泥河湾盆地麻地沟遗址地层易溶盐沉积及其环境意义

SOLUBLE SALT IN THE SEDIEMNTS AT THE MADIGOU SITE,NIHEWAN BASIN AND ITS ENVIRONMENTAL IMPLICATIONS

麻地沟遗址地处泥河湾盆地东部岑家湾台地古人类活动集中区,是近年来新发现和发掘的早更新世古人类活动遗址之一。对遗址湖滨相沉积物易溶盐类的测试和分析表明,此剖面代表的泥河湾古湖易溶盐为SO_4^(2-)-Na^+-HCO_3^--C^l-型,剖面平均含盐量为11.41‰,属于半咸水湖,处于半干旱区湖泊演化中后期的硫酸盐湖向氯化物湖的过渡阶段。K^+、Na^+、Ca^(2+)、Mg^(2+)、SO_4^(2-)和Cl^-等6类离子的变化曲线表现出较大的相似性,且它们与含盐量的变化大体一致。地层含盐量的变化和沉积物中细颗粒含量变化具有一致性,细颗粒含量较高对应含盐量相对较高时期。根据含盐量和各主要离子比值并结合平均粒径和磁化率的变化将湖泊气候演化划分为5个阶段,古人类在该遗址活动时期对应于湖泊演化的第2—4阶段,处于气候相对较为温湿、动植物资源丰富、湖水含盐量较低时期。该项研究对探讨麻地沟遗址利用者的生存行为与环境的关系具有重要意义。

The Madigou site lies on the northeast margin of the Nihewan Basin,North China.It is one of the newly discovered Early Pleistocene archaeological site in the Basin.The Madigou site is dominated by lake deposits located at the lower part of the Madigou section.Based on a well constructed soluble salts sequence of the section,the processes of hydrochemical and environmental evolution as well as human activities are studied by the authors.Results show that the Nihewan lake near the Madigou site was characterized by SO_4^(2-),Na^+,HCO_3^- and Cl^-ions,and the average content of the total soluble salts reaches 11.41‰,suggesting that the paleo-lake belonged to the kind of brackish water lake between the sulphate and the chloride lake in terms of lake evolution phase in a semi-arid area.The variation in K^+、Na^+、Ca^(2+)、Mg^(2+)、SO_4^(2-),and Cl-and the total content of soluble salts are well correlated.Upon the basis,five paleoclimatical stages were recognized according to the changes in mean grain size,susceptibility content,total soluble salt and soluble salt indicators in the profiles,which indicate the corresponding changes of lake environment.The middle stages of 2,3and 4,which were relatively warm and wet,are the periods dominated by active paleoanthropological activities.There were rich animal and plant resources in these periods and the salinity of the lake was relatively low.The results bear great significances in the research of the adaptive environment and behaviors of the early humans at the Madigou site.