珠江磨刀门河口表层沉积物磁性特征及其动力沉积环境意义

Magnetic properties of surficial sediment and its implication for sedimentation dynamic environment in the Modaomen Outlet of the Pearl River Estuary

基于2015年3月珠江磨刀门河口表层沉积物磁学和粒度测量结果,研究磨刀门河口磁性特征空间分布规律,分析磁性参数与沉积物粒度的关系,并探讨其对沉积动力环境的响应。磁性参数磁化率(χ)和饱和等温剩磁(SIRM)均在拦门沙处出现低值区,并在10m等深线外呈现向海递减趋势;频率磁化率(χfd%)、非磁滞剩磁磁化率(χARM)以及比值参数χARM/SIRM和χARM/χ在拦门沙处出现低值区,而在拦门沙外呈现高值:表明研究区域磁性特征由亚铁磁性矿物主导,而拦门沙区域存在一定量的不完全反铁磁性矿物。粒度是影响沉积物磁性特征的重要因素,SIRM/χ等参数与粗颗粒组分(大于63μm)呈显著正相关,χfd%等参数与小于16μm粒级组分高度相关,结果显示χfd%、χARM、χARM/SIRM以及χARM/χ等参数可作为本区域沉积物细颗粒组分(小于16μm)的代用指标,而SIRM/χ则可作为粗颗粒组分(大于63μm)的代用指标。基于沉积物类型、动力环境等综合考虑,选取SIRM、S-300、SIRM/χ参数聚类分析,可将磨刀门河口动力沉积环境分为4个区,结果与该区域动力环境及动力地貌格局具有一致性。本研究不仅对了解新动力格局下磨刀门河口演变模式具有重要意义,还可以丰富河口沉积动力学研究方法。

Based on the magnetic measurement of surficial sediment in the Modaomen Outlet of the Pearl River Estu ary in March 2015, we explored spatial distribution of magnetic properties, examined the relationship between magnetic parameters and sediment particle size, and addressed its response to the sedimentary dynamic environment. The values of susceptibility（Х） and saturation isothermal remanent magnetization（SIRM）were low in the sediment bar, and generally displayed a decreasing trend toward the sea outside the ten-meter isobaths. The values of frequency dependent susceptibility（Хfd% ）, anhysteretic remanent magnetization（HARM ）, ХARM/SIRM and ХARM/Х were also low in the sediment bar, however, it was high outside the sediment bar. These results revealed that the magnetic properties of study area were dominated by ferrimagnetic mineral, but there were still some antiferromagnetic minerals in the sediment bar. Particle size is an important factor affecting magnetic properties, SIRM/Х shows positive correlation with 〉63 μm fraction, magnetic parameters such as Хfd% .ХARM .ХARM/SIRM and ХARM/ Х display significantly positive correlation with 〈16 μm fraction, these results indicated that Хfd%,ХARM,ХARM/ SIRM and ХARM/Х could be used as proxies for finer fraction of sediments （%16 ffm fraction）, and SIRM/Х could be used as proxies for percentages of coarser fraction of sediments 〉63 μm fraction）. In light of the sediment types, dynamic environment in the Modaomen Outlet, the SIRM, S -300 and SIRM/Х were applied to carry out cluster analysis, and the result has a remarkable consistency with the sedimentary dynamic environment and the dynamic geomorphology pattern. Our study is not only of great significance to understand the new evolution mode of the Modaomen Outlet in new dynamic patterns, but also can enrich the research method of sedimentation dynamics of estuary.