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The Lower Cretaceous Wakino Subgroup, the lower part of the Kanmon Group, is exposed extensively in North Kyushu and in the western area of Chugoku, Southwest Japan. This subgroup rests unconformably ...on Permian metamorphic rocks and Upper Jurassic brackish-water deposits. The sedimentary facies and depositional environments of the Wakino Subgroup were examined on the basis of lithofacies, fossil assemblages and primary sedimentary structures. The Wakino Subgroup consists of seven sedimentary facies which can be organized into three facies suites：the disorganized conglomerate and purple siltstone facies suite, sandstone and black mudstone facies suite, and turbidite and rhythmite facies suite. The disorganized conglomerate and purple siltstone facies suite occurs in the lower part of the Sengoku Formation and is represented by disorganized conglomerate of debris flow origin and purple siltstone with frequent intercalations of channe1－fill sandstone with cross-stratified bed. This facies suite is interpreted as the alluvio-fluvial deposits. The sandstone and black mudstone facies suite occurring in the upper part of the Sengoku Formation is composed of sandstone with parallel lamination and low angle cross-lamination, and black mudstone with parallel lamination. The facies suite is interpreted to show the marginal lacustrine environment. The turbidite and rhythmite facies suite is characterized by turbidite sandstone (mostly Ta and Tab), rhythmite and massive and parallel laminated mudstone with sporadic intercalations of conglomerate as channe1-fill deposits. This facies suite is one of the most striking features of the Wakino Subgroup, which is interpreted as deposits of the offshore lacustrine environments.show more
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