Structural Research And Basement Lithology Prediction Of The Paleo-central Uplift Belt In Northern Songliao Basin

Focusing the main research goal on paleo-central uplift belt of northern Songliao basin,guided by the train of research thought of integrating geology and geophysics, and usingmultiple means and methods, this paper reveals the structural characters and the evolutionaryprocess of paleo-central uplift belt in different aspects, and also disclose the distribution statusof basement lithologies. This paper determines the features of the paleo-central uplift belt innorthern Songliao basin by using the method of the unconformity analysis of the stratigraphicsequence boundary in combination with the thickness analysis of relic strata;finds out thetectonic subsidence characters for different periods through the analysis of tectonicsubsidence history;recognizes the erosion range and the erosion thickness of theunconformity surface through the study of eroded thickness on the paleo-central uplift belt;represents the evolution process of the paleo-central uplift belt by means of the tectonicdevelopment history section map compiled according to the balance section principle;exhibitsthe structural characters of the paleo-central uplift belt utilizing the high-precision structuralmap and the statistical information of structure elements;and predicts the distribution statusof the basement lithologies making use of the analysis of the geophysics and the basementevolutionary history.The research of this paper acquired the following several cognitions: 1. The paleo-central uplift belt of northern Songliao basin is a paleohigh with differentialsubsidence and denudation, which includes multiple uplifts and denudations. Thepaleo-central uplift belt start to develop in Huoshiling period, extended intensively in faultdepression period, and ceased developing and was buried and saved in the late deposition ofDenglouku Formation.2. in the late depositional stages of Shahezi Formation and Yingcheng Formation, owingto the basin being elevated in large areas, the range of denudation extended to the total basinand thus both the uplift belt and the slope region suffered from denudation, which resulted inthe 2200 meters of total eroded thickness,1500 meters for the late stage of Shahezi Formationstratum, and 700 meters of total eroded thickness for the late stage of Yingcheng Formationstratum.3. The formation of the paleo-central uplift belt not only was controlled by the easternlarge-scale fracture of Xuxi and the western step faults of Daqing fault bench belt in east-westorientation, but also was incised by two groups of NW-trending transitional faults insouth-north orientation. This led to the formation of three growth zones of anticline trap in thepaleo-central uplift belt: the northern Weixing uplift and Zhongneipao uplift, the middleChangde uplift, and the southern Zhaozhouxi uplift and Yuaner structure.4. The distribution of the basement lithology of paleo-central uplift belt was markedlycontrolled by the basement faults, which resulted in the lithology distribution features ofbelting in east-west oriention and of blocking in south-north orientation. There were largeareas of granite in the paleo-central uplift region along south-north trend, and distributed in awidespread range, especially in the central uplift area where the granite was the mostdeveloped and the types of rocks were almost confined to the only granite with the charactersof slight magnetic anomalies and gravity negative anomalies.5. The slope region was the most favorable development area of the reservoir bodies, andlow-lying area can form a good sealing cap formation. The paleo-weathering effect not onlycontrolled the formation and evolution of the reservoir bodies in the research area, but alsocontrolled the accumulation of natural gas. The evolutionary process of structure for theresearch area indicated that in the depositional period of Huoshiliang-Yingcheng Formation,the dominant traps are not structural traps but lithologic traps, stratigraphic overlap traps andthe combination traps formed by the allied actions of lithologic traps and stratigraphic overlaptraps;while in the depositional stage of Denglouku Formation, the structural traps play adominant role.