【作者】 许冬；

【导师】 李家彪； 初凤友；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质学， 2014， 博士

【摘要】 为了深入认识泥质沉积在北部湾东部的展布、物质来源、输运路径、堆积速率及形成机制，本文对1522个表层沉积物样品进行了粒度分析，对421个表层沉积物样品进行了地球化学分析，对16只柱样进行了210Pb现代沉积速率分析。同时为了揭示末次冰消期以来北部湾东部沉积环境的整体变化，深入认识环流对北部湾沉积的控制作用，对位于北部湾东部的15只柱样进行了粒度、碳酸盐含量、C/N和稀土元素参数的分析，并测定了其中11只柱样的AMS14C年代。结果表明，在北部湾东部，从北向南具有Ⅰ1湾顶东北角砂质区、Ⅰ2琼州海峡砂质区和Ⅰ3海南岛西南砂质区这3个不连续分布的砂质区，而泥质沉积区基本上连成一体，在砂质沉积区外呈弯月形顺岸展布，从北至南有Ⅱ1钦州湾外泥质区、Ⅱ2雷州半岛西侧泥质区（由Ⅱ2-1和Ⅱ2-2构成）、Ⅱ3海南岛西侧泥质区和Ⅱ4海南岛西南泥质区这4个亚区。这一泥质带覆盖在晚更新世陆相地层上，厚度并不大（一般小于2m），主要是全新世末次海侵以来沉积。残留沉积Ⅲ见于湾中部白龙尾岛周围，有现代沉积混入，但未被完全覆盖。化学风化指数（CIA）、Σ LREE/Σ HREE、(La/Yb)N、 Eu和Ce可作为研究区沉积物来源的识别指标。砂质区沉积物来源具有近源性特点，其中湾顶东北角砂质区Ⅰ1和海南岛西南砂质区Ⅰ3的沉积物均源自海岸的侵蚀，Ⅰ2琼州海峡砂质区的沉积物则主要源自海峡内海底的侵蚀。Ⅲ残留沉积区主要物源为古红河三角洲，但在一定程度上接受了现代沉积的改造。泥质沉积区的物源则有近源和远源2种情况，Ⅱ1钦州湾外泥质区属近源沉积，其物源是广西近岸河流携带的入海物质。Ⅱ2雷州半岛西侧泥质区则属远源沉积，其中Ⅱ2-2物源可能主要与琼州海峡一带侵蚀产物有关，Ⅱ2-1区沉积物源则相对更多元化。海南岛西侧泥质沉积Ⅱ3和海南岛西南泥质沉积Ⅱ4受珠江和红河的影响极小，沉积物应该主要源自海南岛本地。沉积物供应量是控制北部湾现代沉积速率区域性差异的主要因素，西侧的沉积中心是红河现代水下三角洲。东侧现代沉积速率相对较高的区域分布在钦州湾附近20m水深以浅的地区和涠洲岛至海南岛西岸一线外水深20-50m的内陆架，前处由湾顶近岸河流供应沉积物，而后处沉积物供应受北部湾环流制约。环流驱动形成了北部湾东侧沉积物“传送带”，输送物应该主要源自海南岛，也有从南部湾口进入的南海外海物质和经琼州海峡向西进入的物质。北上和西进海流在琼州海峡西口外汇合，流速减弱导致沉积物卸载形成细粒沉积物堆积中心。未卸载物质一部分向西北方向运移，形成泥质沉积区Ⅱ2-1，另一部分则向东北方向偏转，在雷州半岛西侧汇集形成泥质沉积区Ⅱ2-2。涠洲岛对北上和南下的物质均起到阻挡作用。沉积物“传送带”似乎具有西边界，在琼州海峡一线以南是在50m等深线附近，以北是在109°E附近，冬季可能略向西拓展。在末次冰消期随海平面上升，北部湾沉积环境由陆相向海陆过渡相和海相转变，沉积物碳酸盐含量和C/N随之出现递增和递减不同变化，其独特型式可用于沉积地层的划分和对比。柱样的稀土元素记录对海平面变化也有响应，还揭示了现代河流水下三角洲的建造。北部湾环流可能形成于7ka BP左右，对沉积物输运有重要影响，全新世中期后北部湾东部沉积物构成基本稳定。北部湾东部全新世中晚期沉积厚度与现代沉积速率有一定对应性，说明从北部湾环流形成至今，沉积物输运模式也并未发生明显改变。更多还原

【Abstract】 To understand the distribution, sediment source, sediment transport path,deposition rate, and the formation mechanism of mud sediment in eastern Beibu Gulf,1522surface samples were analyzed in grain size and421surface samples wereanalyzed in elementary geochemistry, and210Pb profiles of16cores were discussed.In order to reveal the general change of sedimentary environment of eastern BeibuGulf since Last Deglaciation, and to understand the influence of circulation tosedimentation in Beibu Gulf, granularity, calcium carbonate content,C/N and rareearth elements parameters of15cores were analyzed, while11cores were dated byAMS14C.The results show that there are3discontinuous sandy areas from north to southin eastern Beibu Gulf: the northeastern corner of the gulf (Ⅰ1), Qiongzhou Strait (Ⅰ2),and southwestern Hainan Island near shore (Ⅰ3). But the muddy area is continuouslydistributed off sandy area with falcate shape, from north to south, there are: outerQinzhou Bay (Ⅱ1), west Leizhou Peninsula offshore (Ⅱ2, with2parts, Ⅱ2-1andⅡ2-2), west Hainan Island offshore (Ⅱ3) and southwest Hainan Island offshore (Ⅱ4).This mud belt lay on late Pleistocene layer and generally with thickness less than2meters and was mainly deposited after last transgression in Holocene. Relict sedimentappeared around Bailongwei Island in central gulf and was mixed with but not totallyoverlapped by recent sediment.Chemical weathering index (CIA), Σ LREE/Σ HREE,(La/Yb)N, δEu and δCecan be used in distinguishing different sediment sources. The sediment ofⅠ1and Ⅰ3both came from coastal erosion, while the sediment source of Ⅰ2was controlled bybottom erosion in Qiongzhou Strait and sediment of Ⅲ mainly came from paleo-RedRiver delta, but generally reformed by modern sediment. The sediment source ofmuddy area is complex and the contribution of near source and remote source differsin area. The main source of Ⅱ1should be the Guangxi coastal rivers. Differently,remote source controlled Ⅱ2, mostly contributed by the erosion products fromQiongzhou Strait sediment, while more complex sources existed in Ⅱ2-1. Ⅱ3andⅡ4were hardly influence by Pearl River or Red River, and mainly controlled by localHainan Island source material.In the eastern part of the gulf, the relatively high sedimentation rates distributedin the area near Qinzhou Bay with water depth less than20m and the inner continentalshelf west to Weizhou Island-west Hainan Island with water depth between20m and 50m. It seems that there is a sediment conveyor belt driven by the anti-clockcircumfluence on the east side of Beibu Gulf which transports fine sediment south tonorth, and the sediment mainly come from Hainan Island, Qiongzhou Starit andbroader water outside the gulf. The converging of north going current with westentering water from Qiongzhou Starit lead to unloading of suspended material andformed the deposition center of fine sediment near west mouth of Qiongzhou Strait.The movement of rest sediment divided into two parts, one pointed to northwest andthe other turned to northeast and deposited off west Leizhou Paninsula. It seems thatthe west border of the sediment conveyor belt at south of Qiongzhou Strait is near50m isobaths while at north of Qiongzhou Strait is near109°E. In winter, this borderprobably moves westward a little.Along with the sea level rose during Last Deglaciation, the sedimentaryenvironment of Beibu Gulf changed from oceanic to terrestrial, and the calciumcarbonate content of sediment increased by degrees but C/N decreased by degrees.Thetypical pattern of calcium carbonate content and C/N curve can be used in comparisonand division of strata. The rare earth elements records also had response to sea levelvavriation and witnessed the construction of modern subaquatic delta.The transport and aggradation of sediment were controlled by the circulation inBeibu Gulf which probably formed at about7ka BP, and the composition of sedimentstayed stable since middle Holocene. The distribution of depositional thickness sincemiddle Holocene was homologous with modern sedimentation rates, indicating thatthe transport pattern expirenced little change since the formation of the circulation inBeibu Gulf in middle Holocene.更多还原