Studies On The Wild Fire And The Pedogenical Environment Changes Of Holocene In The Middle Reaches Of The Jinghe River

Loess plateau is a district that has sensitive response to the global changes. The objects of this paper are the Changwu ETC section and the XHC section in the middle reaches of the Jinghe River of the middle loess plateau. The developments of the two sections are continuous, integrate, typical and representative. We collected the samples from the sections every two centimeters from the top to the bottom, there are 185 samples of the ETC section and 135 samples of the XHC section. We carried out the analysis of the magnetic susceptibility of the samples and distilled the charcoal from the stratum and combined with the archaeology data and history literature to study the relationship between the environment changes and the human activities of Holocene in the middle reaches of the Jinghe River. Through the study, the main results of the paper is as follows:1. (-11500 a B.P.) In the last ice age, the climate is cold and arid, the vegetable is scarce, and the pedogenesis is weak, the humidity of the soil is low. The deposition of the dust is distinct. In the early period of the Holocene (11500-8500 a B.P.), the climate changed from cold and arid to warm and humid but the main characteristic is cold and arid. The temperature and precipitation increased. The dust storm distinctly decreased, the pedogenesis reinforced, the vegetable began to recover. From the last ice age to the early period of Holocene, the climate changed from cold and arid to warm and humid. In the Holocene Megathermal (8500-3100 a B.P.), the annual average temperature is 1-3 ℃ higher than that of today, the annual average precipitation is 50-150mm higher than that of today, the pedogenesis is strong. The climate is warm and humid, the summer monsoon is the strongest and the precipitation distinctly increased, the vegetable is flourish, the dust storm seldom occurred and the dust seldom piled up. The efflorescence of creatures and the pedogenesis is very strong. In the late period of Holocene (3100-0 a B.P.), which is represented by the Lo and Ts, the monsoon changed, the climate is arid. With the enhancing of the human activities, the degeneration of the water and soil is evident.2. (-11500 a B.P.) Aridity is one of the reasons of the occurrence of the wild fire.