不同计算方法的云南省永胜县下院滑坡堰塞湖沉积物粒度特征及沉积历史重建

Grain size characteristics and sedimentary history reconstruction of the Xiayuan ancient landslide−dammed lake in Yongsheng County,Yunnan Province,based on different calculation methods

【研究目的】滑坡堰塞湖灾害链危害大,其形成和溃决过程中受外部环境影响大。堰塞湖沉积物作为记录堰塞湖全生命周期的载体,具有良好的古环境和古气候的指示作用,采用最佳解析方法对其进行解读有利于还原沉积物沉积过程及古环境变化。【研究方法】通过野外调查采样和室内测试分析相结合的方法,采用图解法和矩值法计算下堰塞湖沉积物统计特征的适用性问题,使用粒度结合有机质含量重建了堰塞湖沉积环境,对堰塞湖的发育过程进行还原。【研究结果】(1)堰塞湖沉积物分层沉积层序明显,为单一水动力湖相沉积,物质来源稳定,非多物源沉积;综合有机质变化和沉积物粒度特征表明该堰塞湖经历了4次干湿周期,在气候和地质活动的共同作用下至少存在3次堵塞−泄流沉积过程,估算沉积旋回周期约为1750 a,该沉积历史应该是断裂带长期复杂的活动和气候−河流共同作用的结果。(2)通过对图解法和矩值法进行统计分析结果表明,两种方法对平均粒径和分选系数评价一致性较好,可直接进行替换;矩值法对偏态峰态整体计算结果比图解法大,在使用中需进行线性代换。由于描述参照值的缘故,偏态、峰态在统计表述中有所偏差。【结论】堰塞湖沉积物粒径分布简单,采用图解法计算更加便捷,与其他沉积物对比方便,推荐图解法对堰塞湖沉积进行计算。研究结果表明粒度特征对堰塞湖的沉积和溃决过程以及滑坡灾害对气候变化的响应研究具有一定的指导意义,可为还原该堰塞湖沉积期的古环境和古气候提供理论依据。

This paper is the result of environmental geological survey engineering.[Objective]The cascade of disasters caused by landslide−dammed lakes is highly destructive,with its formation and outburst processes significantly influenced by the external environment.The sediment within the dammed−lake serves as a valuable tool for documenting the entire lifecycle of thedammed−lake,offering important insights into paleoenvironment and paleoclimate.Utilizing the most effective analytical methods to interpret this sediment can aid in reconstructing the sediment deposition process and understanding changes in paleoenvironment.[Methods]Through sediment sampling for field investigation and laboratory analysis,the suitability of statistical characteristics of dammed lake sediments is assessed using graphical and moment methods.The sediment environment of the dammed lake is reconstructed by analyzing particle size in conjunction with organic matter content,allowing for the restoration of the development process of the dammed lake.[Results](1)The stratified sediment sequence of the dammed lake sediment is distinct,representing a monogenic hydrodynamic lacustrine sediment with consistent material sources rather than polygenic sediment.Analysis of the organic matter and sediment grain size variations indicates that the dammed lake has undergone four cycles of wet−dry periods,with at least three instances of blockage−overflow deposition processes resulting from the combination of climatic and geological factors.The estimated sedimentary cycle period is approximately 1750 a.It is suggested that the sedimentation history is a consequence of prolonged and intricate activities within the fault zone,as well as the combined influence of climate and river dynamics.(2)The statistical analysis results from the graphical method and the moment method indicate a high level of agreement in assessing the average grain size and sorting coefficient,suggesting that they are interchangeable.However,the partial kurtosis values obtained from the moment method are greater than those from the graphical method,necessitating a linear adjustment for practical application.Additionally,deviations from statistical expressions are observed in the skewness and kurtosis due to the reference value description.[Conclusions]The grain size distribution of the sediment from the dammed lake is straightforward and easily calculated,making it convenient for comparison with other sediment types.The graphical method is suggested for these calculations.The findings indicate that the grain size characteristics offer valuable insights into understanding the deposition and outburst processes of dammed lake,as well as the response of landslide disasters to climate change.This information can serve as a theoretical foundation for reconstructing the paleoenvironment and paleoclimate of the dammed lake during its deposition phase.