Study On Human Activities And Its Environmental Adaptation In The Source Region Of The Yangtze-Lancang River During The Prehistoric Times

The Tibetan Plateau accounts for the highest and most harsh environment in the world.Therefore,the ability and mechanism of human adaptation to the extreme environment on the plateau have become a key research topic in the international academic community.As a typical area of high altitude and cold temperatures on the Tibetan Plateau,the Yangtze-Lancang River source area is located in the hinterland of the plateau.The study of prehistoric human activities in the area is a way to learn about the history and adaptation process of early human occupation to the harsh environment of the plateau hinterland,which has a special and important scientific significance.In recent years,with continuous research,important breakthroughs have been made in the study of ancient human adaptations to the harsh environmental conditions of the Tibetan Plateau.However,there are still deficiencies in the following aspects:1)Majority of the studies are mainly focused in the Hehuang Valley,Qinghai Lake-Gonghe Basin and Qilian Mountains areas,while there are dearth of field investigations and studies in the Yangtze-Lancang River source area,resulting in an unclear understanding of the chronological sequence of ancient human activities,vague understanding of their mode of livelihood and environmental background in the region.2)Research on prehistoric humans'survival strategies in hypoxic environments at high altitudes is weak,especially in the Yangtze-Lancang River source area,where the average altitude is above 4000 m.3)Lack of a comprehensive and integrated exploration of the connections between different cultural eras and regions within the Tibetan Plateau and the exterior(Loess Plateau,Yunnan-Guizhou Plateau,Tarim Basin,etc.)of the plateau on a larger spatial scale.Based on the above questions,this paper collected 269 various kinds of stone artifacts from 41 sites recently discovered in the source area of the Yangtze-Lancang River 462 fragments of pottery,3 loess paleosol sections were selected in the study area(since the Tangda and Wene profiles are subject to significant natural or anthropogenic effects,the Zhongda profile,which is stable in deposition and has a good chronological sequence,was selected as the main object of study)and 2exploration methods,16 OSL dating samples,4 AMC¹⁴C dating samples,and 289environmental samples were collected as research carriers,using field investigation,AMS¹⁴C dating,OSL dating,granularity,magnetic susceptibility,charcoal,fungal spores,pollen,chromaticity,pottery analysis and stone artifacts types,analyzed time duration of the prehistoric human activities,mode of livelihood,site natural environmental background,and the study preliminarily reveals the coupling relationship between prehistoric human activities and environmental evolution in the study area.On this basis,relevant data from other regions of the northeastern Tibetan Plateau(Hehuang Valley and Qinghai Lake-Gonghe Basin)were consolidated and analyzed using archaeological integration methods to explore the differences in modes of livelihood(adaptation strategies)and the influencing factors in different altitude regions during the same period.The main conclusions are listed below:(1)Based on the typology of the stone tool,the stone artifacts found in Tangda,Xiege,Bangbunan Locality 1,Bangbunan Locality 3,Bangbunan Locality 4,Tongtianhe Locality 1,Tongtianhe Locality 2,Tongtianhe Locality 3,Tongtianhe Locality 4,Tongtianhe Locality 10,Tongtianhe Locality 11,Zengfuqu Locality 1,Dongkouria,Zhongda and fourth terraces of Bangbu and Bangbudong are all beaten stone tools based on core-and-flake lithic industrial technology,by comprehensively comparing the core-and-flake lithic industrial technology in the same period,it is determined that the age range is at least the end of the Late Pleistocene(40?30 ka BP),which is the earliest human activity time determined in this study.The total concentration of charcoal reached its peak during the period of 12.5?10.0 ka from the Late Pleistocene to the Early Holocene,indicating that there may have been strong human activities at this stage.According to the analysis of stone artifact typology,the age of the microlithic products found in the third terraces of Bangbu and Bangbudong is roughly the same as that of Xidatan 2,Yeniugou,and Tshem gzhung kha thog,indicating that human activities also existed in this area in the Middle Holocene.However,the overall low concentration of charcoal at this stage indicates that human activities in the main stream valley of the Tongtian River are weak.It is speculated that strong human activities may occur in the main stream and tributary basins of the Tongtian River at higher altitudes.The concentration of charcoal and fungal spores as well as pottery shreds increased gradually in the mid-late Holocene(6.0?4.0 ka BP),indicating a growth in human activities.The concentration of charcoal and fungal spores increased further in the Late Holocene(4.0?2.0 ka BP),indicating a high intensity of human activities and which may have continued to historical times(the pottery sherds of this stage are found in the area).In summary,humans were active in the Yangtze-Lancang River source area from the late Pleistocene until historical times.(2)The results of multi-environmental proxies such as granularity,magnetization rate,pollen,and chromaticity show that the median and average granularity fluctuated greatly during the Last Glacial Maximum(19.0?17.0 ka),and the content of sand grains>63?m,sorting coefficients,and L*and a*values were all high,while the content of mucilage grains<4?m and low magnetization rate,indicated that the sedimentary environment in the canyon was unstable,with strong wind and sand activities,poor sediment sorting,low organic matter accumulation,low biological production,and weak soil formation and low precipitation.However,the development of coniferous forests dominated by spruce indicates that the river valley was probably a“biological refuge”for spruce,and the climate was relatively cold and wet.The median and mean grain size,content of fractions>63?m,sorting coefficient,and L*and a*values all decreased during the Last Deglaciation period(17.0?10.7 ka),while the content of fractions<4?m and magnetization rate increased significantly,reflecting a more stable depositional environment,weak wind and sand activities,better sediment sorting,better organic matter accumulation,higher biological production,strong soil formation,and increased precipitation.The vegetation is mainly alpine grassland,and the climate is better than in the previous stage,but the overall tendency is dry and cold.In the Early-mid Holocene(10.7?6.0 ka),the median and mean grain size,>63?m fraction content,sorting coefficient,and magnetization rate increased compared with the previous stage,while the<4?m fraction content and L*and a*values decreased significantly compared with the previous stage,indicating an unstable depositional environment,strong wind and sand activities,and poor sediment sorting,but precipitation,organic matter accumulation,and biological production further increased and developed paleosols.This indicates that the regional climate has changed significantly,but the overall climate is still warm and humid.In the Mid-late Holocene(6.0?2.0 ka),the median and mean grain size of>63?m fraction content and magnetization rate had all reached high values,while the<4?m fraction content,sorting coefficient,and L*and a*values hit their lowest values,indicating unstable depositional conditions,more frequent wind and sand activities,poor soil formation,but abundant precipitation,better sediment sorting,accumulation of organic matter,and high vegetation cover,mainly alpine meadow,and a cool to wet-dry climate.(3)Based on the indications of multi proxies and regional archaeological evidence,we found that the warm and humid climate at the end of the Late Pleistocene prompted the ancestors to engage in hunting and gathering activities in the study area,and it is assumed that the hunting objects were large and medium-sized mammals.The climate shift from the Last Deglacial to the Early-Mid Holocene prompted humans to further explore the region and adapt to this relatively harsh environment with scarce flora and fauna by adopting transient,high-mobility migratory strategies for hunting small and medium-sized mammals.In the late-mid Holocene,with the proliferation of millet farming and the emergence of a livestock economy,the area formed a hunter-gatherer economy,supplemented by livestock and millet farming.The gradual diversified pattern of production contributed to the ancestors'adaptability to adverse climate conditions and the possible realization of the perennial occupation on the plateau.In the Late Holocene,due to the introduction of western hardy wheat farming and development of the livestock economy,a mixed agro-pastoral economic system with livestock-hunting-wheat farm-millet farm co-existed in the region.This rich and diversified mode of livelihood has,to a certain extent,enhanced the ability of human beings to adapt to or cope with adverse climatic conditions,and the lifelihood gradually changed to nomadic pastoralism.(4)Comparing the mode of livelihood(adaptation strategies)of the Yangtze-Lancang River source area(?4000 m)with those of the Hehuang Valley(1600?3000m)and the Qinghai Lake-Gonghe Basin(2600?3500 m),it was found that:From the end of the Late Pleistocene to the early-mid Holocene,the ancestors of different altitude regions were engaged in hunting and gathering activities with the strategy of frequent seasonal migration,relying only on hunting and gathering to achieve the initial adaptation to different altitude regions.In the mid-late Holocene,millet agriculture was the main mode of subsistence in the low altitude region,while hunter-gatherers dominated in the high altitude region.In the Late Holocene,an economy based on wheat farming,animal husbandry,and hunting activities was formed at different altitudes,and this mixed economy of subsistence contributed to the full adaptation of the ancestors to the plateau.(5)Different cultures in the northeastern Tibetan Plateau adapted to the environment of different altitudes of the plateau by adopting the same or different strategies of production,while production tools and technological innovations(e.g.,stone tool technology),climate change,development of millet agriculture,cultural exchanges between East and West(introduction of wheat crops and domestic cattle and sheep),and geographical factors were the main factors that influenced the differences in livelihood modes(adaptation strategies)at different altitudes.