Sequence Stratigraphy of Low Cretaceous in the Wuerxun Depression

Key words: 
• Wuerxun Depression /
• sequence stratigraphy

Abstract:  Taking the structural sequence stratigraphic analysis as the thread, through the study of architecture of faulted basin and regional paleogeomorphology change analysis, based on the geological and geophysical data, this paper analyses sequence stratigraphy of the main oil formation  K1t, K1n and K1d1 of Low Cretaceous in Wuerxun Depression. Five isochronous sequence boundaries are identified by which regional well profiles are correlated, then the purpose layer sequence stratigraphic framework has been established. This study suggests that the sedimentary history of Wuerxun Depression includes a few stages corresponding with structural evolution. The pattern of strata filling and the structural of sequence are controlled by sag structure. Western steep slope of the depression, alluvial fan and fan delta are developed. But fine depositional system of fluvial delta and coastal shallow lake are developed in the eastern gentle slope of the depression. Among them, single fault bench type is developed as aggradational sequence sets pattern, single fault trough type is developed as aggradational or progradational sequence sets pattern, and single fault overlap type is similar developed as passive continental margin slope type sequences. Based on the tectonic paleogeomorphology and the sequence constitute analysis. Slump turbidities rock  located in lowstand system tract of SQd1 is the main reservoir of northern Wuerxun Depression. It is lithologicstructural oil reservoir, rather than structural oil reservoir which at the top of K1n2 of predecessors. 