The Characteristics Of The Sediment And Environmental Significance Of LB Profile In Lop Nur Since Late-middle-pleistocenethe

Lop Nor is the extremely arid area on Earth, located in the eastern part of the Tarim Basinwhich is one of the largest inland arid basins on Earth. Lacustrine sediments have formedin the Lop Nor since the Quaternary System due to the global environment change and thegeological tectonic movement. Lacustrine sediment is one of the important informationcarriers for inversion regional climate and the warning of global change, which play anirreplaceable role on the palaeoclimate and environment change. A palaeosol profile with adepth of4.5m in the east of the Lop Nur was selected for paleoenvironmental studies.18samples were collected from the bottom to the surface of the profile based on lithologiccharacteristics in September2012and labeled as LB1, LB2...LB18. A chronology sequenceis inferred from the stratigraphic-lithologic. With the predecessors to lop nur weresystematically stud Ed sequence division results comparison, combination of quaternarylithostratigraphic and lop nur were systematically stud Ed division determine the LBprofile relative time sequence.Analyses, including granularity, magnetic susceptibility, totalorganic carbon contents (TOC), pH value and soluble salts contents, were performed toreconstruct the ancient climate and ancient environmental evolution, which covers thespecial period from the Tertiary System to the Holocene. The conclusions as follows:1. Basal LB1is brick-red sandstone of Tertiary System, followed by granular gravel,gray gypsum, gray silt, yellow silt and pale yellow clay sand. A chronology sequence ofwhole profile in order: Tertiary (LB1,4.5-3.32m), late Mid-Pleistocene (LB2-LB4,3.32-2.87m), late Pleistocene (LB5-LB14,2.87-1.24m), Holocene (LB15-LB18,1.24-0m).2. The Tertiary System sand and soluble salt contents are relatively high, frequencymagnetic susceptibility and the TOC contents are low and the soil pH value is alkaline.Hydrodynamic is weak, climate is warm and the type is warm and dry climate.3. Comparing the late Mid-Pleistocene with the Tertiary System, coarse particle (>63μm) and frequency magnetic susceptibility shows increasing trend after decreasing, andsoluble salt contents and TOC contents shows increasing trend after increasing first andthen decreasing. The climate tends to be warm and moist due to strong hydrodynamic andrising temperature.4. The late Pleistocene is divided into three stages (A, B, C) from the base LB5toLB14according to these indexes change. Comparing the stage A (LB5-LB8) with the lateMid-Pleistocene, the coarse particles (>63μm), frequency magnetic susceptibility andTOC contents shows increasing trend after decreasing, and soluble salt contents has beendecreasing. The succession of climate is cold-dry, warm-dry and warm-wet. Comparing the stage B (LB9-LB12) with the LB2, frequency magnetic susceptibility and TOC contentsare higher, the temperature is high. Coarse particles (>63μm) shows a trend of firstincrease then decrease and finally increase. The change trend of soluble salt contents, pHvalue are opposite as coarse particles. It shows that the climate is altered with wet and dryclimate. The succession of climate types are as follows: warm-wet, warm-dry and warmand wet. Comparing the stage C (LB13-LB14) with the LB12, coarse particle andfrequency magnetic susceptibility are decreased, however, frequency magneticsusceptibility and TOC contents tend to be increase from LB13to LB14. Depositionalenvironment is alkaline. The climate succession of the late Pleistocene is: cold-dry,warm-dry, warm-wet, warm-dry, warm-wet and warm-dry.5. Comparing the Holocene (LB15-LB18) with the late Pleistocene, various indicatorsare at a higher level which shows the Pleistocene come into high temperature period.Compared to LB15, coarse particle (>63μm) shows increasing trend, and the frequencymagnetic susceptibility, TOC and soluble salt contents shows a trend of gradually decrease,among which the reduction of soluble salt is bigger with47.8%, pH value is alkaline. Itdemonstrated that the climate type change from warm-dry to warm-wet and cold-wet.6. In this paper, relative chronology sequence was established based on lithologicalcharacteristics during different periods in Quaternary System, and through multiple indexanalysis, the types of climate in late Mid-Pleistocene were obtained. Five phases which arecold-wet, warm-dry, warm-dry, cold-wet and warm-wet in order. The research enriched theprecision of inversion chronology sequence by palaeoclimate change in Mid-Pleistocene inLuo Nor area.