乌鲁木齐周边黄土沉积特征及其沉积环境分析

Analysis of sedimentary characteristics and environment of loess around Urumqi

【目的】探讨乌鲁木齐周边黄土的沉积环境及海拔高度对黄土理化性质的影响。【方法】通过统计分析和Sahu沉积环境判别公式研究乌鲁木齐周边黄土的沉积特征。【结果】乌鲁木齐东侧黄土的粒级主要由极粗粉砂、粗粉砂、极细砂、中粉砂组成,平均体积分数分别为33.89%、22.87%、14.83%、11.63%,其他组分不足7%。黄土的平均粒径介于12.47~26.78μm之间,分选系数介于2~4之间,偏度值介于-1~-0.5之间,峰度值介于0.87~1.46之间,表明分选性差,黄土粒度频率曲线均呈负偏态,且趋于常-较窄峰态分布,不同剖面及不同深度各项指标的波动幅度均较大,气候变化显著。乌鲁木齐周边气候整体趋势表现为越来越干旱,大致发生6次旋回。黄土的磁化率数值介于21.17×10^(-5)~77.5×10^(-5)SI之间,平均49.35×10^(-5)SI,波动范围较大,说明不同时期西风环流强弱变化明显,且不同时间段气候变化显著。黄土在0~80 cm处有机质量均值为1.396%,且随深度增加而降低,较适宜农作物种植。【结论】乌鲁木齐周边黄土的沉积环境为风力沉积环境,且随海拔高度上升,黄土的粒级粗组分含量相对升高,平均粒径均值增大,分选性更好,磁化率数值降低。

【Objective】To investigate the influence of the sedimentary environment and the altitude of the loess around Urumqi on the physico-chemical properties of the loess.【Method】The depositional characteristics of the loess around Urumqi were studied using statistical analysis and the Sahu sediment environment discrimination formula.【Result】The grain size of loess on the east side of Urumqi is mainly composed of very coarse silt,coarse silt,very fine sand and medium silt,with the average volume percentage of 33.89%,22.87%,14.83%and 11.63%,respectively,and the other components are less than 7%.The average particle size of loess is between 12.47~26.78μm,the sorting coefficient is between 2~4,the skewness value is between-1~-0.5,and the kurtosis value is between 0.87 and 1.46,indicating that the sorting is poor,the loess particle size frequency curve is negatively skewed and tends to be normal-narrow peak distribution,the fluctuation range of different profiles and different depths is large,and the climate change is significant.The overall trend of the ambient climate in Urumqi is becoming drier,with about six cycles occurring.The susceptibility value of loess is between 21.17×10^(-5)~77.5×10^(-5)SI,with an average of 49.35×10^(-5)SI,with a large fluctuation range,indicating that the strength of the westerly wind circulation changes significantly in different periods,and the climate change in different periods is significant.The average organic mass of loess at the depth of 0~80 cm is 1.396%,and decreases with increasing depth,which is more suitable for planting crops.【Conclusion】The sedimentary environment of the loess around Urumqi is a wind-deposited environment,and with altitude,the coarse component content of the loess is relatively higher,the average particle size increases,the sorting is better,and the magnetic susceptibility value decreases.