Abstract
Lake Jinzai is a small brackish water lake which locates 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 by the 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 initial description and eleven AMS radiocarbon dating of organic materials and shell fragments. And it could reconstruct detailed Holocene environmental changes from the records of mineral and main chemical composition analyses. The water condition changes at Lake Jinzai was presented by the variable authigenic iron minerals as Pyrite, Marcasite and Siderite contents and the sulfur content of the sediment as a proxy. The results demonstrate that lake water condition have drastically changed through the Holocene with the periods of the brackish water condition from 9,500 to 7,300, 4,100 to 1,900 and refer to 400 cal. yr B.P. at Lake Jinzai. Also the influence of human impacts to the lake began to since 2,000 cal. yr B.P. which might be related to the formation of ruins in the Ancient Izumo Kingdom.
