Structural Feature And Tectonic Evolution Of Fault Depressed Zone Of Southeast Songliao Basin

The southeastern fault depressed zone is located in the south of the eastern fault depressed zone of the Songliao Basin, which has a good resource exploration potential. However, its research degree is obviously lower than that of the central fault depression zone and the central uplift belt in the Songliao Basin. The understanding of the structure, tectonic feature and tectonic evolution of the fault depression zone is not very clear so far, which restricted the exploration and deployment of the fault basin, so systematic regional geological studies is much-needed. Based on systematic interpretation of typical seismic sections of the southeastern fault depressed zone of the Songliao Basin, we recognized stratigraphic sequences and structural features of 8 fault depressions, analyzed the evolution history of each fault depressions by using the method of balanced section, aiming to provide fundamental geological basis for the deep-exploration of oil and gas in the southeastern fault depressed zone of the Songliao Basin.According to the interpretation of 4 continuous NW-extending seismic sections, namely the Zengsheng-Sanchahe-Yuxi-Yudong, Wangfu-Buhai, Shuanglong-Dehui and Shuangliao-Lishu fault depression in the southeastern fault depressed zone, combining the thickness picture of Huoshiling Formation, Shahezi Formation and Yingcheng Formation of the southeasten fault depressed zone, we revealed the regional tectonic feature of the southeastern fault depressed zone. In the Huoshiling Age fault depression zones and dome zones show as basically contiguous distribution, and in the Shahezi and Yingcheng Age fault depression zones and dome zones show as alternative distribution.The southeastern fault depressed zone underwent multiple tectonic movements, resulting in the complexity of depression structures and the multiformity of structural styles. Based on precision seismic profile interpretation, we summarized the southeastern fault depressed zone has three types of fault depression, the unilateral type, bilateral type and compound type, respectively. The Yuxi, Wangfu and Lishu fault depressions belong to the unilateral type; the Sanchahe, Zengsheng, Dehui and Shuangliao fault depressions pertain to the bilateral type; the Yudong fault depression belongs to the compound type. Among which, the accumulation belt of the secondary dome in the central Yudong fault depression and the accumulation belt of Huajia volcanic secondary dome in the Dehui fault depression are the most favorable exploration zones.Basin-controlling faults of the southeastern fault depressed zone development in the lower Huoshiling Formation, and end mainly in the upper Yingcheng Formation, parts of which end in the upper Denglouku and upper Quantou Formation. The most important basin-controlling time of the faults is the Shahezi Age. The southeastern fault depressed zone occurs a strike-slip event in the Yingcheng Age, the event performs significantly in the Dehui fault depression, and also shows in the Wangfu fault depression. The southeastern fault depressed zone has two stages of crucial structural inversion, which are the late sedimentary stage of the Huoshiling and Yingcheng Formation, respectively.The tectonic evolution of the southeastern fault depressed zone is divided in 6 stages of initial fault depression stage(sedimentary stage of the Huoshiling Formation), intense structural inversion stage(late sedimentary stage of the Huoshiling Formation), intense fault depression stage(sedimentary stage of the Shahezi Formation), partial uplift and denudation stage(late sedimentary stage of the Shahezi Formation), fault depression shrinking stage(sedimentary stage of the Yingcheng Formation) and intense structural inversion and strike-slip stage(late sedimentary stage of the Yingcheng Formation).