During the Cambrian, gypsum-bearing evaporites formed in the Sichuan Basin, SW China. These rocks are important for oil and gas sealing, but details of their distribution and origin are not well established. This stud...During the Cambrian, gypsum-bearing evaporites formed in the Sichuan Basin, SW China. These rocks are important for oil and gas sealing, but details of their distribution and origin are not well established. This study examines the regional distribution and origin of the gypsum-bearing evaporites using a comprehensive analysis of drilling data from 34 wells, 5 measured cross-sections in the basin and surrounding area, and 96 maps of area-survey data. Results show that in the stratigraphic succession, the gypsum-bearing evaporites occur mainly in the Lower Cambrian Longwangmiao Formation, the Middle Cambrian Douposi Formation, and the Middle-Upper Cambrian Xixiangchi Group. Geographically, the rocks are found mainly in the southeastern part of the basin, and the distribution of deposits shows an overall SW-NE trend. The sedimentary environments for evaporite formation were evaporative lagoon and inter-platform basin in a platform setting. Gypsum was generated by the underwater concentration of sea water in a strongly evaporative environment. Both an evaporative restricted platform and a mixeddeposition restricted platform model appear to be applicable to the development of gypsum in the Sichuan Basin. The gypsum-bearing evaporites with the best sealing capacity are located mostly in the southeastern part of the basin. These constraints can be applied directly to regional exploration, and have implications for the regional paleogeography and paleoclimate.展开更多
The Qiangtang Basin(QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed...The Qiangtang Basin(QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium(Na-+) contents had been identified in the Late Jurassic Xiali Formation(Fm.) in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However, few studies have explored the formation conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO4(2-) and Cl-- and the significant correlation coefficients of Ca2+-SO42-(R = 0.985) and Na-+-Cl--(R = 0.8974) reveal that the upper member of the Xiali Fm.(the upper Xiali Fm.) formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K-+ and Na-+ ion concentrations and the significant correlation coefficient of Na-+-Cl--(R = 0.8974) suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg-(2+) /Ca-(2+) values(mean value = 1.82) and significant Na-+-Cl-- correlation coefficient(R = 0.8974) also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In addition, the macroscopic correlations of tectonism, provenance, paleoclimate, saliferous strata and sedimentary environment between the QB and the adjoining Amu Darya Basin in Central Asia reveal that the two basins shared similar geologic settings that were favorable for the formation of evaporites during the Late Jurassic. Therefore, the upper Xiali Fm. is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the QB.展开更多
Studies on organic geochemistry indicate that the origin, type and maturity of organic matter are different among coal-bearing, copper-bearing and evaporite formations in the Mesozoic continental Chuxiong Basin, Yunna...Studies on organic geochemistry indicate that the origin, type and maturity of organic matter are different among coal-bearing, copper-bearing and evaporite formations in the Mesozoic continental Chuxiong Basin, Yunnan, China. A mechanism has been proposed that (1) during the diagenetic mineralization stage the short-chain organic acids dervied from kerogen played an important role in remobilizing copper from source beds, while oils acted as important carrier of copper, and that (2) during the transformation or remolding mineralization stage, meteoric water leached the evaporite layers and formed downward-percolating oxidizing SO42-rich fluids; meanwhile, the copper-bearing fluids migrating upwards along growth faults from the basement was contaminated by the coal-bearing series on the way and formed reducing organic-rich fluids; oxidation-reduction occurred and sulfides formed when the two kinds of fluids met within sandstones.展开更多
The Quaternary was the main evaporite deposition period in the Qaidam Basin(QB), but the correlation between the evaporite deposition period and the glacial period is still unclear. In this study, the research objects...The Quaternary was the main evaporite deposition period in the Qaidam Basin(QB), but the correlation between the evaporite deposition period and the glacial period is still unclear. In this study, the research objects are primarily evaporite-bearing strata in a 461.58 m-long drill core in the QB. X-ray powder diffraction(XRD) and scanning electron microscopy(SEM) were applied to study the evaporite minerals, U-Th dating being applied to construct the ~(230)Th geochronological framework. Evaporite deposition from Marine Isotope Stage(MIS) 15 to MIS 4 in the borehole was reconstructed via mineralogical and geochronological data. The evaporite minerals are mainly halite(NaCl), mirabilite(Na_(2)SO_(4)·10H_(2)O), thenardite(Na_(2)SO_(4)) and gypsum(CaSO_(4)·2H_(2)O). A total of 9 effective ~(230)Th data points, ranging from 492.5 ± 43.0 ka to 62.0 ± 11.9 ka, were obtained. The depositional age of the earliest halite layer in the borehole is 592.5–563.0 ka. There were mirabilite deposits in the QB during the cold glacial environment of MIS 6. During MIS 4, the study area desiccated, with mirabilite and halite being deposited. This study suggests that mirabilite is an indicator mineral for the glacial environment in the QB, while halite deposition does not correspond well to glaciation.展开更多
It is well known that oil generated from source rocks of saline-lake facies is characteristic of low Pr/Ph ratio and high contents of gammacerane.The authors found that gas generated from the same source rocks was hig...It is well known that oil generated from source rocks of saline-lake facies is characteristic of low Pr/Ph ratio and high contents of gammacerane.The authors found that gas generated from the same source rocks was high in benzene and cyclohexane contents and had light carbon isotope compositions.In this study,a series of thermal simulations of gas generations on source rock with/without evaporites(such as carbonate,gypsum,and sodium chlorite,respectively),were conducted.It was found that the gypsum played an important role on the catalyzsis of gas generation in the thermal simulations.Compositions of the gaseous hydrocarbons generated from source rocks with evaporites are very similar to those of natural gases discovered from northern Dongying Depression.Meanwhile,in the thermal simulations,it was found that the carbon isotopic compositions of gaseous hydrocarbons generated from source rocks with evaporites are lighter than those of the gases from source rocks without evaporites.Therefore,it is concluded that natural gases discovered from northern Dongying Depression are the product of interaction between source rocks and evaporites(especially gypsum) of the saline facies.展开更多
The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth ...The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth member of Ordovician Majiagou Formation(M56)in the central-eastern Ordos Basin as an example.(1)Seven sub-geomorphic units(Taolimiao west low,Taolimiao underwater high,Taolimiao east low,Hengshan high,East salt low,North slope and Southwest slope)developed in the study area.(2)The“three lows”from west to east developed dolomitic restricted lagoon,evaporite evaporative lagoon and salt evaporative lagoon sedimentary facies respectively,the"two highs"developed high-energy grain beach and microbial mound,and the north and south slopes developed dolomitic flats around land.(3)The paleogeographic pattern caused natural differentiation of replenishment seawater from the northwest Qilian sea,leading to the eccentric sedimentary differentiation of dolomite,evaporite and salt rock symbiotic system from west to east,which is different from the classic“bull's eye”and“tear drop”distribution patterns.(4)As the Middle Qilian block subducted and collided into the North China Plate,the far-end compression stress transferred,giving rise to the alternate highland and lowland in near north to south direction during the sedimentary period of M56 sub-member.(5)Taolimiao underwater high and Hengshan high developed favorable zones of microbial mounds and grain shoals in south to north strike in M56 sub-member,making them favorable exploration areas with great exploration potential in the future.展开更多
Uranium(U)provides especially useful information for reconstructing paleoredox conditions due to its unique geochemical properties and behavior in supergene environments.The proxy potential under suboxic-oxic
Evaporite series is both an important target area looking for high-quality large potash deposits,but also one of the main types of hydrocarbon cap.Outcrops and drilling results indicate that five sets of evaporites we...Evaporite series is both an important target area looking for high-quality large potash deposits,but also one of the main types of hydrocarbon cap.Outcrops and drilling results indicate that five sets of evaporites were developed展开更多
1 Introduction Today,Industrial value of oil and gas basin in the world for a total of more than 120,which contain lamellar or lenticular evaporite a total of 66,about 55%of the basin.According to statistics,in the ba...1 Introduction Today,Industrial value of oil and gas basin in the world for a total of more than 120,which contain lamellar or lenticular evaporite a total of 66,about 55%of the basin.According to statistics,in the basin of oil,salt,symbiosis,46%of the oil and gas layer in the basin was展开更多
Two different evaporitic sequences occurred in the latest Cretaceous-Early Paleocene in Yarkand Basin,southwestern Tarim Basin,Xinjiang Province,China:one is characterized by poor gypsum and some small,lenticularshape...Two different evaporitic sequences occurred in the latest Cretaceous-Early Paleocene in Yarkand Basin,southwestern Tarim Basin,Xinjiang Province,China:one is characterized by poor gypsum and some small,lenticularshaped halite layers in the Tuyiluoke Formation of the latest Cretaceous,the other is characterized by very thick gypsum and halite layers in the Aertashen Formation of the early Paleocene.In the early developmental stage of the Tuyiluoke Formation,the Yarkand ancient saline lake was a long,strip-shaped depression,NW-SE oriented,along the West Kunlun piedmont,with its eastern boundary to the line along bores Ys1-T1-Ks101,the concentrated center located in the area of borehole S1.In the later developmental stage,the depositional scope was shifted inch by inch to the NW of this saline lake,forming a triangular depositional area,with apices at boreholes Wx1,Ak2 and S1,the concentrated center of the saline lake gradually migrating from borehole S1 region to the northwestern area of the lake,developing four small,evaporatedconcentrated sub-depressions,depositing lenticular-shaped halite.In the early Paleocene,the ancient saline lake was stretched from the West Kunlun piedmont in the west,to the Markit slope in the east,from the South Tianshan piedmont in the north,to the Hotan area in the south,accompanied by giant thicknesses of halite and large-scale gypsum layers,mainly interbedded with limestone in the Aertashen Formation.The evaporites in the latest Cretaceous-early Paleocene were controlled by the marine transgression-regression geological background in the Yarkand Basin.Generally,integrated evaporitic depositional sequences,such as clasolite-gypsum-halite-potash,usually occur in the presence of persistent seawater through evaporation,but this is not the case in the Tuyiluoke Formation.In contrast,very thick gypsum layers are common in the early Paleocene.Typically,adequate mineral sources for evaporites are found within seawater,such as in large basins undergoing long-term marine transgression-regression cycles,where adequate seawater remains,even though the basin was going through a marine regression stage.In the latest Cretaceous,thin gypsum layers indicate a lack of mineral sources.In contrast,the early Paleocene has far larger evaporites,both in width and thickness.This suggests a short-term marine regression stage must have occurred during the spatiotemporal evolution of the evaporites in the latest Cretaceous-Early Paleocene in the basin,meaning that a rapid marine regressive episode has been identified at the end of the Cretaceous.展开更多
基金funded by the Major State Basic Research Development Program of China ("973" project, Grant No. 2012CB214803)National Science and Technology Major Project of China (Grant No. 2016ZX05004)
文摘During the Cambrian, gypsum-bearing evaporites formed in the Sichuan Basin, SW China. These rocks are important for oil and gas sealing, but details of their distribution and origin are not well established. This study examines the regional distribution and origin of the gypsum-bearing evaporites using a comprehensive analysis of drilling data from 34 wells, 5 measured cross-sections in the basin and surrounding area, and 96 maps of area-survey data. Results show that in the stratigraphic succession, the gypsum-bearing evaporites occur mainly in the Lower Cambrian Longwangmiao Formation, the Middle Cambrian Douposi Formation, and the Middle-Upper Cambrian Xixiangchi Group. Geographically, the rocks are found mainly in the southeastern part of the basin, and the distribution of deposits shows an overall SW-NE trend. The sedimentary environments for evaporite formation were evaporative lagoon and inter-platform basin in a platform setting. Gypsum was generated by the underwater concentration of sea water in a strongly evaporative environment. Both an evaporative restricted platform and a mixeddeposition restricted platform model appear to be applicable to the development of gypsum in the Sichuan Basin. The gypsum-bearing evaporites with the best sealing capacity are located mostly in the southeastern part of the basin. These constraints can be applied directly to regional exploration, and have implications for the regional paleogeography and paleoclimate.
基金supported by the National Basic Research Program of China (Grant Nos.2011CB403003 and 2013CB956403)"Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No.XDB03020402)+1 种基金the National Natural Science Foundation of China (Grant No.41272128)the College Research Program of Gansu Province (Grant No.2016A-123)
文摘The Qiangtang Basin(QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium(Na-+) contents had been identified in the Late Jurassic Xiali Formation(Fm.) in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However, few studies have explored the formation conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO4(2-) and Cl-- and the significant correlation coefficients of Ca2+-SO42-(R = 0.985) and Na-+-Cl--(R = 0.8974) reveal that the upper member of the Xiali Fm.(the upper Xiali Fm.) formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K-+ and Na-+ ion concentrations and the significant correlation coefficient of Na-+-Cl--(R = 0.8974) suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg-(2+) /Ca-(2+) values(mean value = 1.82) and significant Na-+-Cl-- correlation coefficient(R = 0.8974) also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In addition, the macroscopic correlations of tectonism, provenance, paleoclimate, saliferous strata and sedimentary environment between the QB and the adjoining Amu Darya Basin in Central Asia reveal that the two basins shared similar geologic settings that were favorable for the formation of evaporites during the Late Jurassic. Therefore, the upper Xiali Fm. is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the QB.
基金This study represents the research result of he project supported jointly by the National Natural Science Foundation of China (No. 49173168)the State Key Laboratory of Organic Geochemistry, Chinese Academy of Sciences (OGL-9213)
文摘Studies on organic geochemistry indicate that the origin, type and maturity of organic matter are different among coal-bearing, copper-bearing and evaporite formations in the Mesozoic continental Chuxiong Basin, Yunnan, China. A mechanism has been proposed that (1) during the diagenetic mineralization stage the short-chain organic acids dervied from kerogen played an important role in remobilizing copper from source beds, while oils acted as important carrier of copper, and that (2) during the transformation or remolding mineralization stage, meteoric water leached the evaporite layers and formed downward-percolating oxidizing SO42-rich fluids; meanwhile, the copper-bearing fluids migrating upwards along growth faults from the basement was contaminated by the coal-bearing series on the way and formed reducing organic-rich fluids; oxidation-reduction occurred and sulfides formed when the two kinds of fluids met within sandstones.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41902190 and 42003044)the Geological Survey Project of China (Grant No. DD20221913)the Qinghai Geological Exploration Fund (Grant No. 2020021068kc035)。
文摘The Quaternary was the main evaporite deposition period in the Qaidam Basin(QB), but the correlation between the evaporite deposition period and the glacial period is still unclear. In this study, the research objects are primarily evaporite-bearing strata in a 461.58 m-long drill core in the QB. X-ray powder diffraction(XRD) and scanning electron microscopy(SEM) were applied to study the evaporite minerals, U-Th dating being applied to construct the ~(230)Th geochronological framework. Evaporite deposition from Marine Isotope Stage(MIS) 15 to MIS 4 in the borehole was reconstructed via mineralogical and geochronological data. The evaporite minerals are mainly halite(NaCl), mirabilite(Na_(2)SO_(4)·10H_(2)O), thenardite(Na_(2)SO_(4)) and gypsum(CaSO_(4)·2H_(2)O). A total of 9 effective ~(230)Th data points, ranging from 492.5 ± 43.0 ka to 62.0 ± 11.9 ka, were obtained. The depositional age of the earliest halite layer in the borehole is 592.5–563.0 ka. There were mirabilite deposits in the QB during the cold glacial environment of MIS 6. During MIS 4, the study area desiccated, with mirabilite and halite being deposited. This study suggests that mirabilite is an indicator mineral for the glacial environment in the QB, while halite deposition does not correspond well to glaciation.
基金prepared under the permission of the authorities of the Shengli Oilfield,and funded by the National Natural Science Foundation of China (No. 40572084)SINOPEC (No. P07008)
文摘It is well known that oil generated from source rocks of saline-lake facies is characteristic of low Pr/Ph ratio and high contents of gammacerane.The authors found that gas generated from the same source rocks was high in benzene and cyclohexane contents and had light carbon isotope compositions.In this study,a series of thermal simulations of gas generations on source rock with/without evaporites(such as carbonate,gypsum,and sodium chlorite,respectively),were conducted.It was found that the gypsum played an important role on the catalyzsis of gas generation in the thermal simulations.Compositions of the gaseous hydrocarbons generated from source rocks with evaporites are very similar to those of natural gases discovered from northern Dongying Depression.Meanwhile,in the thermal simulations,it was found that the carbon isotopic compositions of gaseous hydrocarbons generated from source rocks with evaporites are lighter than those of the gases from source rocks without evaporites.Therefore,it is concluded that natural gases discovered from northern Dongying Depression are the product of interaction between source rocks and evaporites(especially gypsum) of the saline facies.
基金Supported by the Fundamental Project of China National Petroleum Corporation(2021DJ0501).
文摘The relationship between paleogeographic pattern and sedimentary differentiation of evaporite-carbonate symbiotic system is examined based on logging,core and thin section data,by taking the sixth sub-member of fifth member of Ordovician Majiagou Formation(M56)in the central-eastern Ordos Basin as an example.(1)Seven sub-geomorphic units(Taolimiao west low,Taolimiao underwater high,Taolimiao east low,Hengshan high,East salt low,North slope and Southwest slope)developed in the study area.(2)The“three lows”from west to east developed dolomitic restricted lagoon,evaporite evaporative lagoon and salt evaporative lagoon sedimentary facies respectively,the"two highs"developed high-energy grain beach and microbial mound,and the north and south slopes developed dolomitic flats around land.(3)The paleogeographic pattern caused natural differentiation of replenishment seawater from the northwest Qilian sea,leading to the eccentric sedimentary differentiation of dolomite,evaporite and salt rock symbiotic system from west to east,which is different from the classic“bull's eye”and“tear drop”distribution patterns.(4)As the Middle Qilian block subducted and collided into the North China Plate,the far-end compression stress transferred,giving rise to the alternate highland and lowland in near north to south direction during the sedimentary period of M56 sub-member.(5)Taolimiao underwater high and Hengshan high developed favorable zones of microbial mounds and grain shoals in south to north strike in M56 sub-member,making them favorable exploration areas with great exploration potential in the future.
文摘Uranium(U)provides especially useful information for reconstructing paleoredox conditions due to its unique geochemical properties and behavior in supergene environments.The proxy potential under suboxic-oxic
文摘Evaporite series is both an important target area looking for high-quality large potash deposits,but also one of the main types of hydrocarbon cap.Outcrops and drilling results indicate that five sets of evaporites were developed
文摘1 Introduction Today,Industrial value of oil and gas basin in the world for a total of more than 120,which contain lamellar or lenticular evaporite a total of 66,about 55%of the basin.According to statistics,in the basin of oil,salt,symbiosis,46%of the oil and gas layer in the basin was
基金supported by the National Natural Science Foundation of China(No.41972082)the Scientific and Technical Supporting Project during the National Twelfth Five-Year Plan Period(No.2011BAB06B06)。
文摘Two different evaporitic sequences occurred in the latest Cretaceous-Early Paleocene in Yarkand Basin,southwestern Tarim Basin,Xinjiang Province,China:one is characterized by poor gypsum and some small,lenticularshaped halite layers in the Tuyiluoke Formation of the latest Cretaceous,the other is characterized by very thick gypsum and halite layers in the Aertashen Formation of the early Paleocene.In the early developmental stage of the Tuyiluoke Formation,the Yarkand ancient saline lake was a long,strip-shaped depression,NW-SE oriented,along the West Kunlun piedmont,with its eastern boundary to the line along bores Ys1-T1-Ks101,the concentrated center located in the area of borehole S1.In the later developmental stage,the depositional scope was shifted inch by inch to the NW of this saline lake,forming a triangular depositional area,with apices at boreholes Wx1,Ak2 and S1,the concentrated center of the saline lake gradually migrating from borehole S1 region to the northwestern area of the lake,developing four small,evaporatedconcentrated sub-depressions,depositing lenticular-shaped halite.In the early Paleocene,the ancient saline lake was stretched from the West Kunlun piedmont in the west,to the Markit slope in the east,from the South Tianshan piedmont in the north,to the Hotan area in the south,accompanied by giant thicknesses of halite and large-scale gypsum layers,mainly interbedded with limestone in the Aertashen Formation.The evaporites in the latest Cretaceous-early Paleocene were controlled by the marine transgression-regression geological background in the Yarkand Basin.Generally,integrated evaporitic depositional sequences,such as clasolite-gypsum-halite-potash,usually occur in the presence of persistent seawater through evaporation,but this is not the case in the Tuyiluoke Formation.In contrast,very thick gypsum layers are common in the early Paleocene.Typically,adequate mineral sources for evaporites are found within seawater,such as in large basins undergoing long-term marine transgression-regression cycles,where adequate seawater remains,even though the basin was going through a marine regression stage.In the latest Cretaceous,thin gypsum layers indicate a lack of mineral sources.In contrast,the early Paleocene has far larger evaporites,both in width and thickness.This suggests a short-term marine regression stage must have occurred during the spatiotemporal evolution of the evaporites in the latest Cretaceous-Early Paleocene in the basin,meaning that a rapid marine regressive episode has been identified at the end of the Cretaceous.