Study on the Tectonic Movements in the Miike Coal Field

Abstract

The history of tectonic movements in the Miike coal field was on the basis of geological data obtained from underground survey, drilling and seismic prospecting. The writer refers to the possibility that there was a western Ariake basin which caused a possible Palaeogene sedimentation to the west of the Miike coal field, from the synthesis of the gravitational prospecting executed in the northern Ariake Sea area, the seismic prospecting in the Okinoshima line and Rass prospecting.
In view of the consistent policy for the future developments of the coking coal production in our country, the writer emphasizes the necessity of further physical prospecting and submarine boring in this coal field. The writer then relates the essential points of tectonic movements in the Miike coal field.
(1) The Miike coal field can be divided into the Yamato Basin in the north and the Omuta basin in the south, according to the difference in distribution of the crystalline schists and granitic rocks which constitute the basement and reveal a characteristic geological structure. At the time of compression from the north or northeast direction caused by the crustal movements at the end of the Cretaceous period, the granitic mass distributed in the southern Miike coal field became the resisting body, and, with Kurosaki bed rocks as a boundary, folds with axis trending approximately east-west were formed in the crystalline schist district of the Yamato basin in the north. Anticlinal parts of these folding structures seem to have resisted weathering even after the peneplanation and formed ridges in the peneplain.
(2) The great geosyncline of the Miike coal field was formed during the continuous orogenic movements and the Tertiary sediments were deposited in this geosyncline. This coal field area was bounded by the Chikugo barrier on the northern margin, the Minenosu barrier on the western margin and the upheaval in the Amagi and Oma mountain blocks on the eastern margin, and was open to the south, while in the Yamato basin, a few gentle upheavals remained as 4 burried hill groups.
(3) The continuous orogenic movements throughout the latest Cretaceous period and the sedimentation of the Palaeogene formations have caused the subsidence of Miike coal field's sedimentary basin—differential sinking movement from east to west—, the local upheaval of burried hill groups, and the transgression of the sea from the south from time to time during the sedimentation of the Palaeogene formations. In the swamp areas left by the regression of the sea, were deposited the coal seams.