Physical-chemical Characteristics And Genesis Of Topsoil In The Indus River Basin

Ancient India and China are both the oldest ancient civilizations in the world.The ancient Chinese civilization is widely believed to have been born in the Yellow River Basin of the Yellow River.However,little is known about the existence of Quaternary aeolian loess in the Indus basin.Studies of Indus Valley loess have only been reported in the northern mountains,and the southern plains have long been thought to have been formed by alluvial deposits carried by the Indus River.We examined the Indus River valley and plains from Islamabad to Karachi,as well as the edge of the Thar Desert,and found that Quaternary aeolian loess is widely distributed in the Indus River plain.The main research purposes are as follows:(1)To explore the genesis of topsoil in the plains of the Indus River Basin;(2)summarizing the magnetic characteristics of the topsoil in the study area,and distinguishing the applicability of magnetic parameters as the climate substitution index in the area;(3)To explore the potential relationship between loess and the development of ancient Indian civilization.The results show that the magnetic minerals in the Indus basin representative samples are consistent with Chinese loess,which are dominated by magnetite and magnetic hematite and may contain hematite;The particle size composition is also highly similar to that of Chinese loess,especially the frequency distribution curve of plain topsoil is bimodal negative skew asymmetric distribution,the cumulative probability curve is single segment,and the grain size index and grain size discrimination formula show the similar characteristics of Chinese loess.the elemental geochemical results show that the rare earth element distribution pattern of the samples shows light rare earth enrichment,heavy rare earth deficit,and moderate negative anomaly in Eu which was basically consistent with the variation trend of typical aeolian loess;The major elements are dominated by Si O₂,Al₂O₃,Ca O and Fe₂O₃.In addition,The Indus Basin topsoil has typical aeolian loess characteristics such as homogeneous texture,loose and porous,which is quite different from the fluvial sediments,Therefore,we believe that Aeolian Loess is widely distributed in the Indus Valley.Thermomagnetic curves and hysteresis loop of typical samples in the study area is dominated by magnetite and contains a small amount of magnetic hematite.Combined with the diffuse reflectance spectroscopy analysis,it can be confirmed that the samples also contain acanthite and a small amount of hematite,which are basically consistent with Chinese loess.The room temperature magnetic parameters show that the SP particles formed after topsoil deposition have little sub ferromagnetic mineral content,which indicates that the soil formation is not strong.The magnetic mineral grain size is mainly coarse-grained stable single-domain(SSD),pseudo-single-domain(PSD)and multi-domain(MD),and the magnetic particles of the dune topsoil at the edge of the desert are coarser and dominated by native PSD and MD.Unlike the Loess Plateau of China,the magnetic properties of Indus Valley topsoil are more influenced by the native magnetic minerals.The correlation between the magnetic susceptibility and precipitation in the study area is poor.It is considered that the effective precipitation in this place swings near the critical value of the magnetic susceptibility curve(Idealized schematic of the relationship between magnetization rate and effective precipitation),so it is difficult to determine the specific relationship between the effective precipitation and the magnetic susceptibility of this place.Therefore,the plain topsoil magnetic susceptibility is not suitable to be used as a substitute indicator of the climate in the study area.The Indus River basin is widely distributed with aeolian loess,and the area of loess distribution overlaps highly with modern agricultural land,which may suggest that ancient Indian civilization was also nurtured and developed on this loess land.The Indus River basin may be similar to the Yellow River basin in China,where the loess promoted the rapid development of agriculture during the primitive agricultural stage with low productivity,thus forming an important driving force for the development of ancient Indian civilization.