SEDIMENTATION AND ENVIRONMENTAL CHANGE FROM SEDIMENTOLOGICAL ANALYSIS OF BOTTOM SEDIMENT OF LAKE KAMO,SADO ISLAND

佐渡岛加茂湖底部沉积物的沉积学分析及环境变化

基本信息

批准号：
07640598
负责人：
TAKEISHI Masaaki
金额：
$ 1.41万
依托单位：
NIIGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Lake Kamo is a coastal lagoon separated from Ryotsu Bay by a sand bar formed at the transgressional stage after the last. To make clear the sedimentation and environmental change of Lake Kamo, echo sounding profiles by SH20 and uniboom were firstly investigated, and diatom and pollen in core dorring samples were secondarily analyzed.The lake is divided into two parts from the geomorphological feature, that is, the southern and northern part. The geomorphology of the southern lake shows the form like a bottom of the ship, which is a broad plain with steep margin. The plain bottom is 7 to 8m in depth. A long and narrow depression with 2 m depth is observed along the eastern margin. On the other hand, the northern bottom slopes gentlly from north to south.The southern bottom is covered by broad dispersive layrs. A sounding basement is cropped out on the lake bottom along the lake coast. In the northern lake the sounding basement is extended to the central part from the eastern margin. The echo sounding profiles by uniboom and boring cores showsthat the sounding basement was formed by progradation of sand bar, which developed after last glacial stage.The base of alluvium sediments is observed at 37 m in depth under the lake bottom. Terrestrial sediment underlying the alluvium sediment is considered to be Upper Pleistocene terrace deposits. The analysis of diatom assemblage about the alluvium sediments show the environmental change of the lake from brackish/fresh through marine to brackish.

加茂湖是一个沿海泻湖，通过最后一次海侵阶段形成的沙洲与两津湾隔开。为了弄清卡莫湖的沉积和环境变化，首先利用SH20和Uniboom回波测深剖面进行了研究，其次对岩心沉积样品中的硅藻和花粉进行了分析。从地貌特征上将卡莫湖分为两部分，即南部和北部。南湖地貌呈船底状，平原广阔，边缘陡峭。平底深度7～8m。沿东缘观察到一处2 m深的狭长洼地。另一方面，北部底部由北向南缓慢倾斜。南部底部被宽阔的分散层覆盖。沿着湖岸，湖底出现了一个听起来像地下室的地方。北部湖区测深基底由东缘延伸至中部。单臂和钻孔岩心的回波测深剖面表明，测深基底是由末次冰期后发育的沙坝进积形成的。在湖底以下37 m深处观察到冲积层沉积物的基底。冲积层沉积物下方的陆地沉积物被认为是上更新世阶地沉积物。对冲积层沉积物硅藻组合的分析显示了湖泊从咸水/淡水到海洋到咸水的环境变化。