黄渤海表层沉积物环境磁学特征分类及物源诊断

MAGNETIC PROPERTIES AND PROVENANCE OF SURFACE SEDIMENTS IN THE BOHAI AND YELLOW SEAS

黄渤海是我国东部陆架的重要组成部分,基于黄渤海130个表层沉积物样品详细的环境磁学研究探讨了磁学特征分类及物源.按照黄渤海表层沉积物样品的S-300、SIRM/x与SIRM磁性参数特征,将研究区表层沉积物分为4个类型：类型1磁性矿物含量较高,亚铁磁性矿物含量中等,磁性矿物颗粒中等,与黄河物质磁学特征极为相似,这里沉积动力中等,为中等水动力黄河沉积区;类型2磁性矿物含量中等,亚铁磁性矿物含量中等,磁性矿物颗粒细,与长江及黄河物质磁学特征较为相似,水动力环境较弱,为弱水动力黄河-长江混合沉积区;类型3磁性矿物含量较低,亚铁磁性矿物含量较低,磁性矿物颗粒中等,主要是该海域存在的残留沉积,水动力中等,命名为中等水动力残留沉积区;而类型4磁性矿物含量高,亚铁磁性矿物含量高,磁性矿物粒级粗,与长江沉积物具有相似的磁学特征,沉积动力强,命名为强水动力长江沉积区.以上四类沉积物具有不同的环境磁学和沉积环境特征,从而可以帮助识别黄渤海沉积物的分布及物源信息.

The Bohai Sea and the Yellow Sea are important regions of the East Chinese Continental Shelf. Although some research on sediment provenance in this area has been conducted, there are still significant gaps in the understanding of sediment dynamics in this region. In this study, surface sediment samples from 130 sites in the Bohai Sea and the Yellow Sea （31.97°- 39.55°N, 118.97°- 124.49°E） were collected. We analyzed the magnetic characteristics, particle size, proportions of sand, silt and clay, magnetic susceptibility （χlf, ;χhf）, anhysteretic remanent magnetization （ARM）, isothermal remanent magnetization （IRM） and to-t curve of all samples. Additionally, S -100 and S-300 were calculated. The results show that： （1） In the research area, χ ranges from 20×10-8 to 96×10-8m3/kg and SIRM from 2100×10-6 to 8639×10-6Am2/kg. The highest values of both Z and SIRM were found in the southwestern South Yellow Sea, with the lowest values in central western South Yellow Sea. （2） S-100, S-300 and the correlation between χ and SIRM, show that the surface sediments of the Bohai Sea and the Yellow Sea are characterized by ferromagnetic minerals, with results of the κ-t curve of typical samples showing these minerals are predominantly magnetite. （3） Within the mud area of the Bohai and Yellow Seas, χARM/χ〉10 and χARM/SIRM〉60×10 5m/A. The magnetic grains are mainly fine single-domain and pseudo-single-domain particles, while in other areas, the magnetic grains are largely multi-domain and pseudo-single-domain particles. （4） The S_300, SIRM/χ and SIRM results, along with a comparison with the sediments of the Yangtze River, the Yellow River and the Korean Peninsula muddy area, allow the classification of the surface sediments of the study area into four types： Type 1 sediments have medium ferrimagnetism, magnetic domain and a high concentration of magnetic minerals. The magnetic characteristics of these sediments are similar to those of Yellow River sediment. The region containing these sediments has a moderate degree of sedimentary hydrodynamic activity, and is classified as the medium dynamic Yellow River sedimentary area. The sediments in Type 2 area have fine magnetic domain with moderate ferrimagnetism and magnetic mineral content. This area is a low hydrodynamic environment with sediment characteristics similar to those of the Yellow River and Yangtze River sediments. Therefore, it is classified as a low dynamic mixing sedimentary area from the Yellow River and Yangtze River. Type 3 is characterized by sediments with a medium magnetic domain, and low ferrimagnetism and magnetic mineral content. Despite close similarities to the features of Yellow River sediments, the existence of relict sediment and medium hydrodynamics, results in this region being classified as a medium dynamic relict sedimentary area. Type 4 sediments have a coarse magnetic domain, along with high ferrimagnetism and magnetic mineral content. This area＇s sediments have similar magnetic properties to the sediments of Yangtze River and it is classified as the strong dynamic Yangtze River sedimentary area. The sediments of this region have different environmental magnetic and sedimentary environment characteristics which can help to distinguish the distributions and provenance of sediments in Yellow Sea and the Bohai Sea.