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The uplift of the Tibetan Plateau is one of the most important geological events in the Cenozoic era, which has had a far-reaching impact on climate change in neighboring regions and even the world. Scholars have already considered that the uplift of this period has a good coupling with the warm and cold climate changes. The Beilianchi section is west of Liupan Mountain, the back edge of the arcuate tectonic belt on the northeast margin of the Tibetan Plateau. The Paleocene Qingshuiying Formation is mainly a set of shallow lacustrine deposits dominated by purple-red mudstone with thin gypsum layers containing rich paleoenvironmental and paleoclimatic information. The article systematically studied the palynological assemblage of the Beilianchi section and identified 60 genera and 65 species of sporopollen types as well as several undetermined species. The assemblage is characterized by dominant angiosperm pollen grains and rare gymnosperm pollen and fern spores. Based on the existing research results of regional sporopollen, the geologic age of the Qingshuiying Formation is believed to be the middle-late Oligocene–early Miocene. The sporopollen flora is dominated by deciduous broad-leaved plants such as Betulaceae, Juglandaceae, and Ulmaceae, and pollens from a few but diverse tropical-subtropical plants also occur in the assemblage. In contrast, the pollen content of typical arid shrubs and herbaceous plants is small, generally reflecting the warm-temperate zone's milder and wetter paleoenvironmental and paleoclimatic background. The absence of pollen from cold-tolerant mountain conifers in the palynological assemblage indicates that the regional climatic environment had not yet changed from warm to cold during this period and that the uplift and expansion of the Tibetan Plateau to the northeast had not yet affected the Liupanshan area. The results of this study provide new evidence to constrain the depositional age of the Qingshuiying Formation on the northeastern margin of the Tibetan Plateau and the impact of the uplift process of the Tibetan Plateau on the paleoecology and paleoclimate of the region.

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The precise age of the strata at the northeastern margin of the Tibetan Plateau in the Paleogene-Neogene, and the initial time when the uplift of the Plateau affected its northeastern margin, have always been two main bone contentions among geologists. The Guanyindian section at the northeastern margin of the Tibetan Plateau is our research subject. We gain new insights to the two mentioned issues by using detrital zircon U-Pb dating in combination with the previous results concerning regional paleontological fossil identification and paleomagnetic dating. The dating results show, among the samples from the upper Paleogene Qingshuiying formation at the northeastern margin of the Tibetan Plateau, the youngest peak is 17.8 Ma. Two conclusions are drawn from the research results. Firstly, the deposition age of the Qingshui formation is from the late Oligecene to early Miocene, showing the characteristic of diachronism. Secondly, the northeastward extension and pushing of the uplift of the Tibetan Plateau has begun affecting the west of the Haiyuan-Liupanshan fault zone since the early Miocene with a coupling relationship among tectonics, sedimentation and climate in the area. The research findings provide a new time scale for determining the initial time when the northeastward pushing of the Tibetan Plateau began to affect its northeastern margin.

Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Yinchuan Graben is an important structural belt in the northwestern part of the Ordos Basin, but the current research on its oil and gas geological conditions is still in its infancy, and it is not possible to fully reveal the characteristics of oil and gas accumulation. This paper analyzes the oil and gas exploration potential of Yinchuan graben based on the existing drilling and geochemical analysis data and predicts the oil and gas accumulation potential of the area. The main source rock in the Yinchuan graben is the lower part of the Qingshuiying Formation of the Oligocene. The amount of source rock in the northern part of the basin is more than that in the southern part, and all four sags contain source rocks. The basin has good oil and gas potential and has oil and gas reservoirs with two accumulation types: self-generation and self-storage type and upper generation and lower storage type. [ABSTRACT FROM AUTHOR]