南黄海东北陆架YSDP 105孔冰消期以来沉积层序的磁学特征研究

A ROCK MAGNETIC STUDY OF THE LAST DEGLACIAL TO HOLOCENE SEDIMENTARY SEQUENCE IN THE YSDP105 CORE ON THE NORTHEAST SHELF OF THE SOUTH YELLOW SEA

尝试对南黄海东北陆架ＹＳＤＰ１０５孔０．６０—２９．６８ｍ的沉积层序进行环境磁学的研究，测量了岩心的磁化率、非磁滞剩磁、等温剩磁、饱和等温剩磁等磁学参数。对磁学参数及其有关比值的研究发现，沉积层序以含碎屑成因的低矫顽力磁性矿物为主，另含少量高矫顽力磁性矿物。磁性矿物大部分为准单畴，少部分为单畴；其粒度受控于沉积环境：从潮间带、浅水潮下带→深水潮下带→浅海，磁性矿物的粒度依次递减，反映了沉积水动力的控制作用。自冰消期以来，沉积层序中高矫顽力磁性矿物的含量逐渐降低，表明进入黄海的风尘物质逐渐减少。

This paper focuses on the rock magnetic study of 0 60-29 68m core from the YSDP 105 drill hole,which was drilled on the northeast shelf of the South Yellow Sea.The 0 60 to 29 68 m core,formed during the last deglaciation and the Holocene,consists of thin interbedded mud and silt/fine sand.Research on sedimentary facies of the core shows that the shelf has experienced two sea level fluctuations ranging from shallow to deep since the deglaciation.The first fluctuation is indicated by change in sedimentary environment from intertidal—shallow subtidal zone(29 68 to 17 83 m)to deep subtidal zone(17 83 to 16 59 m),and the second is from intertidal—shallow subtidal zone(16 59 to 10 90 m)to deep subtidal zone(10 90 to 6 68 m) to shallow sea (6 68 to 0 60 m).For the rock magnetic measurements,142 samples were selected,more or less evenly placed over the drill core between 0 60 and 29 68 m.The following magnetic parameters were measured:low field susceptibility (K),anhysteretic remnant magnetization(ARM),isothermal remnant magnetization(IRM),IRM 300 (induced in a field of 300 mT),and saturation isothermal remnant magnetization(SIRM).Analyses of magnetic parameters demonstrate that magnetic minerals in the sequence are dominated by low coercivity ferrimagnetic minerals with subordinate high coercivity canted antiferromagnetic minerals and are characterized by pseudo single domain(PSD)and single domain(SD)with a detrital source.Variation in grain size of magnetic minerals is controlled by sedimentary environment in which they were deposited:they are relatively coarse sized in intertidal shallow subtidal zone,medium sized in deep subtidal zone,and fine sized in shallow sea,reflecting control of water dynamic on the granularity of detrital magnetic minerals.The content of high coercivity magnetic minerals(indicated by two magnetic parameter ratios:S and HIRM)gradually decreases from bottom to top in the sequence,suggesting that eolian dust entering the sea area declines with time,which is in good agreement with the climate-environment evolution of the eastern part of China since the deglaciation.