Magnetic Properties Of Borehole Sediments In Fuzhou Basin And Their Response To Holocene Environmental Changes

In this paper the experimental results show that the dominant magnetic minerals in sediments of the ferrimagnetic minerals(magnetite or maghemite),also contains a small amount of hard magnetic minerals,and the sediment is mainly affected by the magnetic strength(MD)effect of concentration of magnetic mineral particles,but in different stages of affected factors have difference.By comparing the LC borehole magnetic susceptibility curve and the ignition loss curve with the adjacent borehole(FZ4),it is found that the borehole sedimentary facies can be divided into three parts,(1)Before the transgression(>9000cal yr BP),The values of magnetic susceptibility and magnetic mineral concentration was the lowest,the climate is dry and cold,less precipitation,oxidation may occur,The magnetic minerals are oxidized to hematite at low temperature and further oxidized to hematite.The magnetic susceptibility of terrigenous clastic materials decreases in provenance,The concentration of magnetic minerals is low(2)In the period of transgression(~9000-2000cal yr BP),the magnetic susceptibility is relatively high,and the ignition loss is also at a high position,and the concentration of magnetic minerals is high.At this point,the climate is warm and humid,and the precipitation is increasing and the magnetic susceptibility decreases from the bottom to the top of the borehole,and also responds to the Holocene climate fluctuations;(3)Regression(~2000cal yr BP):The magnetic susceptibility increases rapidly.At this time,human activities increase,a large number of vegetation destroyed by human,resulting in bare surface,erosion increased,providing a large number of clastic materials,the deposition rate are also increased,resulting in increased concentration of magnetic minerals.The clay layer of representative samples of rare earth elements and the experimental results of loess in Loess Plateau area and the upper crust(UCC)REE distribution pattern comparison analysis that the distribution patterns are similar,are rich in LREE,Eu moderate negative anomalies,and the silt layer of rare earth elements in the large amount of clay layers,indicating the changes sedimentary environment.From the size of the experimental results,mainly through the grain size distribution curve and the probability of different sedimentary facies in a representative sample of the cumulative curve analysis,the first layer of clay grain size distribution curve and the loess plateau loess distribution is similar to that of the cumulative probability curves of overall roughly single type,suspension components accounted for more than 95%,combined with the distribution patterns of rare earth elements that cause and genesis of loess in Loess Plateau is similar,the distribution pattern of the silt layer size distribution curve of loess is large,mainly concentrated in the range of 10?m,fine grain size,showed that the effect of silt layer is different and the power handling of loess,the cumulative probability curves in multi section.Second layers of clay particle size distribution curve"Double peak",further observation can be found,the size and shape of the Loess peak distribution pattern of particle size distribution on the left side of the similar peak shape and the silt layer on the right side of the similar layer shows that the clay layer is affected by two different handling power,from the probability cumulative curve,suspension components the proportion is about 80%,saltation components accounted for about 20%,also showedthat the effect of the clay sediments by two different power handling.