Reconstructing the thermal evolution of the eastern Qaidam Basin is important for gaining a deeper understanding of its lithospheric geodynamics and for more accurate hydrocarbon evaluation and prediction. This articl...Reconstructing the thermal evolution of the eastern Qaidam Basin is important for gaining a deeper understanding of its lithospheric geodynamics and for more accurate hydrocarbon evaluation and prediction. This article presents a set of new apatite and zircon(U-Th)/He thermochronological ages.Combined with 336 vitrinite reflectance(R_(o)) data, the thermal history of the Ouanan Sag in the eastern Qaidam Basin has been reconstructed using inversion models. Three detrital samples from the Ounan Sag shows that the apatite(U-Th)/He ages are primarily concentrated in the range of 17.0 Ma to 76.5 Ma and that the zircon(U-Th)/He ages range from 200 Ma to 289.3 Ma. The time-temperature models demonstrate that the Ounan Sag experienced rapid subsidence and heating from the Carboniferous to late Permian, and exhumation/cooling events from the end of Permian to the Triassic. This thermal evolution was influenced by the widespread intrusion of plutons, and the collision and orogenesis caused by asthenosphere upwelling below the Qaidam arc, and slab rollback of the Southern Kunlun oceanic lithosphere, respectively. Additionally, our models depict the main exhumation/cooling stages since the Paleogene and a reheating event in the Miocene as a result of the intensifying growth of the Qinghai-Tibet Plateau and local sedimentary loading, followed by the initial India-Eurasia collision. Furthermore, the eastern Qaidam Basin experienced consistent heating during the late Paleozoic, reaching the maximum paleotemperature and geothermal gradient in the late Permian, with values of ~230℃ and~43-44℃/km, respectively. This study suggests that the source rocks in the most upper member of upper Carboniferous Keluke(C_(2)k) Formations in the Ounan Sag reached the gas generation stage in the late Permian.展开更多
Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift(SNLU)of the Qiongdongnan Basin.These findings indicate that the bedrock buried hills in this basin hold g...Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift(SNLU)of the Qiongdongnan Basin.These findings indicate that the bedrock buried hills in this basin hold great potential for exploration.Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track(AFT)and zircon(U-Th)/He data to unravel the thermal history of the basement rock.This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation.Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period(~80-23.8 Ma),followed by a heating stage from the Miocene epoch until the present(~23.8 Ma to present).In contrast,the sample from the eastern bulge experienced a more complex thermal history.It underwent two cooling stages during the late Mesozoic to late Eocene period(~80-36.4 Ma)and the late Oligocene period(~30-23.8 Ma),interspersed with two heating phases during the late Eocene to early Oligocene period(~36.4-30 Ma)and the Miocene epoch to recent times(~23.8-0 Ma),respectively.The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity.Unlike typical passive continental margin basins,the SNLU has experienced accelerated subsidence after the rifting phase,which began around 5.2 Ma ago.The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere.Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs.On the other hand,rapid post-rifting subsidence(sedimentation)promotes the formation of cap rocks.展开更多
The Pearl River Mouth Basin(PRMB)is one of the most petroliferous basins on the northern margin of the South China Sea.Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evoluti...The Pearl River Mouth Basin(PRMB)is one of the most petroliferous basins on the northern margin of the South China Sea.Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history.Our investigations in this study are based on apatite fission-track(AFT)thermochronology analysis of 12 cutting samples from 4 boreholes.Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution.Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene.The cooling events occurred approximately in the Late Eocene,early Oligocene,and the Late Miocene,possibly attributed to the Zhuqiong II Event,Nanhai Event,and Dongsha Event,respectively.The erosion amount during the first cooling stage is roughly estimated to be about 455-712 m,with an erosion rate of 0.08-0.12 mm/a.The second erosion-driven cooling is stronger than the first one,with an erosion amount of about 747-814 m and an erosion rate between about 0.13-0.21 mm/a.The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m,which is speculative due to the possible influence of the magmatic activity.展开更多
Studies in the northern South China Sea(SCS)basement remain important for understanding the evolution of the Southeast Asian continental margin.Due to a thick cover of sediments and scarce borehole penetration,little ...Studies in the northern South China Sea(SCS)basement remain important for understanding the evolution of the Southeast Asian continental margin.Due to a thick cover of sediments and scarce borehole penetration,little is known about the age and tectonic affinity of this basement.In this study,an integrated study of zircon U-Pb geochronology,Hf isotopes,and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out.New zircon U-Pb results for these granitoids present middle-late Permian((270.0±1.2)Ma;(253±3.4)Ma),middle to late Triassic((246.2±3.4)Ma;(239.3±0.96)Ma;(237.9±0.99)Ma;(228.9±1.0)Ma)and Late Cretaceous ages((120.6±0.6)Ma).New data from this study,in combination with the previous dataset,indicates that granitoid ages in northern SCS basement vary from 270 Ma to 70.5 Ma,with three age groups of 270–196 Ma,162–142 Ma,and 137–71 Ma,respectively.Except for the late Paleozoic-Mesozoic rocks in the basement of the northern SCS,a few old zircon grains with the age of(2708.1±17)Ma to(2166.6±19)Ma provide clues to the existence of the pre-Proterozoic components.The geochemical signatures indicate that the middle Permian-early Cretaceous granitoids from the Qiongdongnan Basin are I-type granites formed in a volcanic arc environment,which were probably related to the subduction of the Paleo-Pacific Plate.展开更多
The widely-developed,mixed clastic-carbonate succession in the northern Qaidam Basin records the paleo-environment changes under the glacial activity during the Late Paleozoic icehouse period in the context of regiona...The widely-developed,mixed clastic-carbonate succession in the northern Qaidam Basin records the paleo-environment changes under the glacial activity during the Late Paleozoic icehouse period in the context of regional tectonic stability,however,the depositional environment and sequence stratigraphy characteristics of the mixed deposits is rarely reported and still not clear.Combined the latest drilling wells data,we analyzed the sedimentary and stratigraphic characterization of the mixed strata via detailed field outcrops and core observations and thin section microscopic observations and recognized three depositional systems,including progradational coastal system,incised valley system,and carbonate-dominated marine shelf system,and identified four third-order sequences,SQ1,SQ2,SQ3 and SQ4,consisting of LST,TST,and HST.The depositional environment is overall belonged to marine-continental transition context and shifted from marine to continental environment frequently,showing an evolutionary pattern from marine towards terrestrial-marine transition and then back into the marine environment again in the long-term,which was controlled by the regional tectonic subsidence and the high-frequency and large-amplitude sea-level changes due to the Late Paleozoic glacial activity.The result is of significance in understanding the evolution of the Qinghai-Tibet Plateau and the sedimentation-climate response.展开更多
In order to understand the geochemical characteristics of Paleozoic reservoir fluids in Xuanjing region,Lower Yangtze area,drilling core samples from Y and D wells were tested and analyzed to study the fluid inclusion...In order to understand the geochemical characteristics of Paleozoic reservoir fluids in Xuanjing region,Lower Yangtze area,drilling core samples from Y and D wells were tested and analyzed to study the fluid inclusion types and composition.Pressure correction was undertaken to determine the temperature and pressure environment for inclusion formation,and the influence of fluid characteristics of the Upper Permian and Lower Triassic reservoirs on the preservation of shale gas was investigated.According to petrograph-ic observations,fluid inclusions are mainly brine and bitumen inclusions.Bitumen inclusions are mainly distributed in holes and fractures,and with smaller individuals.No visible fluorescence was observed,and the vitrinite reflectance is 3.39%–3.92%.This indicates that there had been oil and gas accumulation in the early stage of diagenesis in the study area,but due to the influence of magmatic hydrothermal solution,oil and gas underwent thermal metamorphism in the early stage,making liquid petroleum into solid bitumen.At present,oil and gas in the reservoir were largely formed in the late stage.During the continuous process in which shale was buried,light oil and gas were generated.Light oil and gas underwent magmatic and tectonic hydrothermal processes in some areas,resulting in high-temperature metamorphic cracking that formed dry gas.Moreover,nitrogen inclusions are found in fluid inclusions,forming metamorphic fluids caused by mag-matic hydrothermal activities.The study shows that Paleozoic reservoirs in Xuanjing area are characterized by self-generation and self-storage.Furthermore,the mechanism of shale gas accumulation is not only related to the buried hydrocarbon generation process of shale itself,but is also related to later magmatic activity and tectonic hydrothermal transformation.Therefore,preservation conditions are generally key factors of shale gas accumulation in this area.展开更多
In the Qaidam basin,Northwest China,karstic fissures and caves are developed in many places of the Lower Carboniferous Chengqianggou Fm.and Huaitoutala Fm.and the Upper Carboniferous Keluke Fm.,in which are found typi...In the Qaidam basin,Northwest China,karstic fissures and caves are developed in many places of the Lower Carboniferous Chengqianggou Fm.and Huaitoutala Fm.and the Upper Carboniferous Keluke Fm.,in which are found typical karstic marks.Several suites of transgressive carbonate rocks formed during the Late Paleozoic epoch are preserved as reservoir properties in the Qaidam basin,with paleokarst-related cave-fractured diagenetic structures,which provided the basis for cavefractured development.Carbonate and clastic samples covering or infilling caves and fractures in Carboniferous strata were collected in the eastern Qaidam basin to focus on petrological and geochemical analyses of karst and infilling materials.Based on this study of the Caledonian diagenetic sequence,and bitumen-infilled inclusion temperature and burial history,there existed a continuous atmospheric freshwater leaching process,which played a critical role in the construction of the Carboniferous supergene paleokarsts.Investigation and survey of the tectonic setting,plate paleolatitude and river development intensity also proves that there was abundant rainfall during the Indosinian period,after which the strata undergo a shallow burial process.Because Indosinian period is earlier than the key timing of hydrocarbon-generation of the Carboniferous source rocks,this kind of karst reservoir has potential significance for oil-gas resources in this area.展开更多
基金financially supported by grants from the Geological Survey Projects of China Geological Survey (grant nos. 20242065, 20230260)the Fundamental Research Fund of Chinese Academy of Geological Sciences (grant no. JKYQN202342)the National Natural Science Foundation of China (grant no. 41772272)。
文摘Reconstructing the thermal evolution of the eastern Qaidam Basin is important for gaining a deeper understanding of its lithospheric geodynamics and for more accurate hydrocarbon evaluation and prediction. This article presents a set of new apatite and zircon(U-Th)/He thermochronological ages.Combined with 336 vitrinite reflectance(R_(o)) data, the thermal history of the Ouanan Sag in the eastern Qaidam Basin has been reconstructed using inversion models. Three detrital samples from the Ounan Sag shows that the apatite(U-Th)/He ages are primarily concentrated in the range of 17.0 Ma to 76.5 Ma and that the zircon(U-Th)/He ages range from 200 Ma to 289.3 Ma. The time-temperature models demonstrate that the Ounan Sag experienced rapid subsidence and heating from the Carboniferous to late Permian, and exhumation/cooling events from the end of Permian to the Triassic. This thermal evolution was influenced by the widespread intrusion of plutons, and the collision and orogenesis caused by asthenosphere upwelling below the Qaidam arc, and slab rollback of the Southern Kunlun oceanic lithosphere, respectively. Additionally, our models depict the main exhumation/cooling stages since the Paleogene and a reheating event in the Miocene as a result of the intensifying growth of the Qinghai-Tibet Plateau and local sedimentary loading, followed by the initial India-Eurasia collision. Furthermore, the eastern Qaidam Basin experienced consistent heating during the late Paleozoic, reaching the maximum paleotemperature and geothermal gradient in the late Permian, with values of ~230℃ and~43-44℃/km, respectively. This study suggests that the source rocks in the most upper member of upper Carboniferous Keluke(C_(2)k) Formations in the Ounan Sag reached the gas generation stage in the late Permian.
基金The National Natural Science Foundation of China under contract No.42072181the CNOOC Research Project"Resource Potential,Reservoir Formation Mechanism and Breakthrough Direction of Potential Oil-rich Depressions in Offshore Basins of China(YXKY-ZX 012021)"。
文摘Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift(SNLU)of the Qiongdongnan Basin.These findings indicate that the bedrock buried hills in this basin hold great potential for exploration.Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track(AFT)and zircon(U-Th)/He data to unravel the thermal history of the basement rock.This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation.Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period(~80-23.8 Ma),followed by a heating stage from the Miocene epoch until the present(~23.8 Ma to present).In contrast,the sample from the eastern bulge experienced a more complex thermal history.It underwent two cooling stages during the late Mesozoic to late Eocene period(~80-36.4 Ma)and the late Oligocene period(~30-23.8 Ma),interspersed with two heating phases during the late Eocene to early Oligocene period(~36.4-30 Ma)and the Miocene epoch to recent times(~23.8-0 Ma),respectively.The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity.Unlike typical passive continental margin basins,the SNLU has experienced accelerated subsidence after the rifting phase,which began around 5.2 Ma ago.The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere.Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs.On the other hand,rapid post-rifting subsidence(sedimentation)promotes the formation of cap rocks.
基金This study is financially supported by the National Natural Science Foundation of China(42072181).
文摘The Pearl River Mouth Basin(PRMB)is one of the most petroliferous basins on the northern margin of the South China Sea.Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history.Our investigations in this study are based on apatite fission-track(AFT)thermochronology analysis of 12 cutting samples from 4 boreholes.Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution.Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene.The cooling events occurred approximately in the Late Eocene,early Oligocene,and the Late Miocene,possibly attributed to the Zhuqiong II Event,Nanhai Event,and Dongsha Event,respectively.The erosion amount during the first cooling stage is roughly estimated to be about 455-712 m,with an erosion rate of 0.08-0.12 mm/a.The second erosion-driven cooling is stronger than the first one,with an erosion amount of about 747-814 m and an erosion rate between about 0.13-0.21 mm/a.The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m,which is speculative due to the possible influence of the magmatic activity.
基金The National Natural Science Foundation of China under contract No.42072181。
文摘Studies in the northern South China Sea(SCS)basement remain important for understanding the evolution of the Southeast Asian continental margin.Due to a thick cover of sediments and scarce borehole penetration,little is known about the age and tectonic affinity of this basement.In this study,an integrated study of zircon U-Pb geochronology,Hf isotopes,and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out.New zircon U-Pb results for these granitoids present middle-late Permian((270.0±1.2)Ma;(253±3.4)Ma),middle to late Triassic((246.2±3.4)Ma;(239.3±0.96)Ma;(237.9±0.99)Ma;(228.9±1.0)Ma)and Late Cretaceous ages((120.6±0.6)Ma).New data from this study,in combination with the previous dataset,indicates that granitoid ages in northern SCS basement vary from 270 Ma to 70.5 Ma,with three age groups of 270–196 Ma,162–142 Ma,and 137–71 Ma,respectively.Except for the late Paleozoic-Mesozoic rocks in the basement of the northern SCS,a few old zircon grains with the age of(2708.1±17)Ma to(2166.6±19)Ma provide clues to the existence of the pre-Proterozoic components.The geochemical signatures indicate that the middle Permian-early Cretaceous granitoids from the Qiongdongnan Basin are I-type granites formed in a volcanic arc environment,which were probably related to the subduction of the Paleo-Pacific Plate.
基金This work was supported by the National Natural Science Foundation of China(41702124,41772272)the China Geological Survey Program(DD20190094).
文摘The widely-developed,mixed clastic-carbonate succession in the northern Qaidam Basin records the paleo-environment changes under the glacial activity during the Late Paleozoic icehouse period in the context of regional tectonic stability,however,the depositional environment and sequence stratigraphy characteristics of the mixed deposits is rarely reported and still not clear.Combined the latest drilling wells data,we analyzed the sedimentary and stratigraphic characterization of the mixed strata via detailed field outcrops and core observations and thin section microscopic observations and recognized three depositional systems,including progradational coastal system,incised valley system,and carbonate-dominated marine shelf system,and identified four third-order sequences,SQ1,SQ2,SQ3 and SQ4,consisting of LST,TST,and HST.The depositional environment is overall belonged to marine-continental transition context and shifted from marine to continental environment frequently,showing an evolutionary pattern from marine towards terrestrial-marine transition and then back into the marine environment again in the long-term,which was controlled by the regional tectonic subsidence and the high-frequency and large-amplitude sea-level changes due to the Late Paleozoic glacial activity.The result is of significance in understanding the evolution of the Qinghai-Tibet Plateau and the sedimentation-climate response.
基金Supported by projects of Fundamental Research Funds for Chinese Academy of Geological Sciences(No.JKYQN202338,No.DZLXJK202208)National Natural Science Foundation of China(No.41802158)the China Geological Survey(No.DD20230023).
文摘In order to understand the geochemical characteristics of Paleozoic reservoir fluids in Xuanjing region,Lower Yangtze area,drilling core samples from Y and D wells were tested and analyzed to study the fluid inclusion types and composition.Pressure correction was undertaken to determine the temperature and pressure environment for inclusion formation,and the influence of fluid characteristics of the Upper Permian and Lower Triassic reservoirs on the preservation of shale gas was investigated.According to petrograph-ic observations,fluid inclusions are mainly brine and bitumen inclusions.Bitumen inclusions are mainly distributed in holes and fractures,and with smaller individuals.No visible fluorescence was observed,and the vitrinite reflectance is 3.39%–3.92%.This indicates that there had been oil and gas accumulation in the early stage of diagenesis in the study area,but due to the influence of magmatic hydrothermal solution,oil and gas underwent thermal metamorphism in the early stage,making liquid petroleum into solid bitumen.At present,oil and gas in the reservoir were largely formed in the late stage.During the continuous process in which shale was buried,light oil and gas were generated.Light oil and gas underwent magmatic and tectonic hydrothermal processes in some areas,resulting in high-temperature metamorphic cracking that formed dry gas.Moreover,nitrogen inclusions are found in fluid inclusions,forming metamorphic fluids caused by mag-matic hydrothermal activities.The study shows that Paleozoic reservoirs in Xuanjing area are characterized by self-generation and self-storage.Furthermore,the mechanism of shale gas accumulation is not only related to the buried hydrocarbon generation process of shale itself,but is also related to later magmatic activity and tectonic hydrothermal transformation.Therefore,preservation conditions are generally key factors of shale gas accumulation in this area.
基金financially supported by the China Geological Survey(Grant No.DD20190107,DD20190094)。
文摘In the Qaidam basin,Northwest China,karstic fissures and caves are developed in many places of the Lower Carboniferous Chengqianggou Fm.and Huaitoutala Fm.and the Upper Carboniferous Keluke Fm.,in which are found typical karstic marks.Several suites of transgressive carbonate rocks formed during the Late Paleozoic epoch are preserved as reservoir properties in the Qaidam basin,with paleokarst-related cave-fractured diagenetic structures,which provided the basis for cavefractured development.Carbonate and clastic samples covering or infilling caves and fractures in Carboniferous strata were collected in the eastern Qaidam basin to focus on petrological and geochemical analyses of karst and infilling materials.Based on this study of the Caledonian diagenetic sequence,and bitumen-infilled inclusion temperature and burial history,there existed a continuous atmospheric freshwater leaching process,which played a critical role in the construction of the Carboniferous supergene paleokarsts.Investigation and survey of the tectonic setting,plate paleolatitude and river development intensity also proves that there was abundant rainfall during the Indosinian period,after which the strata undergo a shallow burial process.Because Indosinian period is earlier than the key timing of hydrocarbon-generation of the Carboniferous source rocks,this kind of karst reservoir has potential significance for oil-gas resources in this area.
