南海北部陆架第四系边缘三角洲地震反射特征

SEISMIC FACIES OF QUATERNARY SHELF-MARGIN DELTAS IN NORTHERN SOUTH CHINA SEA

陆架边缘三角洲因其具有面积广、厚度大、储层发育等特点,在世界上已成为重要的油气勘探目标。运用高分辨率单道地震资料,对南海北部珠江口盆地番禺低隆起陆架边缘三角洲第四系地震相和沉积特征进行了详细分析,认为第四系陆架边缘三角洲主要为三角洲平原、三角洲前缘和前三角洲沉积。三角洲平原主要以水道—天然堤相组合为局部特征,频繁发生水道下切与改道。三角洲前缘主要以大型的前积地震相为主,随着海平面升降及物源供给变化,前缘带不断进积,由陆架向陆坡方向生长,三角洲前缘砂体前积受控于坡折带。前三角洲特征不明显。综合分析表明,研究区第四纪以来相对海平面经历了多次缓慢下降再迅速上升的旋回,形成了慢速海退和快速海侵交替进行的陆架边缘三角洲沉积。

Shelf-margin deltas have been regarded as one of the important hydrocarbon exploration tar- gets in the world for years for its wide distribution, big thickness and well-developed reservoirs. U- sing high-resolution seismic data, the authors analyzed the seismic facies and sedimentary characteris- tics of the shelf-margin deltas of Quaternary in details located in the Panyu Low Uplift of the Pearl River Mouth Basin （PRMB）, South China Sea. A shelf-margin delta is composed of three components i.e. a delta plain, a fore-delta and a delta front. The shelf-margin delta plain consists of the channel- levee complexes with frequent ravinement and deposition. The delta front usually shows a large scale of foreset seismic facies. When sea level rises and if the supply of sediment is sufficient, it moves quickly seawards, and the shelf-edge grows toward the slope. The delta front deposits are much influ- enced by shelf break. The depositional pattern of the fore-delta in the region is not clear to present. An integrated study of the deltaic deposits shows that the sea level changes in a cyclic manner in Qua- ternary. It drops slowly and rises rapidly in the research area. As the results, the deltaic deposits show a clear pattern of slow regression and fast transgression.