噶顺戈壁地表砾石粒度特征分析

Size characteristics of surface gravels in Gaxun Gobi

对戈壁表面砾石粒径的研究,可帮助了解戈壁特征,分析戈壁造成自然灾害的原因,认识沙粒迁移、沙漠扩展以及指导防沙工程。本研究结合野外调查,分析噶顺戈壁洪积扇21个样点砾石的粒度组成、平均粒径、分选系数、偏度和峰度等粒度特征。结果表明:1)受洪水、重力与风蚀等作用的影响,戈壁地表砾石均以中砾为主(66.35%~95.04%)。海拔最高处以石质为主(85.54%),平均粒径值为-9.09(545.2 mm)。砾石质量分数呈现出随海拔增加,中砾质量分数降低,而粗砾质量分数升高的趋势。2)粒度特征为:平均粒径值变化范围为-9.09(545.2mm)^-6.15(153.9 mm);除样点12为分选中等外,其余样点的均处于分选较好以上水平(0.28~0.53);偏度以负偏为主导(80.95%),地表以细砾和中砾等细粒径砾石为主;峰度中,宽平和很宽平占整体的57.14%,中等占23.81%,尖窄和极尖窄占19.05%,显示砾石分布相对较均匀,在不同位置的砾石,具有微弱的地表过程差异性。3)分选系数与平均粒径之间,无明显的相关关系;而偏度与平均粒径间,存在正相关关系。研究结果对物源的岩性及戈壁发育环境具有重要的指示意义。

[ Background ] Study on the gravel size of gobi surface provides a better understanding about gobi characteristics, and analyzing the reasons of natural disasters in association with gobi. It can also be used to know better about sand migration, desert spread and provide the guidance of sand control engineering. [ Methods] In alluvial fanof Gaxun Gobi, the grain size composition, average grain size, sorting coefficient, skewness and kurtosis from 21 gravel samples were analyzed by means of field investigation and granulometry. [ Results] The results showed： 1） The major grain size of surface gravels was occupied by mediumsize ones （66.35% -95.04% ） due to the effect of flooding, gravity and wind erosion. The size on the top of altitude was dominant by stone （85.54%） , average size was - 9.09φ （545.2 mm）. The content of mediumsize gravels decreased while the coarse size gravels increased with the altitude increasing. 2） The average range of size variation was -9.09φ （545.2 mm） - -6.15φ （153.9 mm） ; the gravels were well sorted （0.28 -0.53） except for sample 12. The grain skewness of surface gravels was dominant by negative, accounting for 80. 95% , and the surface gravel size was mainly fine and medium. The kurtosis was flat and very flat （80.95 % ） , followed by medium （23.81% ） , while sharp or very sharp accounted for 19.05% , which showed the granularity characteristics were evenly distributed. 3） There was no significant correlation between sorting coefficient and average grain size, while there was positive correlation between skewness and average grain size. [ Conclusions ~ The research result can provide useful instructions for lithology of the provenance and gobi development condition.