南海涠洲岛区现代沉积环境和沉积作用演化

EVOLUTION OF MODERN SEDIMENTARY ENVIRONMENTS AND SEDIMENTATIONS IN THE WEIZHOU ISLAND AREA,SOUTH CHINA SEA

涠洲岛区沉积环境的演化导致陆源碎屑沉积作用转化为礁源和陆源的混合沉积作用,并将向纯礁源碳酸盐沉积作用方向转化;其主要控制因素是陆源碎屑供应量.陆源沉积和礁源沉积之间可以互相制约,沉积环境和沉积作用可以互为因果.文中还指出涠洲岛区的沉积组分特征和南海北部礁坪沉积组分随纬度变化的规律.

Weizhou Island is a Quarternary volcanic island in the South China Sea. As a result of the eyolution of modern sedimentary environments, the terrig-enous sedimentation was replaced by the mixed sedimentation of reefoid car-bonates and terrigenous clastics since middle Holocene (about 3100 a. B. P.), and the latter will be replaced by the pure reefoid carbonate sedimentation. There are two kinds of mixed sedimentations: one is uniform mixed sedimentation, which is mixed stochastically by reefoid carbonates and terrigenous clastics contemporaneously, and the other is alternating mixed sedimentation, which is formed by alternating deposition of two derived materials periodically, or by facies change. It is realized that terrigenous clastics and reefoid carbonate sedimeuts can control each other, and that there is a causality between sedimentary environments and sedimentations. Detailed studies of sediment composition and distribution have revealed that the composition of sediments is dominated by shell debris in the Weizhou Island, and that the content of shell debris in reef flat sediments is incr-easing with the increase latitude in the north part of the South China Sea.