南沙海区礼乐盆地沉积地层与构造特征分析

通过对地震剖面、钻井及拖网采样资料的分析,认为礼乐盆地发育有海相的中、新生代地层,存在晚白垩世与晚渐新世两个区域性不整合面,将沉积层分为三套构造层:下构造层较厚,为中生代地层,表现为翘倾断块和宽缓背斜两种构造样式;中构造层较薄甚至局部缺失,为古新世-早渐新世充填的张裂期沉积,表现为半地堑构造样式;上构造层为晚渐新统至第四系沉积,充填区域沉降期海相地层,地层较为平稳。在中构造层沉积过程中发育多排NE向控洼断裂,断裂倾向NW,形成多个半地堑,控制了新生代早期的沉积充填,同时也表现出礼乐盆地在新生代早期受明显的张裂作用。通过对各构造层的构造、沉积特征分析,认为礼乐盆地经历了挤压、拉张、漂移、区域沉降四个构造演化阶段,是一个以中生代地层为主的叠合盆地。

STRATIGRAPHIC AND STRUCTURAL CHARACTERISTICS OF LILE BASIN IN NANSHA AREA

The Lile basin, located in the north of the Nansha block, is a complicated superposition basin,which underwent four tectonic phases.Through seismic reflection profiles, drilling and dredge sample analysis, we believe there develop Mesozoic and Cenozoic marine strata in this area.The sedimentary strata are divided into three structural layers by two territorial uncomformable surfaces, which are Late Cretaceous and Mid-Miocene interfaces respectively. The infrastructural layer is the thick Mesozoic sediments, and presents tilting fault blocks and broad fold structure modes. The middle layer is thin Palaeocene-Mid-Miocene rift sediments, locally absent in the uplift area, displaying the typical half graben sedimentary filled by. The upper layer, filled by local subsidence marine sediment, is continuous and steady. The NE-trending faults developing in early Cenozoic, controlled the early Cenozoic sediment filling in half grabens. These faults may indicate the Lile basin underwent intensive tensional tectonic movement above the Mesozoic sedimentary formation.