Early Pleistocene(1.45?1.291.45?1.29Ma) Environmental Evolution And Huminin Activities In Nihewan Basin

The Early Pleistocene was an important period of global climate change and also an important stage in the emergence and evolution of hominins.Hence,there is much research interest in determining the climatic and environmental context of Early Pleistocene hominin sites in order to explore the relationship between climate change and human evolution.In this paper,a total of 213 pollen and charcoal samples and213 grain size samples were obtained from the MJG-1B artefact layer of Majuangou Site to the Banshan Site(1.452?1.290 Ma)in Nihewan Basin.Based on principal component analysis(PCA)and Biomization method,the characteristics of paleo-environmental changes with high-resolution during this period in Nihewan Basin were revealed.This paper analyzed the environmental characteristics of the period of hominin occupation,compared the difference between artefact layers and natural layers,and tried to explore the relationship between hominin activities and environmental change.The results were shown as following:(1)During the Early Pleistocene(1.452?1.290 Ma),the climate and vegetation in nihewan Basin changed frequently and experienced eight stages.During the period of1.452?1.425 Ma,the climate was characterized by semi-warm and semi-humid,and the vegetation was forest steppe or forest dominated by Pinus.During 1.425?1.379 Ma,the climate changed from cool dry to semi-warm dry,and the vegetation was steppe or forest steppe dominated by Artemisia,Chenopodiaceae and Poaceae.During1.379?1.370 Ma,the climate was cold and humid,and the vegetation was mainly Picea forest.During 1.37?1.34 Ma,the climate was semi-warm and dry,and the vegetation was mainly steppe or forest steppe dominated by Artemisia,Chenopodiaceae and Poaceae.During 1.34?1.33 Ma,the climate was cold and humid,and the vegetation was mainly Picea forest.During 1.330?1.323 Ma,the climate was cool and dry,and the vegetation was mainly dominated by Artemisia,Chenopodiaceae.During 1.323?1.310 Ma,the climate was warm and semi-humid,and the vegetation was mainly Pinus forest,but there was a certain area of grassland.From 1.31?1.29 Ma,the climate changed to cool and dry again,and the vegetation was mainly dominated by Artemisia,Chenopodiaceae,with a small amount of broad-leaved trees and shrubs.(2)The Majanggou 1B artefact layer(1.45 Ma)and banshan artefact layer(1.32Ma)have some similarities in environmental characteristics during the period of hominin occupation.The climate is relatively warm,the concentration of charcoal and pollen is higher than that of other natural layers,and the sedimentary facies is lakeshore with shallow water.However,the pollen content of Pinus was basically the same as that of Artemisia,Chenopodiaceae and Poaceae during hominin occupation in MJG-1B artefact layer.The vegetation was forest steppe and the sedimentary environment was shallow lake swamp;During the hominin occupation in the Banshan site,the content of Pinus pollen was higher than that in MJG-1B artefact layer,but there was a certain amount of herb pollen(about 20%),indicating that the regional vegetation was a forest environment dominated by Pinus,but there was a certain area of grassland.Hominin activitied at the lakeshore,local vegetation openness should be higher.In the charcoal composition of Banshan site,the content of medium and coarse particles is more than 40%,indicated hominins' ability to deal with fire.(3)The disappearance of the artefact layers were also closely related to environmental changes.After the disappearance of the BS artefact layer,the pollen composition did not change significantly,but the grain size became significantly finer,and the sedimentary facies changed from lakeside facies to typical lacustrine facies,indicated that the disappearance of artefact layer is closely related to the expansion of lake;After the disappearance of MJG-1B artefact layer,the sedimentary facies changed slightly,but the pollen composition changed significantly.The pollen content of Pinus,Picea and other trees increased significantly and occupied a dominant position(more than 80%),indicating that the climate became wet and the water level at the site increased.It can be seen that the expansion of forest vegetation and climate humidification are important factors restricting ancient human activities and life here.