同沉积断层控砂模式——以南堡凹陷南部地区Es^1段为例

Models of contemporaneous fault controlling sandstone deposition:a case study of Es^1 in southern Nanpu Sag

同沉积构造活动的时空差异性对盆地的可容纳空间、沉积速率、物源体系的类型及展布特征等都具有深刻的影响。南堡凹陷幕式构造活动是沉积物可容纳空间的主要贡献者,其南部物源区沙河街组沉积时期发育的多条NE-SW向同沉积断层增强了湖盆的分隔性,一系列向湖盆内延伸、呈雁列状排布的生长断层控制了沙河街组地层的分布,与生长断层走向一致并形成于断层下降盘的线状洼槽是沉积物的主要卸载区,辫状河三角洲、远岸水下扇、滩坝以及湖泊体系是南堡凹陷南部物源区主要的沉积体系组合。在此基础上,建立了南堡凹陷南部地区同沉积断层控洼槽、洼槽控砂的沉积模式,总体上表现为:向湖盆内部伸展的同沉积断层控制了辫状河三角洲砂体的展布,呈现出平面上沿断层走向分布于下降盘的朵状沉积体,剖面上呈楔状叠加的沉积特点。辫状河三角洲、辫状河三角洲前缘末端形成的远岸水下扇以及断块翘倾一侧发育的滨浅湖滩坝砂体是下一步油气勘探的有利目标。

Temporal-spatial differences of syndepositional tectonics have profound impact on accommodation space,sedimentation rate,types and distributional characteristics of provenance systems of a basin. Episodic tectonic movement of the Nanpu Sag is a major contributor to accommodation space. Several NE-SW-trending contemporaneous faults that were developed in the period of Es in the southern provenance enhanced the compartmentalization of lake basin. A series of echelon growth faults extending toward the basin controlled the distribution of the Shahejie Formation. The linear subsags with the same strike as the growth faults formed in the downthrown blocks are the main unloading areas for sediments. The main depositional system is the combination of braided river delta,infralittoral subaqueous fans,beach bar and lake system in the southern provenance. On this basis,a model of contemporaneous fault controlling sandstone distribution is established in southern Nanpu Sag. The contemporaneous faults stretching into the lake basin controlled the sandstone distribution of braid river delta,with lobate deposits occurring laterally along strikes on the downthrown blocks of faults and superimposing vertically in the shape of wedges. The favorable objectives for future exploration are braided river delta,infralittoral subaqueous fans at the distal end of these deltas,and the beach bars developed on the tilted blocks.