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从中国黄土沉积中提取古环境演化信息已取得重大进展,然而,如何有效区分黄土中原生和次生碳酸盐,进而用于追踪粉尘的来源和揭示风化成壤的强度,仍有很大困难。为了辨别黄土中不同成因的碳酸盐矿物,本文从黄土高原西部靖远和古浪剖面中选取2个典型古土壤和黄土样品(S_0和L_1),分为5个粒级(<4μm,4~8μm,8~16μm,16~32μm和32~63μm),进行了热重分析(TGA)和X射线衍射测试(XRD)。结果表明:1)黄土中的碳酸盐主要由方解石和白云石组成,原生方解石和白云石在黄土中的含量比古土壤中含量高,并偏富集于粗颗粒组分;2)次生方解石在古土壤中的含量比黄土中高,并显著富集于细颗粒组分。在黄土和古土壤全样和分粒级样品中,TGA和XRD方法分别测出的Carb-B/Carb-A和(方解石+白云石)/方解石比值变化一致,有望成为反映黄土风化成壤强度的新代用指标。
Significant progress has been made in extracting paleoclimate evolution information from Chinese loess sediments. However, it is still very difficult to effectively distinguish between primary and secondary carbonate in loess so as to trace the source of dust and reveal the strength of weathered clay . In order to distinguish carbonate minerals of different origin in loess, two typical paleosol and loess samples (S 0 and L 1) were selected from Jingyuan and Gulang profiles in the western Loess Plateau and divided into five grain fractions (<4μm, 4 ~ 8μm, 8 ~ 16μm, 16 ~ 32μm and 32 ~ 63μm), TGA and XRD were performed. The results show that: 1) The carbonate in loess is mainly composed of calcite and dolomite. The contents of primary calcite and dolomite in loess are higher than those in paleosol and are enriched in coarse fraction. 2) Secondary Calcite is higher in ancient soil than in loess and is significantly enriched in fine-grained components. Carb-B / Carb-A and (calcite + dolomite) / calcite ratios measured by the TGA and XRD methods in the whole sample and the fractionated samples of loess and paleosol are all consistent, which is expected to be a reflection of loess weathering intensity The new generation of indicators.