The tectono—stratigraphic sequence and reservoir formation cycle in Tarim basin, NW China
|Location||International Geological Congress,oslo 2008|
|Author||Wang, Yi; Jin, Zhijun|
|Holding Date||07 October 2008|
Tarim Basin, the largest composite basin with area of 56×104 km2 located in the northwestern part of China, is the large poly-cycle basin, which was superposed by different geologic epoch proto-type basins through the reconstruction of multi-tectogenesis since Sinian. This study documents the characteristics of the Tectono-stratigraphic Sequences in the basin and discusses the tectonic Control on the Seqences and their relations to the petroleum reservoir formation cycle. The Sinian-Quaternary in the Basin can be divided into 3 mega-sequence sets which represent the features of the three regional tectonic cycles and the affection of the related regional tectonic episode to the evolution of the mega-sequence sets, 6 I order sequences (mega-sequence) formed under the same tectonic regime, 16 II order sequences (supersequence) formed in the one cycle of basin evolution under the same tectonic settings or in the larger cycle of relative change of sea level and 42 III order sequences (sequence) formed in one tectonic stage during a cycle of basin evolution or in the smaller cycle of relative change of sea level. The basin evolution went through Sinian-early and middle Devonian, late Devonian-Triassic and Jurassic-Quaternary three tectonic cycles.
Each tectonic cycle can be further divided into early basin evolvement stage, which is characterized by extensing, and rifting and late basin evolvement stage, which is characterized by compressing and flexing. Due to the regional tectonic events, the boundaries of the various order sequences were not in agreement with those of the global sequences. In the various order sequences, the tectonic actions were in the dominant places in the factors controlling the sequences, and the global sea level changes in secondary ones. The global sea level changes determined the sequences either in the tectonically stable periods such as passive continental margins or cratons or in the low orders of sequences. Several sets of source rocks formed in Tarim basin, leading to composite petroleum systems. Several cycles of tectonic movements and changes of the tectonic regime determined the cycles of hydrocarbon generation, and the reservoir formation cycles reflect the history of petroleum migration and accumulation in the basin. Based on geological background, the author suggested that there were three cycles of reservoir formations in Tarim basin, which were from the late Caledonian movement to the early Hercynian movement (from the Silurian to the Devonian), from the late Hercynian movement to the Indosinian movement (from the Permian to the Triassic), and in the Himalayan movement (the Cenozoic). The three reservoir formations were corresponding to the cycles of the three mega-sequences. The reservoirs formed in the former two periods, particularly those formed in the second period, mainly distributed in the inner basin, and the reservoirs formed in the third period were mainly around the margins of the Tarim basin.