This study for the first time demonstrates that some of the so-called clay-sized mudstones observed by the naked eye,such as clay-sized black mudstones and clay-sized oil shales,which are rich in black organic matter(...This study for the first time demonstrates that some of the so-called clay-sized mudstones observed by the naked eye,such as clay-sized black mudstones and clay-sized oil shales,which are rich in black organic matter(including oil and asphaltene),in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin of China are actually clay-sized tuffaceous rocks(including tuff,sedimentary tuff and tuffaceous sedimentary rock)with high hydrocarbon generation capacities.Thus,these rocks can be defined as clay-sized tuffaceous source rocks.Identification of this lithology has important theoretical and practical significance for the exploration and development of shale oil in the Chang 7 Member.Through the macroscopic observation of drill cores and outcrop profiles,microscopic observation of electron probe thin sections and whole-rock inorganic geochemical analysis(including major,trace and rare earth elements),this work demonstrates that the organic matter-rich clay-sized tuffaceous rocks,especially clay-sized tuffs,have the following characteristics.First,the clay-sized tuffaceous rocks with little black organic matter are mainly greyish white,yellowish brown and purplish grey,and mixed colors occur in areas with strong bentonite lithification.Second,the clay-sized tuffaceous rocks have experienced strong devitrification and recrystallization,forming abundant flaky aluminosilicate minerals with directional arrangement.In thin sections under a polarizing microscope,the interference colors generally show regular alternation between the lowest interference color of first-order yellow and the highest interference color of second-order blue-green.Third,the rock samples plot in the igneous rock field in the TiO2-SiO2 cross-plot and exhibit similar trace element and rare earth element patterns on spider diagrams,indicating that the samples are derived from the same source.The results prove that clay-sized tuffaceous rocks may be widespread in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin,China.展开更多
Based on the element geochemistry and biomarkers of the oil shale from the Chang 7 sub-unit in the southern Ordos Basin,the depositional conditions and organic source of the oil shale are discussed.Biomarkers analyses...Based on the element geochemistry and biomarkers of the oil shale from the Chang 7 sub-unit in the southern Ordos Basin,the depositional conditions and organic source of the oil shale are discussed.Biomarkers analyses show that the oil shale has a homologous organic matter source,with a mix of plankton and advanced plants.U/Th and V/Ni ratios suggest that the redox condition is dominated by a reducing condition,and the degree of anoxia in the Tongchuan area is higher than that of the Xunyi area.Sr/Ba ratios illustrate that the oil shale is deposited in fresh water and the paleosalinity in the Tongchuan area is slightly higher.Fe/Ti ratios imply that the Tongchuan area underwent obvious hydrothermal fluid activities.Sr/Cu ratios show warm and humid paleoclimate in both areas.As assessed by(La/Yb)NASC,the deposition rate in the Tongchuan area is relatively lower.Fe/Co and Th/U ratios suggest that the paleo-water-depth in the Tongchuan area is deeper.The source rock could have the advance plants source,which must have close relationship with the Qinling orogeny.Comparing the paleoenvironment,the Tongchuan area has better depositional conditions,and is the key oil shale exploration area in the southern Ordos Basin.展开更多
基金Project(18GK28)supported by the Doctoral Scientific Research Staring Foundation for Yulin University,ChinaProject(20106101110020)supported by the University Research Fund of Science and Technology Development Center of Ministry of Education,ChinaProject(BJ08133-3)supported by the Key Fund Project of Continental Dynamics National Key Laboratory of Northwest University,China。
文摘This study for the first time demonstrates that some of the so-called clay-sized mudstones observed by the naked eye,such as clay-sized black mudstones and clay-sized oil shales,which are rich in black organic matter(including oil and asphaltene),in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin of China are actually clay-sized tuffaceous rocks(including tuff,sedimentary tuff and tuffaceous sedimentary rock)with high hydrocarbon generation capacities.Thus,these rocks can be defined as clay-sized tuffaceous source rocks.Identification of this lithology has important theoretical and practical significance for the exploration and development of shale oil in the Chang 7 Member.Through the macroscopic observation of drill cores and outcrop profiles,microscopic observation of electron probe thin sections and whole-rock inorganic geochemical analysis(including major,trace and rare earth elements),this work demonstrates that the organic matter-rich clay-sized tuffaceous rocks,especially clay-sized tuffs,have the following characteristics.First,the clay-sized tuffaceous rocks with little black organic matter are mainly greyish white,yellowish brown and purplish grey,and mixed colors occur in areas with strong bentonite lithification.Second,the clay-sized tuffaceous rocks have experienced strong devitrification and recrystallization,forming abundant flaky aluminosilicate minerals with directional arrangement.In thin sections under a polarizing microscope,the interference colors generally show regular alternation between the lowest interference color of first-order yellow and the highest interference color of second-order blue-green.Third,the rock samples plot in the igneous rock field in the TiO2-SiO2 cross-plot and exhibit similar trace element and rare earth element patterns on spider diagrams,indicating that the samples are derived from the same source.The results prove that clay-sized tuffaceous rocks may be widespread in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin,China.
基金Projects(41173055,41772118)supported by the National Natural Science Foundation of China
文摘Based on the element geochemistry and biomarkers of the oil shale from the Chang 7 sub-unit in the southern Ordos Basin,the depositional conditions and organic source of the oil shale are discussed.Biomarkers analyses show that the oil shale has a homologous organic matter source,with a mix of plankton and advanced plants.U/Th and V/Ni ratios suggest that the redox condition is dominated by a reducing condition,and the degree of anoxia in the Tongchuan area is higher than that of the Xunyi area.Sr/Ba ratios illustrate that the oil shale is deposited in fresh water and the paleosalinity in the Tongchuan area is slightly higher.Fe/Ti ratios imply that the Tongchuan area underwent obvious hydrothermal fluid activities.Sr/Cu ratios show warm and humid paleoclimate in both areas.As assessed by(La/Yb)NASC,the deposition rate in the Tongchuan area is relatively lower.Fe/Co and Th/U ratios suggest that the paleo-water-depth in the Tongchuan area is deeper.The source rock could have the advance plants source,which must have close relationship with the Qinling orogeny.Comparing the paleoenvironment,the Tongchuan area has better depositional conditions,and is the key oil shale exploration area in the southern Ordos Basin.
