东台吉乃尔盐湖沉积物硼同位素组成及其古环境意义

Boron Isotope Compositions and Environmental Significance of Sediments from the East Taijnar Salt Lake

硼(B)同位素组成可以反映地质成因及演变,因此,在许多领域的研究中都有较为广泛的应用。文章通过对位于柴达木盆地的东台吉乃尔盐湖沉积物开展元素地球化学分析、矿物组成与分布及水溶组分B同位素的研究,得出剖面沉积物B含量在5.82~677.70μg/g之间,平均含量为296.26μg/g;δ^(11)B值的变化范围在-8.52‰~7.93‰之间,平均值为-2.81‰,B含量与δ^(11)B值相关性较弱(R=0.15)。结果表明,东台吉乃尔盐湖自晚更新世以来历经盐湖沉积演化的逆向(氯化物型-硫酸盐型)及正向(硫酸盐型-氯化物型)演变,具体表现为,(1)更新世晚期至全新世中期(27~4.6 ka):干冷气候条件下,湖水处于蒸发浓缩过程;(2)全新世中期至晚期(4.6~0.3 ka):暖湿气候条件下,湖水处于淡化过程;(3)全新世晚期至今(0.3 ka~):湖水受蒸发作用影响,沉积物与气候变化之间的对应关系较弱,总体上处于蒸发浓缩过程。这不仅重建了东台盐湖晚更新世以来的古环境演化过程,也为现阶段该盐湖的资源开发提供了基础数据。

The isotopic composition of boron(B)can reflect its geological origin and geological evolu-tion,so it has been widely used in many fields.Through the analysis of geochemistry elements,mineral composition and distribution,and water-soluble component B isotopes in the sediments of the East Taijnar Salt Lake,it was found that the B content of the profile sediment ranged from 5.82μg/g to 677.70μg/g,with an average content of 296.26μg/g.The variation range ofδ^(11)B value was between-8.52‰~7.93‰,the average value was-2.81‰,and the correlation between B content andδ^(11)B value was relatively weak(R=0.15).The results indicate that the East Taijnar Salt Lake has undergone reverse(chloride type-sulfate type)and forward(sulfate type-chloride type)evolution of lake sedimentation since the late Pleistocene.The specific characteristics of the lake are as follows,1)the Late Pleistocene to the middle Holocene(27~4.6 ka):under dry and cold climate conditions,the lake was undergoing processes of evaporation and con-centration;2)the Middle to Late Holocene(4.6~0.3 ka):under warm and humid climate conditions,the lake was undergoing the process of dilution;3)the Late Holocene to Present(0.3 ka~):the lake water was affected by evaporation,and the corresponding relationship between sedimentation and climate change was relatively weak,overall being in a state of evaporative concentration.This not only reconstructs the ancient environmental evolution process of Dongtai Salt Lake since the Late Pleistocene,but also provides basic data for the current resource development of the Salt Lake.