Geological Age and Structure of the Hina Limestone, Okayama Prefecture, Southwest Japan

The geologic structure of the Carboniferous Hina Limestone exposed at Hina, near Nariwa, Okayama Prefecture, is described with the aid of subsurface data obtained from boring cores, and the geological age is discussed from the standpoint of brachiopod fauna.
The Hina limestone forms a complicated folding structure for the most part overturned towards the south, and is marked off by thrust-faults from the northern non-calcareous Permian rocks and the southern Upper Triassic strata. The axial planes of folding, as well as the thrust-planes, seem to incline steeply in a deeper part and then become nearly horizontal upwards. The writers are inclined to consider that the limestone is not a "Klippe" but a mass squeezed out or injected from the deep-seated autochthonous complex.
Brachiopods from the Hina limestone and the neighbouring Shodera limestone are classified into two faunal types: the one is characterized by Spirifer sp. aff. S. besnossovae ABRAMOV, Schizophoria sp. aff. S. re-supinata (MARTIN), Syringothyris sp., etc., of which the first is most predominant, and the other by the abun-dance of Striatifera striata (FISCHER), with Schizophoria sp. aff. S. resupinata (MARTIN), Phricodothyris insolita GEORGE, etc. The former is distributed in the Endothyra zone, the lowest foraminiferal zone of the limestone, and the latter in the overlying Eostaffella—Millerella zone. It may be concluded that the Spirifer sp. aff. S. besnossovae fauna is assigned to the early Visean in age and the Striatifera striata fauna to the late Visean.