Mesozoic tectonics and sedimentation, and petroleum systems of the Qaidam and Tarim basins, NW China.

摘要

A comprehensive basin analysis of Mesozoic strata in the Qaidam and southeastern Tarim basins was conducted in order to more completely document the Mesozoic geology, tectonic history, and petroleum potential of northwestern China.; The Mesozoic Qaidam basin consisted of at least two noncontiguous basins. The NE Qaidam basin was bounded to the northeast by the Qilian Shan, which was a contractional mountain belt that controlled flexural subsidence, drainage patterns, and sediment supply in the basin. The north-central part of Qaidam consisted of a foreland uplift that separated NE Qaidam from the western Qaidam basin. Western Qaidam consisted of a foreland basin controlled by contraction in the Keeling Shan. The western Qaidam basin was at least intermittently connected to the southeastern Tarim basin, which was bounded to the north by a foreland uplift.; Basin studies along the northern and southern margins of the Altun Shan suggest that the range was not a major physiographic feature for most of the Jurassic and Cretaceous. Furthermore, lacustrine facies in SE Tarim and NW Qaidam are apparently correlative across the Altun Shan. Not only does this correlation across the Altun block place constraints on its Mesozoic expression, it also provides a piercing point for restoration of post-Jurassic, probably Cenozoic, strike-slip on the left-lateral Altyn Tagh fault system. An Aalenian-Bajocian lacustrine shoreline facies is recognized in both SE Tarim and NW Qaidam, and correlation of the facies belt is supported by lithostratigraphy, biostratigraphy, paleocurrents, and detrital composition. Realignment of the lacustrine shoreline and examination of potential offset plutons suggests 360 km of post-Bajocian left-lateral strike-slip.; Geological and geochemical investigation of crude oils and potential Lower-Middle Jurassic source rocks document for the first time two petroleum systems in the northern Qaidam basin, one of which derives from Tertiary hypersaline lacustrine source rocks, the other from Middle Jurassic freshwater lacustrine source rocks. The characteristics and history of the Jurassic petroleum system is investigated and a comprehensive petroleum system model is developed. This model provides a useful exploration concept for not only northern Qaidam, but also other nonmarine basins of central Asia with similar Jurassic source rocks.