一个大陆坡环礁—南海华光珊瑚环礁的沉积相模式及其演化趋势

华光珊瑚环礁是一典型的大陆坡环礁,区别于大洋环礁和大陆架环礁。其发育既受全球板块运动,又受海面升降运动的控制。现代环礁的结构是在冰期时形成的先成台地之上复盖着一薄层的全新世礁相沉积。东亚季风的作用使礁形成各向相似的沉积相带。环礁礁冠与泻湖宽度之比可作为现代环礁成熟度的定量标志。华光环礁目前尚处于幼年期。

Sedimentary Facies Model and Evolution of a Continental Slope Atoll-Huaguang Coral Atoll in the South China Sea

Huaguang Coral reef is one of the continental slope atolls in the South ChinaSea, which are distinguished from oceanic atolls and shelf atolls. Since the trans-gression before 17 million years B. P., on the relict mountains, bioherms havedeveloped and formed carbonate platforms. The regression of Quaternary glacialperiod has made the sea level 135m down under the recent one, and carbonateplatform has been electively corroded, karsted and planated. The rising sea levelsof postglacial period has formed again coral atoll on the karst platform. Hence,the construction of modern coral atoll is a thin veneer of Holocene reef al sedi-ments over the antecedent platform. The condition of continental slope will profit the growth of reef-building or-ganisms and form coral reef. The alternation of the NE and SW monsoons formeda nearly equal balance of hydrodynamic conditions from all directions, and itresulted in a symmetrical morpholigy of Huaguang Coral Atoll. Sea water of the atoll lagoon has a better circulation, and on the lagoonalfloor there is a lush growth of corals and sponges. According to the ratio ofbreadth of reef crest versus breadth of lagoon we may define three stages of ma-turity of atoll development: juvenile, mature and senile. The condition of Hua-guang Coral Atoll is in the juvenile stage. The authors proposed a sedimentary facies model of Huaguang Coral Atoll,which may apply to the juvenile coral atolls and may partly apply to the othercoral atolls of various stages of reef development in the South China Sea.