洪湖沉积物的磁性特征及其环境意义

Paleoenvironmental Implication of Magnetic Measurements on Sediments Core from Honghu Lake

以洪湖沉积物为研究对象,通过对Hh01-2(B)孔岩芯磁参数的测量发现在岩芯所代表的时间段内洪湖沉积物磁化率呈现了明显的四个主阶段变化;频率磁化率变化与磁化率变化具有较好的相关性,亚铁磁性矿物的变化主导了沉积物磁化率的变化.同时结合年代、孢粉分析以及参考相关历史记载资料,发现磁化率高值段对应湖水动力强、湖面较宽、气候较湿润,而磁化率低值段对应湖水动力弱、湖面较小、气候偏干旱.从而得出了洪湖沉积物磁参数曲线波峰和波谷分别对应洪湖在历史上曾经历了扩张和收缩、气候温湿和冷干的旋回.

Honghu Lake is a shallow lake in the Jianghan Plain. The sediment core Hh01-2(B) from Aug.,2001 was selected for analysis. Based on magnetic measurements of the core, we can find that the changes of magnetic susceptibility appear as four obvious main stages since 900a B.P. The changes between frequency dependent magnetic susceptibility (χfd%) and magnetic susceptibility(χ) of the core have close relations, whereas the contents of finer grain ferrimagnetic minerals play a leading role in the changes of magnetic susceptibility. Meanwhile, according to 210Pb dating and spore pollen analysis and referring to the relevant historical materials, we get the following conclusion: the sections with higher magnetic susceptibility correspond to the periods with stronger hydrodynamics, wider surface of the lake, and relatively moist climate; otherwise, those with lower magnetic susceptibility correspond to the periods with softer hydrodynamics, narrower surface of the lake, and relatively droughty climate.