【作者】 王珊珊；

【导师】 曹志敏；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2008， 博士

【摘要】 珠江三角洲及其近岸河口区既是人类活动频繁区域又是陆海相互作用显著区域。因此,对于该区域现代环境研究和古环境研究都具有很大的科学价值和现实意义。本文对三角洲近岸河口海域78个表层沉积物样品的粒度特征、矿物成分、微量元素及其地球化学特征的研究,阐明珠江河口区表层沉积物的来源、搬运过程以及人类活动对该区沉积环境的影响,进一步探讨了其源一汇意义;通过对河口海域内3个晚更新世以来沉积岩心的粒度、碎屑矿物、微量元素以及微体古生物、孢粉和¹⁴C测年数据等综合分析和对比,从时、空二维角度研究该区晚更新世以来海平面变化、气候交替、区域构造活动对该区沉积环境的影响及该区环境演变的过程。通过对各类矿物含量和空间分布特征的研究,矿物的分布和富集不仅受矿物自身物理化学性质和沉积条件的影响,还受到经常性近岸输沙的明显影响。不稳定重矿物的分布特征就反映了周边城市填海造田工程对海洋环境的影响。碎屑矿物以石英、长石类轻矿物为主,重矿物含量低于10%,主要为花岗岩类的副矿物兼具浅变质岩副矿物组合特征。海洋自生矿物量微,表明该区受陆源输入、近岸输入以及岛屿输沙影响,即珠江口海域主要接受珠江河系携带、搬运的物质。对表层沉积物微量元素地球化学研究表明,Co、Cu、Ni和Ba主要受控于母岩,一定程度上受人类活动影响,该组元素空间分布主要受水动力条件的控制。元素Sr在该区的分布和富集受海洋环境的影响明显,尤其受到该区水产养殖业的影响。Pb、Zn在该区的含量和空间分布不仅表现出陆源输入的影响,同时具有受点源输入影响的特征。富集因子分析表明,人类活动对该组元素的贡献不容忽视。三角洲近岸河口海域源-汇模型计算可知,每年在该海域沉降和输入到南海以及远岸海域的金属元素数量极大,现代珠江河口作为珠江向南海输移泥沙过程中最理想的沉积场所和海-陆环境过渡地带,是珠江口外以至南海海域重要的物质来源,环境意义举足轻重。通过对岩心沉积环境的演化和不同岩心沉积环境对比研究,认为末次冰期之前现代珠江河口和近岸海域主要是陆地环境,东侧岛屿区为侵蚀丘陵地带,末次冰期最高海平面时期,现代珠江三角洲以及珠江河口区统一为一个河口湾,且其东侧边界为现在的岛群区;末次冰期盛冰期海平面下降时期,该区域大部分出露于海平面之上,仅西部低洼地或者河流溺谷区会受到海水入侵的影响。东侧丘陵地带由于多年的侵蚀剥蚀,其高度不断下降,并开始沉积河流冲积物;冰后期大规模海侵导致海平面不断上升,现在的整个珠江河口区域逐渐由陆变海,且随着海侵的演进海洋环境影响逐渐增强,该区受到陆架水体的影响明显,成为陆架浅海环境;在距今5000年左右,海侵基本停止,海平面稳定,现代珠江三角洲向海淤进,造成海岸线向海推进。受河流冲淡水和三角洲沉积影响,高盐陆架水向海退,形成现代珠江河口湾及三角洲近岸浅海环境。因此现代珠江河口三角洲很年轻,主要形成于全新世中期以来,是海陆相互作用的产物。珠江三角洲区域地质构造活动对该区沉积环境演变的影响表现在末次冰期早期西江-磨刀门断裂以西发生构造下沉,导致该区地势降低,受到海洋环境的影响并最早沉积海相沉积物,东部断裂凹陷区全新世构造沉降造成海进期及其稳定后的三角洲堆积极厚的沉积物。岩心的沉积环境演变研究发现,珠江河口区除存在晚更新世以来两次大的海侵事件——礼乐海进和桂州海进之外,还在全新世和晚更新世过渡期存在一次短期的范围较小的海平面波动。植物孢粉分析反映了该区晚更新世以来热带-亚热带温暖、潮湿气候状况以及在此气候条件下的两个明显的气候阶段——末次冰期气候干凉阶段和冰后期气候暖湿阶段。孢粉分析同因子分析曲线都记录了冰期转暖之后的一次气候变冷事件——YD事件。气候的冷暖变化同海平面的升降具有极好的耦合性,反映了气候的冷暖变化是珠江三角洲和珠江河口湾环境变化的根本原因。更多还原

【Abstract】 With active interactions between ocean and land, the near sea and estuary areas around deltas response sensitively to natural processes and human activities. So, studies of modern and paleo-environments around those areas are valuable for science and social development.Through the analysis of grain size, minerals and trace metal elements of 78 surficial sediments from the Pearl River estuary and near sea area, the impact of sediment sources, transport processes and human being activities on the sedimentary environments were studied. Further more, the signification of source-sink was discussed via simple model. Data of grain sizes, detrital minerals, trace elements, microfossils, sporopollen and ¹⁴C dating of 3 sediment cores were used in the interpretation of the evolvement of depositional environment from late Pleistocene epoc and the impaction of sea level fluctuation, paleo-climate changes and the instability of regional tetonics on the sedimentary environments.Mainly composed of quartzs and feldspars with less than 10% heavy minerals, which characterised with mineral assemblages of granitic and metamorphic rocks, detrital minerals in surficial sediments indicated the contributions of terrigenous deposition via runoff, land and islands direct inputs. Other sources of the sediments include authigenic biogenic deposition and volcanignic via tide and seawater mass from the slope. The content and distribution of several minerals such as olivine and limonite revealed the obvious influence from public works such ad sea-filling project.Spatial distributions of trace metal elements showed following features: Distributions of Co, Cu, Ni and Ba showed their connections with the compositions of source rocks, indicating that, they were dominated by hydrodynamics, coupled with mild anthropogenic influence. Sr were mainly controlled by sea environment factors especially aquiculture. Pb and Zn showed unnatural characteristics, and enrichment factor analysis confirmed significant anthropogenic influence.Modal calculation showed that, the amount of annual deposition and exportation of metal elements in the studied area was huge. As an ideal place of sedimentary environment and transition place between the sea and land, the Pearl River estuary showed important source-sink functions, providing sediments to South China Sea and around the estuary.Studies of 3 sediment cores revealed the following pictures. Before Late Pleistocene epoc, Pearl River estuary and near sea area were main land, with the east islands and inlets as corroded and denudated foothills. In the time in LGH, the modern Pearl river delta and Pearl river estuary was unified to be a big estuary, with the east edge as islands in the east side. In LGL, most of the area was bared in air, leaving some low area in the west influenced by the sea, the hypsography of foothills in the east becoming low and aggregated fluvial sediments for long time denudation and corrosion. In the post-glacial period, with the invadation of the sea, the area became gradually to be shallow slope area. Around 5000 a B.P., the sea level didn’t fluctuated as before, so the modern Pearl river delta intruded to the sea and the coast line intrude too, the slope sea water with high salinity fell back, therefore, study area became to be near land shallow water area just like today. All these indecated that, Pearl river was a young delta, generated from mid-Holocene Epoch, as the outcome of the interactions between the sea and the land.The movement of geologic structure around the Pearl River delta also had an influence on the sedimentary environment. In the early stage of the last glacial age, the subsidence of the west part of Xijiang-Modaomen Fault resulted in the transgression of the sea, received the earliest marine sedimentation. In the Holocene epoch, the tectonic sinking of the depressed area between the east Faults resulted in huge sedimentary layers as witnessed by the core NNZ1.Sedimentary core studies also revealed that, besides two big transgressions since, namely, Lile and Guizhou transgression, the Pearl river estuary region also suffered a short time and small scale sea level fluctuation between them.The pollen analysis reflected the tropical-subtropical climate characteristics since Late Pleistocene epoch and several climate changes in the period. Especially, Pollen and factor line marked Young Dryas event in this area. The well coupling of paleoclimate and sea level fluctuation reflected that the paleoclimate controlled the environmental evolvement ultimately.更多还原