湘赣丘陵区红土剖面磁化率分布特征及其环境记录

Magnetic susceptibility distribution characteristics and environmental records along red clay section in Hunan-Jiangxi hilly area

南方红土是记录古环境信息的良好载体。为了揭示南方红土剖面磁化率的古环境意义及其与化学蚀变指数之间的关系,采集了湘赣地区黄金(HJ)、沙河(SH)、田村(TC)、高兴(GX)和松木(SM)5个红土剖面共计263个样品,同时进行低频磁化率和化学元素测量和分析。研究结果显示:①赣南地区均质红土层、红壤层低频磁化率均值小于网纹红土层,红土剖面的低频磁化率均值分布范围介于(12.1~463.91)×10^-8m^3/kg之间。②衡阳地区红土低频磁化率与对应化学蚀变指数(CIA)值相关性较好,即为磁化率高值区指示暖湿沉积环境,磁化率低值区指示暖干沉积环境。③低频磁化率曲线波动频度和幅度存在区域性差异,但从剖面底部往上一致呈现为递减的变化趋势,揭示了湘赣地区红土沉积环境整体上由暖湿向温干方向演变。

The red earth in southern China has been generally considered potential paleoenvironmental record.In order to reveal the paleoenvironmental implications of the red clay profile in southern China and its relationship with chemical index of alteration(CIA),the authors measured magnetic susceptibility and chemical elements of two hundred and sixty-three samples collected from Huangjin(HJ),Shahe(SH),Tiancun(TC),Gaoxing(GX),Songmu(SM)in Xianggan area.Some conclusions have been reached:(1)The average magnetic susceptibility of the vermiculated red clay layer is higher than that of homogeneous red clay layer and red soil layer in Gannan region.The low frequency magnetic rate of granite clay in Gannan region is higher than that of granite clay in Hengyang region.The distribution ranges of the low frequency magnetic susceptibility of red clay sections vary from 12.1×10^-8 m^3/kg to 463.91×10^-8 m^3/kg;(2)There is still preferable relationship between the low frequency magnetic susceptibility and chemical index of alteration(CIA)in Hengyang region.The high magnetic susceptibility values correspond to the high CIA values,indicating a warm and humid envirenment;the low magnetic susceptibility values correspond to the low CIA values,indicating a cold and dry envirenment.(3)The low-frequency magnetic susceptibility curves are regionally different in frequency and amplitude,the low frequency magnetic susceptibility of the red clay section shows a consistent downward trend,which reveals the change trend of palaeoclimate from warm-wet to warm-dry during the red clay deposition period.