愛知県弥富町稲狐から得られた試錐試料を用いて行った地球化学的な古環境復元

抄録

Chemical and isotopical analyses were carried out of cored sample taken from Yatomi area, Aichi Prefecture, southwestern part of the Nobi Plain, in order to restore the paleoenvironment of this area. Based on analyses of nitrogen/carbon ratio and carbon isotopic ratio of sedimentary organic matter, acid-insoluble-sulfide content and its sulfur isotopic ratio in sediment, followings are clarified. (1) The Nobi Formation (12000〜10000y.B.P.) was deposited first under lacustrine/back-swamp condition, and later this swamp area was filled up with fluvial deposits. (2) The lowermost part of the Nan-yo Formation (10000〜8000y.B.P.) was deposited first under meromictic-lake condition. Sea-level rising began gradually and depositional condition became near shore condition about 9000y.B.P. But temporal stagnancy or lowering of sea-level occurred about 9000y.B.P. (3) The lower and middle part of the Nan-yo Formation (8000〜2500y.B.P.) was deposited under inner bay (off shore) condition. About 8000y.B.P., sea-level began to rise rapidly and depositional conditon changed quickly from near shore condition to off shore condition. About 6000y.B.P., depositional condition became most off shore condition, 30〜40km offshore. From about 5000y.B.P., the influence of land-derived deposits increased gradually. (4) The upper and uppermost part of the Nan-yo Formation (2500y.B.P.) was deposited under near shore to deltaic/estuarine condtion. The geochemical restoration of paleoenvironment is consistent with several paleontological restorations. The geochemical restoration method is useful for providing continuous information even for non-fossil layers.