Holocene Paleomagnetic Secular Variation Recorded By Lacustrine Sediments From The Eastern Part Of Inner Mongolia

Paleomagnetic secular variation?PSV?can provide information on the mechanisms of the geodynamo,which is useful to understand the physical processes the geomagnetic field and the Earth's interior,especially the fluid dynamics of the core-mantle boundary.In addition,high resolution PSV curve also can be used to correlate sedimentary stratigraphy correlations,as well as to establish the time frame of sedimentary sequences.In this study,we carried out detailed paleomagnetic and rock-magnetic studies on the three lacustrine sections including Daihai Lake?SG?,Huangqihai Lake?EWD?and Dali lake?BY?in the eastern part of Inner Mongolia,and established their PSV curves.The main results were drawn as follows:?1?.Magnetic susceptibility anisotropy?AMS?results confirm that the maximum(K_max)and minimum(K_min)inclinations of the AMS axes are nearly horizontal and vertical,respectively.The plot of magnetic foliation?F?versus lineation?L?reveals that most of the specimens have oblate AMS ellipsoids.These results show that the studied lake sediments still preserve the primary sedimentary fabric.?2?.Isothermal remanent magnetization?IRM?curves and thermomagnetic analyses suggest that the predominant magnetic carrier is magnetite in most samples,and that hematite is also included in some samples.The Day-plots indicate that the magnetic mineralogy is dominated by pseudo-single domain?PSD?magnetic grains.These results support that the studied lacustrine sediments are suitable for the PSV study.?3?.Stepwise alternating demagnetization shows that a stable magnetization component decaying toward to the origin can be isolated between 20 and 100mT for most samples.Combined with the age of ¹⁴C,we established the PSV curves of these three sections.The PSV curve of the SG section records three main inclination peaks and three declination eastward-swings;the PSV curve of the EWD section exhibits two major inclination peaks and two major declination eastward-swings;the PSV curve of the BY section shows three major inclination peaks and four major declination eastward-swings.These three PSV records show similar patterns with other East Asian PSV curves,supporting that they are reliable and should reflect the PSV characteristic of East Asia.