Framework of Sequence Stratigraphy, Sedimentary System andEvolution of Southeastern Songliao Basin: An example from Yingcheng Formation in Lishu Fault Depression

Key words: 
• Northwest Lishu fault depression /
• Early Cretaceous /
• Yingcheng Formation /
• sedimentary facies /
•  /
•  /
•  /
•  /

Abstract: This paper focuses on the sequence stratigraphy and sedimentary facies of Yingcheng formation in the southeastern margin of the Songliao Basin. The degree of previous studies in this area is lower, based on seismic，logging and core analysis, the sequence stratigraphy and sedimentary facies are studied. Rift basin is characterized by deposition which is significantly controlled by tectonic movements and episodic tectonic cycles, sedimentary and tectonic evolution of the Songliao Basin experienced the initial rift period, strongly faulted period, faulted the peak late, the conversion period of faulted and depression and depression period amounting to five stages of evolution. Northwest of Lishu depression is the most promising oil and gas rich region. The block Shahezi 2nd member & Ying 1st member deposition period are extended strong faulted period of the rapid subsidence and deep water, provided the preconditions condition for gravity flow deposits development, especially in the braided river delta front near the deep water, easily turbidite sandstone develops, turbidite sand embedded in thick dark mudstone which creates a unique condition for lithologic reservoir formation. With the gradual indepth exploration and geological theory oil and gas exploration gradually to the west of the central belt with a particular deep extensions to the northwest, and achieved encouraging preliminary exploration results. The study area is located in the transition belt of northern slope and southern deep depression zone, and the structure superimposed over the same period as a background, is favorable area to find the structure and construction of reservoirscomplex reservoir lithology. However, the deposition type ,evolution of sedimentary facies, reservoir characteristics etc. is with little facility in the northwest of the studied area. So it is necessary to conduct a detailed study of sedimentary features of northwest.
  Use of geological and geophysical data for the Yingcheng formation strata from Northwest Lishu fault depression to identify sequence boundaries, the Yingcheng formation was studied, and which was divided into two thirdorder sequences, respectively, from bottom to top with SQ5 and SQ6, corresponding to the three sequence boundaries are SB5, SB6 and SB7. The thirdorder sequences were further subdivided into lowstand system tract, transgressive systems tract and highstand system tract. Lowstand system tract mainly is composed of the composition of parasequence sets, transgressive systems tract mainly is composed of the retrogradation parasequence set, and highstand system tract is made of the accretion type parasequence set. Sediment types are composed of nearshore subaqueous fan, fan delta, braid delta and lakes, and the lakes and braided river delta are the most developed type. Nearshore subaqueous fan and fan delta depositional systems develop in the downthrow side of fault for each sequence unit, which is controlled by the tectonic movements significantly, and always developed in the steep belt; braided delta sedimentary system are often associated with abundant long axis of the material source, which often developed in the gentle slope. The evolution and tectonic with deposition system configured are controlled by the ancient tectonic and landscape. Concluded that the most favorable reservoir area is located in the gentle belt of northwest Lishu fault depression.