伶仃洋钻孔岩芯的磁学记录及其对海水进退的响应

Magnetic variations of sediments from a drilling core in the Lingdingyang Bay,Zhujiang River Estuary,and their responses to marine transgression and regression

华南珠江三角洲河口地区受到珠江流域和近海海洋环境的共同影响,其沉积体系中承载的古地质记录对于揭示海陆交互作用下的地质地貌过程演化具有独特意义。本研究对珠江伶仃洋湾口的一条钻孔岩芯进行了环境磁学研究。研究发现,在晚更新世以来海水入侵的相对高海平面时期,岩芯沉积物中磁性矿物的组成或高矫顽力组分的来源更稳定,反映了沉积区环境的稳定性或沉积物源区的相对固定;在海水退出的风化剥蚀期,沉积序列中磁性矿物组合出现大幅度旋回变化,这表明同时期碎屑物质源区可能经历了显著的环境更替。多重磁学参数包括低频磁化率、非磁滞剩磁、饱和等温剩磁以及HIRM参数,在全岩芯中指示了比较一致的磁性变化特征;相较之下,S-ratio参数的变化更灵敏地响应了伶仃洋湾口地区海水入侵和退出背景下的沉积演化历史。

The estuary area of the Zhujiang River Delta is significantly influenced by its drainage and offshore environment.Since being under the interaction of sea and land,the depositional system within the estuary area could be of great potential to reveal the simultaneous succession of geological and geomorphic processes.This paper presents a magnetic investigation report of a sedimentary core drilled from the Lingdingyang Bay at the Zhujiang River Estuary.Results of this study show that,the concentration of magnetic minerals or the source area of the high-coercivity magnetic minerals within the core sediments is relatively constant during the two periods of relatively high sea-level(i.e.,under marine transgression)since late Pleistocene,revealing a stable sedimentation environment or a relatively fixed sediment source,respectively;however,during the period of marine regression,when the weathering and denudation processes dominate,the magnetic mineral composition in sediments is characterized by significant large-scale fluctuations,possibly indicating that the source areas of detrital materials have undergone a dramatic climate evolution.Multiple environmental magnetic parameters,including low-frequency magnetic susceptibility,anhysterestic remanent magnetization,saturation isothermal remanent magnetization,and HIRM(the‘hard’isothermal remanent magnetization),reveal a synchronous pattern of magnetic variations through the core.In comparison,the S-ratio record of the core sediments is more sensitive to the sedimentation evolution history during the marine transgression and regression in the Lingdingyang Bay at the Zhujiang River Estuary.