Study On The High-resolution Sequence Of Vegetation Change During The Last Glacial Recorded In The Loess Of Xishan Moutain Of Beijing Area

In recent years, the loess studies on the loess-palaeosol sequence has obtained many achievements that have attracted the attention of the world, but it mainly relies on the indirect physical and chemical proxies. But the pollen studies the opposite less, and the study district primarily distribute over the loess plateau region. For this, we selected Dongzhaitang profile in the Zhaitang Basin of Xishan Mountain, Beijing area from which the Malan Loess got its name and study the sequence of vegetation change recorded in the Malan Loess of Xishan Mountain by means of spore-pollen analysis. By the sample selection and dating at smaller intervals, increases the resolution of pollen sequence; and by the methods which was improved by the Mingjian Wei, proceeds the laboratory analysis of the sample, to guarantee the dependability of the experiment data. A known amount of Lycopodium spores was added to each sample to calculate the concentration of pollen, and regenerate the sequences of vegetation in last glacial at Xishan Mountain Beijing aera, adding the data of dating, discuss the characteristic of the palaeoenvironment evolvement.The result reveals that the characteristics of the environment evolvement which was reflected by the pollen sequence of the Xishan Mountain Beijing aera, has the good consistency with the other region of our country, but has its own characteristics. Different ages in the last glacial epoch in Xishan Mountain,Beijing area, the pollen that loess contained, all regard herbs pollen as principle. The pollens of Artemisia,Chenopodiaceae which lived in dry environment were overwhelming parts of the herbal pollens. And the concentration of arboreal and shrubby pollens is very low and mainly are pinus and betula which reflects the palaeoclimate loess formation are dry and cold. But the category and quantity of the pollen in palaeosol are more abundant than in loess which reflects the palaeoclimate palaeosol formation are opposite better. There is three times obviously cold period in the sequence which correspond with MIS4, the middle of MIS3 and MIS2; And two obviously warm period MIS3c, MIS3a. Through the meticulous analysis, the density of the pollen in earlier and later stage is still very low, and the category is monotonous, illuminating the range of temperature declined distinguishly at that time, estimate the temperature lower at least 8-9C than now, and the amount of water declined more than 200-300mm, the natural environment is very bad, may be an periglacial weather. In earlier and later cold period, the range of the temperature decline is almost equal, but the natural environment condition of later cold period is worse than the earlier. The weather condition of the two warm period in Malan loess are preferable, particularly the condition of early warm period is already near to the modern weather environment. The pattern of evolvement and the degree of vegetation has much distnict with the High Temperature and Large Precipitation Event dming MIS3, so it can be deduced that the high temperature and large precipitation event recognized in the Tibet Plateau could not occurred in Xishan Mountain Beijing aera or the influences were very weak. In addition, the sequences of vegetation in MIS3 at Xishan Mountain Beijing aera showed a series of fluctuation, explaining the environment conditional of MIS3 isunsteady. There is five times rapid decline in pollen density in the sequences of vegetation in last glacial at Xishan Mountain Beijing aera, exsit five stage of pollen density sharply decline, particularly is the arboreal and shrubby pollens, and the pollen is monotonous, the herbs pollen occupies the advantage absolutely, representing there is five worse period in term in five weathers, can be see as to make the record that the affairs of Heinrich, equal to H1- H5.