島根県神西湖堆積物の層序と完新世環境変遷史

Lake Jinzai is a small brackish water lake located in the southwestern part of the Izumo Plain, Shimane Prefecture, western Japan. The JZ-01 sediment core was taken at the center of the lake(35°19′N, 132°41′E; water depth 1.55 m)using a thin-wall type piston core sampler. The core length is 24.3 m. This study clarified the stratigraphy and sedimentation rates in the JZ-01 core on the basis of an initial core description and eleven AMS radiocarbon dates of organic material and shell fragments. This study also reconstructs high resolution Holocene environmental change from the mineralogy and chemical composition of the core sediments. The variability in Lake Jinzai water conditions is apparent in the content of authigenic iron minerals(pyrite, marcasite and siderite)and the sulfur content of the sediment. These results demonstrate that lake water conditions changed drastically throughout the Holocene, with brackish water intervals from 9,500 to 7,300, 4,100 to 1,900 and from 400 cal. yr B.P. to the present. Also the influence of human activity on the lake environment began around 2,000 cal. yr B.P. - a time which may be related to a significant increase in the number and size of archaeological sites of the Ancient Izumo Kingdom.