Palynological Assemblages And Quantitative Reconstruction Of Paleoclimate In Ningxia Plain Since Quaternary

Vegetation is extremely sensitive to the changes of climate elements(etc.temperature,rainfall,humid and so on),there is great indicative significance for forecasting future climate change by using spore and pollen stored in strata.The Ningxia Plain is selected as the research area in this paper,through the analysis of modern pollen assemblage,the modern pollen in surface soil and fossil pollen in stratum are compared,which provides the basis for restoring the climate change of Quaternary.Based on 93 sporopollen samples of surface soil in Ningxia plain and its adjacent areas,and climate elements of 42 meteorological stations from 1981 to 2011,the particle size and pollen assemblage of borehole LS01 in Ningxia were analyzed by means of photoluminescence,ESR and paleomagnetism,and the paleovegetation and Paleoclimate in the Quaternary period of Ningxia Plain were reconstructed quantitatively.First of all,the age strata of the borehole are determined by means of photoluminescence,paleomagnetism and ESR dating.The bottom of quaternary or early Pleistocene is defined at the depth of 205 m,and the bottom of Middle Pleistocene is located at the depth of 152 m.The bottom of Lower Pleistocene is set at the depth of 205m;The bottom of late Pleistocene is defined at the depth of 60 m,The top of late Pleistocene is defined at the depth of 4.3m.There is no Holocene sediments due to human disturbance.According to the changes of sporopollen assemblage and their percentages in the sediments of borehole LS01,8 sporopollen assemblage zones were divided by combining with the paleo annual mean temperature and annual precipitation quantitatively restored by WAPLS model,and the change of sedimentary environment reconstructed by particle size.These 8 zones can reveal the evolution stage of Quaternary climate environment in Ningxia Plain,which can be depicted as follows: before Quaternary,Coniferous forest shrub steppe zone had cold and dry climate,indicates that they are mainly beach deposits;2580-1970.5ka B.P.,coniferous forest steppe zone,had cold and dry climate,indicates that they are mainly fluvial deposit;1970.5-781 ka B.P.,coniferous broadleaved mixed forest shrub steppe zone had cool and wet climate,indicates fluvial deposition;781-538.4ka B.P.,coniferous forest desert steppe zone had mild and dry climate,indicates the sedimentary environment is flood plain facies;538.4-303.8 Ka B.P.,coniferous broad-leaved mixed forest mountain steppe zone had warm and humid climate,indicates fluvial sedimentary environment;303.8-126 ka B.P.,coniferous forest desert steppe zone had warm and dry climate,indicates flood plain facies deposition;126ka-83.3ka B.P.,coniferous broad-leaved mixed forest shrub steppe zone had warm and humid climate,indicates flood plain facies deposition.By comparing LS01 borehole with previous studies in Ningxia Plain,we can better reveal the characteristics of paleoclimate and environmental evolution in Ningxia plain.