Post-Rift Sequence Stratigraphy Framework Modified by Compression Stress: Case Studies from Cretaceous Deposits of the Northern Songliao Basin
Xinong Xie1, Zhiqiang Feng2, Yongchao Lu1, and Jianye Ren1
1Faculty of Earth Resources, China University of Geosciences, Wuhan, China
2Institute of Exploration and Development of Daqing Oilfield Company Ltd, Daqing, China
Thermal subsidence is dominated in post-rift stage of a typical rifting basin, but it is quite different in the Songliao basin, which has been modified by post-rift tectonics. The post-rift Cretaceous deposits of the north Songliao basin can be classified into two substages based on the tectonic regimes. During the early post-rift stage, rapid subsidence driven by thermal cooling resulted in the formation of fluvial-flooding plain facies due to plentiful sediment supply and arid climate condition, in which ponds and small shallow lakes occurred only in the Quantou Formation. And a wide lake basin began to form in the Qingshankou Formation due to humid climate condition. During the later post-rift stage, however, subsidence has been modified by transpressional stress. Obvious compression westwards resulted in difference on sequence boundaries, i.e. the overlying unconformities occurred in the West Slope and the erosional unconformities formed in the East Uplift zone. This fact indicates a main compression stress originate from the collision of Pacific plate. The sharp change of tectonic stress field from regional thermal subsidence to compression westwards is in agreement with regional tectonic movement. Variation in angle of convergence of the Pacific plates and the Asian continent took place since 88Ma, which results in increases of compression intensity with time in the Songliao basin, especially in the sequence boundary of T03, the onset of invasion tectonics resulted in the strong erosion in the eastern part of the Songliao basin, even the formation of thrust faults and folds since 65 Ma. Hence, sequence stratigraphic framework and internal architectures are quite different due to the turnaround of regional tectonic regimes.
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