Turbidite and bottom-current evolution revealed by anisotropy of magnetic susceptibility of redox sediments in the Ulleung Basin,Sea of Japan  

作　　者：GE ShuLan SHI XueFa LIU YanGuang WANG KunShan ZOU JianJun DIAO JingYu ZHU ZhiWei WANG ChunJuan 

机构地区：[1]First Institute of Oceanography,State Oceanic Administration,Qingdao 266061,China [2]Affiliated Middle School of China Ocean University,Qingdao 266003,China

出　　处：《Chinese Science Bulletin》2012年第6期660-672,共13页

基　　金：supported by the International Cooperation Program (40710069004);the Key Program (40431002);the Ordinary Program (40876036,41076038) from the National Natural Science Foundation of China;the Basic Research Program of the First Institute of Oceanography (2007T09)

摘　　要：Anisotropy of magnetic susceptibility(AMS) from above and below 7.31 m in a core from the southern Ulleung Basin shows clear differences on an equal area projection of the lower hemisphere.Rather concentrated steep inclination of K 3 and horizontal inclination of K 1 and K 2(K1 ≥K2 ≥K3) are located within the upper part,and the latter two axes lie perpendicular to each other near the bedding plane.In contrast,random distribution of the three axes and extremely high value of shape parameters(Q=(K1-K2)/[(K1+K2)/2-K3]) are evident in the lower part,indicating complete destruction of the original sedimentary structure.This result is consistent with data from X-radiographs,which show numerous conglomerates,distortions and cleavages in the lower part.According to age models by Liu et al.(2010) and Zou et al.(2010),the bottom age at 7.31 m is 48 cal ka BP,and the time domain is discussed below.The degree of AMS(P) is low,1-1.08,and linearly related to the foliation(F)(R2 =0.95,N=176).The relationship between F and linearity(L) implies oblate aligning patterns that are typically sedimentary in origin.At least five redox couplets were found with the aid of S ratios and other rock magnetic parameters,and in most cases,the original signals of climate survived early diagenesis.The paleomagnetically reoriented AMS show corresponding changes with millennial events in the last 48 cal ka.Clearly tilted K 3 directions and reduction of P and F occurred within DO1-BA warm events,when melt water pulse 1A nd the YD cold event took place.The turbulent conditions therein,synchronous with coarsening of sediments,provide evidence of strong bottom currents and possible directional changes,as evidenced by different K3 tilting directions.A NE current direction in the last 4.5 cal ka is consistent with in situ measurements of bottom currents.Responses of AMS,mainly to climatic modulation,show on the one hand,the limited influence of diagenesis on rock magnetic signals and,on the other hand,the dramatic change of hydrodynamic conditions aAnisotropy of magnetic susceptibility （AMS） from above and below 7.31 m in a core from the southern UUeung Basin shows clear differences on an equal area projection of the lower hemisphere. Rather concentrated steep inclination of K3 and horizontal inclination of K1 and K2 （K1≥K2≥K3） are located within the upper part, and the latter two axes lie perpendicular to each other near the bedding plane. In contrast, random distribution of the three axes and extremely high value of shape parameters （Q=（K1-K2）/ [（Kl＋K2）/2-K3]） are evident in the lower part, indicating complete destruction of the original sedimentary structure. This result is consistent with data from X-radiographs, which show numerous conglomerates, distortions and cleavages in the lower part. According to age models by Liu et al. （2010） and Zou et al. （2010）, the bottom age at 7.31 m is 48 ca1 ka BP, and the time domain is discussed below. The degree of AMS （P） is low, 1-1.08, and linearly related to the foliation （F） （R2=0.95, N=176）. The relationship between F and linearity （L） implies oblate aligning patterns that are typically sedimentary in origin. At least five redox couplets were found with the aid of S ratios and other rock magnetic parameters, and in most cases, the original signals of climate survived early diagenesis. The paleomagnetically reoriented AMS show corresponding changes with millennial events in the last 48 cal ka. Clearly tilted K3 directions and reduction of P and F occurred within DO1-BA warm events, when melt water pulse 1A nd the YD cold event took place. The turbulent conditions therein, synchronous with coarsening of sediments, provide evidence of strong bottom currents and possible directional changes, as evidenced by different K3 tilting directions. A NE current direction in the last 4.5 ca1 ka is consistent with in situ measurements of bottom currents. Responses of AMS, mainly to climatic modulation, show on the one hand, the limited influence of diagenesis on rock magnetic

关 键 词：磁化率各向异性 电流方向 氧化还原 沉积物 底部 盆地 日本海 早期成岩作用 

分 类 号：P736.41[天文地球—海洋地质] TB332[天文地球—海洋科学]