| Abstract |
Since 1955, the author has engaged in a study of heavy minerals in the sandstones from several Tertiary coal fields in northern Kyushu (Figure 1). Results of heavy mineral analyses have already been p...ublished in a series of papers (OHARA, J., 1955-1961c). The states of heavy mineral content, heavy mineral composition, and heavy mineral zone in the Paleogene formations in northern Kyushu are summarized in this paper, together with further descriptions of the volcanic activities and migration of the depositional basins in the area during Tertiary time. The total amount of heavy minerals in the sandstones is controlled by some factors such as granularity of sandstone, frequency number of authigenic minerals, sedimentary environments, kinds of source rock (either tuffaceous or not), and so on. Five types of heavy mineral composition and fourteen heavy mineral zones are recognized in the Tertiary formations in the area (Figures 4 and 7). One tyre (tyre A) of the heavy mineral composition, the heavy minerals of which can not be considered to be derived from the basement rocks of the coal fields in northern Kyushu, is widely distributed in the western and southwestern coal fields of the area (Figure 6). Most of the variations in these heavy mineral compositions are probably caused by the crustal movements which took place widely in several coal fields in northern Kyushu. Andesitic volcanisms inferred by the presence of tuffs and tuffites are conspicuous in Paleogene period.show more
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