长江中游堤防溃口沉积物的磁组构特征

通过对 1998年 8月 1日湖北 竹牌 洲湾溃口沉积物的系统采样和磁组构测量与计算 ,发现溃口沉积物的磁组构特征为 :由溃口扇的扇顶→扇缘 ,磁组构参数各向异性度 P、磁面理度 F、磁线理度 L、水流速度函数因子 Fs的统计平均值均具有由大逐渐变小的特点 ;在溃口扇的不同部位磁化率量值椭球的主轴平均方向具有不同的特点 ,其规律是 :在扇顶或扇缘处平均方向变化较大 ,尤其在扇缘处 ,最大磁化率主轴方向比较随机 ,没有明显的主方向 ,而在扇中磁化率量值椭球的主轴平均方向比较稳定 ,最大主轴的优选方向比较明显。初步探讨和建立了长江中游现代溃堤溃口沉积物的磁组构特征识别标志

Magnetic Fabric Characteristics of Flooded Sediments in the Middle Reaches of the Yangtze River

Flooded sediments provide important material for studying the scale and law of ancient flood disaster events in the middle-lower reaches of the Yangtze River. Through systematical sampling, measuring and calculating the sediments of the dam break, occurring in Paizhouwan of Hubei Province in Aug. 1, 1998, identification marks of magnetic fabric characteristics of the modern dam-break flooded sediments in the middle reaches of the Yangtze River are established and discussed in this paper. The magnetic fabric characteristics of the dam-break fan sediments are as follows. From the foot to the edge of the dam-break fan, the statistical average values of the magnetic fabric parameters (anisotropy degree of magnetic susceptibility P, magnetic facet F, magnetic lineation L and velocity of water flow Fs) all change from large to small. The statistical directions to the principal axis of the magnetic susceptibility magnitude ellipsoid in different positions of the dam-break fan have different features, that is, the statistical direction changes greatly at the foot and the edge of dam-break fan. Especially, at the edge of the dam-break fan the direction of the maximum susceptibility principal axis is at random with no obvious main direction. But it is relatively stable in the middle of the fan. And the optimum direction of the maximum axis is very clear.