山西应县护驾岗冲沟阶地地层粒度特征与沉积环境

山西应县护驾岗冲沟阶地地层形成于66.46～33.62 ka,根据该剖面地层的粒度分布特征对该地区冲沟阶地的沉积环境进行了探讨。护驾岗冲沟阶地剖面的粒度分布特征显示:(1)剖面地层总体表现为自下而上由粗到细的正韵律沉积特征,结合野外观察将其分为4段(A—D段);(2)A段粒度分布特征变化不大,均以细砂为主,频率曲线为不对称单峰,概率累积曲线为2段式,以跃移搬运为主,分选相对较好,水动力较强,沉积环境稳定;(3)B—C段粒度分布特征变化较大,以粉砂和细砂为主,频率曲线为不对称双峰,概率累积曲线为2段式,以跃移搬运为主,分选较差,水动力较强,沉积环境不稳定;(4)D段粒度分布特征变化不大,以粉砂为主,频率曲线为不对称单峰,概率累积曲线为2段式,以悬移搬运为主,分选相对较好,水动力较弱,沉积环境稳定。总体来说,冲沟阶地形成于河流沉积环境,顶部为河漫滩沉积环境。粒度分布特征与古里雅冰芯氧同位素变化基本一致,因此护驾岗冲沟阶地粒度特征与沉积环境的变化归因于气候变化。

Grain Size Characteristics and Deposit Environment of Strata in Hujiagang River Terrace in Yingxian, Shanxi Province

Hujiagang is located in Yingxian,Shanxi Province.The river terrace in Hujiagang was formed between 66.46 ka and 33.62 ka.The grain-size distribution characteristics were used to interpret the deposit environment of Hujiagang river terrace.The grain-size distribution characteristics show the following four aspects:(1)the grain sizes of strata in Hujiagang river terrace upwardly change from coarse to fine with a positive rhythm sedimentary characteristics,and the strata can be sorted into four sections,i.e.A,B,C and D;(2)sediments in section A which mainly consist of fine sands have similar grain-size distribution characteristics and were mainly transported in saltation,showing asymmetrical single hump and two parts in probability accumulation curves,and the sorting is good,indicating that the hydrodynamic activity is strong and the deposit environment is stable;(3)sediments in sections B and C which mainly consist of fine sands and silts have different grain-size distribution characteristics and are mainly transported in saltation,showing asymmetrical two humps and two parts in probability accumulation curves,and the sorting is bad,indicating that the hydrodynamic activity is strong and the deposit environment is instable;(4)sediments in section D which mainly consist of silts have similar grain-size distribution characteristics and are mainly transported in suspension,showing asymmetrical single hump and two parts in probability accumulation curves,and the sorting is good,indicating that the hydrodynamic activity is weak and the deposit environment is stable.The strata in Hujiagang river terrace in general are formed in fluvial facies and the top is alluvial plain sediments.The change of these grain-size distribution characteristics is in accord with the oxygen isotope variation of Guliya ice core,thus the change of grain size and the deposit environment of Hujiagang river terrace are controlled by the climate change.