松辽盆地姚家组-嫩江组地层层序及沉积演化

Stratigraphic sequences and sedimentary evolution in the Yaojia and Nenjiang Formations,Songliao Basin

松辽盆地姚家组-嫩江组是晚白垩世形成的一套完整的水进-水退沉积旋回,分为2个二级层序,6个三级层序,持续时间约4Ma。嫩江组二段最大湖泛期在底部形成了盆地范围内稳定分布的油页岩,其不仅是层序及地层对比的标准界面,而且是重要的烃源岩层和盖层。姚家组与嫩江组一段是水进期大型退积型三角洲沉积,嫩江组三段是水退期大型湖泊与快速进积大型三角洲沉积。嫩江组在水进期长轴物源方向发育大型重力流水道及末端浊积扇,水道延伸距离64km,最大宽度600m;在水退初期短轴方向发育滑塌浊积扇,扇体有复合式和单体式,滑塌最小古坡度为5%～12‰,表面均发育弧状滑塌波纹,波纹密度4～10条/km,最小滑移距离2～10km。

The Yaojia and Nenjiang Formations in the Songliao Basin consist of a succession of transgressive-regressive depositional cycles deposited during the Late Cretaceous,which may be subdivide into two second-order cycles and six third-order cycles,with a time duration of about 4 Ma.The oil shales at the base of the second member of the Nenjiang Formation deposited during the maximum flooding period are interpreted as both the type boundary for stratigraphic correlation and important reservoir and cap rocks.The first member of the Yaojia and Nenjiang Formations may be assigned to the retrogradational delta deposits buried during the transgressions,while the third member of the Nenjiang Formation is built up of mixing lake and delta deposits formed during the regressions.The large-sized gravity flow channels and terminal turbidite fans appeared during the trangressions,whereas the fluxoturbidite fans occurred during the regressions in the Nenjiang Formation.The Upper Cretaceous Yaojia and Nenjiang Formations are believed to be the key hydrocarbon reservoirs in the Songliao Basin.