查干诺尔凹陷南屯组湖底扇沉积特征及沉积模式研究

Sedimentary Characteristics and Sedimentary Model of Sublacustrine Fan of Nantun Formation in Chaganuoer Depression

在区域层序地层格架内,根据岩石相、地震剖面相、测井相特征并结合粒度分析等资料,对海拉尔盆地查干诺尔凹陷下白垩统南屯组内发育的湖底扇沉积体系、沉积特征及模式进行了系统的研究,认为研究区南屯组湖底扇沉积体系主要发育有3类亚相和5类微相。在此基础上,建立了查干诺尔凹陷南屯组的湖底扇沉积模式,认为平面微相相序表现为“内扇主沟道→中扇辫状沟道→外扇浊积岩→深湖泥”的变化规律,且水道体系(主沟道、辫状沟道)之间,都被明显规模的深湖相泥岩所分隔。在这一沉积模式控制下,湖底扇沉积在研究区南部由东侧陡坡带向湖盆中心延伸较远,而由南向北则随着构造坡折带影响能力的减弱,逐渐过渡为扇三角洲沉积体。

Sublacustrine fan is a very important place for oil and gas accumulation in continental rift basins. Establishing an accurate and reliable sedimentary model of sublacustrine fan is of great significance to the prediction of dominant reservoirs. Based on the data of lithofacies, seismic profile facies, logging facies and grain size analysis, the sedimentary characteristics and models of sublacustrine fan depositional system developed in Nantun formation of lower cretaceous in Chaganuoer depression of Hailar Basin are systematically studied in this paper. It is considered that there are three subfacies and five microfacies in the sublacustrine fan depositional system of Nantun formation in the study area. On this basis, the lake floor fan sedimentary model of Nantun Formation in Chaganuoer depression is established. It is considered that the planar microfacies sequence is characterized by the variation of "main channel of inner fan, braided channel of middle fan, turbidite of outer fan and mud of deep lake", and that the channel systems (main channel and braided channel) are separated by obvious scale mudstones of deep lake facies. Controlled by this sedimentary model, the sublacustrine fan deposits extend far from the eastern steep slope zone to the center of the lake basin in the southern part of the study area, while the sublacustrine fan deposits gradually transit to fan delta deposits from south to north with the weakening of the influence of structural slope breaks.