琼东南盆地深水区松南-宝岛凹陷同沉积断裂活动及其对沉积充填的控制

Evolution of syndepositional faulting and its controlling effect on sedimentary filling in Songnan-Baodao sag of Qiongdongnan basin,South China Sea

综合利用大量二维、三维地震数据以及钻井资料,运用古落差法和断层活动速率分析法系统阐明2号断裂带时空演化规律,并重点分析同沉积期断裂活动及其所形成的古构造格架对松南-宝岛凹陷北缘层序地层整体构型、层序充填样式以及砂分散体系时空配置的控制作用.研究表明:2号断裂带活动在时间上呈现出明显的幕式特征,整体表现为"弱—强—弱—消亡"的演化趋势,主要活动期集中在古近纪裂陷期;在空间上显示出显著的分段性特征,可细分出松南段和宝岛段,且松南段活动性较宝岛段更为强烈.2号断裂带同沉积期断裂活动对松南-宝岛凹陷北缘沉积中心的展布及其动态迁移规律、层序内部体系域发育和沉积充填样式均具有明显控制.在裂陷期,松南-宝岛凹陷北缘分别发育陡坡断阶型层序样式和多级断阶陡坡型层序样式,在裂后坳陷阶段主要发育挠曲坡折型层序样式、沉积坡折型层序样式以及滑塌坡折型层序样式.此外,沿F2断裂上升盘发育的2个横向凸起调节带和2个走向斜坡调节带对盆缘水系的汇聚具有明显控制,其所在位置发育大型储集砂体.

Based on substantial 2-D,3-D seismic and drilling data,spatial-temporal evolution of the No.2fault zone was studied quantificationally and in great detail by using the methods of palaeo-drop and fault activity rate.The controlling effect of syndepositional faulting and corresponding structural framework of the No.2fault zone on geometry and its inner constitution of sequence stratigraphy,and spatial-temporal configuration of sand dispersal systems in the north margin of Songnan-Baodao sag were further studied.The results showed that activities of the No.2fault zone were characterized by obvious episodes in time,which presented an evolutional style of＂weak-strong-weak-dormancy＂and the main active stage was in palaeogene-rifting stage.In addition,it showed obvious segmentation in space,which can be divided intoSongnan segment and Baodao segment,and the activity rate of Songnan segment was much larger than that in Baodao segment.The spatial-temporal evolution of syndepositional faulting with different syndepositional structural frameworks had a significant controlling effect on the distribution and dynamic evolution of depocenters as well as the development of system tracts and the depositional constitution of sequence strata in north margin of Songnan-Baodao sag.At the rifting stage,there were abrupt step-fault slope break type of sequence pattern and abrupt multi-stepped fault slope break type of sequence pattern.However,flexure slope break type of sequence pattern,sedimentary slope break type of sequence pattern and slump slope break type of sequence pattern developed at the post-rifting stage.Moreover,two transverse relay zones and two strike-overlapping accommodation zones were identified along the footwall of fault F2,where large-scale reservoir sandbodies were well developed because of their controlling on convergence of large basin-marginal drainage systems.