庐山地区第四纪泥砾沉积物的成因探讨

庐山第四纪泥砾沉积物的砾石组构特征表明, 砾石岩性与山体基岩基本一致, 砾石的等体积球径较小, 加权平均砾径较中值砾径大, 分选系数大于1, 分选性差, φ值相对较小, 平均为0.66, F值相对较大, 在2左右, F/φ比值介于2.75～4.75, ρ值集中且较小, 为22.75%～37.75%, 砾石以棱角、次棱角状为主, 磨圆较差; a轴和ab面都倾向沟谷下游, a轴倾角集中且较小, 为7～8°, ab面倾角为7～21°, a轴较ab面具有更为优势的组构倾向; 沉积物粒度频率曲线在4～5?范围内表现为峰; 石英砂颗粒为次棱角状, 贝壳状断口发育, 具平行擦痕、上翻解理片、V形坑和硅质沉淀。上述沉积学特征表明庐山第四纪泥砾沉积物系冰碛冰水沉积, 而非泥石流或河流堆积。 

ORIGIN OF QUATERNARY MUDDY GRAVEL DEPOSITS IN THE LUSHAN AREA

The gravel fabric characteristics of Quaternary muddy gravel deposits in the Lushan area indicate the following:the lithology of gravels is almost consistent with that of bedrocks in the mountains; the isometric sphere diameter of gravels is small, the weighted average diameter of gravels is lower than the median diameter of gravel; the gravels are poorly sorted with a sorting coefficient of >1;the values are relatively lower, averaging -0.66;the F values are higher, being 22.75%-37.75%;the ratios of F/φ range from 2.75 to 4.75;the φ values are lower and concentrated, ranging from 22.75 to 37.75%, and the gravels are mainly angular and subangular.Both the a-axis and ab-plane dip towards the downstream, the dip angles of the a-axis are low and concentrated, being 7-8°, the ab-plane dips at 7～21°, and the a-axis has more preferred dip of fabrics than the ab-plane; the peak of the grain-size frequency distribution curve of deposits in the Lushan area is in the range of 4 and 5φ; The quartz sand grains are subangular and have well-developed conchoidal fractures, parallel striations, upturned cleavage flakes, "V"-shaped holes and siliceous deposits.The above-mentioned sedimentary characteristics indicate that the Quaternary muddy gravel deposits in the Lushan area should be till and glaciofluvial deposits rather than fluvial deposits or mudflows.