A Basis of the Argument for Possibility of a New Coal-Field in Kumamoto Prefecture, Middle Kyushu

Abstract

The Paleogene formation, scattered in the vicinity of Hokonoko, Kumamoto Prefecture, has been described in a few reports, but until now, its stratigraphy and geologic age had not been determined We have recognized, in this area the following two new formations in the Paleogene: the Kannondake formation and the Hokonoko formation.
The Kannondake formation contains coal seams and represents the upper half of the Paleogene in question. Some fossil marine mollusks obtained from this formation indicate the stratigraphic position of the formation. They are : Faunus nipponicus NAGAO, Melania (?) miikensis NAGAO, etc. Considering these fossils and rock facies, the Kannondake formation is equivalent to the coal-bearing Komenoyama. formation, which belongs to the lowermost part of the Ariake group.
The Hokonoko formation is the lower half of the Paleogene in question. The formation closely resembles the Akasaki formation, Amakusa stage, in all of the important points: non-marine, non-fossiliferous and purplish, and the formation stratigraphically underlies the coal-bearing formation.
The geologic structure of the formations in this area is very simple. The Paleogene is divided into segments and scattered in tiers along the valley walls by some 'graben'-faults trending NE.
These formations are distributed in the region between the Amakusa and the Asakura coal-field and are equivalent to the Komenoyama formation of the Miike coal-field. The distribution of the lowermost part of the Paleogene coal-bearing formation is presented as one of the proofs of the existence of a new coal-field under the Plain of Kumamoto.