河流相层序地层划分方法——以松辽盆地下白垩统扶余油层为例

Division of fluvial sequence stratigraphy——an example from the Lower Cretaceous Fuyu oil-bearing layer,the Songliao Basin

以松辽盆地下白垩统泉头组扶余油层为例,探讨了河流沉积体系的层序地层分析方法。首先确定河流的成因类型和相域(微相)的构成,包括曲流河道、决口河道、决口扇、冲积平原和浅水湖泊,识别河流演化过程中由于河流冲溢形成的自旋回沉积作用和基准面变化产生的异旋回沉积作用,即基准面旋回;然后运用河流沉积学理论分析构成河流相的不同相域的形成与基准面变化的关系,识别基准面转换位置(基准面上升到下降或基准面下降到上升)的沉积学和地层学响应,从而建立等时地层对比格架。

Taking Fuyu oil-bearing layer of the Lower Cretaceous Quantou Formation in the Songliao Basin as an example, this article discusses the analysis methods of sequence stratigraphy of fluvial sedimentary system. It starts with the identification of the genetic types of fluvial system and facies tracts （ micro-facies）, including meander channels, crevasse channels, crevasse fans, alluvial plains, and shallow lakes, and recognition of the autocyclicity caused by fluvial overflow and the allocyclicity （base-level cycle） caused by base level changes. Then it analyzes the relation between the formation of different facies tracts and base-level change and identifies the sedimentologic and stratigraphic responses of turning points of base-level changes （i.e., the base level turning from ascending to descending or vise versa） by applying the fluvial sedimentology theory. Finally, it establishes a framework for isochronous stratigraphic correlation of fluvial sequences.