| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Silurian limestones in the Japanese Islands, representing the Silurian reef carbonates on arc-island shelves, are investigated in the methods of stratigraphy, sedimentology and paleontology. Based on detailed works including lithostratigraphic subdivisions, sedimentary facies estimations, and fossil organic compositions, the Silurian reefs and their surroundings are reconstructed and then compared with the other coeval reefs in the world. Elucidated points are summarized as follows:
1)Silurian carbonates in the South Kitakami Terrane, newly subdivided into three members, may have been formed by whole sedimentary process from the deposition of shallow carbonates on unstable island-shelf, consequent formation of organic reel-mound, through the collapsing of carbonate bank slope into the off-shore basin.
2)Silurian carbonates in the Kurosegawa Terrane indicate the same lithostratigraphy as those of the South Kitaikami Terrane, presuming the similar tectonic environment and sedimentary process around the island-arc.
3)Red-colored limestones of the both Silurian carbonates strongly suggest the emergent weathering of carbonates, possibly caused by hydro-eustatic changes in Late Silurian age.
4)Organic constitution of reef-mound carbonates includes various metazoan fossils, which compositions are equivalent to those of coeval reefs of the world.
5)Reef-mounds newly reconstructed were mainly built in the manner of encrusting or binding by red algae and calcimicrobes, not of framing by metazoans previously estimated.
6)Internal frameworks of the island-shelf-type reefs must have been more rigid than those of the continental-shelf-type reefs, because larger amount of calcimicrobes may have joined and closely packed the interstices between skeletal frames.
7)Records of microfacies pictures collected from the Silurian carbonates possess an archive value for the coming geological researches and scientific educations.
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