| Abstract |
Sandstones of the Shimanto Supergroup in Kyushu and adjacent islands were petrographically examined. Although the present paper represents a preliminary phase of study, some interesting results have b...een brought about: (1) The Shimanto sandstones characterised by feldspathic arenite are stratigraphically subdivided into three petrographic groups, for which the concept of "Petrographic Zone" has been applied. (2) Petrographic Zone I is characterised by coarse-grained, ill-sorted and angular sands containing 35-55 percent feldspars, and the Zones II and III consists generally of medium to fine-grained, better-sorted and subrounded to rounded particles containing feldspars of 22-35 percent and 10-22 percent, respectively (Fig. 7). These petrographic zones are useful for the purpose of stratigraphic correlation. (3) One of important compositional features of sandstones is that fresh microcline grains are commonly found throughout the whole sequence, which show better roundness stratigraphically upwards. As a possible source of these microcline sands should be taken into account microcline gneisses (see Plate 19, Fig. 3), which are not known in the Japanese Islands .at all, but are common in Archaean granites and gneisses in the Korean Peninsula. In this context, Precambrian microcline gneisses on eastern borders of the Eurasian Plate are worthy of consideration as a provenance of the sands. (4) Much sand, but not all, of younger sediments of the Shimanto sequence might have been multi-cycled from older formations within the Shimanto itself.show more
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