青藏高原现代湖泊沉积物碳酸盐矿物氧同位素组成特征及影响因素

选择青藏高原14个代表性现代湖泊的表层沉积物为研究对象,它们是冷湖、大苏干湖、小苏干湖、大柴旦湖、小柴旦湖、托素湖、尕海、茶卡湖、唐古拉-1、错鄂、乃日平错、纳木错、空姆错和普莫雍错,探讨这些湖泊碳酸盐矿物组成及相应氧稳定同位素组成的影响因素。XRD结果显示这些湖泊的碳酸盐矿物多以方解石为主,并含白云石。其中冷湖以白云石为主,尕海还含有一定量的文石。碳酸盐氧同位素分析结果显示总碳酸盐δ¹⁸O在-15.9‰到2.6‰范围变化,方解石δ¹⁸O变化范围为-16.2‰～3.9‰,白云石δ¹⁸O变化在-15.3‰～-5.4‰范围内。通过氧同位素与湖区环境因素的相关性分析,认为总碳酸盐δ¹⁸O受湖水δ¹⁸O组成、温度、降水量/蒸发量、盐度、海拔和纬度多种因素影响;方解石δ¹⁸O主要受湖水δ¹⁸O、温度、盐度、海拔和纬度的影响;白云石δ¹⁸O受降水量/蒸发量和盐度的影响。总碳酸盐δ¹⁸O对湖水δ¹⁸O、温度、海拔和纬度的响应是以方解石为载体而体现的;总碳酸盐δ¹⁸O对降水量/蒸发量的响应则归因于白云石δ¹⁸O对其的响应结果;另外总碳酸盐δ¹⁸O通过方解石和白云石δ¹⁸O的叠加作用响应于盐度。该研究初步建立了总碳酸盐、方解石和白云石氧同位素与环境各个指标之间的响应关系,对于揭示过去青藏高原地区环境变化有重要意义。

OXYGEN ISOTOPIC COMPOSITIONS OF CARBONATES OF MODERN SURFACE LACUSTRINE SEDIMENTS AND THEIR AFFECTING FACTORS IN TIBET PLATEAU

14 typical lakes in Tibet Plateau were taken as our study object.They were Leng Lake,Dasugan Lake,Xiaosugan Lake,Dachaidan Lake,Xiaochaidan Lake,Tuosu Lake,Gahai Lake,Chaka Lake,Tangula Lake,Cuo'e Lake,Nairiping Co,Nam Co,Kongmu Co and Pumoyum Co.Their modern surface lacustrine sediment samples were collected.Carbonate mineral compositions and the environmental significance of their δ¹⁸O were investigated.The result of XRD analysis showed that dominate calcite and lower content dolomite was universal in all lakes except for Leng Lake in which dolomite was dominate.Also a little amount of aragonite was found only in the Gahai Lake.The result of oxygen isotope analysis showed the variation ranges of δ¹⁸O of bulk carbonate,calcite,and dolomite corresponding to-15.9‰～2.6‰,-16.2‰～3.9‰,and-15.3‰～-5.4‰ respectively.Correlation analysis between δ¹⁸O and corresponding environmental indicators around each lake showed that the δ¹⁸O of bulk carbonate was affected by multi-factors such as the δ¹⁸O of lake water,temperature,precipitation/evaporation,salinity,altitude and latitude.The δ¹⁸O of calcite was mainly controlled by the δ¹⁸O of lake water,temperature,salinity,altitude and latitude and the δ¹⁸O of dolomite was in response to precipitation/evaporation and salinity.Calcite was responsible for the relationship between δ¹⁸O of bulk carbonate and the δ¹⁸O of lake water,temperature,altitude and latitude.Via dolomite,the δ¹⁸O of bulk carbonate was linked to precipitation/evaporation.The response of the δ¹⁸O of bulk carbonate to salinity was due to both calcite and dolomite.This study constructed the primary relationship between the δ¹⁸O of bulk carbonate,calcite and dolomite and environmental indicators.It may have important significance to the investigation of the past environmental change.