The Sedimentary Characteristics And Cause Analysis Of Yardangs In Lop Nur

Yardangs are typical wind erosion landforms, which are generally defined asstreamlined hills or ridges produced by wind erosion. Yardangs are present in allcontinents on Earth except for Antarctica and Oceania. About20000km2of Yardangsare distributed in China, among which are the3000km2. Lop Nur Yardangs inXinjiang, the second largest Yardang distribution area in China. Lop Nur Yardangsrange in four subregions, two of which are concerned in the studied: Bailongdui andAqikegudi. Field work investigation was made and sediment samples were collectedthere in September2012. Combined with the evolution of Lop Nur salt lake, thegrain size, TOC, pH, total salt, eight ions and magnetic susceptibility of the sampleswere measured and used to detect the origin and characterisitics of Lop NurYardangs and the sedimentary environment. It is revealed that Bailongdui Yardangsand Aqikegudi Yardangs were formed by eolian erosion and they differ from eachother in sedimentary features and origin due to difference in hydrochemistry. Thefindings and results include:(1) On average, deposits from Bailongdui Yardangs and Aqikegudi Yardangsconsist of15.52%clay,73.44%silt,7.89%fine sand,2.19%medium sand and0.96%coarse sand. The concentration of silt and other grain size fractions variednoticeably between the samples. Samples from Bailongdui Yardangs are well sorted,symmetrical, positively skewed or very positively skewed, platykurtic or leptokurtic.Samples from Aqikegudi Yardangs are well sorted, negatively skewed andplatykurtic. This suggest that fine grains are more highly concentrated in sedimentsof Bailongdui Yardangs and eolian erosion plays a more dominant role in Bailongdui.Sahu’s discrimination formula indicates the Lop Nur Yardangs have been initiatedfrom the fluvio-lacustrine sediments.(2) TOC and pH values are indicative of an upward increase in the organicmatter content of the sediments and alkaline environment. The sediments has highcontent of K+、Na+、Cl-、SO42-. The content of total salt and various ions are allhigher in Bailongdui sediments than in Aqikegudi ones. The reason is that a lot ofwater eroded mineral salts from rocks in the wide northern areas input by rainfallsand floods are responsible for the formation of Bailongdui Yardangs. AqikeqgudiYardangs has less material source and low content of salts.(3) Bailongdui sediments show higher concentration of magnetic mineralsthan Aqikequdi ones. Both Bailongdui and Aqikequdi sediments exhibit>90%F300and <50mT Bcr, which reveal the dominance of magnetically soft ferrimagnetics (magnetite and maghemite).(4) Comparative study on various characterisitics, besides eolian erosion,watererosion significantly in the formation of Bailongdui Yardangs. Hydrochemistry playa less significant role for Aqikegudi Yardangs, which were produced by eolianerosion. Hydrochemistry makes the difference between Bailongdui Yardangs andAqikegudi Yardangs in origin and sedimentary characterisitics.