摘要:
为探析我国干旱地区地表硫酸盐沉积物中δ17O异常的存在及其变化特征,在西北额济纳盆地采集地表盐结层、现代风尘土、湖底沉积物和盐池土壤四种不同类型的硫酸盐沉积物样品。利用硫酸银(Ag2SO4)热解法同时测定硫酸盐样品中的δ17O和δ18O值,其δ17O、δ18O和Δ17O的分析精度分别为0.5‰、0.3‰和0.1‰。研究发现:(1)四种不同硫酸盐沉积物中均存在δ17O异常,其Δ17O值为0.2‰~1.0‰,这表明具有δ17O异常的硫酸盐能够从大气圈转移到陆壳矿物中,并在特定的地表环境中累积起来;(2)西戈壁的吉格德查盐池土壤剖面上硫酸盐Δ17O值随深度增加而增大,变化范围为0‰~0.6‰,这可能是干旱区极其有限的降水淋滤作用使具有较大Δ17O值的硫酸盐优先淋滤的结果,这种分离效应揭示的是在干旱的气候条件下,硫酸盐在土壤剖面上分离的过程。本研究证明我国干旱沉积环境中的硫酸盐δ17O异常的存在,为大气中臭氧(O3)和过氧化氢(H2O2)的氧同位素异常能够转移到地表矿物中提供新的证据,为地表沉积物中硫酸盐的来源、迁移、混合及沉积后的变化提供有效信息。
Abstract:
Four types of sulfate deposits were sampled in the Ejin Basin, a typical arid area in China, to explore the existence of 17O-excess (defined byΔ17O=δ17O-0.52δ18O≠0) in sulfate and its post-depositional variability in vertical profiles. Both δ17O and δ18O values of collected samples comprising modern windy dust, surface salt crust, dried lake sediments and playa soil were determined simultaneously by the Ag2SO4 pyrolysis method. The analytical error ofδ17O,δ18O andΔ17O in this method is 0.5‰, 0.3‰and 0.1‰, respectively. Some conclusions have been reached: (1) The 17O-excess was found in all the four types of surface deposits in the Ejin Basin (Δ17O=0.2~1.0‰), which proves that 17O-excess in sulfate can be transferred from the atmosphere to minerals in the earth and is preserved in a specific surface environment as a geological record. (2) The Δ17O values varied from 0‰ to 0.6 ‰ in sulfate and increased from the soil surface downward to about 1m in depth in the vertical soil profile in the Jidegancha playa, which probably resulted from post-depositional leaching and might reveal a unique physical-chemical process during which different sulfate components may be separated in soil profiles under extremely arid climatic conditions. This study has provided new evidence for the argument that 17O-excess of O3 and H2O2 in atmosphere could be transferred into minerals at the earth surface and also supplied effective information to the origin, migration, mixture and post-depositional variation of sulfate.
下载: