| The impact of the uplift of the Qinghai-Tibet Plateau on the western Sichuan environment is one of the most concerned scientific issues.At present,the study on the genesis of the loess and the recorded environment using the Ganzi loess in the western Sichuan Plateau has yielded fruitful results,while the researching on the loess in Aba Prefecture is involved little.The loess in the southeastern part of Aba Prefecture is divided into two types.The first type is distributed on the slopes far away from the river.The characteristics on the field are:uniform texture,no bedding,developed vertical joint,and the characteristics of grain size and chemical composition of loess have a good correspondence in space,represented by Jiazhai loess section;The other type is mostly distributed on the river terraces and the gentle slopes of the canyon.The characteristics on the field are:the inclusions in the soil,and the debris with certain roundness.represented by the Lama Temple section.The paper forces on the two sections of Lama Temple and Jiashanzhai,resarching on the grain size characteristics and geochemical characteristics of the loess section,and discussesing characteristics of the loess in the southeast of Aba Prefecture since the last interglacial period and the environmental information recorded by the loess.The grain size of the loess section of Lama Temple is bigger than 50μm which composeing by sand grains,the average size is 5.09Ф,the average value of standard deviation is 1.99,poor sorting,the grain size frequency curve is double or multi-peak.,which belongs to positive skewness.The environmental discriminant parameter Y>0,which accordance with the characteristics of waterborne loess.The results of the Lama Temple loess section researching by geochemical means show phenomenon of calcium-riching and silicon-deficientence,The total content of MgO、CaO and Na2O is 10.60%,which is higher than the total content of the corresponding components of Ganzi loess（8.64%）,The components gradually decreased from bottom to top.which indicates that the paleo-climate in the southeastern part of Aba Prefecture is mainly dry and cold,and develop to wet gradually.The characteristics of the development towards wetness.The chemical alteration index（CIA）of the loess section of the Lama Temple indicates that the chemical weathering degree in the southeastern part of Aba Prefecture is low.The Jiashanzhai loess section is mainly composed by coarse silt which main size is 1050μm,the average particle size is 6.37Ф,the standard deviation is 1.57,good sorting,the particle size frequency curve is double peak,which accordance with the characteristics of wind-loess.and the environmental discrimination parameter Y<0,so Jiashanzhai loess belongs to aeolian loess.The big value of Kd of the Jiashanzhai loess section indicats that the paleoclimate in the southeastern part of Aba Prefecture is dry and cold.X-ray diffraction results show that the clay mineral combination of loess are illite and chlorite,which verifies the paleoclimate characteristics of dry and cold in southeastern Aba Prefecture,and the degree of chemical weathering is weak.Since the last interglacial period of about 130ka BP in the southeastern part of Aba Prefecture,the degree of chemical weathering is low,and the paleoclimate is mainly dry and cold,and develops to wet gradually. |
