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.