Eighty-one species of fossil spores and pollen assigned to 52 genera are found from the Middle Jurassic Xishanyao, Sanjianfang and Qiketai Formations of boreholes Le 1, Mi 1, Shan 1 and Dun 1 in the northern Turpan De...Eighty-one species of fossil spores and pollen assigned to 52 genera are found from the Middle Jurassic Xishanyao, Sanjianfang and Qiketai Formations of boreholes Le 1, Mi 1, Shan 1 and Dun 1 in the northern Turpan Depression, Xinjiang, northwest China. Three assemblages have been proposed as: Cyathidites-Psophosphaera-Cycadopites assemblage, Cyathidites-Quadraceculina-Classopollis assemblage and Cyathidites-Callialasporites-Classopollis assemblage obtained from the Xishanyao Formation, the Sanjianfang Formation and Qiketai Formation respectively. Based on the sporo-pollen assemblage features and con-elation, their geological ages are regarded as of Middle Jurassic, probably Aalenian to Bathonian. The results of the study indicate that the vegetation of early Middle Jurassic in this region consisted mainly of Gymnospermae of Ginkgoaceae of Cycadales, Podocarpaceae, Pinaceae and Pteridophyta of Cyatheacene, Osmundaceae, Lycopodiaceae and Dicksoniaceae, etc. They reflect a warm-moist subtropic climate. To the middle-late Middle Jurassic, Cheirolepidaceae was dominant in the vegetation, which indicates that the climate was in the trend of becoming dry.展开更多
The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in...The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.展开更多
文摘Eighty-one species of fossil spores and pollen assigned to 52 genera are found from the Middle Jurassic Xishanyao, Sanjianfang and Qiketai Formations of boreholes Le 1, Mi 1, Shan 1 and Dun 1 in the northern Turpan Depression, Xinjiang, northwest China. Three assemblages have been proposed as: Cyathidites-Psophosphaera-Cycadopites assemblage, Cyathidites-Quadraceculina-Classopollis assemblage and Cyathidites-Callialasporites-Classopollis assemblage obtained from the Xishanyao Formation, the Sanjianfang Formation and Qiketai Formation respectively. Based on the sporo-pollen assemblage features and con-elation, their geological ages are regarded as of Middle Jurassic, probably Aalenian to Bathonian. The results of the study indicate that the vegetation of early Middle Jurassic in this region consisted mainly of Gymnospermae of Ginkgoaceae of Cycadales, Podocarpaceae, Pinaceae and Pteridophyta of Cyatheacene, Osmundaceae, Lycopodiaceae and Dicksoniaceae, etc. They reflect a warm-moist subtropic climate. To the middle-late Middle Jurassic, Cheirolepidaceae was dominant in the vegetation, which indicates that the climate was in the trend of becoming dry.
基金supported by Basic Scientific Research Operation Cost of State-Leveled Public Welfare Scientific Research Courtyard (Grant No. K0926)National Natural Science Foundation of China (Grant Nos. 40543013, 40873003)Key Laboratory of Isotope Geology, Ministry of Land and Resources
文摘The recently discovered nitrate ore field in the Turpan-Hami Basin of western China represents an estimated resource of 2.5 billion tons, and is comparable in scale to the Atacama Desert super-scale nitrate deposit in Chile. The research on this area is rarely carried out, and the origin of the deposits remains uncertain. In this study, new methods were used to systematically analyze N and O isotopes in nitrate minerals collected from the Kumutage, Xiaocaohu, Wuzongbulak, Dawadi, Tuyugou, and Shaer ore deposits in the Turpan-Hami Basin. The data showed that the δ15NAir value ranges from 0.7‰ to 27.6‰, but mostly between 2‰ and 6‰, which was similar to atmospheric NO3-. The 18O was highly enriched with δ18OV-SMOW varying from 30.2‰ to 46.7‰. This differs from levels in deposits derived from microbial nitrogen fixation, but is similar to those in atmospheric nitrates. N and O isotopes data indicated that nitrate deposits in Turpan-Hami Basin must be the result of deposition of atmospheric nitrate particles. Although atmospheric nitrate particles are common, the nitrate deposits could form only under the condition of long-term extreme drought climate and very limited biological activity. This paper summarized the ore-forming mechanism of different types nitrate deposits based on their geological setting.
