Uigur Basin Organic Geochemistry Research and Jurassic Stratigraphy

Author: Yang Dianzhong, Yu Man
Publisher:
Publish Date: 2006-07-01
Features: This book conducts research on the sandstone-type uranium deposits in the Turpan Basin from two aspects: one is the systematic description of the Jurassic flora in the Turpan Basin and the stratigraphic division of the Middle-Lower Jurassic System; the other is the organic geochemical study. In some of the research, the author carefully sorted and identified 129 paleontological fossils collected from nine boreholes and 21 surface exposures in the Turpan Basin. The plant fossils in the Turpan Basin were divided into three assemblages from bottom to top: ① Neocalamites shoerensis-Ginkgo itessibiricus assemblage; ② Equisetites brevidentatus—Cladophlebis kaxgerensis assemblage; ③ Cladophlebis famgtzuensis-Raphaeliadia mensis assemblage. Based on this, the Middle-Lower Jurassic System in the Turpan Basin was divided into three formations: the Lower Jurassic lower Badaowan Formation, the Lower Jurassic upper Sangonghe Formation, and the Middle Jurassic lower Xishanyao Formation. In the organic geochemical study of uranium, the organic matter in the sedimentary environment was first classified. Broadly speaking, the organic matter was divided into non-humic substances (mainly including sugars, lipids, and amino acids) and humic substances (further subdivided into fulvic acid, humic acid, and humin). The study confirmed that the fulvic acid in the humic substances of the Turpan Basin had low C content, high H, S, and O content, and a low C/H atomic ratio. Functional group analysis confirmed that the fulvic acid had high total acidic groups, carboxyl groups, and phenolic hydroxyl groups, reflecting its high reactivity. Secondly, it was found that in the geochemical zones of the sandstone uranium deposits in the Turpan Basin (oxidation zone, redox transition zone, and reduction zone), the redox transition zone had the highest content of uranium, organic carbon, and humic substances. The experiments also confirmed that during the formation of the sandstone uranium deposits in the Turpan Basin, the adsorption of organic matter (mainly humic substances and asphaltene) played a partial role in uranium accumulation, with fulvic acid playing the main role. The migration of uranium was mainly in the form of uranyl complexes with fulvic acid. Infrared spectroscopy (IR) results also confirmed the above views. Through experiments and analysis, the author believes that the complexation and adsorption of humic substances are closely linked in the migration of uranium, rather than being two isolated processes. In the migration and precipitation enrichment of uranium, fulvic acid and humic acid play different roles.