【摘要】 在古环境研究中, Sr、Ba、Ca等碱土金属元素在沉积物中的含量及比值是一种较为常用的、识别海陆相环境的指标.但元素多赋存于矿物晶格中,而这些矿物基本上存在于酸提取后的残渣态中,与沉积物沉积时的物理-生物-化学环境没有直接关系.因此,选择性提取沉积物中与沉积环境相关的碱土金属元素,才能将该方法更好地应用于解释沉积环境.本研究采集了宁波平原盐沼潮滩、河漫滩、感潮河道3种环境的表层沉积物,采用等离子光谱仪测试了稀醋酸和稀盐酸提取液、酸提取后剩余残渣以及全量的Sr、Ba、Ca含量.结果表明:醋酸提取态对沉积环境变化最为敏感,盐酸提取态次之,全量Sr/Ba(摩尔比)无法区分3类表层沉积物的沉积环境;用不同的样品量和仪器测量验证醋酸提取态的效果,显示结果稳定.此外,宁波平原及邻近岛屿盐沼潮滩表层沉积物醋酸法提取的Ca和Sr浓度远高于河漫滩沉积物和山麓黄土,感潮河道则介于两者之间, Ba的分布与Ca、Sr相反.因此,通过醋酸态碱土金属元素的端元分析,可以有效地识别海岸带地层的海陆沉积环境演变.更多还原

【Abstract】 The concentrations and relative ratios of alkaline earth metals, such as Sr, Ba, and Ca, in sediments are widely used to discriminate marine and terrestrial environments in paleoenvironmental research. However, geochemical elements occur mostly in mineral crystal lattices(namely, the residual phase after acid extraction), which is not linked to the physical, biological, or chemical environments of the deposition processes. Hence, only selective extraction of phases can be used to interpret changes in the sedimentary environment. In this study, we collected surficial sediments from the present-day saltmarshtidal flat, alluvial plain, and tidal river(Yaojiang River) in Ningbo Plain and used a plasma spectrometer to measure the concentrations of Sr, Ba, and Ca in: the leachates extracted by diluted acetic acid(HAc)and diluted hydrochloric acid(HCl), the residues after acid extraction, and the bulk samples. The results showed that alkaline earth metals in the HAc-leachates were most sensitive to changes in the sedimentary environment, followed by the HCl-leachates. No variation in Sr/Ba(molar ratio) could be distinguished in the bulk samples of surficial sediments collected from different sedimentary settings. Furthermore,consistent results were obtained by using different sample amounts and measuring instruments when applying the HAc method. Significant variations in alkaline earth metals in the HAc-leachates were observed for the surficial sediments in this study. Ca and Sr showed the highest concentrations in the saltmarsh-tidal flat sediments and the lowest concentrations in the alluvial sediments; Ba concentration showed the opposite trend. We thus suggest that end-member analyses of the alkaline earth metals in HAc leachates can be used to effectively identify transgression/regression recorded in sedimentary stratigraphy in the coastal zone.更多还原