渭河流域先周-西周时代环境和水土资源退化及其社会影响

采取多学科交叉的方法,研究了渭河流域先周-西周时代主要考古遗址的全新世黄土-古土壤剖面,获得了较高时间分辨率的磁化率、粒度成分、总有机碳和CaCO3含量等环境代用指标系列.结合该时期人类活动遗物分布的层位关系、考古断代、历史年代和大量14C年代数据,以及古文献有关环境演变和灾害的记载,形成了对该区域人类活动和环境演变过程的综合断代.各项指标综合反映了从3100aB.P.(1150B.C.)开始,渭河流域气候向着干旱化发展,降水量减少、蒸发量增大、植被退化、土壤生物活动减弱、土壤矿物次生风化强度降低、土壤颗粒变粗、水份减少、CaCO3淋溶减弱、土壤碱性增强,表现出由气候干旱化造成的土壤退化.对于当时旱作农业和游牧业来说,这则是水土资源的自然退化.这个时期发生了游牧民族大规模南移,也发生了周人历史上著名的"古公迁岐"、"文王迁丰"和"平王东迁"等事件.通过深入分析论证,认为环境恶化和水土资源退化是引起周人都邑迁移的主导因素,虽然游牧民族南侵占领也是重要的驱动力,但是引起游牧民族南下的根本原因,也同样是环境恶化和水草资源的退化.

LAND DEGRADATION AND ITS SOCIAL IMPACT IN THE WEIHE RIVER DRAINAGE BASIN DURING THE PREDYNASTIC ZHOU-WESTERN ZHOU DYNASTY

Several Holocene loess soil profiles at the archaeological sites of major political center,and later,the capital cities of the predynastic Zhou and Western Zhou Dynasty (ca. 3 350～ 2 721a B.P. /1400～771 B.C.) in the Weihe River drainage basin were studied multi disciplinarily. Higher resolution proxy climatic data of magnetic susceptibility,particle size distribution,total organic carbon and CaCO 3 were obtained from the profiles. Chronology of the data series was decided by a combination of archaeological dating,ancient literal records and 14 C dating. It provides insights into environmental change and its impact on the Zhou culture in this climatically sensitive zone. Both the analytical data and literal records indicate that increased climatic aridity from 3 100a B.P. (1150 B.C.) caused a considerable environmental deterioration and degradation of natural resources,especially water shortages,decreases in precipitation and deficits in soil moisture. These resulted in poor harvest and great famines,plagues,domestic upheavals of the Zhou people who subsisted on dry farming,and also the south migrations of the nomadic tribes from the northern steppe. In the meantime,the major political center,and later,the capital cities were relocated several times. Even though there could be some other political and military reasons,the persistent droughts may dynamically forced Zhou people to move from the upland plateau to the lowland riverbanks step by step through relocations,following a direction of increasing climatic humidity,soil moisture,water availability and biodiversity. The southward migration of the nomads from the steppe of the northern Loess Plateau and the Mongolia Plateau in response to the climatic aridity was another dynamic force that caused the relocations of the Zhou culture.