Climate Changes In The Central And Western Of Guangxi Since The Early Pleistocene And Its Influence On Early Human Activities

It is well known that global warming has become a climate warming trend.However,the question how long the trend will last has drawn much attention of both the scientists and the public.Understanding the patterns of climate change in the past is an effective way to predict the future.As we humans emerged in the Quaternary,the study of the change of East Asian monsoon since the Early Pleistocene will help us understand current climate change and predict future climate trends better.In a large number of studies,various paleoclimate proxies which are gathered from geological archives such as loess-paleosol sequences,marine and lacustrine sediments and stalagmites have been used to investigate the climate change and the East Asian monsoon evolution since the Early Pleistocene.Nevertheless,the mentioned research is mainly concentrated in the North China region.The strong weathering in the South China region makes it difficult for us to have further understanding of the East Asian monsoon,especially the high-resolution climate reconstruction.Three Pleistocene cave sites(i.e.,the early Pleistocene Mohui Cave,the Middle Pleistocene Ganxian Cave,and the Late Pleistocene Luna Cave)in the Bubing Basin in western Guangxi and the Holocene Shichuantou shell mound site in the Nanning Basin in the central area were selected as the research objects in this thesis.The three cavies were analyzed for clay minerals,geochemical,and biomarkers;The age of the Holocene shell mound site was determined by AMS¹⁴C;The chemical weathering intensity was indicated using clay minerals,iron minerals,major chemical elements,trace elements and biomarkers in soil sediments.By integrated analysis of high-resolution paleoclimate proxies,the evolution of East Asian monsoon in Holocene was discussed,and the results are as follow:1.During the Early Pleistocene Olduvai period,the Mohui Cave experienced three stages of climate change:hot—relatively cold—humid;During the Middle Pleistocene Jiaramilo period,the 190cm in the Ganxian Cave sedimentary profile served as a leap-type point which divided the climate into two cycles in which the weathering intensity varied from strong to weak;The Luna Cave in the late Pleistocene exhibited the climate change from hot and humid to relatively dry and cold.2.Multiple paleoclimate proxies of the Holocene shell mound site in the Nanning Basin presented three stages of climate and vegetation change:Stage I(?10482±82 cal yr BP—7902±57 cal yr BP),the chemical weathering and pedogenesis became intensity.It could be confirmed by the increasing of the values of CIA,CPA,CIW, PIA,as well as the ratios between easily soluble elements K,Rb,and Ba and stable elements Na and Sr.The herbaceous vegetation was predominant,followed by aquatic vegetation.In the second stage(7902±57 cal yr BP—3295±80 cal yr BP), the aquatic vegetation decreased rapidly and woody plants presented predominance instead.The temperature dropped to dry and cold and the content of illite and goethite had relatively increased.The chemical and microbial weathering were weakened.In the third stage(3295±80 cal yr BP—?952±27 cal yr BP),the alternation of wetting and drying promoted the formation of kaolinite and hematite which increased the relative content in clay and iron minerals relatively.The proportion of woody vegetation is relatively stable,while the aquatic plants showed an opposite variation with herbaceous vegetation which flourished under the changeable environment.The results were consistent with the high-resolution research in other geological archives(e.g.,Donggedong stalagmite in Guizhou)in the East Asian monsoon region.The Holocene Shichuantou profile made a good record of two weak monsoon events,indicating that the East Asian summer monsoon generally had a synchronous trend on the orbital scale.3.Comparing the species and positions of fossils in the section,we found the Lufengpithecus disappeared at the same time the Hystrix Magra emerged while the temperature cooled down.The Macaca and the Ailuropoda Microtia existed through almost an entire sedimentary section but disappeared in the environment dominated by woody vegetation.It could be inferred that species that were largely affected by vegetation distribution and climate changes,such as the Lufengpithecus, extincted in the subsequent fauna evolution,and the living species these days showed extreme adaptability.4.The fossils of Homo erectus and the Homo sapiens discovered in the early Pleistocene Mohui Cave and the Late Pleistocene Luna Cave relatively supported the view that the caves in the Bubing Basin had been used as living places for the ancient human.With a large number of Holocene shell mound sites found by Yongjiang River,the change of the Pleistocene human's habitat in Guangxi that was from caves to coastal areas can be inferred.The evident influences of Holocene climate changes to the survival ways of ancient humans were roughly discussed by reconstructing the climate and vegetation changes together with the excavated stone tools and animal bones at the Shichuantou shell mound site in the Nanning Basin.It could be inferred that early humans relied more on natural plant and animal resources.The variation of the use of three ways of obtaining living resources(i.e.,hunting,catching,hunting and fishing)implied that the climate environment had main effect in ancient human lifestyles.5.Connecting the discoveries in cave sites and shell mound sites,there were several reasons why the activities of animals and ancient human changed from the Pleistocene to the Holocene:First of all,the riverbank environment could supply richer resources of food than the cave environment;Secondly,compared with the Pleistocene,the Holocene climate is more suitable for ancient human habitation. Moreover,Holocene Megathermal arrived after the New Dryas event which was more beneficial to vegetation distribution and animal reproduction,therefore ancient human could acquire more abundant food;Thirdly,the living skills of ancient human had an obvious development.It could be confirmed from the simple stone tools for hunting to the equipment to catching aquatic animals and to gaining water as well as the use of fire.