The Characteristics Of Climate Since Late Pleistocene In Lenghu Area Of Qaidam Basin And Its Response To Global Climate Change And Uplift Of The Plateau

The formation of Qinghai-Tibet Plateau is closely connected to the patterns of global climate which has been a hotspot by international and domestic academics. Qaidam Basin is the ideal place to study the pattern of uplift and climate change, due to its special geographical location that can be directly affected by climate and environment effects caused by the plateau uplift. Minerals formed by chemical sedimentation are closely associated with the background climate conditions; pollens are useful to reconstruct the paleoclimate during the deposition. Clay minerals as the main basin sediments have been widely used in Quaternary climate reconstruction in recent years for its simple sampling. By doing an integrated reseach on Quaternary sediments chronology, mineral assemblages, pollens, magnetic susceptibility and characteristics of clay minerals, combining available data of the study area, achievements are obtained as follows:1. Basic stratigraphic sequence of lacustrine deposit in study area since 45175 cal.a BP was established through field and laboratory work. And the age of the depth from 2.5m to 44m of drilling hole 1405 was 15283.0-45175 cal.a BP by using 14C dating and difference method. The main mineral assemblages and contents in sediments of drilling hole 1405 were confirmed by using semiquantitative analysis of X-ray diffraction. Pyrophyllite and tremolite were found in Quaternary sediments for the first time. The clustering analysis showed the negative correlation between gypsum, halite, dolomite and other mineral contents, then the genetic mechanism in mineralogy of dry-cold and moist climate was suggested. Identified gypsum deposit horizonss are 0-4m,20-23m,25-27m,30-35m and 42-44m. Drilling hole 1405 were divided into three mineral assemblages via CONISS clustering:assemblage zone Ⅰ (38585～45175 cal.a BP), assemblage zone Ⅱ(18739-38585 cal.a BP), assemblage zone Ⅲ (15283～18739 cal.a BP). These three zones represent the study area experienced three climate stages of dry-cold--dry and humid alternating--dry-cold between 45175～15283 cal.a BP. Pollens were divided into three zones by using cluster analysis:1) Desert zone which was mainly strong arid in 45175-37199 cal. a BP.2) Mostly humid climate, scarcely arid in 37199-36224 cal. a BP.3) Dry and humid alternating climate in 35983-18373 cal. a BP. Semi-arid state in 35511-34547 cal. a BP. Six stages were divided according to the range of<1,1-2,2-3,>3 of frequency magnetic susceptibility. And the magnetic susceptibility in study area shows it experienced six stages containing a dry-cold-- mainly dry-cold-- dry and humid alternating-- mainly dry-cold-- mainly dry-cold-- dry-cold in 45269-13789 cal. a BP. The V (Ch+I)/V (Kao+S) ratio of clay minerals display three stages of climatic drying event in study area:1) 45000-40000 cal a BP; 2) 32000-30000 cal.a BP; 3) 25000-22000 cal a BP2. Weather events in this region show good response relationship with global climate change DO and Heinrich (H) event:strong dry-cold climate (H5) in 45175-44339 cal. a BP, strong dry-cold climate (H4) in 41552-38904 cal. a BP. dry-cold climate (H3) in 32859-31412 cal. a BP, dry-cold climate (H2, D-O) in 27885-23007 cal. a BP, strong dry-cold climate (H1) in 18739～15283 cal. a BP.3. Abnormalities are found on pollens, gypsum, magnetic susceptibility and clay minerals during 38735-38609cal.a BP. Eliminating the effect of global climate, this stage may be the result of a relatively large-scale uplift of plateau.4. Combined with previous data, paleoclimate environment in Qaidam Basin was reconstructed since 370 ka BP:1) Climate turned cold in 370.2-354.9ka.B.P which corresponded to late interglacial period before Guxiang Glaciation.2) Climate quickly changed to cold in 354.9-325.8ka.B.P and entered stage Ⅰ of Guxiang Glaciation.3) Warm and moist interglacial period in 325.8-247.7ka.B.P, and then entered stageⅡof Guxiang Glaciation.4) Warm and dry climate in 247.7-218.1ka.B.P which corresponded to interglacial period between stage Ⅱ and stageⅢof Guxiang Glaciation.5) The temperature suddenly dropped in 218.1-209.4ka.B.P which corresponded to stageⅢof Guxiang Glaciation. respectively.6) Subhumid-semiarid climate in 209.4-164.9ka.B.P and entered the last interglacial after the end of stageⅢof Guxiang Glaciation.7) Dry-cold climate in 45-40 ka B.P matched the middle part of the last glacial period and stage H4 and H5 in Heinrich events.8) Warm climate appeared in 38-32 ka B.P.9) The environment was cold in 32-30 ka B.P which corresponded to the mid-last glacial and stage H3 in Heinrich events.10) The environment was still cold in 25-22 ka BP which corresponded to the mid-last glacial and stage H2 in Heinrich events.11) The climate was humid in 21-20.3ka B.P.12) The climate was cold and dry in 20-13kaB.P and corresponded to the late last glacial and stage H1 in Heinrich events and D-O event.13) Climate was humid in 13.0-8.6kaB.P which corresponded to the Younger Dryas event (11.7a BP).14) The climate was dry-cold in 8.6-8.1kaB.P.15) The climate was humid in 8.1-2.1kaB.P.16) The climate was dry-cold in 2.1～0.0kaB.P. And there was once a wet event in 1.5 ka B.P (Fig 7-1).