| Chinese loess research plays a very important role in Quaternary paleoclimate research.It records detailed paleoclimate information and is of great significance for studying paleoenvironmental changes.It has always been one of the hotspots in the field of geosciences.The loess-paleosol sequence study on the Loess Plateau has made brilliant achievements in recent decades.However,due to the different regional locations of the loess section,there are still many differences in the geomagnetic polarity reversal position,sediment source and regional climate response..Therefore,it is necessary to conduct further in-depth research in the Loess Plateau.The basis for conducting research on paleoenvironment is to obtain high-resolution chronograph scales.The study of magnetic stratigraphy is an important means of chronological work of the Quaternary long-scale loess-paleosol sequence.This article mainly relies on the National Geological Survey of Shaanxi Province,“1:5 million Caobi Town,two pavilions,Zhaoxian,Qianyang,Fengxiang,Yaojiagou six loess covered areas mapping project” project,in Baoji Fengxiang loess The core obtained by the loess drilling in the reclamation area is the research material.The high-precision paleomagnetic research work on the loess-paleosol stratum is combined with the paleomagnetic results of the typical section of the Loess Plateau.The following conclusions are drawn:(1)After the study,it is considered that the thick positive strip of the loess section belongs to the phenomenon of heavy magnetization.The reason is mainly that the lithology is loose,and the lithology description shows that there is sand in the fine sand.After the mud immersion,the direction of the magnetic mineral changes and then Positive polarity band in the direction of modern geomagnetic field;(2)Combining the demagnetization of long core with the thermal demagnetization data of separated samples,the high-precision paleomagnetic polar column of Baoji Fengxiang borehole loess layer is obtained and compared with the international standard polar column(Gradstein et al 2012).Combined with the magnetic susceptibility data of the typical loess section,the specific age of the magnetic core transition event of the borehole core is obtained.Based on this,a linear scale interpolation method is used to establish a scale with a resolution of 5 cm since the 2.58 Ma of the loess section.(3)The B/M limit of the borehole is roughly at the bottom of L8,that is,about 46 m,which corresponds to the deep sea oxygen isotope MIS20.The range of the Jaramillo event is roughly around 62-65m;the range of the Olduvai event is roughly 110-115 m.Nearby,the M/G limit is at the bottom of L33.(4)According to the magnetic susceptibility curve,the loess-paleosol layer is divided and compared with the deep sea oxygen isotope,showing a good correlation.The magnetic susceptibility value of 2.58~1.7Ma is low at the whole,indicating that the climate is cold and dry,mainly Controlled by the winter monsoon;the amplitude of the 1.7-0.8Ma peak trough is relatively large,and the frequency of change is also relatively high.It can be seen that the intensity of the winter-summer wind is increased compared with the previous one,and the variation range is larger and the period is shorter.Since 0.8Ma,the variation of the magnetic susceptibility curve is also relatively large,and the intensity of change and the period of change are also relatively large.(5)This study provides a high-resolution chronological basis for the paleoenvironment of the Weihe River and the Qianhe terrace and the neotectonic movement of the study area. |
PDF Full Text Request