Late Pliocene Palynological Records On Vegetation And Climate Changes In The Taiergou Profile, Nihewan Basin

The past is a key to open the future.Studying the past climate change rule has always been a key issue in the world.It can better predict the future and benefit human activities.The Nihewan basin contains thick lacustrine sediments from late Pliocene to late Pleistocene,and it an extremely valuable book for human to explore nature.So it is a perfect distrct to study the vegetation and climate changes from late Pliocene to late Pleistocene.The Taiergou profile in Nihewan basin was selected as the study area.Through the pollen analysis of 136samples,we explored and revealed the characteristics of vegetation and climate change in the study area in the late pliocene.According to the existing paleomagnetic and stratigraphic contrast,the age of the sampling strata is from 2.92 to 2.56Ma.The results showed that the vegetation in the study area was controlled by woody plant pollen,and the vegetation landscape was mainly forest vegetation in whole area.From whole profile,the vegetation through 3 stages,in the first stage,vegetation was dominated by spruce coniferous forest,in the second stage,it was dominated by deciduous broad-leaved forest?mainly Betula,Quercus,Ulmus?,in the third stage,it was dominated by coniferous forests?mainly Pinus,Pinus?.Corresponding to vegetation change,the climate experienced several stages?cold and moist,warm and moist,wet and cool,warm and cool alternative change,cool and dry?.But in different periods,there are significant differences in vegetation and climate change.According to the pollen assemblage,the total is divided into 6 bands and subbands.Brand1 is 3.3 to 3.06Ma,which is mainly controlled by picea,and its content is much higher than 50%.It is speculated that there exists a certain area of spruce forest,and the climate is cold and humid.Brand2 is 3.06 to 2.852Ma,and it was divided into two subbands.The subband1 is 3.06 to 2.96Ma,the picea content below 5%,pinus pollen content increased sharply?more than 30%?,and Betula pollen content is 10²0%,some subtropical elements,such as evergreen oak and pecan also appear,that reflect the vegetation was dominated by dominated deciduous broad-leaved forest?mainly Betula?,and the climate is warm and moist.The period is best in whole study stage.Subband2 is 22.96 to 2.852,the pinus pollen content remained at about 20%,and Betula reducted,but the Ulmus increased,with the content is 20⁴0%,the vegetation was mainly controlled by deciduous broad-leaved forest,?mainly is Pinus,Ulmus?,the climate is more dry than before.The brand3 is 2.852 to 2.56Ma,and it was divided into three subbrands.The subbrand1 is 2.852 to 2.82Ma,the pinus and ulmus is still dominant species,and herbaceous plants also have certain content,the climate is more warm and humid than before,and the vegetation is mainly controlled by deciduous broad-leaved forest.The subbrand is 2.82 to 2.644Ma,the Pinus is also increased largely,with the content is more than 55%,and the pollen concentration reached the peck.Affected by the alternative change of Pinus and Picea,the climate also appear the alternative change in cool and warm,but the trend of climate is cool than before.The vegetation is controlled by coniferous forest?Pinus and Picea?.The subbrand is 2.644 to 2.56Ma,the Pinus is the dominant species,and the Artemisia and Chenopodiaceae also increased largely,with the majority is more than 30%.The main vegetation is coniferous forest,but it has a trend toward the grassland environment,which indicates that the climate becomes more cool and dry in this period.On the basis of pollen assemblage,Taiwan profile in the late Pliocene experienced two obvious cold period?3.3 to 3.06Ma,2.852 to 2.56Ma?.The cool climate at 3.3Ma is affected likely by the events of Mammoth reverse polarity.The cool climate at 2.82Ma is affected likely by more factors,such as CO₂ concentration,tectonic movement,the expansion of land-ice in northern hemisphere.And the coldest stage is respond with MISG10,G2,102 and104 in the deep sea oxygen isotope,also is consistent with the Northwest Pacific sea temperatures of the same period.2.82Ma cold climate is a regional,but whether it has a global characteristic,that need to be further studied.The cool climate in 2.64Ma is global.