Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolu...Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ 13C background values are intensively controlled by palaeogeographic environment. In general, δ 13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan- Olenekian boundary and the Lower Triassic-Middle Triassic boundary.展开更多
The Early and Middle Triassic primary lower Yangtze sea basin was formed before the Yangtze and Sino. Korean blocks collided and were assembled. showing the characteristics of an open continental shelf.continental mar...The Early and Middle Triassic primary lower Yangtze sea basin was formed before the Yangtze and Sino. Korean blocks collided and were assembled. showing the characteristics of an open continental shelf.continental margin sea. In order to provide evidence useful for oil and gas exploration in the studied region, this paper centres on the features of the sediments and their facies framework in the basin and the sedimentation parameters such as the deposition rate, palaeotemperature, palaeosatinity, palaeodepth of water and palaeocurrents of the basin.展开更多
The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapota...The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation, respectively. The repre-sentative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating. The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks. The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation, and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation. These U-Pb ages are interpreted to represent the formation times of the volcanic rocks. In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region, it is proposed that the latest volcanic activations in the Jinniu, Luzong, Fanchang and Ningwu volcanic basins probably came to end prior to ca. 128 Ma. There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins, suggesting a short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region. Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension, followed by delaminating of the lower part of the thickened lithosphere, lithospheric thinning, asthenosphere upwelling, and crust-mantle interaction.展开更多
Fish-bearing-nodules are found in Early Triassic marine strata in many regions, including East Greenland, East Spitsbergen, Northwest Madagascar, Canada, Angola, and South China. A new Olenekian(Early Triassic) conodo...Fish-bearing-nodules are found in Early Triassic marine strata in many regions, including East Greenland, East Spitsbergen, Northwest Madagascar, Canada, Angola, and South China. A new Olenekian(Early Triassic) conodont biostratigraphic study for stratum that contains fish-bearing-nodule levels is conducted based on the Longtan(LT) Section of Nanjing City and the Qingshan(QS) Section of Jurong County, Jiangsu Province, South China. A total of 101 samples were collected at the two sections and three conodont zones were recognized: in ascending order, they are Scythogondolella(Sc.) milleri Zone, Novispathodus(Nv.) pingdingshanensis Zone, and Triassospathodus(Tr.) aff. homeri Zone. The Scythogondolella milleri Zone is globally recognized as the uppermost conodont zone of the Smithian and the base of the Novispathodus pingdingshanensis Zone was previously suggested as the marker of the Smithian-Spathian boundary in the Yangtze region. The fish-bearing-nodule levels of Nanjing and Jurong are within the conodont Scythogondolella milleri Zone, laterally correlated well with the upper part of the Novispathodus waageni Zone in Chaohu of Anhui Province that also contains fish-bearing-nodule levels. The conodont biostratigraphic correlation confirms the Early Triassic fish-bearing-nodule levels in the Lower Yangtze region are coeval, with an end-Smithian in age.展开更多
Based on detailed field observation and multidisciplinary studies of integrated stratigraphy, the marine Lower and Middle Triassic of Lower Yangtze region is divided into five third order sequences, the general approa...Based on detailed field observation and multidisciplinary studies of integrated stratigraphy, the marine Lower and Middle Triassic of Lower Yangtze region is divided into five third order sequences, the general approach of the outcrop sequence stratigraphical study of carbonate ramp is proposed, the pattern in the development of the Early and Middle Triassic sequence under the major regression is summarized, and the sequence stratigraphical and chronostratigraphical frameworks across various paleogeographical facies zones on the marginal platform are established.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40325004)the Ministry of Science and Technology of China(Grant No.G2000077705).
文摘Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ 13C background values are intensively controlled by palaeogeographic environment. In general, δ 13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan- Olenekian boundary and the Lower Triassic-Middle Triassic boundary.
文摘The Early and Middle Triassic primary lower Yangtze sea basin was formed before the Yangtze and Sino. Korean blocks collided and were assembled. showing the characteristics of an open continental shelf.continental margin sea. In order to provide evidence useful for oil and gas exploration in the studied region, this paper centres on the features of the sediments and their facies framework in the basin and the sedimentation parameters such as the deposition rate, palaeotemperature, palaeosatinity, palaeodepth of water and palaeocurrents of the basin.
基金Supported by the National Basic Research Program of China (Grant No. 2006CB403508)Key Project of Ministry of Education of China (Grant No. 108511)National Natural Science Foundation of China (Grant No. 40730313)
文摘The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation, respectively. The repre-sentative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating. The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks. The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation, and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation. These U-Pb ages are interpreted to represent the formation times of the volcanic rocks. In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region, it is proposed that the latest volcanic activations in the Jinniu, Luzong, Fanchang and Ningwu volcanic basins probably came to end prior to ca. 128 Ma. There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins, suggesting a short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region. Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension, followed by delaminating of the lower part of the thickened lithosphere, lithospheric thinning, asthenosphere upwelling, and crust-mantle interaction.
基金funded by the Stratefic Priority Research Program of the Chinese Academy of Science(No.XDA14010404)the National Science Foundation of China(Nos.41572008,U1663201,41372016,40920124002,1402014)+2 种基金the Ministry of Science and Technology(No.2016YFC0503301)the State Key Laboratory of Palaeobiology and Stratigraphy(Nanjing Institute of Geology and Palaeontology,CAS)(Nos.123107,143108,173123)the China Geological Survey(No.121201102000150012-09)
文摘Fish-bearing-nodules are found in Early Triassic marine strata in many regions, including East Greenland, East Spitsbergen, Northwest Madagascar, Canada, Angola, and South China. A new Olenekian(Early Triassic) conodont biostratigraphic study for stratum that contains fish-bearing-nodule levels is conducted based on the Longtan(LT) Section of Nanjing City and the Qingshan(QS) Section of Jurong County, Jiangsu Province, South China. A total of 101 samples were collected at the two sections and three conodont zones were recognized: in ascending order, they are Scythogondolella(Sc.) milleri Zone, Novispathodus(Nv.) pingdingshanensis Zone, and Triassospathodus(Tr.) aff. homeri Zone. The Scythogondolella milleri Zone is globally recognized as the uppermost conodont zone of the Smithian and the base of the Novispathodus pingdingshanensis Zone was previously suggested as the marker of the Smithian-Spathian boundary in the Yangtze region. The fish-bearing-nodule levels of Nanjing and Jurong are within the conodont Scythogondolella milleri Zone, laterally correlated well with the upper part of the Novispathodus waageni Zone in Chaohu of Anhui Province that also contains fish-bearing-nodule levels. The conodont biostratigraphic correlation confirms the Early Triassic fish-bearing-nodule levels in the Lower Yangtze region are coeval, with an end-Smithian in age.
文摘Based on detailed field observation and multidisciplinary studies of integrated stratigraphy, the marine Lower and Middle Triassic of Lower Yangtze region is divided into five third order sequences, the general approach of the outcrop sequence stratigraphical study of carbonate ramp is proposed, the pattern in the development of the Early and Middle Triassic sequence under the major regression is summarized, and the sequence stratigraphical and chronostratigraphical frameworks across various paleogeographical facies zones on the marginal platform are established.
