Lake Mochirippu is a brackish lagoon extending for a few kilometers from the narrow entrance on the Pacific coast, eastern Hokkaido, where a series of Tsunami have attacked. The previous studies presumed that the lake sediments contained more than 17 times of Tsunami deposits (Sawai et al., 2009). In this paper, we reported the details of diatom assemblages from the Tsunami layers and would discuss their sedimentary environment and transportation processes of Tsunami deposits using diatom valves. The drilling core (3.8 m) was taken at the lake side peat land east of the lake, and be divided into five sedimentary zones by their lithofacies and diatom characteristics. The second and fourths layers were Tsunami deposits, dated 17th Century and 2500-5500 years BP respectably. Although the tsunami deposits of the two layers were composed mainly by marine sands, the 80% of the diatom fossils were consist of freshwater species, and very few of oceanic species. They presumed that the marine sands were secondary shifted during and just after the tsunami event, and contained a lot of fresh water diatoms in them. The detail observation of tsunami layer, sliced 1-2 cm each, made clear diatom assemblages shifted systematically according to the small sedimentary units in the Tsunami.
|ジャーナル||Chikei/Transactions, Japanese Geomorphological Union|
|出版ステータス||出版済み - 1月 1 2016|
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