Study On Lower Cretaceous Sedimentary Facies In Beier Depression, Hailar Basin

Hailar basin is the biggest oil and gas basin on the periphery of Songliao basin. Beir depression lies in the middle of Hailar basin,which is about 3000km2 and trends northeast. The east margin of the depression is a fault and the west is overlaying on Cuogang uplift. The northern is adjacent to Wuerxun depression by Bayantala fault. The dissertation mainly deals with sedimentary features of Lower Cretaceous of the Beir depression Hailar basin. The strata include Tongbomiao Formation,Nantun Formation, Damoguaihe Formation and Yimin Formation. Based on the analysis of core, logging and seismic data, results about sedimentary features and facies is acquired. In the course of the analysis,the core of 15 logs was observed and described, the thin section datum and grain size analysis were done at the same time.As a result,the sedimentary features and facies types and their distribution of the Beir depression were obtained. Further regularity of the sedimentary facies distribution and the tectonic evolution process of the basin were discussed. The facies types of the Lower Cretaceous are mainly delta,lake and turbidity. The main type of microfacies include distributary channel, subaqueous distributary channel, distal bar, swamp, interdistributory bay, bar and lake peat swamp. The basin evolution process can be recognized by the change of the sedimentary facies. The bottom beds of Lower Cretaceous is mainly coarse detrital rock, upward the grain changes to fine. This reflected the water depth of sedimentary basin change deeper gradually. The basin sedimentary evolution process is divided into four stages: initial down-faulted basin, violent down-faulted basin, deep extend basin and fault down-warping basin. The course of four stages reflect the basin structure evolution from aulacogen to down-warped basin.