason, why is the Guryompo peninsula similar to the Shimane peninsula. However, we suppose the myths have been born through the people interchanged between Shiragi and Izumo countries. We suggest thus high potential of people's observing ability to the geology and topography of the earth indicated in the "Izumo Province fudoki."