成都平原4ka以来地层磁化率特征及气候变化意义

Magnetic susceptibility characteristics and paleoclimate explanation of Chengdu plain since 4000 a

对成都金沙遗址IT6814探坑约4 m厚地层的5 cm间距磁化率分析,建立了成都平原4 ka以来的质量磁化率曲线和频率磁化率曲线。根据质量磁化率和频率磁化率特征结合粒度中值曲线对比,探讨了金沙遗址4 000 a来的气候环境变化,划分出成都平原的三个气候阶段:4 000~3 380 aBP,气候偏湿;3 380~1 700 aBP,气候条件相对湿热;1 700 aBP^20世纪90年代初,气候逐渐偏干冷。

As a paleoclimatic proxy index, magnetic susceptibility parameter widely used in studing climatic changes is applied in studing the sediment of Chengdu plain. In the research, 83 pieces of samples were collected at the interval of 5 cm in Jinsha site IT6814. Based on the susceptibility measurement, the quality magnetic susceptibility curve and the frequency magnetic susceptibility curve have been established. The climatic conditions of Chengdu plain since 4000 a can be divided into three phrases according to the characteristics of susceptibility and median size of grain. By comparing the parameter characteristics, people can conclude that the high values of susceptibility are related to large size of grain at about 3.6 m and 2.2-2.5 m of the profile, while the high value of susceptibility is controlled by pottery shards at 1.4-1.8 m of the profile, and that the relatively lower value of that at the bottom of the profile is the result of being overwhelmed by water.