广西八仙天池表层沉积物中磁性矿物源-汇过程探讨  

The transformation of magnetic minerals in source-sink process for surface sediments of Baxian Tianchi,Guangxi

作　　者：韦若梅 杨小强 张玲 周绮娴 张庭伟 WEI Ruomei;YANG Xiaoqiang;ZHANG Ling;ZHOU Qixian;ZHANG Tingwei(School of Earth Science and Engineering/Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,Sun Yat-sen University,Zhuhai 519082,China)

机构地区：[1]中山大学地球科学与工程学院/广东省地球动力作用与地质灾害重点实验室,广东珠海519082

出　　处：《中山大学学报（自然科学版）（中英文）》2021年第4期76-89,共14页Acta Scientiarum Naturalium Universitatis Sunyatseni

基　　金：国家自然科学基金(41672162)。

摘　　要：湖泊沉积物中的磁性矿物由于源区复杂或成岩作用过程中可能发生矿物转化,导致利用磁性参数重建古环境时存在诸多不确定性。阐明沉积物中磁性矿物的来源以及磁性参数在沉积物的源区和汇区可能发生的变化,是准确理解磁性参数环境意义的基础。本文选择位于广西武宣县的一个封闭性岩溶湖泊,采取湖区汇水面积区域表层土壤样品和表层沉积物样品,进行较为详细的岩石磁学测量,分析磁性矿物从湖区周围的表层土壤搬运至湖泊沉积之后,磁性参数和磁性矿物在浓度、类型和粒度等方面的变化。结果表明,湖泊表层沉积物与土壤样品均以磁铁矿为主要的载磁矿物,其中,前者以单畴(SD)磁铁矿为主,后者磁铁矿粒度较粗并含有大量的超顺磁(SP)矿物和纤铁矿等物质。两组样品的磁性特征差异指示湖泊表层沉积物存在后期改造,导致碎屑成因的磁性矿物发生一定程度的还原溶解和生物成因的磁性矿物生成。详细区分湖泊沉积物中磁性矿物"从源到汇"的转换过程,是利用环境磁学恢复沉积环境的必要前提。The diverse sources of magnetic minerals in lake sediments usually cause uncertainties in the reconstruction of the paleoenvironment using the magnetic parameters. Clarifying the sources of magnetic minerals and the possible changes in magnetic parameters for the source and the sink area of the sediment respectively,is the basis for a more accurate interpretation of the magnetic parameters representing the environmental significance. In this paper,the sediments of a closed karst lake in Wuxuan County,Guangxi Province was selected to discuss this transform. Surface soil samples from the catchment area and top sediments samples in the lake were taken respectively for performing the detailed rock magnetic measurements,then discussing the variations of the magnetic minerals in concentration,assemblage and domain state. The results show that the magnetic minerals of lake surface sediments and catchment soil samples dominated mainly by the magnetite,however,the lake sediments are mainly composed of SD magnetite while the soil samples characterized mainly by the PSD magnetite,containing higher percentage of superparamagnetic minerals and lepidocrocite. The difference in magnetic properties between the two groups of samples indicates the post-depositional effects in the surface sediments of the lake,which resulted in a degree of reduction and dissolution of the detrital magnetic minerals and the formation of biogenic magnetic minerals. Therefore,the magnetic susceptibility(χ),frequency dependent susceptibility(χfd),saturation magnetization(Ms)and related magnetic parameters of the sediment may remain some uncertainties for reconstructing the environmental background during deposition. The anhysteretic remanent magnetisation(ARM)and saturation isothermal remanence(Mrs or SIRM)are less affected by postdepositional alternation and may be good substitute indicators for recovering environmental information when sediments were formed.

关 键 词：岩溶封闭性湖泊 湖区表层土壤 湖泊表层沉积物 岩石磁学 磁性矿物 

分 类 号：P318.41[天文地球—固体地球物理学]