GEOCHEMICAL BEHAVIORS OF STRONTIUM ISOTOPE AND RELATED ELEMENTS OF THE LACUSTRINE DEPOSITS AND THEIR APPLICATION TO PALEOENVIRONMENT RECONSTRUCTION
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摘要: 以柴达木盆地察尔汗古湖贝壳堤剖面的沉积物样品为研究对象,分离其酸溶组分(AS)和残留组分(AI)并分别测试 87 Sr/86 Sr 值和元素含量,在区分了酸溶组分和残留组分 87 Sr/86 Sr 与相关元素的基础上,进一步应用主成分分析方法(PCA)对筛选的环境指标进行分析,通过降维提取环境因子,并分析各指标间的相互关系,进而解释湖泊沉积物中酸溶组分中的多维数据,其目的主要是更好地理解湖泊形成和演化过程中所选指标对气温和降水的响应过程和特征。结果表明,贝壳堤剖面中酸溶组分和残留组分 87 Sr/86 Sr 组成及Sr元素含量之间不存在明显相关关系,它们各自代表了不同物质来源和影响因素; 酸溶组分的各项指标更好地表征了沉积区气候环境和湖泊水化学性质的特征和变化,其中Sr同位素和 Rb/Sr 值与Sr的活动性有很大关系,与 Sr/Ca 和Sr/Ba比值一起可以作为湖水盐度指标,但不呈线性响应关系; Rb/Sr 值与 Fe/Mn 值很高的相关性证明 Rb/Sr 值不仅与盐度相关,也可在水热同期的气候条件下与 Fe/Mn 值一起作为湖水深度的指标之一。
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关键词:
- 87Sr/86Sr值 /
- 元素比值 /
- 盐度 /
- 化学风化 /
- 湖泊沉积物
Abstract: Based on the detailed analyses of the Qarhan Shell bar section,which is located at the Eastern Qaidam Basin and is one of the most important geological archives in the north Eastern Tibetan Plateau,the 87 Sr/86 Sr and the contents of other elements in the acid soluble(AS)and acid insoluble(AI)fractions were tested separately. The purpose of such analyses is to explore how the strontium isotope and other elements react to the rock weathering,material transportation and sedimentation in the lake system,and distinguish climate sensitive index from massive dataset. To realize such purpose,the principal component analysis(PCA)method,which is one of the most applied statistical methods to extract the useful information from a large number of original data and converts correlative variables into a few independent indexes was applied to separate the environmental proxies,e.g. to distinguish the precipitation sensitive proxy from temperature sensitive ones. Through such analyses,we hope to reduce the uncertainty of the proxies and improve the reliability of the climato-environmental reconstruction. The analyses results show that the 87 Sr/86 Sr values and Sr contents in the acid soluble and acid insoluble fractions vary independently in the studied section and there is no linear relationship between them. They represent the different material sources,transportation and change procedures and influential factors. The proxies given by acid soluble faction of the lacustrine deposits are more suitable and reliable to reveal the regional climate change history and the geochemical properties of the lake water than the data given by bulk samples and/or acid insoluble fraction,the later is more loosely related to the rock types and weathering procedures. The δ18 O of CaCO3、CaCO3 contents and the Mg/Ca ratios of the acid soluble fraction are more closely related to the regional temperature changes,the strontium isotope and the Rb/Sr ratio changes are influenced by the activity property of the element strontium. 87 Sr/86 Sr values and Sr/Ba ratios,together with Sr/Ca and Rb/Sr ratios are proxies of the water salinity,as the Rb/Sr ratios also correlates to Fe/Mn ratios,it also one of the proxies of water depth when temperature changes consistent with precipitation.-
Key words:
- 87 Sr/86 Sr values /
- elemental ratios /
- salinity /
- chemical weathering /
- lacustrine deposits
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