衡阳盆地红土剖面的磁化率、Rb/Sr值及其古气候指示意义

The Magnetic Susceptibility, Rb/Sr Ratio of Red Earth Profile in Hengyang Basin and Its Significance of Palaeoclimate

通过对衡阳市区高兴红土剖面元素含量分析、磁化率分析和ESR年代测定,探讨该剖面的低频磁化率值（χ_（lf））、Rb/Sr值、化学蚀变指数（CIA）、退碱系数（Bc）和化学淋溶系数（BA）等的分布特征及其古气候意义。研究表明：（1）样品Rb/Sr值与化学风化参数值有显著的相关性,磁化率值与化学风化参数值有很好的相关性,Rb/Sr比值和磁化率值一同可以作为红土沉积古环境变化的替代性指标,极好地记录了衡阳盆地更新世以来古气候的变化,大致可以划分为3个阶段：2.23～1.323 Ma B.P.期间,Rb/Sr值和磁化率值为相对高值区,气候特征为温暖湿润;1.323～0.76 Ma B.P.期间,Rb/Sr值、低频磁化率值和CIA值呈现最高值区,气候为本区最温暖湿润阶段;0.763Ma B.P.以来,Rb/Sr值、磁化率值和CIA值为最低值区域,气候特征为温暖干燥。（2）Rb/Sr值、低频磁化率值、CIA值曲线从剖面底部往上呈现出先波动递增后快速递减的变化趋势,反映了衡阳盆地早更新世以来,气候整体上是由暖湿向温干的方向发展。

Based on the analysis of elements, magnetic susceptibility and Electron Spin Resonance（ESR） dating of samples from Gaoxing red clay profile in Hengyang City. The result indicates that： the Rb/Sr ratios and chemical weathering parameters values of Gaoxing profile showed a significant positive correlation, and the magnetic susceptibility ratios and chemical weathering parameters values showed a good positive correlation.The results revealed that Rb/Sr ratios and magnetic susceptibility values would be alternative index in red clay sedimentary environmental. recording the climate change in Hengyang Basin since the Pleistocene epoch. The paleoclimatic changes of Hengyang City can be divided into three periods： during 2.23-1.323 Ma B.P., the Rb/Sr value and magnetic susceptibility value were in relatively higher value area,the climate features were mainly warm and wet; during 1.323-0.763 Ma B. P. the Rb/Sr value, CIA value and magnetic susceptibility value reached the highest value area in profile,the climate was the hottest and wettest phase in this region; 0.763 Ma B.P. later, the Rb/Sr value, magnetic susceptibility value and CIA value showed the lowest value in profile, illustrating that the chemical weathering is relatively weaker with mainly warm and dry climate environment.The change tendency of Rb/Sr ratios curve and magnetic susceptibility values curve in Gaoxing profile,which firstly increases fluctuantly and then decreases rapidly from the bottom to the top, generally suggesting that Hengyang Basin has witnessed climate change, from warm-wet to warm-dry since the early Pleistocene.