中中新世以来南海南部前隆的迁移:来自北康盆地的证据

利用二维地震资料探讨南海南部北康前隆的迁移现象及其对形成油气圈闭的影响。在南沙海域,早中新世不整合(EMU)是一个区域性不整合面,EMU之上的地层可以简单归结为披覆层系和水平层系。披覆层系直接覆盖在EMU上,具有连续薄层的平行地震反射特征,向南东方向加厚,属于悬浮沉积;而水平层系同期充填在低凹处,不断上超和覆盖早期的披覆层系,厚层状,呈不连续或弱反射特征,属于浊积物与悬浮物的混合沉积。通过上超反射终止的迁移和披覆层系的加厚两个特征判断,中中新世以来北康前隆在向上隆升的同时不断向南东方向迁移,反映了南沙海域减薄的陆壳有一个强烈挠曲和均衡反弹过程。前隆的迁移留下了一系列的古潜山,披覆层系和水平层系是很好的盖层,有利于圈闭的形成。

Forebulge migration since the Mid-Miocene in the southern South China Sea: evidences from the Beikang Basin

The 2D seismic data were used to discuss the migration of the Beikang forebulge in the southern South China Sea and its impact on trap formation.The strata overlying the Early Miocene Unconformity(EMU),a regional unconformity,could be simply categorized as draping and horizontal layer series in the Nansha sea area.The draping layer series overlie the EMU directly,show parallel seismic reflection characters of continuous thin layers and thicken southeastward,suggesting suspended sediments.While the horizontal layer series were deposited synchronously in structural lows and continuously onlapped and overlay the draping strata formed early.They are mixed thick sedimentary layers of turbidites and suspended sediments featuring discontinuous or weak seismic reflection.Judged by the migration of onlap reflection termination and thickening of the draping strata,the forebulge has migrated southeastward during its uplifting since the Mid-Miocene,indicating a process of intense flexure and equilibrium rebound occurring at the thinned continental crust in the Nansha sea area.The forebulge migration has caused the formation of a host of buried hills,with the draping and horizontal series of strata serving as favorable seals,which in turn will be conducive to the formation of traps.