Vegetation And Climate Change On The Southeast Chinese Loess Plateau During The Early To Middle-Pleistocene And Implications For Hominin Occupation

From“the savannah hypothesis”to“the pulsed climate variability hypothesis”and“paleoclimate-variability transitions possibly related to human evolution”,not only can the exploration of ancient human origins,evolution and the relationship between humans and climate changes satisfy natural curiosity but also provides better guidance for people to live in harmony with nature in the context of global climate change.From the excavation of the first Australopithecus afarensis skeleton fossils of“Lucy”in the Hadar region of Ethiopia to the spread of Asherian technologies around the world along with the migration of Homo erectus,palaeontological fossils and stone tools are the most direct materials to reconstruct the past three-million-year history of the hominins.However,the scarcity of ancient human fossils and the movement of lithic artefacts after being buried have largely hindered related scientific research.The discontinuity of terrestrial sedimentary and the variability of local climate changes have also prevented researchers from clarifying the relationship between climate changes and the evolution of the early human.The largely continuous artefact sequence at Shangchen indicates hominin occupation since at least about 2.12 Ma,forcing a re-think of links between ancestral humans and environmental conditions on the Chinese Loess Plateau（CLP）.The artifacts sequence in situ,the deposition of continuous loess-paleosol strata,the many surrounding sites and the fossil faunas are uniquely placed to explore many scientific questions.Based on evidence from loess deposits at and around Shangchen that cover the period from the onset of hominin occupation at the site,including magnetic susceptibility,total organic carbon content and its carbon isotopes,black carbon content and its carbon isotopes,and branched glycerol dialkyl glycerol tetraether（br-GDGTs）,four distinct vegetation-climate periods are recognized（2.1-1.8 Ma,1.8-1.3 Ma,1.3-0.9 Ma and 0.9-0.6 Ma）.Faunal remains and artefacts during each period also show distinct characteristics.During the period 2.1-1.8 Ma,the climate was dry and cold,with a relative high proportion of C₄ vegetation of arid species.A total of12 stone tools were found in three loess layers（L25,L27 and L28）at Shangchen,while only seven stone tools were found in two paleosol layers（S26 and S27）between 2.1 Ma and 1.8 Ma.The occurrence of artefacts,albeit in low numbers,dating to long glacial periods at Shangchen is revealing,as it suggests a continuation of occupation by early hominins throughout the relatively long,cold glacial periods.From 1.8 Ma to 1.3Ma,the periodicity of glacial-interglacial cycles is much shorter,and stone tools show a different distribution among interglacial and glacial periods,with eight artefact-bearing paleosol layers（70 artefacts in all）,and a much lower count for loess deposits(only two stone tools in total in loess layers L17 and L21.In addition,the Gongwangling fauna experienced concentrated extinction and burial at this stage.Therefore,it is inferred that ancient humans tended to be more active in the Shangchen area during the relatively warm and humid interglacial periods,but decreased activities in the study area during the dry and cold glacial periods.There remains the possibility that it reflects the challenges faced by early hominins in adapting to rapidly changing climate conditions,and the associated availability of food,water and shelter,across the interglacial-glacial transition.These challenges could have continued from 1.3 Ma to 0.9 Ma,a period at Shangchen when climate varied greatly between interglacial and glacial conditions and that have yielded only a single stone artefact（from S15）.Several animal taxa that had a more southerly distribution,such as Ailuropoda melanoleuca fovealis,Stegodon orientalis,Elaphodus cephalophus,appeared among the faunal remains recovered from the Gongwangling site along with a Homo erectus cranium（1.62-1.63 Ma）.However,these faunal remains have yet to be discovered between 1.3 Ma and 0.9 Ma.The change in fauna from taxa associated with areas well to the south of the study area to those more closely associated with temperate areas to the north,was likely driven by climate cooling and aridification during the Mid-Pleistocene climate transition（MPT）.By comparison,a total of 20 artefacts have been recovered from the site between 0.9 Ma and0.6 Ma,together with a Homo erectus mandible（～0.65 Ma）.According to the evidence presented,major oscillations in climate conditions related to MPT and an expansion of C₄ herbaceous vegetation from about 1.3 Ma may have forced abandonment of the Shangchen site in favor of more hospitable locations in the region.Large-scale variations in local climate conditions on glacial-interglacial timescales and their effects may have exerted a strong influence on hominin occupation in central China during the Early and Middle-Pleistocene.The differences in vegetation,topography and rivers between Duanjiapo and Shangchen sections,which are only separated by Bahe River,are also compared.And the reasons why the areas around Lishan Mountains were more favoured by ancient humans than the Baluyuan Loess Plateau areas are discussed in terms of shade,shelter and water sources.In summary,this paper reconstructs the relationship between ancient humans,vegetation and climate changes at the southeastern edge of the Chinese Loess Plateau from 2.1-0.6 Ma,taking into account vegetation types,topography,local climate changes and the distribution of stone artefacts and faunal fossils and supposes that big climate shifts and increasing climate variability have an influence on the occupation of the early human.