南海南部1百万年以来的放射虫动物群特征

RADIOLARIAN FAUNA CHARACTERS IN SOUTHERN SOUTH CHINA SEA SINCE 1MaB.P.

定量分析了ODP184航次1143站岩心中的117个放射虫样品,得出南海南部1MaB.P.以来地层中的放射虫动物群特征如下:自1MaB.P.以来放射虫的数量分布丰度值呈现由低到高的变化趋势,并具有规律性的旋回特征,体现了1MaB.P.以来该海区放射虫动物群由贫乏向繁盛的逐步演化过程,以及海洋环境的几个阶段性变化。放射虫属种组成呈现明显的热带暖水动物群的组合面貌,优势种的组成与南海中北部海区及其它低纬度大洋相比存在一定差异,体现了该海区独特的放射虫组成特征。此外,指示温度的特征种在1MaB.P.来地层中的分布也显示了热带、亚热带海区放射虫的特殊指示作用。

Totally 117 samples at site 1143 of ODP leg 184, the only site of this leg that is located in the southern South China Sea, were analyzed to discuss radiolarian fauna changes in the stratum of this region since 1Ma B.P.Based on identification and statistics, totally 124 genera and 251 species of radiolarian were found, in which the dominant species are Tetrapyle quadriloba, Lithomelissa monoceras, Lithomelissa thoracites, Artostrobium auritum, O.tetrathalamus tetrathalamus and Botryocyrtis scutum, etc. Some conclusions were reached by the quantitative analysis as below. The quantitative distribution of radiolarian since 1Ma B.P.showed an obvious increasing trend and regular periodic changes. Before 0.9MaB.P., the radiolarian abundance remained at an extremely low level, all less than 100 individual·g-1 and some even zero. Between 0.9—0.65Ma B.P., it increased to a certain extent, but generally less than 1000 individuals·g-1. A rapid increase appeared since 0.65MaB.P., and obvious abundance change cycles existed respectively in 0.65—0.47MaB.P.,0.47—0.29MaB.P.,0.29—0.19MaB.P.,0.19—0.024MaB.P., and from 0.024MaB.P. to present. The average abundance became higher and higher at each stage of the whole process, reflecting the change stages of oceanic environment and the evolution process of radiolarian from poor to prosperous in this region. In addition, the composition of radiolarian genera and species showed a significant tropic warm water fauna characteristic, the dominant species assemblages were different from the northern and central SCS as well as the other low latitude sea areas, indicating a special fauna composition characteristic. Furthermore, the distribution of indicator species indicated the physical structure and chemical feature of water mass, and showed a particular indicating significance of radiolarian in subtropic or tropic region.