AN APPROACH TO TECTONIC EVOLUTION AND DYNAMICS OF THE SONGLIAO BASIN
Hu Wangshui1, L? Bingquan2, Zhang Wenjun1, Mao Zhiguo1, Leng Jun3, Guan Dayong1
1. Department of Geoscience, Changjiang University, Jingzhou, Hubei 434023; 2. Department of Marine Geology and Geophysics, Tongji University, Shanghai 200092; 3. Jianghan Oilfield Branch Corp., China Petroleum & Chemical Corp., Qianjiang, Hubei 434124
In the Songliao Basin, the extensional depression occurred from Late Jurassic, experienced a long process of strong—weak—stronger—strongest—weak—stop evolution, with the stronger extension in phase of the Shahezi Formation(J3sh)depositing, the strongest extension in period of the Quantou(K1q)and Qingshankou(K1qn)Formations depositing, and the extension stopped after the Nenjiang Formation(K1n)depositing. With the rifting and extensional depression stopped, the inversion occurred, and the differentiated depression experienced a long course of weak—strong—weak—stop evolution, with the strongest compression in period of the Sifangtai(K2s)and Mingshui(K2m)Formations depositing. The post-inversion tectonic strata were depressed by the differentiated rising in Pleistocene and Holocene. The growth-structure trellis of the basin consisted of four styles: 1)normal growth fault and its extensional structural combination, 2)growth syncline, growth anticline and T2 normal growth fault, 3)positive inversion structure and growth structure, and 4)post-inversion growth syncline. The Songliao Basin could be divided into six units: the Southwest Rise, the Southeast Rise, the Northeast Rise, the North Plunge, the West Slope and the Central Depression. Based on the distribution and deformation of the inversion structures in the Songliao Basin, four zones of inversion structures were recognized, namely, the Deshu-Changchunling, the Wangkui- Renminzhen, the Daqing-Gudian and the Lindian-Honggang inversion structures. The extent of the inversion structures decreased from the east to the west. The basin evolution experencied 10 phases: initial rifting—fast depression, accelerated rifting—fast depression, deceleration rifting—slow depression, slow rifting—fast depression, accelerated rifting—accelerated depression, deceleration rifting—deceleration depression, rifting-depression termination—slow inversion, fast inversion—fast difference depression, slow inversion—slow differentiated depression, inversion—depression termination. The tectonic development resulted in the constitutions of the Late Jurassic extensional growth structure, the K1d～K1y growth structure, the K1n inversion structure and K2～Kz post-inversion structure. 46% of the depositing accommodation space of the K1d～K1y came from sediment compression, and other 54% from the long-term depression of the basin basement; 69% the depositing accommodation space of the K1n from sediment compression, and other 31% from the compression depression of the basin basement. The inversion structure resulted from the change of regional stress field in east China.