成都平原宝墩遗址中晚全新世孢粉记录的环境变迁及人类活动

ENVIRONMENTAL CHANGES AND HUMAN ACTIVITIES RECORDED BY THE POLLEN IN THE MIDDLE-LATE HOLOCENE AT BAODUN SITE,CHENGDU PLAIN

对宝墩遗址T3321剖面第9~13层(深度为150~308 cm)的53个样品进行孢粉分析,结合AMS~(14)C测年和考古断代,恢复了遗址区全新世适宜期至4300 cal.a B.P.前后的古植被及古气候演变过程。遗址区古环境演变可以划分为4个阶段:阶段1(7400~6500 cal.a B.P.)和阶段2(6500~6000 cal.a B.P.)的孢粉组合反映了以亚热带常绿落叶阔叶林为主的森林植被景观,气候较为温暖湿润;阶段2环纹藻属(Concentricystes)的出现以及大量蕨类植物的增加暗示着遗址区开始出现湖沼。阶段3(6000~4700 cal.a B.P.)主要以稀疏乔木、灌木及陆生草本为主的植被景观,本阶段后期气候由暖湿向冷干方向发展;环纹藻属比例在本阶段达到剖面最大后逐渐降低,表明遗址区水域面积大幅增加后逐渐减小。阶段4(4700~4300 cal.a B.P.)为古蜀先民在遗址生活时期,孢粉组合反映出人类活动明显增强。T3321剖面孢粉所揭示的古环境演变趋势与西南地区中晚全新世以来气候由暖湿向冷干转变的过程基本一致。阶段3和阶段4孢粉组合的变化揭示了古环境变迁与人类活动的关系,人类活动对植被变化产生深刻影响。陆生草本植物,尤其是伴人植物的增多以及湖沼面积的减少反映出人类对环境的改造作用以及农业种植活动的出现。

Baodun culture( 4500 ~ 3700 a B. P.) is the earliest archaeological culture in the Chengdu Plain. Baodun site( 30°28’53″N,103°44’53″E) is the most typical site of Baodun culture. The study of the ancient environment of the Baodun site is helpful to understand the natural environment of Chengdu Plain before the Shang and Zhou Dynasties and the environmental background of ancient Shu ancestors coming to the Baodun site. Baodun site is located in the south of Chengdu Plain. The site area is a typical alluvial proluvial stratum. In this study,the sediments of 150 ~ 308 cm profile T3321 of the site were continuously sampled at an interval of 2 cm,and a total of53 samples were collected. Based on the pollen analysis results of these samples,combined with AMSC dating and archaeological dating,this study reveals the vegetation evolution and climate characteristics in Chengdu Plain during 7400 ~ 4300 cal. a B. P. The evolution of the paleoenvironment can be divided into four stages: The pollen assemblage of stage 1( 7400 ~ 6500 cal. a B. P.) and stage 2( 6500 ~ 6000 cal. a B. P.) reflects the forest vegetation landscape dominated by subtropical evergreen deciduous broad-leaved forest,with a warm and humid climate. In stage 2,the appearance of Concentricystes and the increase of ferns suggested that the lakes and marshes began to appear in the site. In stage 3( 6000 ~ 4700 cal. a B. P.) ,the vegetation landscape mainly consisted of sparse trees,shrubs,and terrestrial herbs,and the climate changed from warm and wet to cool and dry in the later stage. At this stage,the proportion of Concentricystes reached the maximum and then gradually decreased,indicating that the water area of the site increased significantly and then gradually decreased. Stage 4( 4700 ~ 4300 cal. a B. P.) is the stable life period of the ancient Shu people in the site. The pollen assemblage reflects that the climate is becoming drier and human activities are enhanced. The pollen of profile T3321 recorded obvious climate cooling events before and after 6000 cal. a B. P. The evolution trend of the paleoenvironment revealed by it is consistent with the process of climate change from warm and wet to cold and dry in Southwest China since the Middle and Late Holocene. The changes of pollen assemblages in the third and fourth stages reveal the relationship between paleoenvironmental changes and human activities,which have a profound impact on vegetation changes. The increase of terrestrial herbaceous plants,especially companion plants,and the decrease of the lake area reflect the emergence of agricultural planting activities and the utilization and transformation of the microenvironment of the site by the ancients.