THE PALAEOENVIRONMENTAL AND PALAEOCLIMATIC RECONSTRUCTION AND THE RELATION WITH THE HUMAN ACTIVITIES DURING THE EARLY AND MIDDLE HOLOCENE IN THE UPPER WESTERN LIAO RIVER REGION
西辽河上游地区位于东亚夏季风边缘,生态环境对气候变化敏感,自全新世以来发育了小河西、兴隆洼、赵宝沟、红山、夏家店等诸多文化,是研究全新世以来人地关系的理想场所。本文通过对科尔沁沙地西南缘其甘湖钻孔的孢粉分析,结合AMS~(14)C测年,恢复了全新世早中期的古植被和古环境,并利用加权平均偏最小二乘法(Weighted Averaging Partial Least Squares Regression,简称WAPLS),定量重建了该地区全新世早中期最冷月和最热月均温、年降雨量,结合文化背景探讨了人地关系变化过程。结果表明,12090~11040cal.a B.P.,其甘湖周围为草原植被,以蒿属(Artemisia)、藜科(Chenopodiaceae)为主,附近分布有桦属(Betula)和云杉属(Picea)为主的林地,反映较凉湿的气候;11040~8590cal. a B.P.,山地林地中桦属成分略有减少,榆属(Ulmus)和云杉属成分升高,反映气候开始转暖;8590~8030cal.a B.P.,木本植物花粉与草本植物花粉的比值(AP/NAP)升高,此阶段气候持续变暖;8030~6950cal.a B.P.,花粉组合以木本植物花粉为主,阔叶树类型成分增加,尤其是栎属(Quercus)、椴属(Tilia)以及胡桃属(Juglans)均出现峰值,反映气候温暖湿润;6950~6720cal.a B.P.,藜科和松属(Pinus)花粉显著增加,花粉组合异常变化可能反映沉积环境的突变。气候定量重建结果显示西辽河上游地区进入全新世之前环境凉湿,进入全新世之后,早期温度快速升高,降水增加幅度缓慢,8500cal.a B.P.前后降水开始快速增加并持续到7350Cal.a B.P.。小河西文化时期年降水量平均值480mm,最热月均温20.9℃,最冷月均温-16.6℃;兴隆洼文化时期年降水量平均值550mm,最热月均温21.5℃最冷月均温-15.0℃;赵宝沟文化时期年降水量平均值440mm,最热月均温21.5℃,最冷月均温-15.3℃。虽然兴隆洼文化时期温度比现代低,但高于之前的小河西文化和之后的赵宝沟文化时期,而且降水丰富,年降水量平均值比现代高约140~190mm,温湿的环境可能孕育了西辽河上游地区繁盛的兴隆洼文化。
英文摘要:
There have been developed various cultures known as Xiaohexi Culture, Xinglongwa Culture, Zhaobaogou Culture, Hongshan Culture, and Xiajiadian Culture in the upper Western Liao River region. The upper Western Liao River region locates on the edge of East Asia summer monsoon and is sensitive to the climatic and environmental change. To study the relation between the human activities and climatic change in the Holocene in this region is appealing. Qiganhu Lake (42°54'N, 119°18'E; 600m a.s.l.) lies on the upper Western Liao River region and on the southwest of Horqin Sandy Land. In the year of 2008,one core with 356cm length was taken from the center of Qiganhu Lake. By every 2cm interval the core was cut into 178 samples in the field. Some samples on the bottom were contaminated by the sediment from upper parts. Therefore, totally 145 samples of 308cm from the top of the core were taken for pollen analysis. There 57 types of pollen, belong to 45 families, were identified. According to the AMS~(14)C dating, the age of the core from Qiganhu Lake covered between 12090cal.a B.P. and 6720cal.a B.P. Based on palynological data of core sediments from Qiganhu Lake, the palaeovegetation and palaeoenvironment during the Early and Middle Holocene in upper Western Liao River region were reconstructed. Using weighted averaging partial least squares regression method (WAPLS),the annual precipitation (PANN), the mean temperature in the warmest month (MTWA) and the mean temperature in the coldest month (MTCO) were quantified. Finally, the relation between the human activities and environmental change was discussed combining the culture development. The results showed that steppe dominated by Artemisia and Chenopodiaceae covered this region between 12090cal.a B.P. and 11040cal.a B.P. The mixed forests consisted of broad-leaves deciduous Be tula and coniferous Picea were distributed on the hills. During this period the region presented cool and wet environment. During 11040~8590cal.a B.P., the vegetation was still steppe. The arboreal Ulmus and Picea increased while Betula decreased, which indicated that the climate started warming up. During 8590~ 8030cal.a B.P., the ratio of arboreal pollen grains and non-arboreal pollen grains (AP/NAP) increased, which illustrated the continual climatic up-warming. The arboreal pollen dominated during 8030~6950cal.a B.P. Besides Betula and Ulmus, other broad-leaves elements such as Quercus, Tilia and Juglans increased.