The Tarim Basin in China comprises eight sets of sandstone reservoirs, five of which are investigated in detail in this study. The main purpose of this study is to investigate the hydrocarbon charging histories of res...The Tarim Basin in China comprises eight sets of sandstone reservoirs, five of which are investigated in detail in this study. The main purpose of this study is to investigate the hydrocarbon charging histories of reservoirs by applying K-Ar dating of authigenic illites. The ages of authigenic illites from the Lower Silurian bituminous sandstones in the Central Uplift area range from 383.5 to 235.2 Ma, suggesting that the Silurian oil accumulations were formed from the late Caledonian till the late Hercynian. The ages of authigenic illites from the Upper Devonian Donghe Sandstone reservoirs range from 263.8 to 231.3 Ma, indicating that hydrocarbon accumulations within the Donghe sandstone were formed mainly in the late Hercynian. The authigenic illites ages from the Lower Jurassic Yangxia Group sandstones in the Yinan-2 gas reservoir (Yinan-2, Kuqa Depression) range from 28.1 to 23.9 Ma, suggesting that the initial hydrocarbon charging occurred in the Miocene. The ages of the authigenic illites from the Lower Cretaceous sandstones in the Akemomu gas field (Ake-1, Kashi Sag, Southwest Depression) range from 22.6 to 18.8 Ma, indicating a probable early oil accumulation or early migration of hydrocarbon within this area. The illites from the Paleogene sandstones in the Dina-2 gas reservoir (Dina-201, Kuqa Depression) have a detrital origin; they cannot be used to study the hydrocarbon charging histories. The ages of authigenic illites in the underlying Cretaceous sandstones in the same well (Dina-201) range from 25.5 to 15.5 Ma, indicating that hydrocarbon charging in this reservoir probably occurred within the Miocene. This study highlights the potential of applying K-Ar dating of authigenic illites to investigate the timing of hydrocarbon charging histories of the Tarim Basin reservoir sandstones.展开更多
In the Ordos basin, two distinct thermal events of different ages have been identified for the first time by means of K-Ar dating combined with illite crystallinity analysis. For the Late Triassic and Late Permian sam...In the Ordos basin, two distinct thermal events of different ages have been identified for the first time by means of K-Ar dating combined with illite crystallinity analysis. For the Late Triassic and Late Permian samples, the K-Ar ages of the < 0.2μm fractions (159-173 Ma) reflect an illitization age related to the Yanshanian movement and indicate a short thermal event in the Middle Jurassic; the K-Ar ages of the <2 μm fractions (210-308 Ma) are interpreted as mixed ages of detrital material and authigenic illites. The K-Ar ages of both < 0.2μm and < 2μm fractions of a Middle Cambrian sample (368 Ma and 419 Ma) correspond to the ages of the metamorphism and earliest granite intrusion in the northern Caledonian Qinling fold zone (380-420 Ma) and show a thermal event during Silurian-Devonian time.展开更多
The Silurian bituminous sandstones（SBS） in the Tarim Basin, China are important basinwide reservoirs with an estimated area of approximately 249000 km^2. We investigated the ages of authigenic illites in the SBS res...The Silurian bituminous sandstones（SBS） in the Tarim Basin, China are important basinwide reservoirs with an estimated area of approximately 249000 km^2. We investigated the ages of authigenic illites in the SBS reservoirs and constrained their formation timing by using the 40^Ar/39^Ar step wise heating method. The age spectra, 39^Ar recoil loss and their controlling factors were investigated systematically. The 40^Ar/39^Ar ages were compared with the conventional K/Ar ages of identical clay fractions. The clay in the SBS reservoirs is dominated by orderly mixed-layer illite/smectite（I/S） with 5%–30% smectite layers. The I/S minerals morphology comprises primarily honeycomb, short filamentous and curved-lath particles, characteristic of authigenic illites. The unencapsulated 40^Ar/39^Ar total gas ages（UTGA） of the authigenic illites range from 188.56 ± 6.20 Ma to 491.86 ± 27.68 Ma, which are 7% to 103% older than the corresponding K/Ar ages of 124.87 ± 1.11 Ma to 383.45 ± 2.80 Ma, respectively. The K-Ar ages indicate multistage accumulations with distinct distribution patterns in the Tarim Basin： older（late Caledonian-early Hercynian） around the basin margin, younger（late Hercynian） in the basin centre, and the youngest（middle to late Yanshanian） in the Ha-6 well-block, central area of the North Uplift. The age difference is believed to have been caused by the 39^Ar recoil loss during the irradiation process. Compared with the K/Ar ages, the estimated 39^Ar recoil losses in this study are in the range from 7% to 51%. The 39^Ar recoil loss appears to increase not only with the decreasing particle sizes of the I/S, but also with increasing percentage of smectite layers（IR） of the I/S, and smectite layer content（SLC） of the samples. We conclude that due to significant 39^Ar recoil losses, UTGA may not offer any meaningful geological ages of the authigenic illite formation in the SBS and thus can not be used to represent the hydrocarbon charge timing. 39^Ar recoil losses during 40^Ar/39^Ar dating can not be neglected when dating fine authigenic illite, especially when the ordered mixed-layer I/S containing small amount of smectite layers（IR30%） in the reservoir formations. Compared with the unencapsulated Ar-Ar method, the conventional K-Ar method is less complicated, more accurate and reliable in dating authigenic illites in petroleum reservoirs.展开更多
Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar a...Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions（〈0.1 μm,0.1-0.4 μm and 0.4-1.0 μm）.The results show that the K-Ar age values decrease from coarser to finer grain fractions（24.1 to 19.2 Ma）,suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite（19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma）.In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi（DNCV） metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone（RR-ASFZ）.During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.展开更多
Radiogenic isotope dating of illitic clays has been widely used to reconstruct thermal and fluid flow events in siliciclastic sedimentary basins,the information of which is critical to investigate mechanisms of hydroc...Radiogenic isotope dating of illitic clays has been widely used to reconstruct thermal and fluid flow events in siliciclastic sedimentary basins,the information of which is critical to investigate mechanisms of hydrocarbon maturation.This study carried out Rb-Sr and^(40)Ar-^(39)Ar dating of authigenic illitic clay samples separated from the Palaeogene sandstone in the northern South China Sea.Our Rb-Sr data further confirm the previously reported three periods of fluid flow events(at 34.5±0.9,31.2±0.6,and 23.6±0.8 Ma,respectively)in the northern South China Sea,which are related to regional episodic tectonism.However,^(40)Ar-^(39)Ar ages of illite obtained in this study are significantly younger than the corresponding Rb-Sr ages.The significantly younger^(40)Ar-^(39)Ar ages were probably due to ^(40)Ar loss caused by later dry heating events on the Hainan Island that have not affected the Rb-Sr isotopic systematics.The inconsistency between Rb-Sr and^(40)Ar-^(39)Ar data should be attributed to different isotopic behaviors of K-Ar and Rb-Sr isotopic systematics in illite.Our results indicate that Rb-Sr isotopic dating method may be a preferential approach for clay dating in geological settings where exist younger dry heating events.展开更多
文摘The Tarim Basin in China comprises eight sets of sandstone reservoirs, five of which are investigated in detail in this study. The main purpose of this study is to investigate the hydrocarbon charging histories of reservoirs by applying K-Ar dating of authigenic illites. The ages of authigenic illites from the Lower Silurian bituminous sandstones in the Central Uplift area range from 383.5 to 235.2 Ma, suggesting that the Silurian oil accumulations were formed from the late Caledonian till the late Hercynian. The ages of authigenic illites from the Upper Devonian Donghe Sandstone reservoirs range from 263.8 to 231.3 Ma, indicating that hydrocarbon accumulations within the Donghe sandstone were formed mainly in the late Hercynian. The authigenic illites ages from the Lower Jurassic Yangxia Group sandstones in the Yinan-2 gas reservoir (Yinan-2, Kuqa Depression) range from 28.1 to 23.9 Ma, suggesting that the initial hydrocarbon charging occurred in the Miocene. The ages of the authigenic illites from the Lower Cretaceous sandstones in the Akemomu gas field (Ake-1, Kashi Sag, Southwest Depression) range from 22.6 to 18.8 Ma, indicating a probable early oil accumulation or early migration of hydrocarbon within this area. The illites from the Paleogene sandstones in the Dina-2 gas reservoir (Dina-201, Kuqa Depression) have a detrital origin; they cannot be used to study the hydrocarbon charging histories. The ages of authigenic illites in the underlying Cretaceous sandstones in the same well (Dina-201) range from 25.5 to 15.5 Ma, indicating that hydrocarbon charging in this reservoir probably occurred within the Miocene. This study highlights the potential of applying K-Ar dating of authigenic illites to investigate the timing of hydrocarbon charging histories of the Tarim Basin reservoir sandstones.
文摘In the Ordos basin, two distinct thermal events of different ages have been identified for the first time by means of K-Ar dating combined with illite crystallinity analysis. For the Late Triassic and Late Permian samples, the K-Ar ages of the < 0.2μm fractions (159-173 Ma) reflect an illitization age related to the Yanshanian movement and indicate a short thermal event in the Middle Jurassic; the K-Ar ages of the <2 μm fractions (210-308 Ma) are interpreted as mixed ages of detrital material and authigenic illites. The K-Ar ages of both < 0.2μm and < 2μm fractions of a Middle Cambrian sample (368 Ma and 419 Ma) correspond to the ages of the metamorphism and earliest granite intrusion in the northern Caledonian Qinling fold zone (380-420 Ma) and show a thermal event during Silurian-Devonian time.
文摘The Silurian bituminous sandstones（SBS） in the Tarim Basin, China are important basinwide reservoirs with an estimated area of approximately 249000 km^2. We investigated the ages of authigenic illites in the SBS reservoirs and constrained their formation timing by using the 40^Ar/39^Ar step wise heating method. The age spectra, 39^Ar recoil loss and their controlling factors were investigated systematically. The 40^Ar/39^Ar ages were compared with the conventional K/Ar ages of identical clay fractions. The clay in the SBS reservoirs is dominated by orderly mixed-layer illite/smectite（I/S） with 5%–30% smectite layers. The I/S minerals morphology comprises primarily honeycomb, short filamentous and curved-lath particles, characteristic of authigenic illites. The unencapsulated 40^Ar/39^Ar total gas ages（UTGA） of the authigenic illites range from 188.56 ± 6.20 Ma to 491.86 ± 27.68 Ma, which are 7% to 103% older than the corresponding K/Ar ages of 124.87 ± 1.11 Ma to 383.45 ± 2.80 Ma, respectively. The K-Ar ages indicate multistage accumulations with distinct distribution patterns in the Tarim Basin： older（late Caledonian-early Hercynian） around the basin margin, younger（late Hercynian） in the basin centre, and the youngest（middle to late Yanshanian） in the Ha-6 well-block, central area of the North Uplift. The age difference is believed to have been caused by the 39^Ar recoil loss during the irradiation process. Compared with the K/Ar ages, the estimated 39^Ar recoil losses in this study are in the range from 7% to 51%. The 39^Ar recoil loss appears to increase not only with the decreasing particle sizes of the I/S, but also with increasing percentage of smectite layers（IR） of the I/S, and smectite layer content（SLC） of the samples. We conclude that due to significant 39^Ar recoil losses, UTGA may not offer any meaningful geological ages of the authigenic illite formation in the SBS and thus can not be used to represent the hydrocarbon charge timing. 39^Ar recoil losses during 40^Ar/39^Ar dating can not be neglected when dating fine authigenic illite, especially when the ordered mixed-layer I/S containing small amount of smectite layers（IR30%） in the reservoir formations. Compared with the unencapsulated Ar-Ar method, the conventional K-Ar method is less complicated, more accurate and reliable in dating authigenic illites in petroleum reservoirs.
基金financially supported by the Vietnam National Foundation for Science and Technology Development(NAFOSTED) under grant number 105.032011.11 to Bui Hoang Bac
文摘Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions（〈0.1 μm,0.1-0.4 μm and 0.4-1.0 μm）.The results show that the K-Ar age values decrease from coarser to finer grain fractions（24.1 to 19.2 Ma）,suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite（19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma）.In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi（DNCV） metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone（RR-ASFZ）.During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.
基金supported by the National Natural Science Foundation of China(Nos.42072142,41702121,U19B2007)。
文摘Radiogenic isotope dating of illitic clays has been widely used to reconstruct thermal and fluid flow events in siliciclastic sedimentary basins,the information of which is critical to investigate mechanisms of hydrocarbon maturation.This study carried out Rb-Sr and^(40)Ar-^(39)Ar dating of authigenic illitic clay samples separated from the Palaeogene sandstone in the northern South China Sea.Our Rb-Sr data further confirm the previously reported three periods of fluid flow events(at 34.5±0.9,31.2±0.6,and 23.6±0.8 Ma,respectively)in the northern South China Sea,which are related to regional episodic tectonism.However,^(40)Ar-^(39)Ar ages of illite obtained in this study are significantly younger than the corresponding Rb-Sr ages.The significantly younger^(40)Ar-^(39)Ar ages were probably due to ^(40)Ar loss caused by later dry heating events on the Hainan Island that have not affected the Rb-Sr isotopic systematics.The inconsistency between Rb-Sr and^(40)Ar-^(39)Ar data should be attributed to different isotopic behaviors of K-Ar and Rb-Sr isotopic systematics in illite.Our results indicate that Rb-Sr isotopic dating method may be a preferential approach for clay dating in geological settings where exist younger dry heating events.
