摘要：

在南海北部大陆架陆源碎屑沉积占优势的背景上，在珊瑚岸礁和堡礁周围，广泛发育着礁源碳酸盐和陆源碎屑组成的混合沉积。它们以砂屑、砂砾屑结构为主并含有生物格架结构。混合沉积的形成条件是具备碳酸盐和硅质碎屑两类物源，活跃的水动力，干湿交替的气候，此外，海平面的相对波动，也会造成积极的影响。混合沉积方式有随机式、相变式和随机 - 相变式等三种。混合沉积体常是多种混合方式交替、叠加而成的沉积复合体。礁源与陆源混合沉积相模式是从岸礁 - 堡礁相模式基础上发展而来，按沉积相和沉积结构可以分为五种混合沉积：1)礁基混积岩和礁格架混积岩，2）礁坪砂砾屑混积岩，3）礁后海滩 - 沙堤砾砂屑混合沉积，4）礁后泻湖砂屑混合沉积和5）礁前（翼）浅海砂屑混合沉积。礁源与陆源混合沉积的鉴别标志是珊瑚骨屑和岩屑各占10 - 50 ％，其它生物碎屑不计。南海大陆架现代混合沉积是一个典型的实例，可为全面研究现代南海沉积学和比较沉积学提供依据。

Abstract:

In the North Continental Shelf of the South China Sea on the background of dominance of terrigenous clastic sediments, around coral fringing and barrier reefs, there widely develop recent mixed sediments, which consist of reefoid carbonates and terrigenous clastics. Textures of these mixed sediments are dominant by arenaceous and arenaceous - rudaceous, and include same biogenic frameworks. Occurrence of both carbonate and ciliciclastic sources, active hydrodynamic regimes and alternate of dry and wet climates are main factors of forming mixed sediments ,besides , the flucture of sea levels also have an active influence on it.There are three patterns of mixed sedimentation: stochastic, facies alternate and stochastic - facies alternate. Mixed sediments always are sedimentary complex, consiste of alternate and repeat of diverse patterns of mixed sedimentation. Sedimentary Facies model of mixed sediments of recent reefoid carbonates and siliciclasstics is developed from the facies model of friging and barrier reefs. Based on the sedimentary facies and textures they may be subdivided into 5 mixed sediments: 1) reef foundamental mixed sedimentary rocks and reef framework mixed sedimentary rocks; 2) reef flat sand - gravel mixed sedimentary rocks; 3) reef back beach - dune gravel - sand mixed sediments; 4) reef back lagaonal sand mixed sediments and 5) fore - reef ( flank ) littoral sand mixed sediments. The distinguish indicates of reefoid carbonate and siliciclasstic mixed sediments are components, which both coral deblis and classtics cosist of 10 - 50 ％ and other biogenic fragments are no counted. Recent mixed sediments in the continental shelf of the South China Sea are a typical example, which may provide scientific basis for all-round research sedimentology of the South China Sea and for comparative sedimentological research.