The petrogenesis and genetic link to polymetallic mineralization of the granites in the Dayishan complex,southern Hunan province remain debated.Here,we present an integrated study on the petrology,zircon U-Pb ages and...The petrogenesis and genetic link to polymetallic mineralization of the granites in the Dayishan complex,southern Hunan province remain debated.Here,we present an integrated study on the petrology,zircon U-Pb ages and whole-rock geochemistry for this complex.Our findings indicate that the southern complex consists of(amphibole-bearing)biotite granites and muscovite granites emplaced at 153-151 Ma,and the central and northern complex consists of two-mica granites and tourmaline-bearing muscovite granites,respectively with the former emplaced at 164 Ma and the latter at 150 Ma.The(amphibole-bearing)biotite granites have SiO_(2) contents of 68.0-73.8 wt% and are enriched in alkalis and rare earth elements and depleted in Sr and Ba.They display Zr+Y+Ce+Nb>350 ppm and 10000×Ga/Al>2.6 along with high zircon saturation temperatures(821-883oC).The two-mica granites and(tourmaline-bearing)muscovite granites have high SiO_(2)(74.4-77.3 wt%)and low Ga/Al,Zr+Nb+Ce+Y,K/Rb,Zr/Hf,and Nb/Ta along with low zircon saturation temperatures(709-817℃).Geochemical characteristics suggest that the(amphibole-bearing)biotite granites are A-type granites generated through shallow dehydration melting of early Paleozoic granitoids,and that the two-mica granites and(tourmaline-bearing)muscovite granites are fractionated A-type granites produced through fractionation crystallization from the(amphibole-bearing)biotite granites accompanied by fluid fractionation.展开更多
A prevailing theory suggests that volcanic eruptions triggered environmental changes,which compelled dinosaurs to migrate in search of new habitats.Compelling evidence for this hypothesis has now been discovered in th...A prevailing theory suggests that volcanic eruptions triggered environmental changes,which compelled dinosaurs to migrate in search of new habitats.Compelling evidence for this hypothesis has now been discovered in the Tunxi Basin of eastern China.During the Late Mesozoic,the subduction of the Pacific Plate beneath southeastern China led to multi-stage volcanic activity.The Tunxi Formation in the basin,the first reported Upper Jurassic volcanic unit in the eastern Jiangnan orogen.It overlies the stratum bearing the easternmost mamenchisaurids,which is the dominant Asian sauropod lineage.Geochemical analyses suggest its affinity with coeval magmatism in southeastern China,while new rhyolite zircon U-Pb dating yields an age of 151.6±2.2 Ma,further indicating a transition from arc magmatism to back-arc extension driven by Paleo-Pacific subduction during the Late Jurassic.These studies also confirm that,as early as 156 Ma,the Tunxi Basin was already a key habitat for mamenchisaurids.The Late Jurassic subduction of the Paleo-Pacific Plate caused extensive magmatism across eastern China.This intense tectonic shift likely induced abrupt environmental changes in relative basins.Severe volcanic activity drastically reduced the habitat of mamenchisaurids,prompting a northwestward and southward radiation trend-presents a coherent scene of volcanic eruptions,environmental catastrophe,and dinosaurs migrating.展开更多
In a re-examination of the Neogene stratigraphy of the Uşak,Güre,and Selendi basins of western Anatolia,western Turkey,the stratigraphic position of the previously definedİnay Group is revised,which was previousl...In a re-examination of the Neogene stratigraphy of the Uşak,Güre,and Selendi basins of western Anatolia,western Turkey,the stratigraphic position of the previously definedİnay Group is revised,which was previously considered to be of the Middle Miocene age.Based on mammalian biochronology and stratigraphic relationships,two sequences are identified,separated by conformable/transitional contacts within the former group:the Middle Miocene Güre Group is composed of the FakılıFormation,characterized by alluvial fan deposits,and the lacustrine Derbent Formation.Radiometric dating of alkaline volcanics laterally associated with Güre Group sediments in the Uşak and Güre basins,and mammalian fossils re-evaluated into the MN5-6 biozones in the Selendi Basin,indicate early Middle Miocene.Considering the stratigraphic relationship with the overlying early Late Mioceneİnay Group as redefined,we estimate that the Güre Group was deposited in the Middle Miocene.Theİnay Group is characterized by a lateral-vertical transition from alluvial deposits of the Ahmetler Formation to the overlying lacustrine Ulubey Formation.An MN9-10 fauna,containing deinotheres,was found within the latter formation.展开更多
The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones.The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district,Erbil...The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones.The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district,Erbil Governorate to identify the lithostratigraphy and microfacies analysis in order to determine the depositional environment of the formation.The formation in the studied section is 116 m thick and mainly consists of reddish-brown,hard,thickbedded,chert-bearing conglomerate,pinkish shale and yellowish-grey,thick-bedded,detrital,fossiliferous limestone.The formation is unconformably underlain by the Upper Cretaceous Tanjero Formation and conformably overlain by the Merga Red Beds series.Four different lithostratigraphic units were identified,based on field observation and petrographic analysis,including a basal conglomerate unit(A),a shale unit(B),a well-bedded limestone unit(C)and a thick and massively-bedded limestone unit(D).The presence of a thick conglomerate bed at the base of the formation indicates a large unconformity that lasted nearly 40 million years.Based on detailed microfacies analysis of carbonate rocks,five main microfacies and 15 submicrofacies are recognized.The main microfacies types include mudstone,wackestone,packstone,grainstone and boundstone microfacies.Based on the microfacies types the depositional environment are defined as open lagoon,reef,fore-reef and back-reef environments of normal to saline,nutrient rich water.展开更多
The Yangtze River,with a length of approximately 6300 km,holds the distinction of being the largest river in East Asia that empties into the Pacific Ocean.Its formation is intricately linked to regional tectonic activ...The Yangtze River,with a length of approximately 6300 km,holds the distinction of being the largest river in East Asia that empties into the Pacific Ocean.Its formation is intricately linked to regional tectonic activity and climate fluctuations.However,the exact timeline for the formation of the Yangtze River remains elusive.This study investigates the provenance of the Late Cenozoic strata in the Wangjiang Basin,situated in the Lower Yangtze River,through the application of detrital zircon U-Pb dating.Seven sand samples were analyzed,leading to the identification of new U-Pb detrital zircon ages(n=577).Our study reveals that the sand materials found in the Pliocene gravel beds of the Anqing Formation originate predominantly from the Yangtze River.The findings of our study,along with the provenance tracing of boreholes in the Yangtze River Basin and the shelf sea in East China,provide compelling evidence for the continuous presence of the Yangtze River throughout the Pliocene period.The development of the Yangtze River during the Pliocene is intricately connected to both the tectonic adjustments occurring at the southeastern margin of the Tibetan Plateau and the intensification of the Asian Monsoon.展开更多
Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequen...Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.展开更多
The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion res...The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.展开更多
The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to b...The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to be limited to north Africa.Here,we describe transgression traces in the Muglad Basin in central Africa that indicate a greater spatial extend of the Neotethys during the late Cretaceous.A series of molecular markers detected in the Upper Cretaceous Santonian-Maastrichtian sediments of the Muglad Basin are typical for marine depositional conditions and differ from those in the typical lacustrine sediments of the Lower Cretaceous Barremian-Aptian.Combining the geological-geochemical implications of these markers with the paleogeographic,paleontological and lithological records,we propose that the Muglad Basin received intermittent marine inundations during the Santonian-Maastrichtian stages(86.3-66.0 Ma)and these special molecular markers are therefore the products of seawater incursion.Consequently,this study proposes that the transgression extent of the Neotethys Ocean into the African continent southern extended to the central Africa during the Late Cretaceous.展开更多
The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Prov...The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Province and the associated release of^(12)C-enriched carbon.The T-OAE coincided with global climate and environmental changes,as well as biotic events,indicating substantial modifications in ecosystems.Recent studies have focused on the evidence of geological responses to the T-OAE in Early Jurassic terrestrial basins in China,particularly the Sichuan Basin.Nevertheless,debate remains over the identification of this event,owing to inadequate age-constraints of many sections,and a lack of robust correlations of the carbon isotope records.Moreover,the long-term evolution of the terrestrial carbon isotope record through the Early Jurassic,and its correlation to marine records,is still not firmly established.In this paper,we present new carbon isotope analyses of carbonate(δ^(13)C_(carb))from lacustrine carbonates and terrestrial organic matter(δ^(13)C_(org))from bulk rocks within the Ma’anshan and Da’anzhai members of the Ziliujing Formation from the Dacao‘D’(DCD)section in the eastern Sichuan Basin.Palynological-palynofacies analysis reveals a predominance of Classopollis pollen together with marker taxa such as Ischyosporites variegatus,Contignisporites problematicus,in the palynological assemblage,indicating a Pliensbachian–Toarcian age.A negative carbon isotope excursion(NCIE)is recorded in the organic carbon isotope data at the topmost part of the Pliensbachian Ma’anshan Member,which can be correlated to the Pliensbachian–Toarcian Boundary Event.This is followed,in the Toarcian Da’anzhai Member,by a major NCIE recorded in both organic matter and carbonate carbon isotope data which can be correlated to the T-OAE NCIE.A long-term carbon isotope record spanning the Sinemurian to Toarcian in Sichuan terrestrial sediments is also been reconstructed and its correlation with coeval marine records is proposed.A broader review of δ^(13)C data from Chinese terrestrial basins spanning the Pliensbachian–Toarcian highlights a distinct^(13)C-depleted signature in the Sichuan Basin compared to basins at higher latitudes.Changes in latitudinal gradients and organic matters in the lake sediments were likely important factors influencing the amplitudes of the T-OAE NCIE and the carbon isotope values in terrestrial sedimentary records.展开更多
基金supported financially by the National Natural Science Foundation of China(Grant Nos.41872054 and 41272083)。
文摘The petrogenesis and genetic link to polymetallic mineralization of the granites in the Dayishan complex,southern Hunan province remain debated.Here,we present an integrated study on the petrology,zircon U-Pb ages and whole-rock geochemistry for this complex.Our findings indicate that the southern complex consists of(amphibole-bearing)biotite granites and muscovite granites emplaced at 153-151 Ma,and the central and northern complex consists of two-mica granites and tourmaline-bearing muscovite granites,respectively with the former emplaced at 164 Ma and the latter at 150 Ma.The(amphibole-bearing)biotite granites have SiO_(2) contents of 68.0-73.8 wt% and are enriched in alkalis and rare earth elements and depleted in Sr and Ba.They display Zr+Y+Ce+Nb>350 ppm and 10000×Ga/Al>2.6 along with high zircon saturation temperatures(821-883oC).The two-mica granites and(tourmaline-bearing)muscovite granites have high SiO_(2)(74.4-77.3 wt%)and low Ga/Al,Zr+Nb+Ce+Y,K/Rb,Zr/Hf,and Nb/Ta along with low zircon saturation temperatures(709-817℃).Geochemical characteristics suggest that the(amphibole-bearing)biotite granites are A-type granites generated through shallow dehydration melting of early Paleozoic granitoids,and that the two-mica granites and(tourmaline-bearing)muscovite granites are fractionated A-type granites produced through fractionation crystallization from the(amphibole-bearing)biotite granites accompanied by fluid fractionation.
基金supported by the China Geological Survey(DD20230221)the National Natural Science Foundation of China(42102018)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB26000000).
文摘A prevailing theory suggests that volcanic eruptions triggered environmental changes,which compelled dinosaurs to migrate in search of new habitats.Compelling evidence for this hypothesis has now been discovered in the Tunxi Basin of eastern China.During the Late Mesozoic,the subduction of the Pacific Plate beneath southeastern China led to multi-stage volcanic activity.The Tunxi Formation in the basin,the first reported Upper Jurassic volcanic unit in the eastern Jiangnan orogen.It overlies the stratum bearing the easternmost mamenchisaurids,which is the dominant Asian sauropod lineage.Geochemical analyses suggest its affinity with coeval magmatism in southeastern China,while new rhyolite zircon U-Pb dating yields an age of 151.6±2.2 Ma,further indicating a transition from arc magmatism to back-arc extension driven by Paleo-Pacific subduction during the Late Jurassic.These studies also confirm that,as early as 156 Ma,the Tunxi Basin was already a key habitat for mamenchisaurids.The Late Jurassic subduction of the Paleo-Pacific Plate caused extensive magmatism across eastern China.This intense tectonic shift likely induced abrupt environmental changes in relative basins.Severe volcanic activity drastically reduced the habitat of mamenchisaurids,prompting a northwestward and southward radiation trend-presents a coherent scene of volcanic eruptions,environmental catastrophe,and dinosaurs migrating.
基金the framework of projects coded 97-20A and 9815 by the General Directorate of Mineral Research and Exploration (Ankara, Türkiye)
文摘In a re-examination of the Neogene stratigraphy of the Uşak,Güre,and Selendi basins of western Anatolia,western Turkey,the stratigraphic position of the previously definedİnay Group is revised,which was previously considered to be of the Middle Miocene age.Based on mammalian biochronology and stratigraphic relationships,two sequences are identified,separated by conformable/transitional contacts within the former group:the Middle Miocene Güre Group is composed of the FakılıFormation,characterized by alluvial fan deposits,and the lacustrine Derbent Formation.Radiometric dating of alkaline volcanics laterally associated with Güre Group sediments in the Uşak and Güre basins,and mammalian fossils re-evaluated into the MN5-6 biozones in the Selendi Basin,indicate early Middle Miocene.Considering the stratigraphic relationship with the overlying early Late Mioceneİnay Group as redefined,we estimate that the Güre Group was deposited in the Middle Miocene.Theİnay Group is characterized by a lateral-vertical transition from alluvial deposits of the Ahmetler Formation to the overlying lacustrine Ulubey Formation.An MN9-10 fauna,containing deinotheres,was found within the latter formation.
文摘The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones.The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district,Erbil Governorate to identify the lithostratigraphy and microfacies analysis in order to determine the depositional environment of the formation.The formation in the studied section is 116 m thick and mainly consists of reddish-brown,hard,thickbedded,chert-bearing conglomerate,pinkish shale and yellowish-grey,thick-bedded,detrital,fossiliferous limestone.The formation is unconformably underlain by the Upper Cretaceous Tanjero Formation and conformably overlain by the Merga Red Beds series.Four different lithostratigraphic units were identified,based on field observation and petrographic analysis,including a basal conglomerate unit(A),a shale unit(B),a well-bedded limestone unit(C)and a thick and massively-bedded limestone unit(D).The presence of a thick conglomerate bed at the base of the formation indicates a large unconformity that lasted nearly 40 million years.Based on detailed microfacies analysis of carbonate rocks,five main microfacies and 15 submicrofacies are recognized.The main microfacies types include mudstone,wackestone,packstone,grainstone and boundstone microfacies.Based on the microfacies types the depositional environment are defined as open lagoon,reef,fore-reef and back-reef environments of normal to saline,nutrient rich water.
基金supported by the National Natural Science Foundation of China(Nos.42030305W2411033)Research Foundation of Chutian Scholars Program of Hubei Province(No.8210403)。
文摘The Yangtze River,with a length of approximately 6300 km,holds the distinction of being the largest river in East Asia that empties into the Pacific Ocean.Its formation is intricately linked to regional tectonic activity and climate fluctuations.However,the exact timeline for the formation of the Yangtze River remains elusive.This study investigates the provenance of the Late Cenozoic strata in the Wangjiang Basin,situated in the Lower Yangtze River,through the application of detrital zircon U-Pb dating.Seven sand samples were analyzed,leading to the identification of new U-Pb detrital zircon ages(n=577).Our study reveals that the sand materials found in the Pliocene gravel beds of the Anqing Formation originate predominantly from the Yangtze River.The findings of our study,along with the provenance tracing of boreholes in the Yangtze River Basin and the shelf sea in East China,provide compelling evidence for the continuous presence of the Yangtze River throughout the Pliocene period.The development of the Yangtze River during the Pliocene is intricately connected to both the tectonic adjustments occurring at the southeastern margin of the Tibetan Plateau and the intensification of the Asian Monsoon.
基金financially supported by the Key R&D Program of Guangxi Zhuang Autonomous Region(2021AB30011)。
文摘Silicalites are extensively developed in the Liujiang Formation(Fm.)of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales.This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments,which not only gives the shales unusual spatio-temporal distribution features,but also induces the shales in the Liujiang Fm.to frequently be rich in organic matter(OM).This study summarises the special deep-water sedimentary succession of the Liujiang Fm.,which is mainly distributed around synsedimentary faults,as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm.in the west-east and southwest-northeast directions.Under the sequence stratigraphic frameworks,the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm.and the regional variations of the Liujiang Fm.were investigated.In addition,the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope.The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage,developed spatially mainly on the east and west sides of the study area,as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a'biological pump'.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC0602704)the National Natural Science Foundation of China(Grant No.U20B6001 and 91755211).
文摘The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.
基金supported by the National Natural Science Foundation of China(No.42202134)Science Foundation of China University of Petroleum,Beijing(No.2462023YJRC010)the postdoctoral fellowship by the Central Research and Development Fund of the University of Bremen.The authors would like to thank the editor and the two anonymous reviewers for their constructive comments and suggestions which significantly improved the quality of the manuscript.
文摘The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to be limited to north Africa.Here,we describe transgression traces in the Muglad Basin in central Africa that indicate a greater spatial extend of the Neotethys during the late Cretaceous.A series of molecular markers detected in the Upper Cretaceous Santonian-Maastrichtian sediments of the Muglad Basin are typical for marine depositional conditions and differ from those in the typical lacustrine sediments of the Lower Cretaceous Barremian-Aptian.Combining the geological-geochemical implications of these markers with the paleogeographic,paleontological and lithological records,we propose that the Muglad Basin received intermittent marine inundations during the Santonian-Maastrichtian stages(86.3-66.0 Ma)and these special molecular markers are therefore the products of seawater incursion.Consequently,this study proposes that the transgression extent of the Neotethys Ocean into the African continent southern extended to the central Africa during the Late Cretaceous.
基金The research of VB is conducted in the scope of the internal research project“WEGETA”at the Croatian Geological Survey,funded by the National Recovery and Resilience Plan 2021-2026 of the European Union-NextGenerationEU,and monitored by the Ministry of Science,Education and Youth of the Republic of Croatia.
文摘The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Province and the associated release of^(12)C-enriched carbon.The T-OAE coincided with global climate and environmental changes,as well as biotic events,indicating substantial modifications in ecosystems.Recent studies have focused on the evidence of geological responses to the T-OAE in Early Jurassic terrestrial basins in China,particularly the Sichuan Basin.Nevertheless,debate remains over the identification of this event,owing to inadequate age-constraints of many sections,and a lack of robust correlations of the carbon isotope records.Moreover,the long-term evolution of the terrestrial carbon isotope record through the Early Jurassic,and its correlation to marine records,is still not firmly established.In this paper,we present new carbon isotope analyses of carbonate(δ^(13)C_(carb))from lacustrine carbonates and terrestrial organic matter(δ^(13)C_(org))from bulk rocks within the Ma’anshan and Da’anzhai members of the Ziliujing Formation from the Dacao‘D’(DCD)section in the eastern Sichuan Basin.Palynological-palynofacies analysis reveals a predominance of Classopollis pollen together with marker taxa such as Ischyosporites variegatus,Contignisporites problematicus,in the palynological assemblage,indicating a Pliensbachian–Toarcian age.A negative carbon isotope excursion(NCIE)is recorded in the organic carbon isotope data at the topmost part of the Pliensbachian Ma’anshan Member,which can be correlated to the Pliensbachian–Toarcian Boundary Event.This is followed,in the Toarcian Da’anzhai Member,by a major NCIE recorded in both organic matter and carbonate carbon isotope data which can be correlated to the T-OAE NCIE.A long-term carbon isotope record spanning the Sinemurian to Toarcian in Sichuan terrestrial sediments is also been reconstructed and its correlation with coeval marine records is proposed.A broader review of δ^(13)C data from Chinese terrestrial basins spanning the Pliensbachian–Toarcian highlights a distinct^(13)C-depleted signature in the Sichuan Basin compared to basins at higher latitudes.Changes in latitudinal gradients and organic matters in the lake sediments were likely important factors influencing the amplitudes of the T-OAE NCIE and the carbon isotope values in terrestrial sedimentary records.
