中国西风区伊犁盆地塔勒德黄土-古土壤元素地球化学特征及环境意义

摘要

The Ili Basin is a Mesozoic-Cenozoic faulted depression surrounded by the Tianshan orogenic be the altitudes are higher in the eastern part and lower in the western part, and the Kazakhstan Gobi Desert is to the west. The Basin has a temperate, continental, arid climate, with the annual average temperature of 8℃ and precipitation of 257. 6 ~ 512. 2mm. It has an even distribution pattern of the seasonal rainfall and the rainfall in spring season is slightly larger than in the other seasons. Westerly airflow from the Atlantic Ocean, the Mediterranean or the Black Seas easily reaches the valley and forms precipitation because of the unique landforms and the mountain strike. In order to obtain the accurate and high resolution samples of loess-paleosol sequence,the exploration well,located in 43°31'53" N,83°18'58"E, was excavated over 17m thick in the middle of seven terraces on the banks of Kunas River. 85 samples of elements analysis at 20cm intervals were collected in total. C and OSL dating on the samples from the different depth suggest that the age at upper part of L2 is about 115kaB. P. The processed sample was analyzed by Philips Panalytical Magix PW2403 X-ray fluorescence ( XRF) spectroscope. Based on the analytical results of the major and trace elements in Talede section, the correlations between the related elements and their ratios,the depositional environment of the section was discussed. The results show that the total amount of the major elements is about 92. 45%. SiO2 had the highest content, which is ranges from 52. 18% to 60. 63% with an average value of 56. 16% ,followed by A12O3 about 13. 37%. All displayed enrichment in silicon and aluminum. The analysis of major element content in the TLD exploration well demonstrated that the order of abundance was generally as follows; SiO2>Al2O3>CaO>Fe2O3>MgO>Na2O>K2O.The trace elements Rb,Sr,Sc,Ni,Cu,Ga,Mo, Y ,Pb,and Th in the paleosol layers(S0,Sm and S, ) ,and loess layer( L, )are enriched relative to underlain loess horizon(L2) ,only the elements of Zr,Cs,Nd,and La show deficit in paleosol layers. The results of geochemical characters and their parameters of Talede section, which compared to the past research of Chinese Loess Plateau, show that most elements were not obvious differentiation in each stratum of the Talede loess-paleosol sequence, and the study area had significant regional characteristics, it means that the climate conditions in the Central Asia and the Chinese Loess Plateau are different. All of these geochemical proxies of Talede section suggest that the loess and paleosol of Hi Basin developed under more arid climate than the Loess Plateau since the last interglacial period,and generally speaking,the climate of Westerly area is more arid than Asian monsoon area. The elemental geochemistry of the loess of Hi Basin is controlled by the geochemistry of the source areas and the climate condition in the deposition area,and the loess possesses a common source area. Therefore, the geochemistry characters could be treated as climate and environmental proxies.%通过对新疆伊犁盆地塔勒德探井黄土-古土壤沉积物中常量、微量元素及其相关指标和参数的分析,讨论了西风区黄土-古土壤序列中各元素的分异规律及其与沉积环境之间的关系.结果表明塔勒德黄土-古土壤序列各层位中常量元素含量均表现出SiO2＞Al2O3 ＞CaO＞ Fe2O3 ＞MgO＞ Na2O＞K2O的变化特征；微量元素Rb,Sr,Sc,Ni,Cu,Ga,Mo,Y,Pb和Th在(弱)古土壤层、黄土层中相对下伏黄土L2层富集,而Zr,Cs,Nd和La在(弱)古土壤层中有不同程度的亏损.塔勒德黄土-古土壤的相关地球化学参数在整个研究地层序列中,黄土与古土壤之间分异并不显著,地球化学特征反映了受西风区影响的伊犁盆地黄土和古土壤形成时期其有效湿度较黄土高原同期小,形成环境更为干旱,具有其显著的区域特征.伊犁盆地黄土剖面元素地球化学特征主要受物质来源和气候环境的控制,当黄土物质具有相同来源时,其元素地球化学特征可以作为区域气候环境变化的良好代用指标.