南海东沙陆坡1144站沉积牵引体的地震层序框架及沉积演化
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摘要
以高分辨率二维地震资料为主,结合ODP184航次1144站位的钻井和测井资料,应用地震地层学原理,对南海北部东沙陆坡1144站所在沉积牵引体的形态、规模、内部结构及沉积演化进行研究,识别出了7个全区分布的不整合型层序界面。1144站合成记录层位标定表明,除最底部的层序界面外,其余6个界面的地质年代自下而上分别约为1.09、0.88、0.65、0.30、0.13和0.02Ma;以上述7个不整合面及海底为边界,划分出了7个地震层序,自下而上依次为层序1～7。其中,层序1以杂乱的弱振幅反射为特征,解释为沉积牵引体发育前的滑塌或碎屑流沉积;层序2～7以平行—波状的连续中强振幅反射为特征,解释为沉积牵引体的主体,由此推测该沉积牵引体主要形成于约1.09Ma以来的中—晚更新世。编制了各层序的等T0厚度图,发现不同层序发育时期沉积厚度的横向变化较大,其沉积中心大致沿陆坡走向发生过4次比较明显的迁移。该沉积牵引体总体沿陆坡走向呈北东—南西向的不规则带状分布,保守估计其面积约为1 100km2,厚度为280～520m。
Seismic stratigraphic framework and depositional evolution of the sediment drift at ODP Site 1144,Leg 184 Dongsha Slope,Northern South China Sea,are studied using high-resolution 2-D seismic data,combined with the drilling data and geophysical well logs.Seven seismic discontinuities with reflection terminations(onlap,downlap,toplap and erosional truncation),named SB1 to SB7 upwards,are identified within the drift.As a result,seven seismic sequences S1 to S7,from bottom to top are defined.The bottommost sequence is characterized with chaotic,weak amplitude reflections and interpreted as pre-drift slumping or debris deposits.The other sequences(S2-S7),which consist mainly of reflections with sub-parallel to wavy,continuous,medium to strong amplitude,are interpreted as the main components of the drift.Well-to-seismic correlation with the synthetic seismogram of Site 1144 suggests that the sequence boundaries of SB2 to SB7 were approximately developed at 1.09,0.88,0.65,0.30,0.13 and 0.02 Ma,respectively.Time thickness maps of the sequences suggest that depositional centers shifted frequently,mostly in a direction parallel to the slope strike.The drift extends in NE—SW along the slope.According to the thickness distribution,the drift is estimated at least 1 100 km2 in area,with a maximum thickness of about 520 m.
Seismic stratigraphic framework and depositional evolution of the sediment drift at ODP Site 1144,Leg 184 Dongsha Slope,Northern South China Sea,are studied using high-resolution 2-D seismic data,combined with the drilling data and geophysical well logs.Seven seismic discontinuities with reflection terminations(onlap,downlap,toplap and erosional truncation),named SB1 to SB7 upwards,are identified within the drift.As a result,seven seismic sequences S1 to S7,from bottom to top are defined.The bottommost sequence is characterized with chaotic,weak amplitude reflections and interpreted as pre-drift slumping or debris deposits.The other sequences(S2-S7),which consist mainly of reflections with sub-parallel to wavy,continuous,medium to strong amplitude,are interpreted as the main components of the drift.Well-to-seismic correlation with the synthetic seismogram of Site 1144 suggests that the sequence boundaries of SB2 to SB7 were approximately developed at 1.09,0.88,0.65,0.30,0.13 and 0.02 Ma,respectively.Time thickness maps of the sequences suggest that depositional centers shifted frequently,mostly in a direction parallel to the slope strike.The drift extends in NE—SW along the slope.According to the thickness distribution,the drift is estimated at least 1 100 km2 in area,with a maximum thickness of about 520 m.
引文
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[3]王律江,Sarmhein M.南海北部陆坡近四万年的高分辨率古海洋学纪录[J].第四纪研究,1999,1:27-31.[WANG Lüjinag,Sarmhein M.High-resolution Paleoceanographic Records dur-ing the last 40000 Years from the Northern Slope of SouthChina Sea[J].Quaternary Sciences,1999,1:27-31.]
[4]Wang P X,Prell W L,Blum P,et al.Leg 184summary:ex-ploring the Asian monsoon through the South China Sea.In:Proceedings of the Ocean Drilling Program,Initial Reports,Volume 184[R].Texas A&M University,College StationTX,2000:18-29.
[5]Shao L,Li X H,Wei G J,et al.Provenance of a prominentsediment drift on the northern slope of the South China Sea[J].Science China Series D:Earth Sciences,2001,44(10):919-925.
[6]Lüdmann T,Wong H K,Berglar K.Upward flow of NorthPacific Deep Water in the northern South China Sea as deducedfrom the occurrence of drift sediments[J].Geophysical Re-search Letters,2005,32:L05614.
[7]Shao L,Li X J,Geng J H,et al.Deep water bottom currentdeposition in the northern South China Sea[J].Science ChinaSeries D:Earth Sciences,2007,50(7):1060-1066.
[8]钟广法,李前裕,郝沪军,等.深水沉积物波及其在南海研究之现状[J].地球科学进展,2007,22(9):907-913.[ZHONGGuangfa,LI Qianyu,HAO Hujun,et al.Current Status ofDeep-water Sediment Wave Studies and the South China SeaPerspectives[J].Advances in Earth Science,2007,22(9):907-913.]
[9]栾锡武,彭学超,邱燕.南海北部陆坡高速堆积体的构造成因[J].现代地质,2009,23(2):183-199.[LUAN Xiwu,PENGXuechao,QIU Yan.Tectonic Control on the Formation ofHigh-deposition-rate Sediment Drift in the Northern Slope ofthe South China Sea[J].Geoscience,2009,23(2):183-199.]
[10]Liu Z,Huang W,Li J,et al.Sedimentology.In:Wang P,Li Q,ed.The South China Sea:Paleoceanography and Sedi-mentology[M].Berlin/Heidelberg:Springer-Verlag,2009:178-180.
[11]Vail P R,Mitchum R M Jr,et al.Seismic stratigraphy andglobal changes of sea level.In:Seismic Stratigraphy-Applica-tions to Hydrocarbon Exploration[C].AAPG Memoir,1977,26:49-212.
[12]Buehring C,Sarnthein M,Erlenkeuser H.Toward a high-resolution stable isotope stratigraphy of the last 1.1millionyears:Site 1144,South China Sea[C]//Proceedings of theOcean Drilling Program,Scientific Results Volume 184.Tex-as:Texas A&M University,2004:1-29.
[13]Wang P X,Prell W L,Blum P,et al.Seismic reflection stra-tigraphy of Leg 184,South China Sea.In:Proceedings of theOcean Drilling Program,Initial Reports,Volume 184[R].Texas A&M University,College Station TX,2000:1-37.
[14]Faugères J C,Stow D A V,Imbert P,et al.Seismic featuresdiagnostic of contourite drifts[J].Marine Geology,1999,162:1-38.
[15]Rebesco M,Stow D.Seismic expression of contourites andrelated deposits:apreface[J].Marine Geophysical Resear-ches,2001,22:303-308.
[16]Faugères J C,Stow D A V.Contourite Drifts:Nature,Evo-lution and Controls.In:Rebesco M and Camerlenghi A,ed.Contourite[M].Elsevier Science,Oxford,2008:259-288.
[17]Chen M T,Beaufort L and the Shipboard scientific Party ofthe IMAGESⅢ(MD106)-IPHIS Cruise.Exploring Quaterna-ry variability of the East Asia monsoon,Kuroshio current,and Western Pacific Warm Pool systems:high-resolution in-vestigations of paleoceanography from the IMAGESⅢ(MD106)-IPHIS cruise[J].Tao,1998,9(1):129-142.
[18]Wang P,Zhao Q,Jian Z,et al.Thirty million year deep-searecords in the South China Sea[J].Chinese Science Bulletin,2003,48(23):2524-2535.
[19]Lin D C,Liu C H,Fang T H,et al.Millennial-scale changesin terrestrial sediment input and Holocene surface hydrogra-phy in the northern South China Sea(IMAGES MD972146)[J].Palaeogeography,Palaeoclimatology,Palaeoecology,2006,236:56-73.
[20]杨文光,郑洪波,谢昕,等.南海北部陆坡沉积记录的全新世早期夏季风极强事件[J].第四纪研究,2008,28(3):425-430.[YANG Wenguang,ZHENG Hongbo,XIE Xin,et al.East Asian Summer Monsoon Maximum Records in NorthernSouth China Sea During the Early Holocene[J].QuaternarySciences,2008,28(3):425-430.]
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