Magnetic properties of sediments from the Pearl River Delta, South China: Paleoenvironmental implications
Magnetic properties of sediments from the Pearl River Delta, South China: Paleoenvironmental implications
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DOI：
10.1007/s11430-007-0151-4
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发表时间：
2008-01
期刊：
影响因子：
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通讯作者：
Xiaoqiang Yang;R. Grapes;Houyun Zhou;J. Yang
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文献类型：
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作者：
Xiaoqiang Yang;R. Grapes;Houyun Zhou;J. Yang
华南珠江三角洲岩心（PD）沉积物的磁性参数及其对环境的影响表明，尽管存在少量的硫化铁，但具有低矫顽力的亚铁磁性矿物（例如磁铁矿）在磁性中占主导地位。硫化铁的比例增加并成为决定灰黑色富含有机物粘土层磁性特征的主要矿物，表明海洋回归造成缺氧、硫酸盐还原的沼泽环境。在“花板粘土”中，硬磁性矿物，如赤铁矿和针铁矿，在很大程度上控制着沉积物的磁性，意味着长期的暴露和风化。当磁铁矿是主要磁性矿物时，其分数和晶粒尺寸决定了磁化率 (κ) 和饱和等温剩磁 (SIRM) 等特性。 SIRM/κ 和χarm/SIRM 的比率反映了海平面的变化，其中高SIRM/κ 和χarm/SIRM 与较小的磁性矿物颗粒尺寸和海平面上升相关。根据这些环境磁参数的地下变化以及沉积物特征和微型动物群，珠江三角洲地区的沉积环境可分为晚更新世和全新世两个主要的海侵旋回和海退旋回，每次海侵期间还存在更多的海平面波动子旋回。
Magnetic parameters and their environmental implications of sediments in a core (PD) from the Pearl River Delta, South China, indicate that ferrimagnetic minerals with low coercivity, such as magnetite, dominate the magnetic properties although small amounts of Fe-sulphides occur. The fraction of Fe-sulphides increases and becomes the dominant minerals determining the magnetic characteristics in grey-black organic-rich clay horizons, indicating an anoxic, sulphate-reducing swamp environment resulting from a marine regression. In the “Huaban clay”, hard magnetic minerals, such as hematite and goethite, largely control the magnetic properties of the sediments and imply a long period of exposure and weathering. Where magnetite is the main magnetic mineral, its fraction and grain size determine properties such as magnetic susceptibility (κ) and saturation isothermal remanent magnetization (SIRM). Ratios of SIRM/κandχarm/SIRM reflect changes in sea level with high SIRM/κandχarm/SIRM correlating with a smaller magnetic mineral grain size and rising sea level. Based on downcore variations of these environmental magnetic parameters along with sediment characteristics and microfauna, the sedimentary environment of the Pearl River Delta area can be divided into two main cycles of transgression and regression during the late Pleistocene and Holocene with more sub-cycles of sea level fluctuation during each transgression.