热带海洋学报 ›› 2020, Vol. 39 ›› Issue (2): 44-53.doi: 10.11978/2019041

• 海洋地质学 • 上一篇    下一篇

南海九章环礁中牛轭礁和西门礁新生沙洲沉积特征与动态

许眸莹1(), 高抒2(), 葛晨东1, 黄梅1   

  1. 1. 中国南海研究协同创新中心, 海岸与海岛开发教育部重点实验室, 南京大学地理与海洋科学学院, 江苏 南京 210023
    2. 河口海岸学国家重点实验室, 华东师范大学海洋科学学院, 上海 200241
  • 收稿日期:2019-04-22 修回日期:2019-10-15 出版日期:2020-02-20 发布日期:2020-03-10
  • 基金资助:
    国家自然科学基金重点项目(41530962);中国科学院院士咨询项目(2016ZWH005A-005)

Characteristics and morphodynamics of newly-formed coral debris deposits on the Niu’e and Ximen Reefs, Jiuzhang Atoll, South China Sea

Mouying XU1(), Shu GAO2(), Chendong GE1, Mei HUANG1   

  1. 1. Key Laboratory of Coast & Island Development of Ministry of Education, School of Geographic and Oceanographic Science, Nanjing University, Nanjing 210023, China;
    2. Stake Key Laboratory of Estuarine and Coastal Research, School of Marine Sciences, East China Normal University, Shanghai 200241, China
  • Received:2019-04-22 Revised:2019-10-15 Online:2020-02-20 Published:2020-03-10
  • Supported by:
    Key Project of the National Natural Science Foundation of China(41530962);Academician Consulting Project of the Chinese Academy of Sciences(2016ZWH005A-005)

摘要:

南沙群岛的珊瑚礁以环礁形式存在, 拥有各具特色的地貌形态。九章环礁中的牛轭礁和西门礁是两座发育有新生沙洲的环礁, 代表灰沙岛形成前一个重要的过渡性地貌演化阶段。这两处新生沙洲表层沉积物样品的粒度分析表明: 沉积物主要组分为珊瑚碎屑, 长轴中值粒径在14~45mm之间, 属于砾石级别; 样品分选系数在4.5~31之间, 分选性很差; 球度值为0.52~0.68, 球度差。粒度特征值中, 中值粒径具有随着到水边线距离的增大而升高的趋势, 而分选性和球度与距水边线距离关系不大。整体上中值粒径与分选系数呈正相关关系, 而与球度呈负相关关系。历史文献记载和卫星图像表明, 牛轭礁和西门礁上的新生沙洲都是近年来才形成的, 与风暴过程及冬季风有关。牛轭礁上沙洲向北迁移, 同时其长轴向东南方向延伸; 西门礁上沙洲整体向东南方向迁移, 并形成回弯形沙嘴形态。新生沙洲的出现与珊瑚碎屑物质供给变化或风暴浪作用变化的关系还需进一步探讨。

关键词: 新生沙洲, 粒度, 珊瑚碎屑, 风暴浪作用, 九章环礁, 南海

Abstract:

Coral reefs over the Nansha Islands have characteristic geomorphological patterns; they exist in the form of atolls. The Niu’e (also known as Mckennan) and Ximen (Whitsum) reefs of the Jiuzhang Giant Atoll are two secondary atolls with newly-formed debris deposits, which may represent an important stage of landform evolution from a submerged atoll towards a reef island. Grain-size analysis of the surficial sediment samples collected from the two reefs shows that gravel-sized coral debris is the main component of the deposit. Medium grain sizes of the samples (measured by the long axis) range from 14 to 45 mm. Sorting coefficients range from 4.5 (being poorly sorted) to 31 with a sphericity value of 0.52 to 0.68 (far from a sphere shape). Medium grain sizes show a trend of increasing away from the shoreline. Medium grain sizes of the sediment samples are positively correlated with sorting coefficients, whereas they are more or less negatively correlated with sphericity values. Based on an analysis of historical records and satellite images, these beach ridge- or sand bar-like deposits represent modern accumulation landforms; their formations are related to storm waves and to some extent to the winter monsoon waves. The sand bar on the Niu’e reef had been extending towards the southeast and at the same time moving towards the north. The sand bar on the Ximen reef had an overall migration towards the southeast, with recurved sand spits on both sides. The mechanisms for the formulation of these features, in terms of changes in coral material supply and storm wave pattern, need further investigations.

Key words: newly-formed reef top deposits, grain size, coral debris, storm wave, Jiuzhang Atoll, South China Sea

中图分类号: 

  • P737.11