Diagenetic control of magnetic susceptibility variation in Core MD98-2172 from the Eastern Timor Sea  

作　　者：李海燕 张世红 白凌燕 方念乔 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences [2]School of Marine Science,China University of Geosciences

出　　处：《Chinese Journal of Oceanology and Limnology》2010年第6期1350-1361,共12页中国海洋湖沼学报（英文版）

基　　金：Supported by the National Basic Research Program of China (No. 2006CB701400);the National Natural Science Foundation of China (Nos. 40621002,40974035,40272074);Projects of Ministry of Education of China ("111" Project B07011,IRT0546)

摘　　要：Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction （XRD） analyses, were made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values of magnetic susceptibility in this core drop sharply down-core from -3.85 m deep below sediment/water interface and are very low at -5.35 m. However, both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation. Mineral magnetic results indicate that the depth of -3.85 m may be an oxic/anoxic boundary. Therefore, the sediments below -3.85 m have been subjected to intense reductive diagenesis, whereas the sediments above -3.85 m are seldom affected. The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain （PSD） magnetite, with little down-core variation in its content and grain size. Below -3.85 m, the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis： （1） the sediments from the 3.85-5.35 m interval are at the stage of iron oxide reduction; t＇SD magnetite is the major magnetic contributor, but it becomes less abundant and coarser down-core; （2） the sediments below -5.35 m are at the stage of sulphate reduction; ferrimagnetie minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations, including pyrite as evidenced by high-temperature magnetic susceptibility measurements. However, the susceptibility variations below -5.35 m of Core MD98-2172 show obvious periodicity, despite the intense effect of reduetive diagenesis. Furthermore, the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles （〈8 μm）, which may come mainly from the advection of the Indonesia Throughflow （ITF） and/or river input from Timor. Therefore, for Core MD98-2172, susceptibility variation below -5.35 m, which potentially correspond to fluctuations inDetailed mineral magnetic measurements,integrated with grain-size distribution and X-ray diffraction(XRD) analyses,were made on the marine sediments of Core MD98-2172,retrieved from the Eastern Timor Sea.Values of magnetic susceptibility in this core drop sharply down-core from-3.85 m deep below sediment/water interface and are very low at-5.35 m.However,both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation.Mineral magnetic results indicate that the depth of-3.85 m may be an oxic/anoxic boundary.Therefore,the sediments below-3.85 m have been subjected to intense reductive diagenesis,whereas the sediments above-3.85 m are seldom affected.The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain(PSD) magnetite,with little down-core variation in its content and grain size.Below-3.85 m,the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis:(1) the sediments from the 3.85-5.35 m interval are at the stage of iron oxide reduction;PSD magnetite is the major magnetic contributor,but it becomes less abundant and coarser down-core;(2) the sediments below-5.35 m are at the stage of sulphate reduction;ferrimagnetic minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations,including pyrite as evidenced by high-temperature magnetic susceptibility measurements.However,the susceptibility variations below-5.35 m of Core MD98-2172 show obvious periodicity,despite the intense effect of reductive diagenesis.Furthermore,the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles(<8 μm),which may come mainly from the advection of the Indonesia Throughflow(ITF) and/or river input from Timor.Therefore,for Core MD98-2172,susceptibility variation below-5.35 m,which potentially correspond to fluctuations in the quantity of fine particles,may record the histories of the developmen

关 键 词：Eastern Timor Sea SUSCEPTIBILITY reductive diagenesis fine detrital particles 

分 类 号：P318.41[天文地球—固体地球物理学]