| This paper studies the sequence stratigraphy and sedimentary system of the lower Cretaceous in the Songliao Basin. Data of seismic, logging, geochemistry and paleontology were used to identify sequence boundaries, correlate stratigraphy and the sedimentary system. Two 2nd-order sequences and eight 3rd-order sequences can be divided from the deposition during the stage of depression of Songliao Basin. The first 2nd-order sequence is from Quantou Formation to Qingshankou Formation, and the second is from Yaojia Formation to Nenjiang Formation. The 3rd-order sequences near the boundary of 2nd-order sequences are often triple-fold sequences and those inside of 2nd-order sequences are binary sequences. In the study of the factors which control the development of sequences, tectonic subsidence analysis with precision up to members, geochemistry and paleontology analysis, sediment supplying curve and Fischer diagram are used. It can be found that the tectonic uplift and subsidence is the main controlling factor. The sequence develops as transgressive systems tract in the stage of strong tectonic subsidence. When the movement becomes weak, it develops lowstand systems tract. The climatic variation and sea-level change are also important factors. Adding with sediment supply, these factors jointly control the development of sequences of a depression basin. Then, four sequence patterns of genetic significance are summarized for a depression basin. They are tectonic subsidence dominative type, sea-level change controlled type, climatic variation controlled type and sediment supply affected type.In addition, depositional models and sedimentary systems within sequence stratigraphic frameworks have been studied. And facies models for alluvial fan, fan delta, delta, lake and storm have been set up. Especially the discovery of storm deposits is significant both in theory and in hydrocarbon reservoir prediction. And favorable sandbodies have been predicted with seismics.
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