A Study On Loess Sedimentation And Environmental Information Since Late Pleistocene In Area Of Hanzhong Basin, Shanxi

Abstract Hanzhong Basin is located in the north-west of China,In the basin,there is loess profile formed in Late Pleistocene .Meanwhile .Hanzhong Basin is one of the headstream of human culture.It is commonly considered that there is no Quaternary aeolian loess accumulation in the basin because of the barrier of the Qinling-Mountain on its morthern side.Based on the field investigation and laboratory analysis in this article,the Late Pleistocene sedimentary stratigraphy in the basin and environmental information are studied.(l)The results Of the studies in Area of Hanzhong Basin show that it has completely recorded the history of climatic environment information since late Pleistocene with a high resolution and clearly displayed Loess-palaeosol sequences and the related palaeomagnetic susceptibility. The results of systematic elemental geochemical analyses support the idea that the main material of Hanzhong Loess is similar to that of Loess Plateau.(2)The Megacircularity and big magnitude properties of the grain size indicate that the transportation of loess material was controlled by the long range changeable wind systems. The granulometric anylysis of the Wujiaping and Yangjiawan section show that the component particles of loess are predominantly less than 0.25mm,with the content of silt(0.05-0.01mm)over 40%.The loess granulometuic composition in the Liangshan area of Hanzhong Shaanxi is very similar to that of the Loess Plateau.(3)According to the analyses from selected profiles,we know that there are several climate changes in Late Pleistocene.The loess in the Liangshan area of Hanzhong Shaanxi is also an atmospheric dust sediment,as is the case with the loess of the Loess Plateau.It is found that during the Quaternary the dust transported by the high-altitude airflow over the Qinling Mountain moved towards the southwest and widely fell under gravity along their journey.Those dusts that fell down to the ground where erosion was weaker formed loess deposits with a continuous sequence and wide distribution.But the loess distribution is fragmentary isstrong erosion regions.The Hanzong Basin is among the Qinling Mountains and the Hanjiang river flows through it.Loess is distributed in the Hanjiang river and the stream terrace..The loess deposit is thin and some stratages are missed.