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《Chinese Journal of Geophysics》 2016-09
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Magnetic properties of turbidites in the Huatung Basin and their environmental implications

LI Bo;WANG Yan;ZHONG He-Xian;ZHANG Jiang-Yong;LI Shun;LI Xue-Jie;GAO Hong-Fang;Key Laboratory of Marine Mineral Resources,Guangzhou Marine Geological Survey, Ministry of Land and Resources;Guangdong Nonferrous Metals Geological Exploration Institution;  
Turbidity currents are part of a continuum of sediment-gravity flows,and are traditionally defined as those sediment-gravity flows in which sediment is suspended by fluid turbulence.Turbidity currents are principal mode of transportation of clastic grains to the deep ocean.The occurrence of turbidity current plays an important role in the formations of canyon,submarine fan and deep-sea oil.Previous study shows lots of turbidite records were identified in the West Philippine Sea and adjacent regions.However,few works focus on the magnetic properties of the turbidites in this area.In this paper,systematic rock-magnetism measurements,including magnetic susceptibility,anhysteretic remanent magnetization,isothermal remanent magnetization,saturation isothermal remanent magnetization,thermomagnetism and hysteresis loops were performed on the marine sediments of core GX168 from the Huatung Basin to uncover the sedimentological characteristics and magnetic features of turbidite sequences and the differences withthe background sedimentation,also,further explore the provenance and formation mechanism.There are overall 12 turbidite layers in the core GX168.There was significant regularity in the distribution of turbidite on profile:11turbidite layers distributed in the interval from 350 cm to 700 cm in depth,but only one turbidite layer was found from the interval of 0~350cm in depth.The results show turbidite characterized by sand and silty sand in lithology contain more coarse sediment grains than background sedimentation with dominant lithology of clay.The content of quartz and feldspar in turbidite is higher than that of background sedimentation,which is the reason of lighter colors of turbidite than that of background sedimentation.The contact between bottom boundary of turbidite succession and underlying sediments is generally sharp and instant;while the contact between the top boundary of turbidite and overlying sediments is transitional transition.The turbidite is characterized by typical graded bedding sequence.Turbidite and background sedimentation share similar magnetic properties including:magnetites are the dominant magnetic carries for both of them,and the grain sizes of magnetite particles are both pseudo-single-domain(PSD)and multi-domain(MD).However,there are some differences between them:the turbidite enrich more magnetic minerals than background sedimentation obviously;the magnetic susceptibility and saturation isothermal remanent magnetization of turbidite is stronger in comparison to that of background sedimentation,and the grain size of magnetite in turbidite is coarser than that of background sedimentation.The similar magnetic properties between the turbidite and background sedimentation suggest the same provenance.However,the differences of concentration and grain size between them were resulted by primary depositional setting of turbidite closer to the provenance than background sedimentation.The occurrence of these turbidity currents sedimentation in the Huatung basin is implied to be potentially related to the gravity-induced slumping of sediments on slope(e.g.slope failure)that caused by sea-level fluctuation frequently during the Last Glaciation,and the sediments on the slope were transported to the deep basin.
【Fund】: 国土资源部海底矿产资源重点实验室开放基金课题(KLMMR-2014-A-12);; 国家自然科学基金项目(41306042 41272384);; 中国地质调查局项目(GZH201300502 GZH201500202 DD20160227)资助
【CateGory Index】: P736.2
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