| 概要 |
The submarine Alluvium in the Bay of Ariake is stratigraphically divided as follows in descending order: Upper Alluvium (I): mainly clay Upper Alluvium (II): mainly sand, often cross-laminated and som...etimes shell-bearing Upper Alluvium (III): sands with abundant shells, pebbles and granules, showing local distribution (not found in the present area) Lower Alluvium: clay and silt The underlying basement is primarily the Aso Welded Tuff, with local gravels of low level terrace on its denudated surface. The Nagasu Formation (of R-W interval stage) is found in certain areas beneath the Aso Welded Tuff. The internal constitution of the submarine Alluvium varies from place to place depending much on the relief of the basement, as has been revealed clearly by the Sonoprobe method as well as by boring. The deeper parts of the basal plane, i.e. -20 to -30 m flattened plain and -30 to -40 m valley form basins off the mouth of the Kikuchi and other rivers, are buried by clay and silt of the Lower Alluvium, with the maximum thickness of about 20m. The sandy sediments of the Upper Alluvium (II) rest not only on the depositional plane of the Lower Alluvium but also on the flattened plane of -10 to -20 m and on a part of that of -20 to -30 m, and themselves are 2 to 5 m thick. They are often cross-laminated, with some magnetite rich laminae, and sometimes contain shells. The thickest part of the sandy deposits is on the flank and foot of a buried uplift, called Minenosu, and also along a transitional belt from a flattened basal plane of -10 to -20 m to that of -20 to -30 m. This may represent the then dune sand of a coastal area. The muddy sediments of the Upper Alluvium (I), which overlie a part of the Upper Alluvium (II), are distributed in the flat part off the mouth of the Kikuchi and a limited area off the coast of Nagasu. The bottom sediments and the submarine topography depend much on the above described distribution and internal construction of the Alluvium sediments and also on the relief of the basal plane. Text-figures 1-7 may illustrate clearly the above summarized features.続きを見る
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Mendeley出力
