渤海湾西岸现代岸线钻孔记录的全新世沉积环境与相对海面变化

以渤海湾西岸现代岸线附近的NP3、CH110和BT113三个钻孔全新世岩心为研究对象,采用沉积岩石学、AMS 14 C(accelerator mass spectrometry 14 C,加速器质谱14 C)测年、微体生物聚类分析等方法精细判别沉积相,重建渤海湾西岸全新世沉积演化历史,并利用微体生物组合分带对水深变化的指示,定量讨论全新世相对海面变化。结果表明:渤海湾西岸全新世受海陆交互作用影响,经历了沼泽—潮滩—浅海—前三角洲—三角洲前缘—三角洲平原环境的演化过程。全新世初始阶段,研究区中部和北部发育沼泽环境,南部未见沉积,与上更新统河流相沉积呈不整合接触。全新世早期,研究区潮滩环境发育。潮滩层厚度约1m,历时数百至1千余年。至7 000cal BP前后水深增大,研究区进入浅海环境。约6 000cal BP,沿岸南北两端先后进入三角洲过渡环境,中部三角洲环境约开始于1 500cal BP。渤海湾西岸地区全新世的环境演化同时记录了该地区的相对海面变化:约10 000cal BP前后,渤海湾相对海平面已接近21.3~20.4m。约8 000cal BP,相对海平面介于18.6~17.0m。约6 000cal BP时相对海平面低于6.8m,5 000~1 000cal BP,相对海平面高于-2.5 m,1 000~800cal BP,相对海平面介于-1.3~-0.4 m。8 000~5 000cal BP时,相对海面上升约15.0m,上升速率达5m/1ka。

Records of Holocene Sedimentation Environment and Relative Sea Level by the Boreholes Collected Along the Present Shoreline of the West Coast of Bohai Bay,China

The three boreholes (NP3 ,CH110 ,and BT113) distribute from north to south along the west coast of Bohai bay .Through sampling the materials of the upper beds of the three cores deposited during Holocene , the authors analyze lithology , ages of AMS 14 C ,the assemblages of benthic foraminifera ,and ostracoda to rebuild the Holocene sedimentation environment ,and discuss the relative sea level changes quantificational . T he results indicate that influenced by land‐ocean interaction , the study area went through various stages of environmental development from swamp ,tidal flat ,shallow sea ,prodelta ,delta front to delta plain .At the beginning of Holocene ,swamps developed in the mid to north parts of the study area ; the south part , however , was exposed without deposition and unconformable contact with the underlying fluvial sediment deposited during Late Pleistocene .In Early Holocene ,tidal flat developed overall with about 1m sediment only which took about several hundred years to more than a thousand years . Around 7 000 cal BP , the sedimentation environment was transformed into shallow sea followed increasing water depth in Mid‐Holocene ,and at 6 000 cal BP , changed into delta regime at north and south ends along the present shoreline .But ,at mid of shoreline , delta regime began at 1 500 cal BP .The environmental change in the west coast of Bohai bay reflects the relative sea level change in Holocene .At the beginning of Holocene ,the relative sea level rose close to 21 .3 20 .4 m .At ca .8000 cal BP ,the relative sea level was 18 .6 17 .0 m ,and below 6 .8 m at ca .6 000 cal BP .At ca .5 000 1 000 cal BP ,the relative sea level was above 2 .5 m .It was between 1 .3 m to 0 .4 m during 1 000 800 cal BP .During the period of 8 000 5 000 cal BP ,the sea level rose about 15 .0 m with a faster rate of 5 m/1 ka .