金属元素及其质量分数比值与湖泊古环境记录——以萨拉乌苏河滴哨沟湾全新世沉积为例

Paleoenvironmental records based on the lacustrine sediment elements and ratios:taking as an example the Dishaogouwan Holocene section along the Salawusu River

通过对萨拉乌苏河滴哨沟湾从末次冰期晚期到中全新世以来的河流相、湖相、泥炭沼泽沉积序列的金属元素分析,探讨了不同环境中沉积物的金属元素迁移、富集特征以及元素质量分数比值代表的环境意义.分析表明:V、Ni可能更多是在黏土中富集,而Fe_2O_3、Mn与还原条件有关,MgO、Sr、CaO与碳酸盐的形成有关.W、Bi、Co、Ce、Hf、Zr、Rb、Ti、Nb、K_2O、SiO_2、Al_2O_3主要赋存于较粗的颗粒中,水体强流动性、较浅水体、酸性氧化环境有利于这些元素的富集.金属元素在不同水介质中的溶解性、水体流动性以及在不同类型矿物中的富集、自生矿物形成时不同元素的富集特征等均影响了金属元素质量分数比值.w(Sr)/w(Ca)、w(Mg)/w(Ca)在水体流动性强、水体较淡、温度较低等环境中不能作为盐度的指标,而在水体滞留时间较长的湖泊环境中则是很好的盐度指标.高w(Fe)/w(Mn)指示了水浅流急的环境,但不能有效地指示水体较浅的还原环境,低值则指示了湖泊较深特征.指示风化作用强弱的w(Rb)/w(Sr)和CIA值与形成不同碳酸盐矿物的盐度状况、湖泊不同环境等有关,CIA值可能对流域的风化作用有较好的指示意义,而w(Rb)/w(Sr)对于水体较淡的湖泊指示意义更大.w(Si)/w(Al)可以有效地指示水体的深浅和水动力的强弱.

Confirmed data concerning the late last glacial to mid Holocene sediment section in the Dishaogouwan along the Salawusu River were used to clarify the environmental characteristics of elements and ratios in the different deposition faces.The results showed that V and Ni were mostly enriched in the fine grain-sized clay,Fe_2O_3 and Mn contents in the sediments had a relationship with reducing conditions therein,and MgO,Sr,CaO contents had a relationship with the carbonate formation.Corse grain-sized minerals had high W,Bi,Co,Ce,Hf,Zr,Rb,Ti,Nb,K_2O,SiO_2,A1_2O_3 contents,and water flowing,shallow water and acid-stage oxidation condition were in favor of high contents of these elements.The characteristics of solubleness in different waters,flowings,enrichment in different minerals,and different authigenic minerals formation could have influenced the element ratios in the sediments.w（Sr）/w（Ca）,w（Mg）/w（Ca） could indicate the water salinity under the high flowing,shallow water and low temperature condition,but it could provide a good salinity indicator for a long residence time lake waterbody.High w（Fe）/w（Mn） could indicate shallow and current waterbody but not stand for shallow reducing water environment.Low w（Fe）/w（Mn） could point to a deep lake environment.w（Rb）/w（Sr）and CIA commonly were used to indicate the weathering in the catchment.Different carbonate minerals formed in different saline conditions and the lake deposition faces could have influenced these ratios indicating characteristics.CIA could be used to point to catchment weathering and w（Rb）/w（Sr） ratio could indicate a fresh deep lake.w（Si）/w（Al） could effectively indicate the depth of a waterbody and its hydrodynamic condition.Arid indicator C could be used in a terminal long-time lake but not in an open and high flowing lake or any other waterbody.