著者

南 秀樹 加藤 義久 和田 秀樹 岡部 史郎

出版者

日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.29, no.2, pp.85-97, 1995

被引用文献数

7

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Four cores, which penetrated into the Holocene, were collected in 1985-1986 from the center to mouth of Lake Hamana, Japan. Sediments were analyzed for the concentrations of organic C, total N, biogenic SiO₂, Mg, Al, Fe, Mn, V and P. The age of the sediment near the bottom part of each core, which exhibited a higher C/N mole ratio, changed from 11,000 yr B. P. at the mouth to 7,000 yr B. P. at the center part of the lake. This indicated a higher sedimentation of land plants enriched in carbon, which probably took place during a period of high sealevel. After 4,000 yr B. P. in the inner part of the lake there were some distinctive changes in the distributions of elements, as related to their ¹⁴C ages : (1) higher content and large fluctuations in both the sediment, organic carbon and biogenic SiO₂, and (2) an excess organic carbon over biogenic SiO₂. Yet, in contrast, the C/N mole ratio≈12 remained constant. These observations suggested that an eutrophic and productive lake was formed when the seawater exchange was restricted. The contents of Fe and Mg also increased remarkably after 4,000 yr B. P. These changes are due to increasing of the transport ation of particles, originating from ultra-basic rocks carried by the Miyakoda River in the northern part of the lake. Before this period marine silt was predominantly transported from the Pacific sea side.