A Study On The Material Source And Characteristics Of Aeolian Loess In The Upper Reaches Of The Han River And Jialing River

Loess accumulation is closely related to Asian dust system.Its provenance has always been the focus of scholars research.Although there is large amounts of loess in the upper reaches of Hanjiang River and Jialing River,there is no unified understanding about the source of loess.After a detailed field investigation in the upper reaches of Jialing River in Hanjiang River,Lijiahe profile and Yangjiashan profile were selected as the representative profiles to study the provenance,and other profiles were selected as the comparison profile.Based on the field observation,combined with the experimental results and analysis of particle size,end-members,quartz surface microstructure and element characteristics,the provenance of loess in the upper reaches of the Hanjiang River and Jialing River can be concluded as follows:(1)The grain size characteristics of the loess in the upper reaches of Hanjiang River and Jialing River indicate that they are all eolian loess.In the Lijiahe profile of the upper reaches of Hanjiang River,the content of silt is 81.17%,the content of sand is 6.51%,the skewness is 0.22,and the kurtosis is 1.19.In the Yangjiashan profile of the upper reaches of Jialing River,the content of silt is 76.67%and 15.11%,the skewness is 0.28 and the kurtosis is 1.36.The content of silt and sand is 84.77%and 7.98%,skewness is 0.27 and kurtosis is 1.36 in the Fanjiacheng section in the west of Liupanshan.Through the detailed comparison of grain size parameters,grain size composition and grain size natural frequency curves of the three regions,it is found that the loess in the upper reaches of Hanjiang River and Jialing River is very similar to the loess in the west of Liupanshan Mountain,and the eolian genesis of the upper reaches of Hanjiang River and Jialing River is determined by the sedimentary genesis formula.(2)The major elemental content of the loess-paleosoil in the upper reaches of Hanjiang River is basically at the same level,indicating that the provenance is stable in different periods,and the difference of elemental content is mainly caused by weathering and peeling.The variation of element content in the loess palaeosols in the upper reaches of Jialing River is slightly greater than that in the upper reaches of Hanjiang River,but it is mainly caused by the leaching of a large amount of Ca.Compared with the loess in the upper reaches of Hanjiang River,the upper reaches of Jialing River and the west of Liupan Mountain,the elemental composition of the three regions is the same,but some elemental levels are different.The main reason is that the loess in the north side of Qinling Mountains is leached by a large amount of Ca,which leads to the overall increase in the contents of other elements.(3)The loess in the upper reaches of the Hanjiang River and the Jialing River are the main components of the loess,and the loess in the upper reaches of the Hanjiang River has the same provenance as the loess in the west of the Liupanshan Mountain.Stable element ratios(Fe/Al,Ti/Al/Al,K and Mn/Al)can effectively trace to source.After comparison of the the stable elements ratio in west of Liupan Moutain region,Loess Plateau,the Qinghai-Tibet Plateau and the western desert and the Midwest desert,we found the Hanjiang River,Jialing River upstream area west of loess and Liupan Moutain loess ratio all at the same level,and the obvious difference compared with that of the Qinghai-Tibet Plateau and the loess plateau loess.Tengger Desert and the Badain Jaran Desert is a large provenance in the study area.The results of end-member analysis indicate that there is still a distant provenance area in the west of Liupan Moutain.The loess of Xining and Lintao area may be homologous through the study of element ratios,and the eastern margin of Qilian Mountain is another provenance area in Tianshui and other areas.The dust from the Tengger Desert and the provenance from the eastern margin of the Qilian Mountains were mixed in the Tianshui area and then transported to the upper reaches of the Jialing River and the Hanjiang River in the southeast direction by wind,and finally formed accumulation.(4)Near-source materials exist in the loess of the upper Hanjiang River and Jialing River.Through the study of surface structure of quartz in the upper Hanjiang River,upper Jialing River and the area west of Liupan Moutain,found three area all have different degrees of grinding,and frequent dish,small pit,the upturn joint lamina such as surface structure characteristics of the representative of the typical eolian origin,which confirms the eolian origin of the three regions of the loess.Due to large Hanjiang River upstream loess selected quartz grains,between 200?300 microns of the quartz sand surface of the v-shape pit,conchoidal fracture,straight ditch(bend)the impact surface structure characteristics of the typical representative of the water into formation,it shows that the Hanjiang River upstream of the proximal substances after the first stream,wind after handling to the terraces form accumulation.However,the surface structure characteristics of the quartz in the upper reaches of the Jialing River are mainly eolian,which indicates that the near-source materials of the loess in the upper reaches of the Jialing River are only transported and accumulated by the wind,and should be supplied by debris inattentive materials from nearby mountains.