河北阳原侯家窑遗址孢粉组合特征及揭示的古环境与古气候演变

PALEOENVIRONMENT AND PALEOCLIMATE CHANGES OF HOUJIAYAO SITE IN YANGYUAN COUNTY,HEBEI PROVINCE BASED ON POLLEN ANALYSIS

结合前人测年资料和本研究孢粉分析结果表明遗址形成于晚更新世,依据花粉组合变化将其划分为6个带:带Ⅰ,以喜冷的针叶树等乔木花粉为主,表明遗址附近为针阔混交林,此带还出土喜冷的披毛犀等动物化石,都表明气候寒冷而湿润;带Ⅱ,乔木花粉减少,草本植物花粉明显增加,遗址附近演变为森林草原植被,气候温暖而干燥;带Ⅲ,乔木花粉骤升,仍以松和云杉属花粉为主,表现为针阔混交林植被,气候寒冷而潮湿,此带为侯家窑遗址文化层(侯家窑人生活时期),光释光测年表明文化层中上部时代为60000～70000aB.P.,时值大理冰期前期,喜冷的披毛犀等动物化石也证明冷期的到来;带Ⅳ,针叶树花粉减少,温带落叶阔叶树花粉增加,草本植物花粉显增,表明遗址附近植被演变为以温带落叶阔叶树为主的森林草原植被,气候温暖而潮湿;带V,松属花粉增加,云杉属花粉减少,草本植物花粉略减,遗址附近为以松属植被为主的森林草原植被,气候变得寒冷而干燥;带Ⅵ,松属花粉减少,榆属和白蜡属花粉略增,草本植物花粉微增,遗址附近发展为草原植被,气候变得温暖而湿润。孢粉分析显示从孢粉带Ⅳ开始,遗址附近的气候由之前的冷湿与暖干的交替演变成之后的冷干与暖湿的交替。侯家窑古人类生存时正值大理冰期,气候寒冷,遗址附近的植被为针阔混交林,周围存在静水湖沼环境,适宜的自然环境是各种动物生存的理想场所。在生产力低下,食物较短缺的旧石器时代,与严寒相比,侯家窑人选择了充足食物来源的湖滨地区。

Houjiayao Site （40°06′2.26″N, 113°58′42.50″E）, located on the right bank of the upstream of the Liyigou, a small tributary of the Sanggan River that passes through Yangyuan City, Hebei Province, is on the northwest of Nihewan Basin . Since it was found in 1974,this site has been playing a very important role in the study of the Paleolithic and the process of human evolution. 86 samples were taken from upper section of 13 meters in thickness from natural soilprofile there, The lithology of the profiles consists of different clay or soil layers, showing the feature of fluviolacustrine sedimentary environment. Pollen analysis shows six different stages as described below. According to the pollen and mammal fossils, the bottom of this soil profile was formed between 80 ~ 90ka B. P. and the upper part was formed between 30 - 40ka B. P. belonging to the MIS 3. Ⅰ. The pollen assemblages were dominated by conifer, such as Pinus and Picea, indicating that the paleovegetation was mainly mixed conifer-broadleaves forest. The climate was cold and humid at that time. The fossils of Coelodonta antiquitatis Blumenbach suggest the existence of the ice age. Ⅱ. The percentage of conifer poller was reduced and the percentage of shurbs was markedly increased. The main vegetation type was forest steppe and the climate was warm and dry. Ⅲ. The conifer pollen was remarkably increased, such as Pinus and Picea. Without doubt,it was a typical time for the mixed conifer-broadleaves forest vegetation cover with a cold and humid climate in the period of Dali Glacial （beginning from 60 -70ka B. P. ）, which was also the time of the Houjiayao human activity as was confirmed by OSL Dating, The fossils of mammalian faunas were also found in this layer, especially Coelodonta antiquitatis Blumenbach,Palaeoloxodon cf. naumanni, Bos primigenius, and so on proving the existence of the ice age. Ⅳ. Afterwards, conifer pollen was reduced obviously, broad-leaves and shurbs were increased fast. Those indicate that the vegetation had changed to a forest steppe dominated by broad-leaves forests. A warm and humid climate could be inferred. Ⅴ. Though the pollen of Picea was diminished, Pinus was increased. At that time, the pollen of herbs was increased. The vegetation was forest steppe dominated by Pinus and the climate became cold and dry. Ⅵ. The pollen assemblages changed again： Pinus was gradually reduced but the herbs was increased a little. The vegetation changed to grass land step by step. There was a remarkable climatic turnaround from cold-wet and warm-dry to cold-dry and a warm-wet one after the pollen stage Ⅳ. The ancient residents of Houjiayao human lived in the Dali Glacial period with cold climate, but there was a mixed conifer-broadleaves forest and a stable water resource around the site. The feasible natural environment was suitable not only for animals to live but also for human beings to capture food. The ancient Houjiayao residents had to develop the experiences for adapting to cold weather because food is more important in cold climates,especially in the Paleolithic period with low productivity.