The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from-24% to-28% in the Latest...The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from-24% to-28% in the Latest Permian which latter value persists into the Earliest Triassic after which it decreases slightly to-26%. Two strongly negative peaks of [-38% in the Latest Permian and a lesser peak of-31% in the Early Triassic are too negative to be due to a greater proportion of more negative organic matter and must be due to very negative methane effects. The overall change to more negative values across the Bulla/Tesero boundary fits the relative rise in sea level for this transition based on the facies changes. A positive shift in organic carbon isotope values at the Late Permian Event Horizon may be due to an increase in land-derived organic detritus at this level—a feature shown by allTethyan Permo-Triassic boundary sections though these other sections do not have the same values. Carbonate carbon isotope trends are similar in all sections dropping by2–3 units across the Permo-Triassic boundary. Gartnerkofel carbonate oxygen values are surprisingly, considering the ubiquitous dolomitization, compatible with values elsewhere and indicate reasonable tropical temperatures of 60 °C in the Latest Permian sabkhas to 20–40 °C in the overlying marine transition beds. Increased landderived input at the Late Permian Event Horizon may be due to offshore transport by tsunamis whose deposits have been recognized in India at this level.展开更多
A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of earl...A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of early Triassic. The thickness of the sectionis about 60 m. Paleomagnetic results indicate that six normal and reversed polarity zoneswere recorded in the section which all belong to the Illawarra mixed interval. Theboundary of Permo-Triassic lies at 1.2 m (or 2.7 m) above the bottom of normal polarityzone V. The magnetic minerals in the rocks of the lower part of the Changxing Forma-tion mainly are goethite, haematite and titaniferous magnetite while in the upper part ofthe formation are chiefly titanomagnetite and magnetite, goethite is secondary. Magne-tite and haematite as the main magnetic minerals were included in marl and mudstone ofthe Qinglong Formation. Based on the results of the magnetically stable samples thepaleopole position of 50.7°N, 230.3°E was obtained, meanwhile, the展开更多
The Permo-Triassic boundary in Wulong area, Sichuan Province, South China lies in a continuous marine carbonate succession with abundant fossil records. Two well-exposed sections were sampled for magnetostratigraphic ...The Permo-Triassic boundary in Wulong area, Sichuan Province, South China lies in a continuous marine carbonate succession with abundant fossil records. Two well-exposed sections were sampled for magnetostratigraphic studies. The experimental results of rock magnetism reveal that the samples from the Triassic limestones contain only magnetites among which 70% are multi-domain. The ChRM direction is carried by remaining 30% of single-domain magnetite. The Permian limestone samples are dominated by single-domain to superparamagnetic magnetites with little ChRM direction due to their fine-grained texture. Nevertheless, the polarity determination is still possible based on the NRM vector changes during thermal demagnetization. A Permo-Triassic polarity profile in Wulong area is established in the paper, and a tentative correlation with other known profiles is pursued. The authors suggest that the Illawarra reversal starts at the upper part of Wujiapingian, while some normal polarity events may exist in展开更多
Based on reconstructions of paleogeography, paleoclimate and paleoceanography of the Chihsian, Wujiapingian, Anisian and Norian intervals in the eastern Tethys, the multiple intrinsic relationship and interaction amon...Based on reconstructions of paleogeography, paleoclimate and paleoceanography of the Chihsian, Wujiapingian, Anisian and Norian intervals in the eastern Tethys, the multiple intrinsic relationship and interaction among the lithosphere, the hydrosphere and the atmosphere as well as their evolutions are discussed. It was demonstrated that paleogeographic change of the eastern Tethys and the northward shift of the Pangea during the Permo-Triassic periods governed the coeval paleocurrent pattern and its evolution, which in turn seems to be a key contributor forcing the Permo-Triassic megamonsoon to the climax.展开更多
The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of l...The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformationai conglomerates to fine-grained sediments, whereas the mudstone-dominated members （Daggaboersnek, Elandsberg, and Palingkloof） are dominated by the facies Fm and FI. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.展开更多
该研究以显生宙碳循环异常环境的地球生物学过程为研究主体,重点研究二叠纪-三叠纪之交和晚泥盆世两大重大地质突变期的地球生物学过程特点和规律,查明碳循环异常的起因及其对生态系统的影响,探索生物与环境的相互作用。二叠纪—三叠纪...该研究以显生宙碳循环异常环境的地球生物学过程为研究主体,重点研究二叠纪-三叠纪之交和晚泥盆世两大重大地质突变期的地球生物学过程特点和规律,查明碳循环异常的起因及其对生态系统的影响,探索生物与环境的相互作用。二叠纪—三叠纪之交是古生代海洋生态系破坏和中生代型海洋生态系开始重建的转折点,古海洋缺氧对该转折影响深远。通过对华南多条剖面高精度碳同位素、碳-硫形态、碳酸盐晶格硫(CAS)、DOP和Δδ13C等分析测试,该年度研究在认识该时期古海洋缺氧的时限、程度、演化和成因机制等方面取得明显进展。大灭绝前的二叠纪浅水碳酸盐岩台地以氧化环境为主。由于火山活动释放大量的CO2、SO2等气体,导致气温上升、陆地生态系统开始瓦解、陆源输入增加、海洋贫氧层(OMZ)扩张,大灭绝后海洋环境向缺氧环境转变。早三叠世早期δ34SCAS明显比晚二叠世偏重,波动剧烈,且与δ13Ccarb明显正相关(3次同步正漂),意味着严重的海洋缺氧、硫化事件,海水硫酸盐浓度很低(<3 m M)。早三叠世早期δ13Ccarb频繁和幅度较大的波动,指示了动荡不稳定的海洋碳循环;之后δ13Ccarb和δ34SCAS变化率同步减小,两者呈现负相关关系,可能是由于海水温度下降、海水循环增强,海洋碳循环趋于稳定。中三叠世δ34SCAS下降,变化率进一步降低,碳-硫同位素的正相关关系逐渐消失,反映该时期海洋硫酸盐浓度进一步升高,以正常的氧化状态为主。大灭绝后动荡的海洋碳-硫循环及缺氧环境导致了生物复苏迟缓。晚泥盆世弗拉斯-法门(F-F)生物大灭绝事件是显生宙又一重大地质转折时期,集中体现在生物礁生态系中,菌藻类取代后生动物(珊瑚-层孔虫)造礁。对华南地区多个剖面细致的观察和统计分析表明,菌藻类可侵入"活着"的后生动物并抑制后生动物的发育。后生动物骨骼虽然具有自我修复功能,并对菌藻类有反抑制作用,但在环境恶化时,这种平衡会被打破,导致后生动物个体无法生长而死亡,直至后生动物生物礁被菌藻类生物礁取代。中-晚泥盆世植物登陆,陆生植物粗大根系的发育,导致陆地生物-化学风化急剧增加,近岸海域海水营养水平激增,可能是晚泥盆世菌藻类"大举入侵"珊瑚-层孔虫礁生态系最终取而代之的直接推手。展开更多
The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans m...The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments,whereas the mudstone dominated members(Daggaboersnek, Elandsberg and Palingkloof) are dominated by the fine-grained facies(Fm and F1).Petrography,geochemistry and palaeocurrent analysis indicated that the source rock of the Balfour Formation was to展开更多
This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic d...This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,China.New zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 Ma.The mafic rocks fall into the alkaline and calc-alkaline series.They are enriched in light rare earth elements,some large ion lithophile elements(e.g.,Rb.Ba,and Sr),K,and Pb,and depleted in Nb,Ta,and Ti.The dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,respectively.Our results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle source.The parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement.Since the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the NCC.The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.展开更多
文摘The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from-24% to-28% in the Latest Permian which latter value persists into the Earliest Triassic after which it decreases slightly to-26%. Two strongly negative peaks of [-38% in the Latest Permian and a lesser peak of-31% in the Early Triassic are too negative to be due to a greater proportion of more negative organic matter and must be due to very negative methane effects. The overall change to more negative values across the Bulla/Tesero boundary fits the relative rise in sea level for this transition based on the facies changes. A positive shift in organic carbon isotope values at the Late Permian Event Horizon may be due to an increase in land-derived organic detritus at this level—a feature shown by allTethyan Permo-Triassic boundary sections though these other sections do not have the same values. Carbonate carbon isotope trends are similar in all sections dropping by2–3 units across the Permo-Triassic boundary. Gartnerkofel carbonate oxygen values are surprisingly, considering the ubiquitous dolomitization, compatible with values elsewhere and indicate reasonable tropical temperatures of 60 °C in the Latest Permian sabkhas to 20–40 °C in the overlying marine transition beds. Increased landderived input at the Late Permian Event Horizon may be due to offshore transport by tsunamis whose deposits have been recognized in India at this level.
文摘A hundred and eleven samples were collected from the Permian-Triassic boundarysection of Meishan (31.1°N, 119.7°E) which includes the Changxing Formation of thelate Permian and the Qinglong Formation of early Triassic. The thickness of the sectionis about 60 m. Paleomagnetic results indicate that six normal and reversed polarity zoneswere recorded in the section which all belong to the Illawarra mixed interval. Theboundary of Permo-Triassic lies at 1.2 m (or 2.7 m) above the bottom of normal polarityzone V. The magnetic minerals in the rocks of the lower part of the Changxing Forma-tion mainly are goethite, haematite and titaniferous magnetite while in the upper part ofthe formation are chiefly titanomagnetite and magnetite, goethite is secondary. Magne-tite and haematite as the main magnetic minerals were included in marl and mudstone ofthe Qinglong Formation. Based on the results of the magnetically stable samples thepaleopole position of 50.7°N, 230.3°E was obtained, meanwhile, the
基金This project was supported by both the National Natural Science Foundation of China and the Swiss Federal Institute of Technology.
文摘The Permo-Triassic boundary in Wulong area, Sichuan Province, South China lies in a continuous marine carbonate succession with abundant fossil records. Two well-exposed sections were sampled for magnetostratigraphic studies. The experimental results of rock magnetism reveal that the samples from the Triassic limestones contain only magnetites among which 70% are multi-domain. The ChRM direction is carried by remaining 30% of single-domain magnetite. The Permian limestone samples are dominated by single-domain to superparamagnetic magnetites with little ChRM direction due to their fine-grained texture. Nevertheless, the polarity determination is still possible based on the NRM vector changes during thermal demagnetization. A Permo-Triassic polarity profile in Wulong area is established in the paper, and a tentative correlation with other known profiles is pursued. The authors suggest that the Illawarra reversal starts at the upper part of Wujiapingian, while some normal polarity events may exist in
基金the National Natural Science Foundation of China (Grant Nos. 49632070, 49972038) and by the Excellent Young Teachers Program of the Ministry of Education of China to the first author.
文摘Based on reconstructions of paleogeography, paleoclimate and paleoceanography of the Chihsian, Wujiapingian, Anisian and Norian intervals in the eastern Tethys, the multiple intrinsic relationship and interaction among the lithosphere, the hydrosphere and the atmosphere as well as their evolutions are discussed. It was demonstrated that paleogeographic change of the eastern Tethys and the northward shift of the Pangea during the Permo-Triassic periods governed the coeval paleocurrent pattern and its evolution, which in turn seems to be a key contributor forcing the Permo-Triassic megamonsoon to the climax.
基金supported by the Govan Mbeki Research Centre(GMRC) at the University of Fort Hare and by the Council for Geoscience
文摘The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformationai conglomerates to fine-grained sediments, whereas the mudstone-dominated members （Daggaboersnek, Elandsberg, and Palingkloof） are dominated by the facies Fm and FI. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.
文摘该研究以显生宙碳循环异常环境的地球生物学过程为研究主体,重点研究二叠纪-三叠纪之交和晚泥盆世两大重大地质突变期的地球生物学过程特点和规律,查明碳循环异常的起因及其对生态系统的影响,探索生物与环境的相互作用。二叠纪—三叠纪之交是古生代海洋生态系破坏和中生代型海洋生态系开始重建的转折点,古海洋缺氧对该转折影响深远。通过对华南多条剖面高精度碳同位素、碳-硫形态、碳酸盐晶格硫(CAS)、DOP和Δδ13C等分析测试,该年度研究在认识该时期古海洋缺氧的时限、程度、演化和成因机制等方面取得明显进展。大灭绝前的二叠纪浅水碳酸盐岩台地以氧化环境为主。由于火山活动释放大量的CO2、SO2等气体,导致气温上升、陆地生态系统开始瓦解、陆源输入增加、海洋贫氧层(OMZ)扩张,大灭绝后海洋环境向缺氧环境转变。早三叠世早期δ34SCAS明显比晚二叠世偏重,波动剧烈,且与δ13Ccarb明显正相关(3次同步正漂),意味着严重的海洋缺氧、硫化事件,海水硫酸盐浓度很低(<3 m M)。早三叠世早期δ13Ccarb频繁和幅度较大的波动,指示了动荡不稳定的海洋碳循环;之后δ13Ccarb和δ34SCAS变化率同步减小,两者呈现负相关关系,可能是由于海水温度下降、海水循环增强,海洋碳循环趋于稳定。中三叠世δ34SCAS下降,变化率进一步降低,碳-硫同位素的正相关关系逐渐消失,反映该时期海洋硫酸盐浓度进一步升高,以正常的氧化状态为主。大灭绝后动荡的海洋碳-硫循环及缺氧环境导致了生物复苏迟缓。晚泥盆世弗拉斯-法门(F-F)生物大灭绝事件是显生宙又一重大地质转折时期,集中体现在生物礁生态系中,菌藻类取代后生动物(珊瑚-层孔虫)造礁。对华南地区多个剖面细致的观察和统计分析表明,菌藻类可侵入"活着"的后生动物并抑制后生动物的发育。后生动物骨骼虽然具有自我修复功能,并对菌藻类有反抑制作用,但在环境恶化时,这种平衡会被打破,导致后生动物个体无法生长而死亡,直至后生动物生物礁被菌藻类生物礁取代。中-晚泥盆世植物登陆,陆生植物粗大根系的发育,导致陆地生物-化学风化急剧增加,近岸海域海水营养水平激增,可能是晚泥盆世菌藻类"大举入侵"珊瑚-层孔虫礁生态系最终取而代之的直接推手。
文摘The Balfour Formation was subdivided into five members based on lithological variation that is characterized by alternating sandstone-and mudstone -dominated members.The sandstone dominated Oudeberg and Barberskrans members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments,whereas the mudstone dominated members(Daggaboersnek, Elandsberg and Palingkloof) are dominated by the fine-grained facies(Fm and F1).Petrography,geochemistry and palaeocurrent analysis indicated that the source rock of the Balfour Formation was to
文摘This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,China.New zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 Ma.The mafic rocks fall into the alkaline and calc-alkaline series.They are enriched in light rare earth elements,some large ion lithophile elements(e.g.,Rb.Ba,and Sr),K,and Pb,and depleted in Nb,Ta,and Ti.The dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,respectively.Our results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle source.The parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement.Since the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the NCC.The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.
