华南陆缘地质特征对南海北部盆地基底的约束

Constraints of geological characteristics of the South China continental margin on the basement of basins in northern South China Sea

通过野外地质考察和资料研究,总结了华南陆缘前新生代地层的地质特征,根据南海北部盆地内钻遇基底的钻井资料和地震剖面,利用区域地层对比方法,将盆地基底的地层、岩性和岩相按构造层从老至新与华南陆缘进行对比,以此对盆地基底的构造属性进行约束,为南海北部盆地基底油气勘探提供必要的基础地质支撑。研究发现,南海北部盆地前震旦系结晶基底属于华夏古陆的一部分,其上的震旦系—中生界特征与华南陆缘相似。震旦系—下古生界广泛分布于南海北部,岩石普遍遭受浅变质作用;上古生界仅分布在北部湾盆地,以碳酸盐岩为主,珠江口盆地及琼东南盆地缺失上古生界;中生界主要分布于阳江—一统暗沙东断裂以东地区,下部以海相碳酸盐岩及碎屑岩为主,向上过渡为陆相碎屑岩;北部湾盆地中生界零星分布。

The geological characteristics of Pre-Cenozoic strata along the South China continental margin are summarized through field geology investigation and data research. Based on seismic cross-sections and drilling data related to the basement of basins in north ern South China Sea and using regional stratigraphic correlation method, stratigraphy, lithology and Lithofacies of the basement is analyzed from lower structural layers to the upper as compared with those of the South China continental margin, thus providing constraints on tectonic attribute of the basement and laying a geological base for oil and gas exploration. The results shows that pre-Sini an crystalline basement of basins in the northern South China Sea is part of the Cathaysia Craton, and the Sinian-Mesozoic strata have similar characteristics with the South China continental margin. The Sinian-Lower Palaeozoic strata are widely distributed in the northern South China Sea, and most have experienced low-grade metamorphism. The Upper-Paleozoic strata, mainly composed of carbonate rocks, are only distributed in the northern Beibuwan Basin, and absent in Pearl River Mouth Basin and Qiongdongnan Basin. The Mesozoic strata are mainly distributed in the east of eastern Yangjing-Yitongansha fault, featured by marine carbonates clastic deposition in the lower layers and terrestrial clastic deposition in the upper layer, and rare in Beibuwan Basin.