Sedimentary microfacies in the lower part of the Qingshankou Formation in the Talin Hiag region,northern Songliao Basin

The present paper deals,in detail,with sedimentary microfacies types,and criteria for the recognition and spatial distribution of facies,subfacies and microfacies developed in the lower part of the Qingshankou Formation in the Talin Hiag region,northern Songliao Basin.The sedimentary facies in the study area consist of the lacustrine facies including the semi-deep lacustrine to deep lacustrine subfacies,and sublacustrine fan facies including the inner fan and outer fan subfacies.Longitudinally,the sublacustrine fan facies is mostly developed at the base of the studied intervals,and gradually decreases in area upwards.Viewed from the planar distribution,the semi-deep lacustrine to deep lacustrine deposits are accentuated.The sublacustrine fan deposits mostly occur in the western,southwestern and northwestern parts of the study area,and have multiphase and polygenic features of origins.The bulk of the sandstones are made up of the debris flow and turbidity current sublacustrine fan sandstones.The dark thick-bedded source rocks in the semi-deep lacustrine to deep lacustrine subfacies are intercalated with the gravity flow sublacustrine fan deposits,between which there is a sharp contact,constituting the good hydrocarbon reservoirs of concealed oil accumulation.