长江三峡地区全新世环境演变及其古文化响应

依据长江三峡地区大九湖和玉溪剖面AMS14C测年数据(校正为日历年)建立了约9.3～2ka BP高分辨率多环境代用指标(δ13C、K、腐殖化度、抱粉总浓度、Rb、Sr及Rb/Sr)的变化曲线,并在此基础上与研究区周边反映全新世气候环境变化的不同沉积记录进行综合对比分析.与此同时,本文还通过对研究区古遗址和古洪水层的统计分析,获取了本区新石器以来古文化兴衰变迁和古洪水发生的完整信息.研究结果表明:(1)本区全新世大暖期约出现在7.6～4 ka BP.9.3～7.6 ka BP,本区气候极不稳定,波动幅度大,总体上冷湿,多次出现显著的降温或干旱事件(9.1、8.2和7.7 ka BP前后);4～2 ka BP,本区气候较此前偏干凉,且波动频繁.(2)7.6～ka BP的大暖期分为三个演变阶段:即6～5 ka BP为大暖期的鼎盛期,气候稳定,温暖湿润,植被及生态条件优越,洪水发生频率低;7.6～6 ka BP和5～4 ka BP为大暖期中具有不稳定特征的过渡期,其中5～4 ka BP及4 ka BP前后的降温事件仍较显著,且多发洪水.(3)本区史前古文化的主要形成发展期与大暖期持续阶段相对应,其中耕作业相对发达的大溪文化繁荣期出现在大暖期中的鼎盛阶段(约6～5 ka BP),大溪文化前后处于低潮及表现为衰退现象的古文化则对应气候环境的不稳定期,总体上,研究区古文化响应气候环境变化的主要方式是通过改变其生业结构的途径来实现的.

Climatic and Environmental Changes as well as Ancient Culture Response in the Yangtze Gorges Region

Yuxi and Dajiuhu profiles in the Three Gorges Region are chosen in this study, and based upon AMS14C dating (calibrated CY), we establish the high-resolution curves of various proxy indicators (δ~(13)C, K, humification coefficient, total concentration of spore-pollen, Rb, Sr and Rb/Sr) during 9.3-2 kaBP. Besides we synthetically compare and analyze the records of climatic and environmental changes in Holocene sediments in the surrounding areas, we also obtain the materials of prosperity, decline and transition of ancient culture as well as the flood information from the Neolithic Age to historical periods by making statistical analysis of archaeological sites and paleoflood layers of the study area. The results show that: (1) Megatherma in Holocene appeared during 7.6-4 kaBP in the Three Gorges Region. During 9.3-7.6 kaBP, the climate in the study area was very unstable, drastically fluctuating, wet-cold in general, occurring cold or arid events more than once (approximately 9.1, 8.2 and 7.7 kaBP). During 4-2 kaBP, the climatic fluctuation was frequent, and trending slightly cold-dry than before. (2) The Megatherma during 7.6-4 kaBP can be divided into three stages: namely 1) the stage of 6-5 kaBP was the prime of Megatherma, when the climate was stable, warm-wet, with predominent vegetation and ecological environment as well as low frequency of flood events; 2) the stages of 7.6-6 kaBP and 5-4 kaBP were the transition periods with unstable characteristics in Megatherma, among them, during 5-4 kaBP as well as around 4 kaBP, the cold events were still remarkable and the flood events were also frequent. (3) The formation and development of ancient culture in the study area in prehistoric period was mainly corresponding to Megatherma, Daxi culture that the planting industry was the most prosperous appeared in the prime (6-5 kaBP) of Megatherma, other types of ancient culture before and after Daxi culture which were at the low tide or showing decline corresponded to the stages that the climate and environment were unstable. Response of ancient culture in study area to the climatic and environmental changes was achieved through altering the modes of subsistence.