西沙海区晚新生代碳酸盐台地的发育模式及控制因素

EVOLUTIONARY MODEL AND CONTROL FACTORS OF LATE CENOZOIC CARBONATE PLATFORM IN XISHA AREA

基于最新的地震资料和已有的钻井资料研究发现,西沙海区的碳酸盐台地自早中新世早期开始发育,活跃至今。其中裂陷期基底断裂活动形成的构造高点为碳酸盐台地的初始发育提供了必要条件。在早中新世早期,碳酸盐台地主要发育在西沙隆起的西部和西南等斜坡之上,台地数目少并且规模有限。中中新世早期,碳酸盐台地全面发育,广泛分布于西沙隆起和广乐隆起以及永乐隆起周缘,单个台地的规模大小不等,台地的总面积达到了55 000km2。中中新世晚期,碳酸盐台地开始衰退,台地逐渐向地形高点迁移,许多类型的生物礁,如点礁、环礁等开始出现。晚中新世至今,只有一些规模有限的孤立台地发育于西沙隆起之上,如永乐、宣德环礁等。早中中新世以来,相对海平面变化和基底构造沉降共同控制碳酸盐台地的初始发育、繁盛、衰退和淹没等阶段。

Based on newly acquired seismic and well data, the present study demonstrates that the carbonate platforms in the Xisha area initiated on some high points of structures in Early Miocene and have remained active up to the present. In the beginning of Middle Miocene, carbonate platforms were only developed on the southwest and west slope of the Xisha Uplift and small in size. The carbonate platforms flourished a- round the Xisha Uplift and Guangle Uplift during Middle Miocene, and expanded to an area of about 50000 km2. Carbonate platforms began to migrate to topographic highs of the Xisha Uplift after Late Miocene. Many reefs, such as patch reefs and atoll reefs grew rapidly on the edge of carbonate platforms. Nowa- days, only a few atoll reefs survived by the Xuande and Yongle Atolls in the area due to sea level change and tectonic subsidence, which have been the major forces controlling the evolution of Cenozoic carbonate platforms in the Xisha area.