冲绳海槽晚第四纪沉积特征及其物源和环境意义

【作者】 蒋富清；

【导师】 秦蕴珊； 李安春；

【作者基本信息】 中国科学院海洋研究所 ， 海洋地质学， 2001， 博士

【摘要】 本文通过对冲绳海槽北端和南部两个海区沉积物样品的粒度、矿物和元素组成与分布特征的研究，探讨了冲绳海槽沉积物的来源，给出了一定元素组合的物源意义。通过对冲绳海槽两个柱状沉积物的粒度、矿物、元素在地层中的分布特征的研究，结合浮游有孔虫氧同位素地层划分，探讨了冲绳海槽晚第四纪沉积记录的古环境意义。 冲绳海槽陆架和陆坡沉积物明显具有陆架残留沉积的特征，沉积物主要由陆源碎屑矿物、生物碎屑、粘土矿物和少量自生矿物组成。在冲绳海槽北端，陆架和陆坡砂质区沉积物的主要来源是冰期低海面时古黄河的残留沉积，在现代沉积环境下受到海洋生物和自生沉积作用的改造；济州岛南部的细粒沉积区的物源主要是周围陆架残留沉积，在黄海暖流和黄海沿岸流的综合作用下，残留沉积中的细粒组分再沉积形成的。冲绳海槽北端海槽区沉积物主要是火山活动的产物，火山玻璃和火山型的辉石、紫苏辉石和磁铁矿明显富集。冲绳海槽南部沉积物的主要物源是长江沉积物，此外还有大量的海相生物沉积和自生沉积。 对元素分布特征的研究表明，冲绳海槽陆架区富含陆源粗碎屑组分SiO₂和生源碎属组分CaO和Sr，生物沉积对陆源沉积明显具有稀释作用。陆坡区由于受黑潮暖流的影响，往往富集Fe₂O₃和P₂O₅。在海槽区，陆源细粒组分以及与细粒组分相关的元素Al₂O₃、K₂O、Cu、Zn、Co、Ni和Cr等明显富集。利用R型因子分析的方法确定了两个研究区元素组合，结合沉积物的矿物组成给出不同元素组合的物源意义。 对冲绳海槽北部（Y127孔）和南部（E017孔）两个柱状沉积物的浮游由孔虫的δ¹⁸O进行了分析，将其与本区具有高分辨率的柱状样氧同位素曲线对比进行，结果表明，δ¹⁸O值较敏感地记录了冲绳海槽晚第四纪以来的古环境变化。δ¹⁸O的高值往往与冷期相对应，δ¹⁸O的低值与暖期相对应。冲绳海槽在12ka BP左右开始了逐渐转暖的过程，在10ka BP左右（YD事件）发生了短暂的降温过程，但降温幅度很小。根据沉积物化学组成在地层中的变化规律，大部分元素较敏感地记录了全新世气候转暖事件，但是对于千年尺度的YD事件，多数元素对此没有明显的响应。 冲绳海用火山活动对沉积物的组成和沉积环境的塑造起到了至关重要的作用。根 据氧同位素地层划分，在冲绳海槽北部 12ha BP曾有火山活动的纪录，距今约 ska Bp 以来，冲绳海槽有两次较大规模火山活动的记录。火山活动往往会在短期引起气候 的变冷，从而造成海区生态环境的破坏，生物沉积作用减弱。但从长期变化来看， 可能是气候变暖的因素之一。火山层的主要特征为沉积物主要由粉砂组成，平均粒 径明显高于周围层位，在矿物组成上表现为蒙皂石、火山玻璃和火山型的辉石、紫 苏辉石和磁铁矿的含量较高，在化学组成上表现为Na刀与Zr的同高于周围层位， 而陆源性较强的元素TFe；O。和民尸，以及生源组分CaCO；和 Sr的含量普遍低于周 围非火山层。更多还原

【Abstract】 The composition and distribution of the grain size, minerals and elements for surface sediments from the north and south Okinawa Trough are investigated. Based on the result, the sources of the sediments are analysed, and the soure indications of some groups of element are given. Based on the distribution of grain size, minerals and elements for two core sediments, combined with the distribution of the oxygen isotopic ratios, the relationship between the sedimentary records and their paleo-environmental indications are investigated. The sediments from the shelf and slope of the north and south Okinawa Trough are similar to the residual sediments. The sediments are mainly composed of terrestrial debris, biogenicial debris, clay minerals and autogenous deposits. In the north Okinawa Trough. the sandy sediments from the shelf and slope mainly derived from the residual sediments of the Yellow River during the ice age, in present envieronment, the sediments are rebuilded by the biogenic and autogenous deposits. The fine-grained sediments from the area to the south of the Chejudo islands mainly derived from the shelf residual deposits. Some of the fine-grained sediments in the residual sediments redeposit in the role of the Huanghai Sea warm current and the Huanghai Sea coastal current. The sediments from the trough of the north Okinawa Trough mainly derived from the volcanic activity. There are a lot of volcanic glass, augite, hypersthene and magnetite in the area. The sediments of the south Okinawa Trough mainly derived from the Yangtz River. In addition, there are some marine biogenic and autogenous deposits. According to the distribution of elements, the sediments of the continental shelf in the Okinawa Trough are mainly composed of terrigenous composition, such as Si02, and biogenic compositions, such as CaO and Sr. The biogenic deposits dilute the terrigenous deposits. The elements, such as Fe203 and P205, rich in the slope, where is influenced by the Kuroshio. Some elements, such as A1203~ K20~ Cu Zn.. Co.. Ni and Cr, mainly hosted in the fine-grained sediment, rich in the trough. Based on the result of the R-model factors analyses, the elements are devided into different groups, combined with the minerals distributions, every elements group are given a different source indication. The 6 18Q ratio of planktonic foraminifera for two core sediments from the north (core Y 127) and the south(core EO 17) Okinawa Trough are analysed. Stratigraphic correlation of oxygen isotopic ratios show that the 6 ISQ ratio record the change of the paleo- environment of the Okinawa Trough. The higher the 6 I8~ ratio, the colder the weather is, and vice versa. The weather becomes warm at about I 2ka BP, and then there is a short cold stage at about 1 Oka BP. According to the change of elements in the stratigraphy, most of the elements recorded the event of Holocene warming, and only several elements recorded the YD event. The volcanic activity plays a very important role on the composition of the sediments and the sedimentatry environment in the Okinawa Trough. According to the oxygen isotopic stratigraphy, There exit two large-scale volcanic activity records from 8.Oka BP to now. Only in the north更多还原