泥河湾盆地吉家庄遗址地层易溶盐沉积记录的古气候信息

Paleoclimatic evidence inferred from soluble salt deposits in the Pleistocene sediments at Jijiazhuang site,Nihewan Basin

泥河湾盆地发育晚新生代河湖相沉积并记录了华北更新世人类活动历史。近年来的发现表明,作为盆地重要组成部分,蔚县盆地是解读中更新世古人类行为演化与环境适应的关键区域。吉家庄遗址地处蔚县盆地东部吉家庄-黄梅台地古人类活动集中区,是近年来新发现和发掘的中更新世古人类活动遗址之一。对遗址湖滨相沉积物易溶盐的测试和分析表明,此剖面代表的泥河湾古湖易溶盐为HCO3^--SO4^2--Na^+型,pH值平均为8.93,偏碱性;剖面平均含盐量为0.67‰,属于半咸水湖,指示半干旱区湖泊演化由碳酸盐湖向硫化物湖过渡阶段。SO4^2-、Cl^-、Na^+、Ca^2+和Mg^2+等5类离子的变化曲线与剖面沉积物易溶盐总含量变化大体一致。依据易溶盐主要离子比值和碳酸盐碳、氧稳定同位素含量,并结合沉积物特点将湖泊气候演化划分为4个阶段,记录了气候由相对冷湿→凉干→相对温暖湿润的变化过程,古人类在该遗址活动时期对应于湖泊演化的第2阶段早期,处在古湖水位降低且气候向干凉转变的湖滨环境。该项研究对探讨泥河湾古湖的演化以及蔚县盆地吉家庄遗址利用者的生存行为与气候关系具有重要意义。

The Nihewan Basin,a Late Cenozoic basin in North China filled by fluvio-lacustrine deposits,preserves a large number of Pleistocene archaeological sites,which well recorded the occupation history of early hominins.The Yuxian Basin,as a major part of the Nihewan Basin(senso lato),is a key region for study of such a relationship between early hominin evolution and climatic changes during Middle Peistocene.The Jijiazhuang site is a newly discovered site complex of human occupation,located in the center of the Jijiazhuang-Huangmei fluvio-lacustrine platform in the northeast Yuxian Basin.It was discovered in 2003 and excavated three years later.The Jijiahzuang-B section(JJZ-B),a key section of the Jijiazhuang site complex,is located along a lake shore.The section includes the fluvio-lacustrine fine sand,silt,and clay of brown-grey,brown-yellow,grey-green,dark-grey in color,capped by loess,with a total thickness of more than 20 m.Based on the soluble salts and stable C-O isotopes from carbonate deposits of the section,the studies of hydro-chemical and climatic evolution as well as human activities are carried out by the author.The results suggest that the Paleo-Nihewan lake at the section of JJZ-B site is characterized by HCO3−-SO42−-Na+ions,and the average content of the total soluble salts is around 0.67‰,which indicate a brackish paleo-lake in a carbonate and sulphate phase of lake evolution in a semi-arid area.The variation and distribution patterns of SO4^2−,Cl^−,Na^+,Ca^2+and Mg^2+are well correlated with the total content of soluble salts.Upon the basis and by the changes in total soluble salt and soluble salt indicators as well as the content of carbonateδ13C andδ18O,four paleo-climatic stages corresponding to paleohydro-climatic changes of the lake were recognized:1)the stage relatively cold and humid with a high lake water level;2-3)the stages relatively cool and dry with a low lake water level and 4)the warm and humid stage with relatively high lake water level.The period occupied by early hominins corresponds to the early episode of stage 2 after the recession of the lake level evidenced by the sporadic lithic artifacts discovered,and the possible behaviors of animal dismemberment and utilization.In conclusion,the results bear great significance to the research of the adaptive environment and behaviors adopted by early hominins at the Jijiazhuang site and even the Yuxian Basin.