The Vegetation Evovement And Climate Change Characteristic During The Penultimate Interglacial Of Luochuan

Polar Ice-Core, Deep Sea Deposit, Loess are good carriers of the Past Global Changes (PAGES), which contain respectively the global environment changes information of the polar region , ocean , land (where the mankind lived) . In recent years , loess studies on loess–palaeosol sequence have obtained many achievements that attracted attention of the world , Luochuan loess plateau preserves a model of loess landscape. Its section is clear and the stratum is entire. It recorded important geological events and information of paleoclimate, paleoenvironment and palaeontology since Quaternary truly.We choose the paleosol of S2 stratum being located in the Heimugou section in Luochuan area as an object of study. We rebuild paleovegetation and paleoenvironment by sporopollen data,and then conclude the discipline of climate evolvement;at the meanwhile, the grain size and magnetic susceptibility are acquired to indicate the discipline of the winter and summer monsoon and the discipline of paleoclimate evolvement in dry and semi-dry zone in S2 stage.Through comparing the discipline of paleoclimate evolvement indicated by different indicators, the way of sporopollen to recover paleoclimation is accuracy. The global tendency and regional characteristic of palaeoclimate change were received through comparing the paleovegetation and paleoclimate among Luochuan and other places profile during the Penultimate interglacial.The conclusion:(1)There were three stages in Luochuan during the Penultimate interglacial:The first stage which was from 243.31 to 233.37ka B.P corresponded with pollen-stripⅠwhich included Artemisia,Chenopodiaceae,Humulus,Betulaceae and Rosaceae indicated the forest-grass climate; The second stage which was from 233.37 to 215.84kaB.P corresponded with pollen-stripⅡ1-7 which included Chenopodiaceae,Artemisia,Betulaceae and Ulmaceae indicated the temperate grass climate,and from 223.2 to 218.7kaB.P ,the concentration of pollen-stripⅡ4 increased which indicated brief Savanna or meadowgrass climate; The third stage which was from 215.84 to 188.76kaB.P corresponded with pollen-stripⅢ1-4 which included Betulaceae,Juglandaceae,Pinaceae,Humulus and Gramineae indicated the deciduous broad-leaved forest climate.(2)The results revealed that pollen beltⅠ,Ⅱ1-3,Ⅱ4,Ⅱ5-7,Ⅲ1-4,which were from lower to upper or older to younger, could couple respectively MIS 7e,7d,7c,7b,7a and the chronozone were 243.3-233.4kaB.P,233.4-221.2KaB.P.,221.2 -218.9KaB.P.,218.9-205.7KaB.P.,205.7-188.8KaB.P..The vegetation types changed from forest-grass,dry grass, Savanna or meadowgrass,dry grass to deciduous broad-leaved forest.Though the pollen data indicated the temperature and precipitation reached the higher value during the Penultimate interglacial, the vegetation in Luochuan was grass in the most time,only in the most moist heat, deciduous broad-leaved forest appeared.(3)Through comparing the data, the climate characteristic in Luochuan put up the global tendency there are differences:2-1,S2-2 and S2-3 which respectively corresponded with MIS7a,MIS7b-7d and MIS7e,and the calefacient event during 221.24-218.88kaB.P corresponded with MIS7c. The magnetic susceptibility in different profiles of the Loess plateau indicated that the climate change was coincident ,but it were different from the east littoral profile and MIS7.Maybe it was affected by the summer monsoon which has different effect in diverse locations of monsoon-triangle.(4)When the time went into the Penultimate interglacial,the grain <2μm reached the peak value firstly,and then the concentration of pollen and magnetic susceptibility increased fastly and reached the peak value respectively. The summer monsoon changed characteristic indicated by grain size and magnetic susceptibility was synchronous,there are about 1.6-5.0ka lag.The pollen data can indicated the event corresponded with MIS7c which cannot showed by magnetic susceptibility,so The pollen are more sensitive to respond climate and coincident with MIS7 better,the reason maybe the vegetation display directly the temperature and precipitation,and the magnetic susceptibility indicate the soil degree which is the indirect indicator affected by precipitation and source of dust.