南海北部新生代海陆变迁与不同盆地的沉积充填响应*

新生代以来南中国海的多幕旋回运动形成了其北部陆坡性质各异、演化有别的多个陆缘沉积盆地。依据各盆地新生界发育特征、主干地震剖面及钻井资料对南海北部的相对海平面变化与沉积环境进行系统分析,采用年代地层对比的方法探讨南海北部构造演化序列与海陆变迁规律的内在联系,再现了南海北部陆缘新生代的海陆变迁过程,从而建立了南海北部陆缘裂谷盆地、走滑拉分盆地和陆内裂谷盆地的构造—沉积充填一体化模式。新生代海平面整体呈上升趋势,古近纪各盆地以陆相河流、粗粒三角洲湖相沉积为主;而新近纪主要发育滨浅海及三角洲相,呈现出明显的早陆后海的规律。靠近陆地一侧的陆内裂谷盆地北部湾盆地海侵最晚,其古近系充填厚度明显大于新近系,以发育近源扇三角洲为特色;而靠近海域一侧的走滑拉分盆地(莺歌海盆地)则以新近纪海相沉积占优势;陆缘裂谷盆地(琼东南与珠江口盆地)古近纪陆相与新近纪海相相对均衡发育,发育大型三角洲与碳酸盐岩台地。不同盆地的沉积充填特征主要受构造运动与海侵规模控制,并由此奠定了不同盆地的资源前景。

The Cenozoic changes of seas and lands and sedimentary filling responses of different basins in northern South China Sea

Multiple continental margin basins of different property and evolution were formed in the multi-cycle movement of the South China Sea since the Cenozoic. Based on the stratigraphic characteristics,seismic and drilling data of the basins,the analyses of relative sea level changes and sedimentary environment were conducted. And chronostratigraphic correlation method was used to discuss the changes of seas and lands in response to the structural evolution. Eventually the structure-sedimentary filling integrated patterns of continental margin rift basin,strike slip pull apart basin and continental rift basin in the northern South China Sea were established. The changes of seas and lands of the continental margin in the northern South China Sea was reconstructed to determine the scope of the sea water in the Cenozoic. The sea level shows a rising trend through the whole Cenozoic,with continental river,coarse delta and lacustrine facies in Paleogene and delta and littoral-neritic sea facies mainly in Neogene. The transgression of sea water occurred later in continental rift basin (Beibuwan Basin, closer to land),resulting in a larger coarse delta filling thickness in Paleogene than that in the Neogene. However,the strike slip pull apart basin(Yinggehai basin,closer to sea)is characterized by fine-grained marine deposits in Neogene. And the continental margin basins show a relative sedimentary balance between the Paleogene and Neogene,respectively deltas and carbonate rock platform. Sedimentary filling of different basins is mainly controlled by tectonic movements and transgressive scale,thus their resource potentials are different.