【作者】 李超；

【导师】 韩宗珠；

【作者基本信息】 中国海洋大学 ， 地球化学， 2008， 硕士

【摘要】 海洋沉积物是一个巨大的信息库,它储存着丰富的有关地球历史和环境演化的信息。陆架海及其延伸海域的沉积物,沉积速率快,记录信息分辨率高,同时包含大量陆源碎屑沉积,是开展海陆相互作用以及全球变化研究的理想场所。作为西北太平洋边缘的弧后盆地,四国海盆海底地势相对平坦,沉积物保存连续而且完整,对探讨西北太平洋古海洋环境演变具有重要意义。本文选择位于四国海盆南部和中部的F120909(54cm)和F130601(88cm)两岩芯沉积物,通过对其粒度和元素地球化学特征的分析,研究该区域的沉积环境,并进一步讨论其物质来源。粒度分析表明,两岩芯沉积物粒度垂向上总体比较均一,主要是粘土质粉砂,但不同层位也稍有差别,表现为自下而上粒度由细逐渐变粗,尤其是表层部分,含砂量有所增加,体现出陆源碎屑沉积的增强。常量元素分析结果显示,两岩芯中主要氧化物依次为SiO2、Al2O3和Fe2O3,此三项约占所有氧化物总含量的75%以上。整个岩芯自下而上各常量组分变化不大,其平均值均与大洋沉积物基本接近;两岩芯中SiO2/Al2O3、Fe2O3/Al2O3和TiO2/Al2O3的比值最接近深海粘土的比值特征。对于岩芯F130601,在30cm～20cm深度上有明显的MnO富集异常,可能与海底热液事件记录有关。从微量元素组成看,两岩芯分别在不同层位上都表现出了Co、Ni、Cu、Pb等元素的富集显示,可能反映了火山物质的影响。微量元素配分模式显示,除明显富集Ba和Th外,其它元素含量均与北美页岩类似;而REE配分曲线较平缓,无明显Eu异常和Ce异常,也与北美页岩类似。上述元素地球化学特征表明,四国海盆沉积物应以半远洋和远洋沉积为主。根据两岩芯所处位置和四国海盆的沉积动力环境,再结合物源判别图的分析结果,我们认为:在深海底流的作用下,岩芯F130601的沉积物主要来源于南海海槽,包括陆源碎屑沉积和火山碎屑沉积;而对于F120909,由于地处盆地南部,远离大陆,陆源性较F130601稍弱,火山物质(可能主要来源于四国海盆中央的扩张带及九州海脊)的影响更为明显。更多还原

【Abstract】 Marine sediment is very huge database, which has abundant records about the evolution of the environment and the earth. The sediment from the continent shelf and outspread area is characteristic of rapid sedimentary rate and high resolution. Besides, massive terrigenous clastic material is included, which is propitious to the study of land-ocean interaction. Shikoku basin, located at the margin of northwest Pacific, is a typical back-arc basin. The smooth terrain there has stored a mass of sediment which contains a lot of information for the environment evolution. Thus, the study of the sediment in Shikoku basin and the adjacent area is of great importance to understanding the paleo-environment of northwest Pacific.In this paper, two sediment cores F120909 (54cm) and F130601 (88cm) from south and middle Shikoku basin are chosen for grain size analysis and element geochemical analysis, including major elements and rare elements. Further more the sedimentary environment and their provenance are also discussed.Grain size analysis shows that, the two sediment cores are mainly made of clayey silt, generally uniform but small changes in different depths. Subsection comparision indicates that the grain size coarsing upwards gradually, especially in the surface where sand is unignored. It probably reveals the enhancement of terrigenous clastic material.Major elements analysis shows that the main components in the sediment cores are SiO2, Al2O3 and Fe2O3, which account for as much as 75%. There is no obverse change in both cores, which are quite similar with ocean mean value. Through comparision of SiO2/Al2O3, Fe2O3/Al2O3 and TiO2/Al2O3 with sediment from other typical areas, the sediment in Shikoku Basin is most close to deep-sea clay. For core F130601, it has an obvious MnO enrichment at 30cm to 20cm depth, probably by seafloor hydrothermal activity. Rare elements analysis reveals both cores are riched in Ba and Th. The other elements are more or less the same with NASC. According to the NASC-normalized REE distribution, both curves are nearly aclinic and there is no Ce and Eu abnormity. According to the geochemistry result above, it is concluded that Shikoku basin is characterized by hemipelagic and pelagic deposit.Considering the samples location and current mode, as well as the result from provenance discriminable diagram, it is inferred that: sediment in F130601 is mainly from Nankai Trough due to the contour current, including terrigenous clastic and volcaniclastic material; F120909, which is far from the continent, is less affected by Nankai Trough but appears more volcanic action affect, probably from the central Shikoku basin spreading center or Kyushu Ridge.更多还原