萨拉乌苏河流域干沟子剖面全新世湖相沉积的地球化学元素特征及其反映的物源变化

Geochemical characteristics of holocene lacustrine sediments in Gangouzi section and its sedimentary sources in the Salawusu River Valley

为探究萨拉乌苏河流域中上游段湖相沉积物的来源及沉积环境,通过测量干沟子剖面3个样品的年代和113个样品的地球化学元素的含量,分析了干沟子剖面地球化学特征反映的沉积物的来源,探讨了其代表的全新世以来的沉积环境变化。结果表明:在剖面垂直方向上,CaO、MgO、Sr、Cl、Br以110 cm为界,含量发生剧烈变化,250—110 cm为明显低值段,而110—0 cm为显著高值段,其余元素多与它们呈现相反的变化趋势或表现为一定范围内的波动。物源的改变是导致CaO、MgO、Sr、Cl、Br等元素在深度110—0 cm显著增加的主要原因:12—6.7 Cal.ka B.P.(250—110 cm)剖面所在古湖为相对封闭环境,其物源主要受周围沙丘来源影响;6.7—2.2 Cal.ka B.P.(110—0 cm),湖泊转为半封闭环境,南部有来源于黄土高原北部白于山的河流(今萨拉乌苏河上游)汇入,此时段其物质来源受到河流携带进来的黄土物质的深刻影响。

In order to explore the source and sedimentary environment of lacustrine sediments in the middle and upper reaches of Salawusu River Valley,the ages of three dating samples and the contents of chemical elements in 113 samples were measured,the origin of sediments reflected by the geochemical characteristics of Gangouzi section was analyzed,and the changes of sedimentary environment since Holocene was discussed.The results show that the contents of CaO,MgO,Sr,Cl and Br change dramatically with the boundary of 110 cm in the vertical direction of the section,showing obvious low value at 250-110 cm,and obvious high value at 110-0 cm.The change of provenance is the main reason for the significant increase of CaO,MgO,Sr,Cl,Br at the depth of 110-0 cm:The paleo-lake in the 12-6.7 Cal.ka B.P.(250-110 cm)was a relatively closed environment,and its provenance was mainly influenced by the source of surrounding dunes;in the 6.7-2.2 Cal.ka B.P.(110-0 cm),the lake changed into a semi-closed environment,the river(upper reaches of the Salawusu River of today)rises in Baiyu Mountain(in the northern Loess Plateau)and into the south of the lake,its material source is profoundly influenced by the material of the loess brought in by the river.