Abstract: Lop Nur is the typical closed inland playa in Xinjiang,its occurrence,development and demise had recorded the miniature of the climate change and environmental evolution in entire sedimentary of the Tarim Basin and Central Asia. Through surveying sample in field,and comparing the features of new and old salt in different "helix" in Lop Nur "big ears",this paper proposed that the different "helix" Ring in "big ears" had five or six sides or polygonal cracking which is its minimum or basic unit,called salt shell unit in salt crust edge,and further analyzed the soil geochemical characteristics,grain size and the magnetic susceptibility of the new and old salt crust element in the dry salt lake of "Great Ear" in Lop Nor to investigate the features of salt shell unit in different developmental stages. Results showed as follows:(1)the soluble salt content varies greatly in the salt crust samples,from high to low the total salt contents were,in ordered:LBⅥ >LBⅦ >LBⅧ >LBⅨ >LBⅤ,and the new salt shell element was higher than the old one except for LB V. The main types of soluble salt were Na⁺ and K⁺-Cl——SO₄^2-. The pH were all over 7,revealing that both the new and old salt shell element were in partially alkaline environment. TOC content varies between 1.19% and 1.21% with smaller difference in each salt shell element.(2)The particle size of sample components were dominated by silty sand(2-63μm)both in the new and old salt shell element,and the mean content was up to 80.52%. The coarse and medium sand contents in the old salt shell element were obviously higher than those in the new one.(3)Difference of magnetic susceptibility among each samples were not significant,and overall shows a gradually increase trend from the middle of the helix to the outward with the average value being 3.7×10^-6 m³·kg^-1,the maximum value being in LBⅨ and the minimum value in LBⅦ. The frequency dependent susceptibility varies between 5.77% and 21.74%,and the mean SIRM value was 314.75×10^-5 Am²·kg^-1,showing that the ferrimagnetic minerals were the main magnetic carriers. (4)The correlation analysis to each parameter showed that the total salt content was positive correlated with pH and TOC,and was negative correlated with magnetic susceptibility and silty sand. In general,the results above indicated that the area of climate has shifted to the drought trend.

Key words: salt crust element, "Great Ear", in Lop Nor, magnetic susceptibility, environmental significance