中坝遗址地层的Cr/Cu值对干湿环境的指示意义

Variation of Cr/Cu Ratios in Zhongba Profile and Its Indication on Palaeo-environment over Last 5 ka

将中坝遗址5 ka以来连续沉积地层按文化序列分为12层,分别测量Rb、Sr和Cr、Cu含量,对比显示,Cr/Cu比值与Rb/Sr比值明显正相关。Cr与Rb的属性相似,Cr化学活性低,易于在粉砂质沉积物中富集;而Cu和Sr在成壤过程中容易迁移,在粘土质沉积层中含量较高。通过对Cr、Cu元素在表生环境下的化学性质、沉积地层的属性、微地貌特征、与泥炭腐殖化度古里雅冰芯氧同位素曲线等指标对比表明,Cr/Cu比值变化对环境干湿变化的指示具有普遍意义。

Applying distribution characteristics of chemical elements during soil-forming process to resume palaeoenvironmental evolution is a key field in the research of past global changes. This paper divided the continuous strata of the Zhongba site in Chongqing into 12 sub-layers according to cultural sequence over last 5 ka, measuring Rb, Sr, Cr and Cu contents respectively by XRF and ICP-AES methods. Results indicated that Cr has similar chemical nature as Rb with low activity and is apt to deposit in fine sand materials. Meanwhile, Cu and Sr are easy to be transported over the weathering process and enrich in claypan. A linear regression demonstrated that Cr/Cu ratios are positively relative to Rb/Sr ratios. After comparing variation curves of Cr/Cu ratios with climatic records of peat humification in Hongyuan, northeast region of the Tibet Plateau in last 5 ka, they both are well consistent with each other. Therefore, this paper suggested that Cr/Cu ratios as Rb/Sr be a reliable proxy to indicate palaeoenvironment even with higher accuratcy. Obviously, Cr/Cu ratios will be significant in geo-archaeological research.