Study On Carbonate Mineral Content And Paleoenvironment In The Loess Plateau Of Fengxiang,Baoji

Monsoon rainfall affects human production,life and survival in East Asia,etc.In the future,the accurate monsoon rainfall forecast under the background of global warming can avoid disasters and reduce losses.However,there are still differences in reflecting the evolution of East Asian summer winds,leading to the evolution of different time scales and the driving mechanism cognition is still in controversy.The study of long interglacial summer wind changes and their driving mechanism similar to the future can better understand the monsoon dynamics and provide parameters and constraints for the prediction model of East Asian monsoon rainfall in the background of future global warming.Under the special climate background of the special loess-ancient soil sedimentary sequence formation between the Quaternary glaciation and the alternation of winter wind and summer wind,the strongly weathered ancient soil during the interglaciation recorded the information of summer wind and rainfall in mainland East Asia.The core obtained by the loess drilling in the Fengxiang Loess Plateau area of Baoji,on the basis of the materials,the determination of the carbonate content and susceptibility was discussed.The following conclusions are obtained:(1)Due to the controversy over the chronology framework established by the comparison of geomagnetic polar columns taking into account the gravity magnetization of the strata during the previous research on magnetic stratigraphy,the paleomagnetic results of boreholes were re-readed to obtain new epoch results.The paper holds that the thick positive polar zone of loess is a normal magnetization phenomenon,mainly due to the accumulation of regional differences of wind and dust due to topographic factors.The magnetic polar column and the international standard polar column obtained from the experimental research are compared again,the paleomagnetic age frame of borehole is redefined,and the high resolution age scale is established by linear interpolation of magnetic stratigraphy.The age of the bottom boundary of loess section is determined to be ma.?1.78(2)Using the new age scale,the magnetic susceptibility curves of the borehole are compared with those of Baoji,Lingtai and Xifeng sections.The results are consistent and confirm the reliability of the paleomagnetic results.On the basis of the field lithology observation and description,combined with the results of Lingtai and Baoji magnetic susceptibility age strata,the loess paleosol stratification results were adjusted to rearrange and divide the loess strata to make them more reasonable and in line with the reality.(3)Comparative analysis of carbonate mineral content and magnetic susceptibility and chromaticity climate index in Fengxiang loess paleosol in Baoji reveals the change process of East Asian summer monsoon since 1.78 ma.Each climate index responds to the fluctuation of East Asian monsoon glacial-interglacial period and records the gradual enhancement of interglacial summer monsoon.