Study on the Magnetic Susceptibility of the Xiashu Loess and the Paleoenvironment Changes in the Middle and Lower Changjiang River
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摘要: 通过对镇江大港剖面地层结构和磁化率曲线特征的分析研究,以及与相邻地区风尘堆积研究成果的比较,认为长江中下游地区磁化率曲线的波动旋回很好的对应了黄土 -古土壤风尘堆积序列,记录着该区中更新世以来七次大的古气候冷暖旋回。古气候的旋回变化幅度较北方黄土区要小得多,冷期和暖期都存在着频繁的小尺度的气候冷暖波动,可与深海氧同位素曲线相比较 但各地下蜀黄土沉积速率和沉积环境有一定的差异。Abstract: The stufy of loess-paleosol sequence reveals the magnetic susceptibility is of indexical significance in identifying loess-paleosol and their progression in the loess section,but also in simulating the changes of paleoenvironment.The magnetic susceptibility is also of indexical significance to Xiashu loess.Therefore,we gathered 595 sample blocks for the study in Zhenjiang Dagang section,which is located in the lower reaches of the Changjiang River. On the basis of systematic testing,we obtain a magnetic susceptibility curve of Dagang section.Compared with the other Xiashu Loess sections in this area,the magnetic suscreptibility curve of Xiashu Loess indicates that the loess-paleosol sequence of Dagang section represented 7 large climatic cycles since the Middle-Pleistocene.It is similar to that disclosed from the other Xiashu sections and the loess-paleosol sequence in north China,reflecting that the middle and lower Changjiang River regions have undergone the same course of the paleoclimate changes in the north China since the Middle-Pleistocene.Comparative study also demonstrates that the extent of the paleoclimate changes is much smaller than that in the loess area in north China.There are frequently minor undulations of climate in both the warm period and the cold period,comparable to the δ18O stage of deep sea.The study also found the sedimentation rate and the depositional environment of Xiashu Loess varied in different area in the middle and lower Changjiang River region. The study of the magnetic susceptibility curve indicates there were a small quantites of aeolian accumulation in the interglacial warm period. S1 and S2 in the magnetic susceptibility curve of Dagang section can be divided into S1a, S1b, S1c and S2a, S2b, S2c respectively. S1a, S1b and S1c of S1 correspond to 5a,5b and 5c of the δ18O stage of deep sea,supporting that the climate changes of the middle and lower Changjian River region are largely affected by the ocean. Climate changes of the middle and lower Changjiang River region are quite sensitive to global changes.
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