The Altay orogenic belt of Xinjiang in NW China represents one of the important sites of juvenile crustal growth during the Phanerozoic. However, some important issues, e.g., tectonic evolution and petrogenesis, still...The Altay orogenic belt of Xinjiang in NW China represents one of the important sites of juvenile crustal growth during the Phanerozoic. However, some important issues, e.g., tectonic evolution and petrogenesis, still remain controversial. The picrites in the south margin of the Altay orogenic belt were discovered in the lower part of marine volcanic-sedimentary sequences of the northwest-striking Middle Devonian Beitashan Formation (Fm.), which consists chiefly of intermediate-basic volcanic rocks intercalated minor carbonate, siltstone and siliceous rocks. The picrites are usually highly porphyritic, and contain abundant forsteritic olivine phenocrysts with minor clinopyroxene distributed in the groundmass, which consist of olivine, clinopyroxene and plagioclase with minor Fe-Ti oxides. The MgO contents of the picrites range from 14 wt% to 22 wt% with Mg# (atomic Mg/(Mg+Fe) ratio) of 0.75-0.80. They are characterized by slightly negative Ti anomalies, remarkably negative Nb and Ta anomalies and slightly positive P and Sm anomalies with the similar abundances of HFSE as MORB on the MORB-normalized trace element patterns, all of which characterize typical island arc magmas. In combing with the southwestward migration of the magmas of the Beitashan Fm., we propose that the magmas may result from the southwestward subduction of Junggar ocean plate. The Zr/Nb ratios (23-66) of both picrites and basalts resemble the MORB (10-66), suggesting that they were derived from the MORB-like sources. However, the basalts and picrites display some distinguishable element ratios and REE patterns, e.g., Ti/V (23-35) and Zr/Sm (18-23) ratios of basalts are higher than those of picrites (14-17 and 14-15 respectively), and the basalts display flat-type REE-chondrite patterns whereas the picrites are characterized by lower total REE concentrations ((26-34)×10^-6) and slight enrichment of light REE. These distinguished geochemical characteristics could be interpreted by different partial melting degrees and mantle sources, i.e., the basalts were generated by lower partial melting of amphibole-bearing spinel peridotite which was metasomatized by fluids released from subducted oceanic crust, and the picrites were resulted from the higher degree of partial melting of metasomatized garnet peridotite under high temperature. In contrast, the andesite with significant LREE and LILE enrichment may be resulted from the partial melting of eclogites.展开更多
The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abun...The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abundant in the reef. Thirty-two genera Belonging to 7 phyla have been recognized. They make up 5 communities composed mainly of stromatopoids, Corals and algae, each of which has its own salient ecological features. An analysis of all communities shows that the organic functions are very complex. The same organisms may possess diverse functions simultaneously as the reef growth enters the late stage. The growth process of the reef may involve five stages’ (l)biostrome stage, (2) stabilization stage, (3) frame-type reef-building stage, (4) binding and covering-type reef-building stage, and (5) baffle- type reef -building stage.展开更多
Analysis, evaluation and statistics of dispersed cuticles, spores and wood pieces in Middle Devouian cutinitic liptobiolith from South China have been made, and the results of the study of various plant remains found ...Analysis, evaluation and statistics of dispersed cuticles, spores and wood pieces in Middle Devouian cutinitic liptobiolith from South China have been made, and the results of the study of various plant remains found in coals can be verified mutually. Meanwhile , the phyteral analysis of coals may contribute to our comprehensive knowledge or fossil floras and be used for the reconstruction of the peatforming plant commuuities.展开更多
Twelve paleocommunities dominated by benthic brachiopod are recognized in the Givetian-Frasnian stages of the Devonian in the Longmenshan area, southwestern China, in which two kinds of brachiopod community replacemen...Twelve paleocommunities dominated by benthic brachiopod are recognized in the Givetian-Frasnian stages of the Devonian in the Longmenshan area, southwestern China, in which two kinds of brachiopod community replacement are classified. One is the abrupt replacement, represented by abrupt alternation between the Leiorhynchus community and Zhonghuacoelia-Striatopugnax community in the Frasnian Tuqiaozi Formation. The other is the gradual one, developed in the Givetian Guanwushan Formation, which had been completed by the shift of the Independatrypa lemma-Uncinulus heterocostellis-Emanuella takwanensis community via the Sinospongophyllum irregulare-Pseudomicroplasma fongi community to the Clathrocoilona spissa-Hexagonaria composite reef community. According to analyses of the paleocommunities, either the abrupt or gradual paleocommunity replacement of the Middle-Upper Devonian in the Longmenshan area is suggested as a response to the 5th-order sea level fluctuation due to the replacements of the paleocommunities in a tracts-system of depositional sequence. It is supposed that changes of paleocommunity diversity, one of the results of paleocommunity replacement, are depended on the range and magnitude of sea level fluctuation, but there is not a linear relationship between them. Furthermore, a suggestion is proposed that the concept of paleocommunity succession seem to be abandoned in the paleocommunity analysis because it almost never be practiced to recover the information of community succession in the geological record at present.展开更多
Chahuaqingolepis magniporus gen.et sp.nov.,a new taxon of Bothriolepididae(Placodermi:Antiarcha),is described from the Middle Devonian in Luquan County,Yunnan Province,South China.The phylogenetic analysis shows that ...Chahuaqingolepis magniporus gen.et sp.nov.,a new taxon of Bothriolepididae(Placodermi:Antiarcha),is described from the Middle Devonian in Luquan County,Yunnan Province,South China.The phylogenetic analysis shows that Chahuaqingolepis is the sister group of Wufengshania with the synapomorphy of the large obtected nuchal area.Together with the findings of other associated antiarchs including Dianolepis,Bothriolepis,and Hunanolepis,the new bothriolepid antiarch is assigned to the Bothriolepis sinensis-Hunanolepis fish assemblage,which characterizes the Eifelian of the Middle Devonian in South China.The fish-bearing Tanglishu Formation can be well correlated with the Tiaomajian Formation in Changsha,Shangshuanghe Formation and lower part of the Haikou Formation in Qujing,and Laohutou Formation in Shaoguan and Lechang areas.This discovery not only enriches the Middle Devonian diversity of bothriolepids,but also provides reliable paleoichthyological evidence on the division and correlation of the fish-bearing Devonian strata in South China and deepens the understanding of the biogeography of the Devonian bothriolepids.展开更多
A great breakthrough has been made on oil-gas exploration of the Middle Devonian Guanwushan Formation in Northwest Sichuan Basin.The further exploration shows that the dolomite reservoir is complicated with insufficie...A great breakthrough has been made on oil-gas exploration of the Middle Devonian Guanwushan Formation in Northwest Sichuan Basin.The further exploration shows that the dolomite reservoir is complicated with insufficient investigation.Taking the Middle Devonian Guanwushan Formation as an example,systematic study has been carried out on its reservoir character,mechanism and genesis of dolostone.The field and core data suggest that reservoir types of Guanwushan Formation consist of crystalline dolomite,breccia dolomite and reef dolomite,and reservoir space is characterized by intercrystal(dissolution)pores,residual pores among breccias,intragranular dissolution pores,pockets as well as fractures.Besides,pore structure is of good configuration,showing medium-low porosity and moderate permeability,with average porosity and permeability of 2.23%and 0.44mD respectively,which suggesting fracture-pore and fracture-cavity reservoir.Combined with the previous research,it is suggested that the reservoir of Guanwushan Formation was controlled by facies,dolomitization and two-step karstification,with reef-shoal facies being material base for reservoir development,early dolomitization being key factor for reservoir space preservation,polyphase karstification being foundation for reservoir development and tectogenesis finally finalizing the reservoir.展开更多
The controversies on the division and correlation of the Devonian have never stopped since Lonsodale found and named the Devonian at Devonshire, Britain, especially on the determination and correlation of the Lower-Mi...The controversies on the division and correlation of the Devonian have never stopped since Lonsodale found and named the Devonian at Devonshire, Britain, especially on the determination and correlation of the Lower-Middle Devonian Boundary. The correlation between the different areas and sedimentary facies are still an international question although the international stratotype section has already been established. Recently,展开更多
文摘The Altay orogenic belt of Xinjiang in NW China represents one of the important sites of juvenile crustal growth during the Phanerozoic. However, some important issues, e.g., tectonic evolution and petrogenesis, still remain controversial. The picrites in the south margin of the Altay orogenic belt were discovered in the lower part of marine volcanic-sedimentary sequences of the northwest-striking Middle Devonian Beitashan Formation (Fm.), which consists chiefly of intermediate-basic volcanic rocks intercalated minor carbonate, siltstone and siliceous rocks. The picrites are usually highly porphyritic, and contain abundant forsteritic olivine phenocrysts with minor clinopyroxene distributed in the groundmass, which consist of olivine, clinopyroxene and plagioclase with minor Fe-Ti oxides. The MgO contents of the picrites range from 14 wt% to 22 wt% with Mg# (atomic Mg/(Mg+Fe) ratio) of 0.75-0.80. They are characterized by slightly negative Ti anomalies, remarkably negative Nb and Ta anomalies and slightly positive P and Sm anomalies with the similar abundances of HFSE as MORB on the MORB-normalized trace element patterns, all of which characterize typical island arc magmas. In combing with the southwestward migration of the magmas of the Beitashan Fm., we propose that the magmas may result from the southwestward subduction of Junggar ocean plate. The Zr/Nb ratios (23-66) of both picrites and basalts resemble the MORB (10-66), suggesting that they were derived from the MORB-like sources. However, the basalts and picrites display some distinguishable element ratios and REE patterns, e.g., Ti/V (23-35) and Zr/Sm (18-23) ratios of basalts are higher than those of picrites (14-17 and 14-15 respectively), and the basalts display flat-type REE-chondrite patterns whereas the picrites are characterized by lower total REE concentrations ((26-34)×10^-6) and slight enrichment of light REE. These distinguished geochemical characteristics could be interpreted by different partial melting degrees and mantle sources, i.e., the basalts were generated by lower partial melting of amphibole-bearing spinel peridotite which was metasomatized by fluids released from subducted oceanic crust, and the picrites were resulted from the higher degree of partial melting of metasomatized garnet peridotite under high temperature. In contrast, the andesite with significant LREE and LILE enrichment may be resulted from the partial melting of eclogites.
文摘The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abundant in the reef. Thirty-two genera Belonging to 7 phyla have been recognized. They make up 5 communities composed mainly of stromatopoids, Corals and algae, each of which has its own salient ecological features. An analysis of all communities shows that the organic functions are very complex. The same organisms may possess diverse functions simultaneously as the reef growth enters the late stage. The growth process of the reef may involve five stages’ (l)biostrome stage, (2) stabilization stage, (3) frame-type reef-building stage, (4) binding and covering-type reef-building stage, and (5) baffle- type reef -building stage.
文摘Analysis, evaluation and statistics of dispersed cuticles, spores and wood pieces in Middle Devouian cutinitic liptobiolith from South China have been made, and the results of the study of various plant remains found in coals can be verified mutually. Meanwhile , the phyteral analysis of coals may contribute to our comprehensive knowledge or fossil floras and be used for the reconstruction of the peatforming plant commuuities.
基金The National Natural Science Foundation of China(Grant 40273014)has funded the project.
文摘Twelve paleocommunities dominated by benthic brachiopod are recognized in the Givetian-Frasnian stages of the Devonian in the Longmenshan area, southwestern China, in which two kinds of brachiopod community replacement are classified. One is the abrupt replacement, represented by abrupt alternation between the Leiorhynchus community and Zhonghuacoelia-Striatopugnax community in the Frasnian Tuqiaozi Formation. The other is the gradual one, developed in the Givetian Guanwushan Formation, which had been completed by the shift of the Independatrypa lemma-Uncinulus heterocostellis-Emanuella takwanensis community via the Sinospongophyllum irregulare-Pseudomicroplasma fongi community to the Clathrocoilona spissa-Hexagonaria composite reef community. According to analyses of the paleocommunities, either the abrupt or gradual paleocommunity replacement of the Middle-Upper Devonian in the Longmenshan area is suggested as a response to the 5th-order sea level fluctuation due to the replacements of the paleocommunities in a tracts-system of depositional sequence. It is supposed that changes of paleocommunity diversity, one of the results of paleocommunity replacement, are depended on the range and magnitude of sea level fluctuation, but there is not a linear relationship between them. Furthermore, a suggestion is proposed that the concept of paleocommunity succession seem to be abandoned in the paleocommunity analysis because it almost never be practiced to recover the information of community succession in the geological record at present.
基金supported by the Strategic Priority Research Program of CAS (Nos.XDB26000000,XDA19050102)the National Natural Science Foundation of China (Nos.42002015,42072026,92255301)+1 种基金the Youth Innovation Promotion Association CAS (No.2021070)the State Key Laboratory of Palaeobiology and Stratigraphy (No.193121)。
文摘Chahuaqingolepis magniporus gen.et sp.nov.,a new taxon of Bothriolepididae(Placodermi:Antiarcha),is described from the Middle Devonian in Luquan County,Yunnan Province,South China.The phylogenetic analysis shows that Chahuaqingolepis is the sister group of Wufengshania with the synapomorphy of the large obtected nuchal area.Together with the findings of other associated antiarchs including Dianolepis,Bothriolepis,and Hunanolepis,the new bothriolepid antiarch is assigned to the Bothriolepis sinensis-Hunanolepis fish assemblage,which characterizes the Eifelian of the Middle Devonian in South China.The fish-bearing Tanglishu Formation can be well correlated with the Tiaomajian Formation in Changsha,Shangshuanghe Formation and lower part of the Haikou Formation in Qujing,and Laohutou Formation in Shaoguan and Lechang areas.This discovery not only enriches the Middle Devonian diversity of bothriolepids,but also provides reliable paleoichthyological evidence on the division and correlation of the fish-bearing Devonian strata in South China and deepens the understanding of the biogeography of the Devonian bothriolepids.
基金We thank Dr.Sicong Luo,Feifan Lu and Chengpeng Su for their constructive comments.We thank Dr.Hao Tang and Cheng Huang for their help in filed work.This research was supported by National Science and technology major project(2016ZX05004002-001).
文摘A great breakthrough has been made on oil-gas exploration of the Middle Devonian Guanwushan Formation in Northwest Sichuan Basin.The further exploration shows that the dolomite reservoir is complicated with insufficient investigation.Taking the Middle Devonian Guanwushan Formation as an example,systematic study has been carried out on its reservoir character,mechanism and genesis of dolostone.The field and core data suggest that reservoir types of Guanwushan Formation consist of crystalline dolomite,breccia dolomite and reef dolomite,and reservoir space is characterized by intercrystal(dissolution)pores,residual pores among breccias,intragranular dissolution pores,pockets as well as fractures.Besides,pore structure is of good configuration,showing medium-low porosity and moderate permeability,with average porosity and permeability of 2.23%and 0.44mD respectively,which suggesting fracture-pore and fracture-cavity reservoir.Combined with the previous research,it is suggested that the reservoir of Guanwushan Formation was controlled by facies,dolomitization and two-step karstification,with reef-shoal facies being material base for reservoir development,early dolomitization being key factor for reservoir space preservation,polyphase karstification being foundation for reservoir development and tectogenesis finally finalizing the reservoir.
基金Project supported by the National Natural Science Foundation of China Doctoral Foundation of National Education Committee
文摘The controversies on the division and correlation of the Devonian have never stopped since Lonsodale found and named the Devonian at Devonshire, Britain, especially on the determination and correlation of the Lower-Middle Devonian Boundary. The correlation between the different areas and sedimentary facies are still an international question although the international stratotype section has already been established. Recently,
