Pedogenic Features And Their Environmental Significance For The Quaternary Aeolian Sediments In Sichuan Basin And The Neighborhood

Quaternary aeolian sediments widely distributed in the Sichuan Basin and the neighborhood are important materials for studying the Asian monsoon evolution and its response to global changes.Previous investigators have focused on the genesis and provenance of aeolian sediments and the paleoclimatic reconstruction,and few discussed the pedogenic indicators and their response to the environment from the paleoeolian sediments.Exploring the characteristics of palaeo-sedimentary strata or paleosol and its response to the later environment would help to further understand the applicability of environmental indicators and provide a scientific basis for more accurate palaeoenvironment reconstruction.Moreover,the differences in weathering and pedogenic characteristics and environmental significance for Chengdu clay and its underlying clays that are brown clay and reticulated red clay need to be further understanded.In this study,the Chengdu clay and its underlying clays,loess in the upper reaches of the Minjiang River,and loess in the upper reaches of the Jialing River were selected to investigate the difference in pedogenic features between the Quaternary aeolian sediments and soils,the response of pedogenic characteristics of aeolian sediments to the current environment,and the quantitative relationship between soil-forming indexes and climate factors on aeolian sediments.The results of the study are as follows:(1)The Chengdu clay and the underlying clays have undergone strong weathering and pedogenic progress.In comparison,the reticulated red clay in the lower layer has the strongest pedogenic intensity,and the brown clay in the middle layer has weaker weathering effect.The pedogenic features of the three-layer clays indicate that a climate evolution process,i.e.,hot and humid-cold and dry-warm and humid since the Middle Pleistocene in the western Sichuan Basin.(2)The pedogenic indicators of the soils developed from the Chengdu brown clay have different degrees of response to the current environment,demonstrated by the weathered and pedogenic indicators such as magnetic susceptibility,Saf,Si O₂/Al₂O₃ and Rb/Sr are more sensitive to the environmental response,while the particle size composition,CIA,(K₂O+Na₂O)/Al₂O₃,and the characteristic values of rare earth elements are insensitivity to the current environment.(3)The pedogenic features respond to the environment of the loess in the upper reaches of Minjiang River and in the upper reaches of Jialing River are as the follows:grain size is inherited from the parent material of loess,and human activities will increase the sand content of topsoil;soil carbonate has obvious leaching phenomenon;magnetic susceptibility responds to modern environment;The element geochemical characteristics show that the modern environment has no obvious influence on the element migration for the loess in the upper reaches of the Minjiang River,while the loess in the upper reaches of the Jialing River has the phenomenon of accumulation of alkaline metal elements such as K,Na,and Ca.There is a significant increase in P₂O₅ content in the topsoil layer of the loess profile,indicating that the soil is significantly affected by modern human activities.(4)Based on the Chinese soil system classification,the types of the soils developed form the loess in the upper reaches of the Minjiang River and the upper reaches of the Jialing River were mainly classed as Primosols and Cambosols.(5)According to the fitting analysis of the relationship between the soil-forming characteristic values for the soils developed on the aeolian sediments and the climatic factors,the pedogenic indices of(K₂O+Na₂O+Ca O+Mg O)/Al₂O₃,(K₂O+Na₂O)/Al₂O₃,and CIA are significantly correlated with climatic factors,and the established empirical formula can be used to quantitatively reconstruct the palaeoclimate in the study area.