The Desertification Evolution Reflected By Grain-size And Magnatic Susceptibility In Maqu Plateau Since Middle-late Holocene

Maqu plateau is located in the east of Qing-Tibetan Plateau. Due to the influence of the plateau climate and the eastern monsoon, widely existing eolian sediments and completely saving the loess-paleosol-antique into sand sedimentary sequence. Maqu plateau is the loess plateau and qinghai-tibet plateau transition zone, so it is sensitive to climate change. Ma qu plateau modern desertification is on the basis of the geological history a renovation of the ancient sand process, In this paper, we select OL profile and MO profile as the research object which are the typical loess-paleosol-antique into sand sedimentary sequence in the eastern Maqu plateau, based on high-resolution sampling and the 14 C age determination, discussed Maqu plateau since Middle-late holocene sandstorm activities, through be compared and analyzed the two profile of sedimentary facies, magnetic susceptibility, organic matter, grain size and its parameters as climate proxies to reconstruct sandstorm activities since Middle-late Holocene in Maqu plateau, and discusses the regular of Maqu plateau response to climate change, the main experimental conclusions are as follows:(1) Climate change always follows “person strong wind-temperature humidity weak wind” pattern changes in Maqu plateau since Middle-late Holocene. We have known that Maqu plateau climate change having synchronicity and northeast qinghai-tibet plateau and global change during Middle-late Holocene by the comparison analysis.(2) Sandstorm activities of Maqu plateau since Middle-late Holocene has experienced the following four stages: cold and arid, the winter monsoon strength is increased, strong sandstorm activities and desertification degree was enhanced before 4.6ka B.P, warm and humid, compared with the former period, sandstorm activities degree becomes relatively weak during 4.6~4.3ka B.P., cold/arid and warm/humid, summer monsoon is stronger, sandstorm activities is weak, desertification degree is very weak during 4.3~0.3ka B.P., We can also said that the climate environment of Maqu plateau had experienced cold-dry- warm-humid- cool- cool-dry since Middle-late Holocene. The third period can be divided into three small stage, the first stage is 4.3~3.6 ka B.P., from the cool to the humid climate transition,sandstorm activities from strong to weak, has developed the weaker paleosol., the second stage is 3.6~3.5 ka B.P., the climate is cool, compared with the first stage, sandstorm activities is relatively strong,thicker loess deposited.the third stage is 3.5~0.3 ka B.P., the climate is warm and humid, summer monsoon is stronger, and andstorm activities weaker, developed the thicker paleosol.(3) The climic temperature humidity in the ancient soil development period and the climic cold in aeolian sand development period, but the loess deposition period by humid climate transition to cold.(4) Climate environment of Maqu plateau had experienced cold-dry-warm-humid-cool-dry since Middle-late Holocene and sandstorm activities also has experienced the evolution of the strong and the weak- strong.Climate proxies reflects that 11 larger cold events happened in Maqu plateau during Middle-late Holocene in 3.57 ka B.P., 3.47 ka B.P., 2.90 ka B.P., 2.50 ka B.P., 2.03 ka B.P., 1.84 ka B.P., 1.57 ka B.P., 1.30 ka B.P., 0.98 ka B.P., 0.80 ka B.P. and 0.62 ka B.P.. Cold event which in 1.57 ka B.P. is consistent with dry climate and strong sandstorm activities between Qinghai Lake in 3.5 ka B.P.. Cold event in 3.47 ka B.P., 2.90 ka B.P., 2.50 ka B.P. is consistent with strong sandstorm activities occurred in Qinghai Lake surrounding areas in 3.37 ka B.P., 2.96 ka B.P., 2.49 ka B.P.. Cold events in 2.96 ka B.P. also correspond with the cold events in the north Atlantic in 3.0 ka B.P. Cool climate in 1.57 ka B.P. has a good corresponding with the cold and dry climate adjacent to qinghai grassland area in 1.5 ka B.P.. Cold events in 1.30 ka B.P., 0.80 ka B.P. and 0.62 ka B.P. are consistent with the cold stage of Gonghe basin which in the northeast of qinghai-tibet plateau at about 1.40 ka B.P., 0.8~0.5 ka B.P. has obvious consistentency.