箕状断陷湖盆初始裂陷期层序地层与沉积充填特征--以松辽盆地梨南洼槽下白垩统火石岭组二段为例

Sequence stratigraphy and sedimentary filling characteristics of a half-graben rift lake basin during the initial rifting period:A case study of the 2^(nd) member of Lower Cretaceous Huoshiling Formation,Linan Sag,Songliao Basin

受侏罗纪—白垩纪区域构造拉张作用,松辽盆地形成一系列箕状断陷湖盆。勘探开发实践表明,箕状断陷湖盆形成较好的生-储-盖组合,具有较好的石油天然气勘探潜力。以松辽盆地南部梨南洼槽火石岭组二段(火二段)为研究对象,综合岩心、测井、录井以及三维地震资料,对断陷湖盆的层序地层、沉积体系以及充填演化规律进行了深入分析。研究认为,梨南洼槽火二段可分为3个中期基准面旋回。在沉积充填过程中,火二段主要发育扇三角洲和湖泊两种沉积相类型。箕状断陷湖盆与地堑式断陷湖盆不同,虽然在断裂发育早期,断阶带和斜坡带均发育扇三角洲,但发育规模存在较大差异。随着盆地范围的扩张,不同构造带上沉积相带分异特征明显,断阶带上往往以狭长式、厚层和粗粒孤立扇三角洲沉积为主;斜坡带以大面积叠置薄层和细粒扇三角洲群沉积为主。在此基础上,深入探讨了梨南洼槽火二段断阶带和斜坡带沉积差异主控因素,提出了早期箕状断陷湖盆的沉积模式。

Due to the Jurassic-Cretaceous regional tectonic extension,a series of half-graben rift lake basins were formed in the Songliao Basin.The latest exploration and development shows good source−reservoir−cap rock combinations and hydrocarbon potential in these basins.The second member of Huoshiling Formation in Linan trough of southern Songliao Basin is chosen as the research object to reveal the sequence stratigraphy,sedimentary system and basin filling evolution characteristics in these basins based on the integration of core,logging and 3D seismic data.The member can be divided into three medium-term base level cycles of fan delta and lake facies.The scales of fan deltas in steep slope zone are different from that in gentle slope zone during the early rifting stage of the half graben rift basins.With the expansion of the basin,the sedimentary facies belts in different structural belts take on obvious differentiation characteristics.The steep slope belt is often dominated by long and narrow coarse-grained isolated thick fan delta deposits,while the gentle slope belt is dominated by large superimposed fine-grained thin fan delta deposits.Based on these understanding,this study discusses the main controlling factors of sedimentary difference between steep slope zone and gentle slope zone of the member and brings forward the sedimentary model for the early stage of half-graben rift lake basins.