新生代夾炭層の花粉分析學の研究 : 1.島根炭鑛

抄録

The most typically developed coal seam in the Shimane coal mine lot is found in the Takakubo group situated at Takakubo, Mitoyamachi, Pref. Shimane. The Takakubo group is divided into the upper and the lower coal bearing formations by the unconformable plain. The workable coal seam is contained exclusively in the upper part of the lower coal bearing formation. As the result of pollen analyses of these two formations, it is found that deciduous troad leaved forests preponderated throughout both formations. From this fact it may be inferred that the formations were deposited in temperate climate. We can divide them into the following 6 stages by their floral compositions. The stages are numbered from the bottom. 1. Alnus stage (Lower coal bearing formation) 2. Ulmus-Rhus-Castanea stage( ) 3. Ulmus stage( ) 4. Ulmus-Liquidambar stage( ) 5. Ulmus-Liquidambar-Rhus stage ( ) 6. Castanea-Liquidambar-Rhus-Ulmus stage (Upper coal bearing formation) In the upper part of the lower formation, Rhus and Castanea are absent or scarce in amount, but they are preponderant in the upper formation and the lower part of the lower formation. This fact may suggest that a closed and wet plant community prevailed succeeding to an open and rather dry one, since Ryus and Castaneaare prosperous in open and dry community in general. The unconformity found between the upper and the lower formations does not indicate a long time gap from the pollen analytical point of view. In temperature the 2 to 3 stage seems to have been warmer and wetter than the others. It is an interesting facf that the above mentioned upper part of this coal bed which is workable was deposited during a warm and wet climate, for it shows that the quality of coal has an intimate correlation to the phytoclimate during its sedimentation. The presence of pollen of fresh water weeds such as Myriophyllum and Nymphaea, that of Platycarya and Celtis which are relatively abundant under the sea shore climate, and the results of geological surveys, all these facts suggest that these coal beds were formed in fresh water basins lying among hills which were at present about the same distances from the sea shore. The Takakubo group may be correlated to the Tamatsukuri formation (middle Miocene).