Study On The Holocene Soil And Environment In The Middle And South Loess Plateau

Study on the Holocene environmental change occupies the important status of studying on global change. The Holocene period is the last stage of Human history. In resent years, Study on the Holocene Environmental Change of Pedogenensis has become focus and focal points. So the author selects the relationship between the Holocene environmental change and the pedological process as the topic of the thesis.Two Holocene loess profiles have been found in the middle and south Loess Plateau. They expose fresh steep bank. And they can be observed that the sediments of the Holocene loess are continuous and thus they reflect the environmental change since the Holocene. On the basis of outdoor observation and indoor experimental analysis, the author selects proxy substitute indexes, such as grain-size, magnetic susceptibility, soil micromorphology, CaC03 and pH value, etc. Through the comparison study of these climatic substitute indexes, the thesis reveals the process of the change of climatic environment in Holocene in the middle and south Loess Plateau. Finally, the thesis investigates the relationship between the Holocene environmental change and the pedological process.This thesis draws the following conclusion:(1) Two layers of soil (S01 and S02) in the Middle Holocene were formed in Luochuan region. S02 should be typical cinnamon soil. The annual pre -cipitation reached about 700mm. The annual temperature reached about 13 ℃. S01 should be carbonate cinnamon soil. The annual precipitation reached about 600mm. The annual temperature reached about 11℃.(2) Two layers of soil (S01 and S02) in the Middle Holocene were formed in Lintong region. They should be subtropical yellow cinnamon soil. The annual precipitation reached about 750mm. The annual temperature reached about 15℃. In the Middle Holocene, two sides of the Qinling Mountains bothwere subtropical climate, and the Qinling Mountains had lost the function as the boundary between temperate zone and subtropical zone.(3) Dust storms in Loess period were much stronger than in paleosol period. In the Holocene, about 7 extraordinary dust storms in the Loess (Lo) have happened, but only 1 extraordinary dust storm in each layer of soil. Dust storms must have been impacted by the orbital factors, and by other unorbital and paroxysmal factors on the scale of hundred to thousand.(4) 11500~8500a B. P., Summer monsoon was stronger and winter monsoon weaker. Therefore, temperature went higher gradually and precipitation got more, dust-storms weakened, pedological process was becoming strong slowly. There were flood sediments in the layer in the later period.(5) 8500~6000a B. P., Summer monsoon reached its maximum, pedological process was the strongest, dust-storms nearly didn't happen. Precipitati -on increased remarkably, so was temperature. 6000~5000a B. P., This is a period of climatic deterioration. Summer monsoon was weaker and winter monsoon stronger. Precipitation and temperature decreased mostly, and eolian dust deposition was accelerated. Dust storms became stronger. Pedological process weakened obviously. 5000~3100a B. P. , Summer monsoon was stronger and winter monsoon was weaker. Temperature raised and precipitation increased. Dust storms weakened, and pedological process was becoming strong.(6) Since 3100a B. P., In this period, climate deteriorated again. Summer monsoon was weaker and winter was stronger. A layer of Loess has been accumulated since then. Dust storms were the strongest.