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Constraining the initial age of the Northern Qaidam Thrust Belt is critical for studying the growth of the Tibetan Plateau. This study presented insights from field observations and seismic profiles, to constrain the structural pattern and the initial age of the eastern segment of the Northern Qaidam Thrust Belt during the Cenozoic. Our research suggested the Aimunike and the Oulongbuluke uplifts, as well as the Ounan Depression between them have been uplifted during the mid-Miocene, and as a result underwent widespread denudation to remove the late Eocene-early Miocene sequences over them. After that, this area was subsided and accepted the deposition of the mid-Miocene to the Pliocene strata. A second phase of thrusting occurred in the Quaternary as those faults initiated in the mid-Miocene rejuvenated. Our results together with the previous studies suggested the N-S compressional stress over the NE Tibetan Plateau strengthened substantially during the mid-Miocene, leading to a widespread plateau growth at that time. [ABSTRACT FROM AUTHOR]

Based on isostasy, this paper elegantly explains the differential modern elevations of the large-scale cratonic basins around the Tibetan Plateau. The Qaidam and Tarim basins are endorheic regions with thick Cenozoic deposits, and they uplifted dramatically during the Cenozoic. In contrast, the Sichuan basin is exorheic and most Cenozoic sediments flowed out of the basin; no visible Cenozoic uplift is observed. We suggest that whether a basin is endorheic or exorheic significantly influences its modern elevation, illustrating how exogenic geological processes impact endogenic geological processes. In addition, a new method of estimating paleoelevation is proposed, which predicts successively accelerating uplift of the Qaidam basin during the Cenozoic and provides good constraints on the geological evolution of the northern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

As revealed from recent drilling and organic geochemical testing and research, a series of lacustrine high-grade hydrocarbon source rocks was discovered in the upper section of the Chang 9 oil reservoir member of upper Triassic in Ordos Basin. The hydrocarbon source rocks show average TOC content as high as 5.03%, average bitumen “A” content as high as 0.8603%, and good quality organic precursors, which are of the sapropelic type mainly derived from lower aquatic plants and have reached the thermal evolution stage featured by oil-producing climax. Generally the lacustrine high-grade hydrocarbon source rocks were developed in local depressions of a lake basin, and the Chang 91 member was particularly formed in a depositional environment characterized by fresh water to weakly saline water, weakly oxidizing to weakly reducing setting and semi-deep lake facies, as was demonstrated by a variety of organic to inorganic geochemical parameters. As a result, high productivity constitutes the principal controlling force for generation of this series of high-grade hydrocarbon source rocks. Deposition of thinly-bedded and laminated tuffs as well as positive Eu anomaly corroborate the possible occurrence of anoxic geological event closely related to contemporaneous volcanic eruption, which would play a key part in development of the Chang 91 member of high-grade hydrocarbon source rocks. [ABSTRACT FROM AUTHOR]