Stratum development characteristics and sedimentary evolution model of the second member of Shuangyang formation in Moliqing area, Yitong Fault Basin

Abstract

During the Second Member of Shuangyang Formation of Moliqing fault in the Yitong Basin, northeast of China, the intermittent transportation and rapid accumulation of nearshore gravity flows make the facies belts of fan apron narrow and changefully. Lacking stable contrastive maker layers, while the several tectonic events such as strike slip, transtension and compression occurring in the later period make the stratigraphic distribution of this area more complex. For these reasons, the research on stratigraphic correlation and the distribution of sedimentary facies are extremely difficult. To solve the above problems, this paper proposes the following solutions: (1) This paper assists to achieve the stratigraphic cycle analysis through logging data entropy spectrum analysis, on which basis and combining with the core data, seismic interfaces and geological markers to achieve the division and correlation of small layers of single sand body; (2) By analyzing the coarse clastic sedimentary system, we research the coarse clastic glutenite sediments of Shuangyang Formation in Moliqing fault from the fluid properties and fluid type conversion so as to clearly understand the vertical sequences and horizontal distribution characteristics analysis of core facies as well as deduce the fluid type of supply source and the characteristics of sediments. The results show that: (1) The sequence development is dominated by tectonic movements, and the strata can be divided into 5 middle-term cycles and 25 short-term cycles adopting T-R mode; (2) studies suggest that because the fluid property of supply source occurs cyclical changes under the condition of multiple sources, and the fluid shows alternation and conversion between gravity flow and traction flow under the control of particular ancient landform, therefore, the sediments of researched area form a mixed sedimentary system of gravity flow and traction flow. On the basis of source characteristics and sedimentary characteristics analysis, this paper proposed the sedimentary type of continental facies slope apron, which is divided into three sub-facies: proximal, middle and distal sub-facies. Among them, proximal sub-facies mainly develop the slop channel sedimentation dominated by mud debris flow deposits, central sub-facies develop the superposition channel microfacies dominated by mix depositions of gravity flow and traction flow and the leading edge microfacies of fan dominated by traction flow, while the distal sub-facies is mainly based on the thin sheet sand body and gravity flow slump depositions.