西土城盐淖近两千年环境变化与人类活动关系研究

The Xitucheng site is located in the west of Kangbao County, Zhangjiakou City, Hebei Province. Based on preliminary archaeological survey, it has been inferred as an important city site dating to Jin dynasty (1115-1234 A.D.); and it also has been approved for all-around exploring and excavating by the State Cultural Relic Bureau in 2014. In this project, the Yannao Lake (a salt lake, 1.5 km south of Xitucheng Site) is chosen as our research object, and the research contents of this study are as follows: i) through the analysis of Chronology, Palynology, Sedimentology and Environmental Magnetism, setting up the high-resolution sequence of climate and environment changes, and then be used to quantitatively reconstruct the past environment evolution since 2000 years; ii) establish the time series of lake level and salinity based on carbonate contents (CaCO3) and saline mineral assemblages, to determine whether the continuous change of lake level may cause the contraction of lake area in different periods, and to prove the possibility and time distribution of Yannao Lake as a main producing area of lake salt production. The aims of this project is to discuss the effect of climate and environment change to human activity in regional scale, and provide better climatic and environmental basis for archaeological research based on multi environment proxy indices. And the outcomes of this project will not only provide the scientific evidence for the changes of city site, human-land relationship study, but will also provide new thinking and orientation for salt archaeology.

西土城遗址位于河北省张家口市康保县二号卜乡西土城村，经考古调查推断为金代城址，2014年已获国家文物局批准进行全面勘探、发掘工作。本项目选择距离西土城南门约1.5km的南盐淖作为研究对象，主要通过孢粉组合、沉积学、环境磁学和年代学研究，建立气候、环境的高分辨率时间序列，定量恢复该区域近两千年来的环境变迁历史；通过对湖泊自生碳酸盐含量及盐类矿物组合的分析，建立盐湖盐度、水位的时间演化序列，分析是否存在水位连续变化进而导致湖泊范围不断收缩的时期，求证历史上盐淖作为池盐产地的可能性及时间分布。本项目通过研究在与遗址相关的小尺度区域范围内，利用多种代用指标重建环境的可行性及可靠性，探讨环境变化，尤其是气候变化引起的小尺度区域环境地貌演变对于人类活动的影响，可以为考古发掘工作提供重要的环境背景资料，为进一步研究古代城址变迁与人地关系提供科学依据，为盐业考古提供新的研究思路和方向。

基于河北省坝上康保县西土城盐淖湖泊沉积岩芯AMS14C测年和多指标（孢粉、粒度和磁化率等）综合分析，构建了研究区中全新世以来的气候环境变化和古人类活动历史。结果显示：中全新世研究区周围发育以云杉属和松属为主的针叶林植被，并伴生有大量喜暖落叶阔叶属种，森林覆盖度高；表明该阶段东亚夏季风强盛，区域气候温暖湿润。晚全新世，研究区周围发育以蒿属和藜科为主的典型草原，区域森林覆盖度显著降低，一方面受东亚夏季风减弱、区域气候变干控制，另一方面可能与区域人类活动增强有关。受测年结果和样品分辨率限制，目前尚无法分析盐淖水位变化序列及其作为池盐产地的时代，区域气候环境与西土城城址变迁的关联性也有待进一步研究。