预处理方法对重庆地区考古遗址粒度分析结果的影响

选取重庆石牛寺和大石洞考古遗址剖面，对比不同预处理方法对粒度测试结果的影响。研究表明：1)加蒸馏水浸泡或0.05 mol/L的(NaPO₃)₆分散剂，并用超声波震荡，分散效果均不明显，主要粒度参数与无预处理实验结果接近，表明物理性预处理方法既不能去除碳酸盐、有机质等杂质，也不能使样品中潜在的胶结团粒分散开。2)加H₂O₂可有效除去地层样品中的有机碎屑物，达到提纯无机颗粒物的目的。该方法预处理后，石牛寺考古遗址沉积物平均中值粒径最小，黏土体积分数最高，相比无预处理测试结果，砂体积分数降低50%左右，且在整个剖面中表现非常稳定；但对于大石洞遗址某些碳酸盐胶结物含量丰富的样品而言，该预处理方法作用有限。3)加10%稀HCl预处理后，石牛寺遗址样品中值粒径有所增大，砂体积分数基本持平，黏土体积分数显著降低，大石洞遗址黏土和砂体积分数同步减少，揭示黏土矿物可能在酸性环境下发生絮凝，从而导致体积分数减少。4)对于碳酸盐胶结物含量较低的环境考古样品，只需加H₂O₂除去有...

The Influence of Different Pretreatment Methods on the Results of Grain Size Analyses for Archaeological Sites in Chongqing

In this study, 24 samples from sections of Shiniu Temple and Dashidong archaeological sites in Chongqing were selected to compare the effects of different pretreatment methods on grain size analysis. Each sample was pretreated using one of five methods: (A) pretreating with distilled water, (B) pretreating with (NaPO₃)₆, (C) pretreating with H₂O₂, (D) pretreating with HCl, and (E) comprehensively pretreating with H₂O₂,HCl, and (NaPO₃)₆. Pretreated samples were ultrasonically dispersed for 10 minutes before examination using a Malvern Mastersizer 2000. First, with the addition of distilled water or the 0.05 mol/L (NaPO₃)₆ dispersant, a dispersion effect was not obvious. Indeed, the main grain size parameters were similar to those seen without any pretreatment (method A), indicating that physical pretreatment methods can neither remove possible impurities, such as carbonates and organic matter, nor disperse the potential cementitious particles in the sample. Second, the addition of H₂O₂ effectively removed organic debris at the archaeological site, enabling the experimental results to accurately reflect the grain size characteristics of inorganic particles in the sediment. The average median grain size of the sediments at the Shiniu Temple archaeological site was the smallest, and the clay content was the highest after being pretreated in this way. The sand content was reduced by approximately 50% compared with that of the sample without pretreatment. The performance is very stable throughout the Shiniu Temple profile; however, for some samples rich in carbonate cement at the Dashidong archaeological site, the effect of this pretreatment method is limited. Third, after pretreatment with 10% dilute HCl, the median grain size of the sample from Shiniu Temple site increased, the sand content remained similar, and the clay content was significantly reduced. The clay content and sand content of Dashidong site decreased simultaneously, revealing that HCl reacts with intergranular carbonate cement to reduce the content of coarse-grained components and causes clay minerals to potentially flocculate in the acidic environment, resulting in content reduction. Acid pretreatment of the grain size was originally suggested from research on loess, aiming to remove a large number of authigenic carbonate minerals in sediments from arid and semi-arid areas. However, it may not be suitable for sediments in humid areas. On the one hand, the content of authigenic carbonate in the sample in such an area is extremely low, making acid treatment nonessential. On the other hand, clay minerals, such as montmorillonite and kaolinite, flocculate under the colloid action of iron oxide in an acidic environment, which makes the grain size coarser, having a counterproductive effect. In this study, archaeological samples from typical karst areas were selected and the optimal particle size pretreatment method was determined through comparative experiments, providing an important reference for follow-up research. Namely, the content of carbonate cement is low, the optimal pretreatment effect can be achieved by adding H₂O₂ to remove organic impurities. If the carbonate composition is significant, the iron oxide in the sample can be removed first and then treated with dilute HCl, effectively avoiding the flocculation of clay minerals. Whether better pre-treatment methods are available needs to be explored further.