南海东北部中生界岩石学特征及沉积环境

Petrology and Depositional Environments of Mesozoic Strata in the Northeastern South China Sea

南海东北部潮汕坳陷发现中—晚侏罗世到白垩纪的海相中生代地层,由泥岩、砂岩、放射虫硅质岩夹鲕粒灰岩及火山岩构成。岩石组合及沉积特征反映出,从中—晚侏罗世到白垩纪沉积水深经历了由浅到深,然后又转为陆地的一个完整旋回,沉积环境则经历了由滨浅海相到深海相,又到滨海过渡相和陆相河湖体系的演变过程,在深海相与滨海陆地过渡相之间存在一个明显的环境突变,为沉积环境缺失所致。与深海相放射虫硅质岩相伴,则夹有玄武岩(细碧岩)层。沉积反应的气候条件从中—晚侏罗世—早白垩世的温暖湿润气候环境过渡到晚白垩世的炎热干旱气候环境。这套海相中生代地层的存在对解释南海北部中生代大地构造演化以及古特提斯洋和太平洋的关系具有重要意义。

Mesozoic marine facies sedimentary rocks recently found in the Chaoshan Depression from the northeastern South China Sea consist of mudstone, sandstone, radiolarian siliceous rock, interbedded oosparite, and volcanics of Middle Jurassic to Cretaceous age. Their petrologic and sedimentary characteristics indicate that depositional environments shifted from shallow marine to deep marine, before returning back to continental facies. There was a sharp break between deep marine and continental facies, indicating a sedimentation hiatus. Thin basalt （spilite） layers are often interbedded in those deep marine radiolaria-bearing siliceous rocks. Paleoclimate turned from humid in the Middle Jurassic to Early Cretaceous to arid in the Late Cretaceous. The existence of these Mesozoic marine strata is very important for interpreting the tectonic evolution of this region and the influence of the Tethys tectonic domain on the Pacific tectonic domain during the Mesozoic.