広島県東部の弱変成古生界の層序

The weakly metamorphosed Paleozoic rocks distributed in the eastern part of Hiroshima Prefecture are classified as follows in ascending order.
Subgroup A (more than 700m. thick): Mainly composed of black slate, with a small amount of sandstone, siliceous rock and geeen rock.
Subgroup B (2500-3000m. thick): Characterized by the predominance of green rock of volcanic and pyroclastic origin and, black slate to phyllitic slate. Layers of sandstone and siliceous rock occur at horizons.
Subgroup C (1500-2000m. thick): Mainly composed of phyllitic slate, with subordinate schistose sandstone and green rock. Thin layers of siliceous rock and acid lava or tuff are intercalated and lenses of conglomerate and limestone are included.
Metagabbro, serpentinite and mylonitic granite.
From the occurrence of Yabeina shiraiwensis and its allies the subgroup C may range up to the Upper Permian and is possibly correlated to the main part of the Maizuru group in Western Honshu.
Geotectonically the surveyed area belongs to the so-called Sanyo branch of the Sangun metamorphic zone, and the stratigraphy described above seems to correspond to that of some parts of the Sangun metamorphic complex in Chugoku and North Kyushu.
The limestones of uppermost Mississippian and Lower Pennsylvanian ages (partly of Middle Permian age) outcrop along the northeastern border of the surveyed area. They are cut off from the subgroup C by a marked thrust-fault.