RECENT STUDIES OF THE PALEOZOIC GROUP OF JAPAN

The history and research on the Paleozoic formations in Japan is summarized.

In the past the Japanese Paleozoic was dealt with as one system under the general name Chichibu Paleozoic, as the Chichibu system in the Kanto region was thought to represent all Paleozoic formations in Japan. However, since the discovery of Lower Carboniferous fossils by Ichiro Hayasaka in 1924, Upper Devonian fossils by Mitsuo Noda in 1934 and Gotlandian fossils by Yoshio Onuki in 1937, the distribution and stratigraphic sequence of the Japanese Paleozoic have become better known.

The Hida metamorphic rocks constitute the basement of Paleozoic sedimentary basins and are assigned to pre-Gotlandian age.

The Gotlandian system is found in regions of complex geologic structure. Its distribution, though sporadic, may bear an important significance in view of structural geology. It consists predominantly of fossiliferous limestone, associated with shale, slate, phyllite and tuff.

Distribution of the Devonian system is limited. It consists of sandstone, shale and slate, accompanied by tuff and limestone lenses. Conglomerate of schistose pebbles is locally found. The system may be conformable with the underlying Gotlandian system.

The carboniferous system is widely distributed, usually associated with the Permian, and consists chiefly of sandstone, shale, slate and schalstein, but is locally represented by limestone facies. The Carboniferous is generally uncomformable with the Permian, although locally it may be conformable.

The Permian system has the widest distribution, amounting to nearly 80 percent of the known Paleozoic, hence its stratigraphic succession, fossil horizons and sedimentary facies are fairly well known. However, varied names now in use for the respective series require unification. The system consists of sandstone, shale, slate, schalstein, chert, often accompanied by limestone and conglomerate. Existence of conglomerate is one of the characteristics of the Permian system, although the constituent pebbles vary regionally and further study is needed to clarify the distribution, stratigraphic position and lithology of the conglomerates.

According to Hisakatsu Yabe, the name Chichibu system should be used only for the Carboniferous and Permian and a new name Kitakami system be used to denote the Gotlandian and Devonian.

Major orogenic movements of the Japanese Paleozoic are, 1) Akiyoshi orogenesis, 2) Setamai fold, 3) Shimizu fold, 4) Kesen fold and 5) Hida orogenesis. — Reiko Fusejima