2014 Vol. 39, No. 1
Display Method:
2014, 39(1): 1-9.
doi: 10.3799/dqkx.2014.001
PDF 3504KB
Abstract:
Fossil caddisfly (Insecta: Trichoptera) larval cases have been recently discovered in the Early Cretaceous lacustine deposits (Madongshan Formation and Naijiahe Formation) in Liupanshan basin, Ningxia. The arrays of caddisfly larval cases occur as superimposed layers of vertically oriented cases. The fossils are gregarious, dense, parallel to each other and closely packed. The single larval case is conical and similar in size (generally 13 mm in length and averagely 2.5 mm in diameter). The wall of the caddisfly larval cases is divided into three layers, including internal, external dark organic matter layers which have micrite structures and are composed of lime muds, and the middle layer of cemented aphanitic particles composed of organic pellets. The calcified organic pellets are orbicular, spheroidicity and ovate, with its size ranging from 0.10 to 0.15 mm wide by averagely 0.3 mm long. The pellets are in regular arrangement, and their long axes are mostly perpendicular to the growth direction of the caddisworm cases. The larval cases in Liupanshan basin are attributed to Coprindusia in ichnology according to the pellets along the walls of the cases. By comparing the features of various tube-maker organism in morphology and bionomy, and the habitat, size and shape of cases, the composition of case-building particles, and case construction way, combining the analysis to insect body fossil from the same layers in which the caddisfly cases preserved, it seems like that the caddisfly larval cases in Liupanshan basin are Ningxiapsyche fangi from Ningxiapsychidae.
Fossil caddisfly (Insecta: Trichoptera) larval cases have been recently discovered in the Early Cretaceous lacustine deposits (Madongshan Formation and Naijiahe Formation) in Liupanshan basin, Ningxia. The arrays of caddisfly larval cases occur as superimposed layers of vertically oriented cases. The fossils are gregarious, dense, parallel to each other and closely packed. The single larval case is conical and similar in size (generally 13 mm in length and averagely 2.5 mm in diameter). The wall of the caddisfly larval cases is divided into three layers, including internal, external dark organic matter layers which have micrite structures and are composed of lime muds, and the middle layer of cemented aphanitic particles composed of organic pellets. The calcified organic pellets are orbicular, spheroidicity and ovate, with its size ranging from 0.10 to 0.15 mm wide by averagely 0.3 mm long. The pellets are in regular arrangement, and their long axes are mostly perpendicular to the growth direction of the caddisworm cases. The larval cases in Liupanshan basin are attributed to Coprindusia in ichnology according to the pellets along the walls of the cases. By comparing the features of various tube-maker organism in morphology and bionomy, and the habitat, size and shape of cases, the composition of case-building particles, and case construction way, combining the analysis to insect body fossil from the same layers in which the caddisfly cases preserved, it seems like that the caddisfly larval cases in Liupanshan basin are Ningxiapsyche fangi from Ningxiapsychidae.
2014, 39(1): 10-20.
doi: 10.3799/dqkx.2014.002
Abstract:
There are pre-, syn-, and post-orogenic granites in Shire region of northern Ethiopia. Whole rock Sm-Nd isochron dating results show that diagenetic age of pre-, and post-orogenic ages are 824.4±15.5 Ma and 517.9±5.8 Ma respectively. Major, rare-earth and trace elements of three kinds of granite are obviously different. The pre-orogenic granites are relatively low in MgO and high in SiO2, belonging to the peraluminous series granite, with low K content and slight light REE enrichment, high large-ion lithophile element abundance and relative depletion of HFSE. The syn-orogenic granite belongs to the quasi-aluminous rock and high-potassium calc-alkaline granite, with the light REE enriched pattern, high large-ion lithophile element and HFSE abundances. The post-orogenic granite belongs to the weakly peraluminous high-potassium calc-alkaline granite, which has the chondrite-normalized REE patterns in the type of "gull" with severe depletion in Eu. The large-ion lithophile elements are concentrated, while P and Ti are severely depleted here. Comprehensive study shows both the pre- and syn-orogenic granites are I-type mantle-source granites in the passive continental margin-volcanic island arc tectonic setting; the post-orogenic granites are A2-type crust-source major granites, which were formed from the melting of thinner crust after the closure of oceanic basins and the growth of Arabian-Nubian shield.
There are pre-, syn-, and post-orogenic granites in Shire region of northern Ethiopia. Whole rock Sm-Nd isochron dating results show that diagenetic age of pre-, and post-orogenic ages are 824.4±15.5 Ma and 517.9±5.8 Ma respectively. Major, rare-earth and trace elements of three kinds of granite are obviously different. The pre-orogenic granites are relatively low in MgO and high in SiO2, belonging to the peraluminous series granite, with low K content and slight light REE enrichment, high large-ion lithophile element abundance and relative depletion of HFSE. The syn-orogenic granite belongs to the quasi-aluminous rock and high-potassium calc-alkaline granite, with the light REE enriched pattern, high large-ion lithophile element and HFSE abundances. The post-orogenic granite belongs to the weakly peraluminous high-potassium calc-alkaline granite, which has the chondrite-normalized REE patterns in the type of "gull" with severe depletion in Eu. The large-ion lithophile elements are concentrated, while P and Ti are severely depleted here. Comprehensive study shows both the pre- and syn-orogenic granites are I-type mantle-source granites in the passive continental margin-volcanic island arc tectonic setting; the post-orogenic granites are A2-type crust-source major granites, which were formed from the melting of thinner crust after the closure of oceanic basins and the growth of Arabian-Nubian shield.
2014, 39(1): 21-36.
doi: 10.3799/dqkx.2014.003
Abstract:
The Yuanshishan granites have large amounts of mafic enclaves. This paper presents new zircon LA-ICP-MS U-Pb age, and the age analysis shows that the granites were generated in Early Jurassic (179±2 Ma). These granites are characterized by uniform silicon contents, enriched in alkali contents and more enriched in K contents, and enriched in iron and depleted in magnesium contents, with high 104×Ga/A1 values and Zr+Nb+Ce+Y contents. The granites belong to A-type granite. The Yuanshishan granites have homogeneous Sr-Nd isotope compositions (ISr＝0.701 7 to 0.710 8, εNd(t)＝-7.77 to - 4.55). Mafic enclaves show lower Isr(0.705 0 to 0.707 1) and higher εNd(t)(- 4.87 to -2.63) values. In situ zircons Hf isotope compositions from these granites have limited ranges (176Hf/177Hf)i=0.282 62 to 0.282 70), εHf(t) = -1.68 to 1.17, and TDM2 =1.25 to 1.43 Ga. We suggest that the Yuanshishan granites were likely generated by partial melting of newly underplated basaltic lower crust in extension setting. Since Early Jurassic (~200 Ma), extension has been the major subject of the tectonic background in the interior of the South China. Multistage basaltic magma underplating is direct inducement to the Yanshanian extension. During the Early Jurassic, the South China interior was most likely in post-collisional setting.
The Yuanshishan granites have large amounts of mafic enclaves. This paper presents new zircon LA-ICP-MS U-Pb age, and the age analysis shows that the granites were generated in Early Jurassic (179±2 Ma). These granites are characterized by uniform silicon contents, enriched in alkali contents and more enriched in K contents, and enriched in iron and depleted in magnesium contents, with high 104×Ga/A1 values and Zr+Nb+Ce+Y contents. The granites belong to A-type granite. The Yuanshishan granites have homogeneous Sr-Nd isotope compositions (ISr＝0.701 7 to 0.710 8, εNd(t)＝-7.77 to - 4.55). Mafic enclaves show lower Isr(0.705 0 to 0.707 1) and higher εNd(t)(- 4.87 to -2.63) values. In situ zircons Hf isotope compositions from these granites have limited ranges (176Hf/177Hf)i=0.282 62 to 0.282 70), εHf(t) = -1.68 to 1.17, and TDM2 =1.25 to 1.43 Ga. We suggest that the Yuanshishan granites were likely generated by partial melting of newly underplated basaltic lower crust in extension setting. Since Early Jurassic (~200 Ma), extension has been the major subject of the tectonic background in the interior of the South China. Multistage basaltic magma underplating is direct inducement to the Yanshanian extension. During the Early Jurassic, the South China interior was most likely in post-collisional setting.
2014, 39(1): 37-44.
doi: 10.3799/dqkx.2014.004
Abstract:
Guangdong Sanshui basin developed with extreme volcanic activities. Eruptions from Paleocene to Eocene were concentrated on Xinzhuang, Buxin, Baoyue and Huayong formations. For research of the relationship between various kind of rocks, geochemistry analyses such as multi-element and rare-earth element determination were launched on basalt, trachyte and rhyolite samples from the research area. Geochemistry diagrams suggest that: REE distribution of basalt followed as mid-plate alkali basalt mode, while their trace element spider diagrams act as continental alkali basalt with Nb, Ti rich and Sr loss. REE distributions of trachyte and rhyolite are similar, which indicate the same crystallization separation process. S-B diagram and pearce diagram show that: granites were partially melted from source region, while trachyte in ZMY and rhyolite in LBS originated from the same source region, and occurred with the process of crystallization separation with plagioclase adventage. Southeast China performed continental rift environment as Red Sea, and its magma may came from lithospheric mantle source. The magmatic activities suspended after 42 Ma because of regional extrusion, while breaking up of South China Sea (SCS) later may be a mixed effect of two functions.
Guangdong Sanshui basin developed with extreme volcanic activities. Eruptions from Paleocene to Eocene were concentrated on Xinzhuang, Buxin, Baoyue and Huayong formations. For research of the relationship between various kind of rocks, geochemistry analyses such as multi-element and rare-earth element determination were launched on basalt, trachyte and rhyolite samples from the research area. Geochemistry diagrams suggest that: REE distribution of basalt followed as mid-plate alkali basalt mode, while their trace element spider diagrams act as continental alkali basalt with Nb, Ti rich and Sr loss. REE distributions of trachyte and rhyolite are similar, which indicate the same crystallization separation process. S-B diagram and pearce diagram show that: granites were partially melted from source region, while trachyte in ZMY and rhyolite in LBS originated from the same source region, and occurred with the process of crystallization separation with plagioclase adventage. Southeast China performed continental rift environment as Red Sea, and its magma may came from lithospheric mantle source. The magmatic activities suspended after 42 Ma because of regional extrusion, while breaking up of South China Sea (SCS) later may be a mixed effect of two functions.
2014, 39(1): 45-63.
doi: 10.3799/dqkx.2014.005
Abstract:
Multi-stage Late Mesozoic magmatism and structural deformation related to the subduction of Paleo-Pacific plate occurred in the coast of Fujian Province, southeastern China. Extensional deformation in Quanzhou area presents high-angular normal faults and low-angular normal faults or detachment faults. The extensional deformation developed in NW-striking extensional setting. Zircon U-Pb geochronological data in this study suggest that Late Jurassic (~155 Ma), middle Early Cretaceous (130-125 Ma), late Early Cretaceous (~109 Ma) and early Late Cretaceous magmatic rocks outcrop in Quanzhou area. The comprehensive analyses of cutting relations and geochronological data of magmatic rocks show that the sinistral ductile strike-slip of the Changle-Nan'ao shear zone occurred in 130-120 Ma, whereas the dextral brittle shear developed between 120 Ma and 100 Ma. The angular variations of subduction for the Paleo-Pacific plate underneath the South China led to the development of the Late Mesozoic orogenic belt in the coast of Fujian Province. This orogen commenced at the beginning of Early Cretaceous and terminated in the latest Early Cretaceous, which is marked by the extensive NW-striking extensional structures. The transform from syn-orogen compression to post-orogen extension occurred at ~120 Ma.
Multi-stage Late Mesozoic magmatism and structural deformation related to the subduction of Paleo-Pacific plate occurred in the coast of Fujian Province, southeastern China. Extensional deformation in Quanzhou area presents high-angular normal faults and low-angular normal faults or detachment faults. The extensional deformation developed in NW-striking extensional setting. Zircon U-Pb geochronological data in this study suggest that Late Jurassic (~155 Ma), middle Early Cretaceous (130-125 Ma), late Early Cretaceous (~109 Ma) and early Late Cretaceous magmatic rocks outcrop in Quanzhou area. The comprehensive analyses of cutting relations and geochronological data of magmatic rocks show that the sinistral ductile strike-slip of the Changle-Nan'ao shear zone occurred in 130-120 Ma, whereas the dextral brittle shear developed between 120 Ma and 100 Ma. The angular variations of subduction for the Paleo-Pacific plate underneath the South China led to the development of the Late Mesozoic orogenic belt in the coast of Fujian Province. This orogen commenced at the beginning of Early Cretaceous and terminated in the latest Early Cretaceous, which is marked by the extensive NW-striking extensional structures. The transform from syn-orogen compression to post-orogen extension occurred at ~120 Ma.
2014, 39(1): 64-72.
doi: 10.3799/dqkx.2014.006
Abstract:
The drilling of Well Jianshen 1 located in Shizhu synclinorium meets overpressure and gas zone in Silurian strata, with pressure coefficients ranging from 1.75 to 2.00. Overpressure generation and preservation are closely related to the sealing efficiency of cap rock. Disequilibrium compaction, hydrocarbon generation, horizontal tectonic compaction and other overpressure generation mechanisms for Silurian abnormal high pressure are analyzed based on mudstone compaction characteristics, tectonic subsidence history, sediment burial history, hydrocarbon generation history, and it is found out that gas generation by kerogen and petroleum cracking during Early Triassic to Late Jurassic is the controlling mechanism for overpressure. Tectonic uplift since Early Cretaceous led to the separation of plenty of gas from gas-saturated formation water and the gathering into the relatively coarse-grained siltstone. Interbedded mudstone and siltstone appear frequently in pressure transition zone at the top of Silurian formation, resulting in several thin layers of gas. Vertical capillary force in each gas-water interface is superimposed and increases cap rock sealing ability, where the abnormally high pressure has been effectively preserved to date.
The drilling of Well Jianshen 1 located in Shizhu synclinorium meets overpressure and gas zone in Silurian strata, with pressure coefficients ranging from 1.75 to 2.00. Overpressure generation and preservation are closely related to the sealing efficiency of cap rock. Disequilibrium compaction, hydrocarbon generation, horizontal tectonic compaction and other overpressure generation mechanisms for Silurian abnormal high pressure are analyzed based on mudstone compaction characteristics, tectonic subsidence history, sediment burial history, hydrocarbon generation history, and it is found out that gas generation by kerogen and petroleum cracking during Early Triassic to Late Jurassic is the controlling mechanism for overpressure. Tectonic uplift since Early Cretaceous led to the separation of plenty of gas from gas-saturated formation water and the gathering into the relatively coarse-grained siltstone. Interbedded mudstone and siltstone appear frequently in pressure transition zone at the top of Silurian formation, resulting in several thin layers of gas. Vertical capillary force in each gas-water interface is superimposed and increases cap rock sealing ability, where the abnormally high pressure has been effectively preserved to date.
2014, 39(1): 73-78.
doi: 10.3799/dqkx.2014.007
Abstract:
The coal reservoir has high reservoir pressure, great pressure gradient and developmental abnormal high pressure in Bide-Santang basin. This paper mainly analyzes the influence factors of abnormal high pressure and illustrates the formation mechanism by studying the distribution characteristics of coal reservoir pressure. Results show that the tectonism is the uppermost factor to the abnormal high pressure formation, hydrocarbon generation of coal reservoir and roof mudstone sealing take second place. There are few faults, good sealed conditions and rich reservoir fluid in the interior of basin, which led to the increase of coal reservoir pressure and abnormal high pressure. The coal reservoir has strong hydrocarbon generation ability, high gas content and low permeability, and generated hydrocarbon gas makes the internal fluid pore volume of coal reservoir expanded and produce high pressure. Moreover, the extra-thick roof mudstone which easily causes undercompacted compaction in the deposition process has good sealing, and further promotes the development of the abnormal pressure.
The coal reservoir has high reservoir pressure, great pressure gradient and developmental abnormal high pressure in Bide-Santang basin. This paper mainly analyzes the influence factors of abnormal high pressure and illustrates the formation mechanism by studying the distribution characteristics of coal reservoir pressure. Results show that the tectonism is the uppermost factor to the abnormal high pressure formation, hydrocarbon generation of coal reservoir and roof mudstone sealing take second place. There are few faults, good sealed conditions and rich reservoir fluid in the interior of basin, which led to the increase of coal reservoir pressure and abnormal high pressure. The coal reservoir has strong hydrocarbon generation ability, high gas content and low permeability, and generated hydrocarbon gas makes the internal fluid pore volume of coal reservoir expanded and produce high pressure. Moreover, the extra-thick roof mudstone which easily causes undercompacted compaction in the deposition process has good sealing, and further promotes the development of the abnormal pressure.
2014, 39(1): 79-90.
doi: 10.3799/dqkx.2014.008
Abstract:
Microthermometry and volumetric analysis have been widely used to reconstruct the composition and pressure-temperature (P-T) trapping conditions of petroleum inclusions. However, a reliable prediction of P-T trapping conditions also depends on accurate prediction of saturation pressure and volume of petroleum in addition to accurate measurements of homogenization temperature (Thoil) and the degree of bubble filling (Fv). Based on the improved prediction accuracy of saturation pressure and gas-liquid phase mole volume of petroleum fluids, the quantitative correlation among C7+ mole fraction and Thoil and Fv has been established. The correlation is still subject to the effect of Fv on the accuracy of petroleum inclusion thermodynamics modeling, although the processes for petroleum inclusion thermodynamics modeling can be largely simplified by using the correlation developed in this paper. So a new methane-constraining model for trapping pressure prediction of petroleum inclusion was developed according to large numbers of known petroleum compositions. The newly developed model has only one variable which is the methane mole fraction of petroleum inclusion and does not depend on professional softwares such as PVTsim, VTflinc, PIT, FIT-OIL and so on. Finally, the accuracy of newly developed model for trapping pressure prediction was tested, and the bulk methane mole fraction is the key control of the trapping pressure reconstruction and future research should be focused on the prediction of methane mole fraction of individual petroleum inclusion.
Microthermometry and volumetric analysis have been widely used to reconstruct the composition and pressure-temperature (P-T) trapping conditions of petroleum inclusions. However, a reliable prediction of P-T trapping conditions also depends on accurate prediction of saturation pressure and volume of petroleum in addition to accurate measurements of homogenization temperature (Thoil) and the degree of bubble filling (Fv). Based on the improved prediction accuracy of saturation pressure and gas-liquid phase mole volume of petroleum fluids, the quantitative correlation among C7+ mole fraction and Thoil and Fv has been established. The correlation is still subject to the effect of Fv on the accuracy of petroleum inclusion thermodynamics modeling, although the processes for petroleum inclusion thermodynamics modeling can be largely simplified by using the correlation developed in this paper. So a new methane-constraining model for trapping pressure prediction of petroleum inclusion was developed according to large numbers of known petroleum compositions. The newly developed model has only one variable which is the methane mole fraction of petroleum inclusion and does not depend on professional softwares such as PVTsim, VTflinc, PIT, FIT-OIL and so on. Finally, the accuracy of newly developed model for trapping pressure prediction was tested, and the bulk methane mole fraction is the key control of the trapping pressure reconstruction and future research should be focused on the prediction of methane mole fraction of individual petroleum inclusion.
2014, 39(1): 91-98.
doi: 10.3799/dqkx.2014.009
Abstract:
In this study, the Miocene carbonate sequence stratigraphy and sedimentary cycle of Nankang platform and L-structure in Zengmu basin are analyzed by using drilling, seismic and some palaeontologic data, and the sequence pattern of Miocene carbonate in the study area is established. The results show that three large-scale carbonate sedimentary cycles occurred during Mid to Late Miocene (5.3-16 Ma) in Zengmu basin, so the strata can be subdivided into three Tertiary sequences (SQ1, SQ2 and SQ3 sequences). SQ1 and SQ3 sequences are defined as the classical type I carbonate sequences, which are composed of dense algal limestone in low-stand system tracts (LST), argillaceous limestone in transgressive system tracts (TST) and coral limestone in high-stand system tracts (HST). And their properties indicate that the carbonate buildups have experienced a process from open marine platform facies to reef flat facies. Being different form SQ1 and SQ3 sequences, SQ2 sequences belong to the drowned unconformity type of carbonate sequences. This kind of carbonate sequences is marked by the successions consisted of argillaceous limestone of condensed sequence (CS) and coral limestone (or clastic limestone) of HST. And its development generally occurred during the phase of continuous decrease of sea level.
In this study, the Miocene carbonate sequence stratigraphy and sedimentary cycle of Nankang platform and L-structure in Zengmu basin are analyzed by using drilling, seismic and some palaeontologic data, and the sequence pattern of Miocene carbonate in the study area is established. The results show that three large-scale carbonate sedimentary cycles occurred during Mid to Late Miocene (5.3-16 Ma) in Zengmu basin, so the strata can be subdivided into three Tertiary sequences (SQ1, SQ2 and SQ3 sequences). SQ1 and SQ3 sequences are defined as the classical type I carbonate sequences, which are composed of dense algal limestone in low-stand system tracts (LST), argillaceous limestone in transgressive system tracts (TST) and coral limestone in high-stand system tracts (HST). And their properties indicate that the carbonate buildups have experienced a process from open marine platform facies to reef flat facies. Being different form SQ1 and SQ3 sequences, SQ2 sequences belong to the drowned unconformity type of carbonate sequences. This kind of carbonate sequences is marked by the successions consisted of argillaceous limestone of condensed sequence (CS) and coral limestone (or clastic limestone) of HST. And its development generally occurred during the phase of continuous decrease of sea level.
2014, 39(1): 99-107.
doi: 10.3799/dqkx.2014.010
Abstract:
Arsenic (AS) mobilization is closely linked to redox state in nature.In basin environment, the primary mechanism governing arsenic mobility is the reductive dissolution of Fe/Mn-(hydr)oxides which results in the subsequent As released into groundwater. Molybdenum (Mo) and Mo isotope can be informative of the redox conditions. Moreover, Mo isotope fractionation is mainly controlled by the adsorption and desorption onto/from Fe/Mn-(hydr)oxides. This study applies Mo isotope ratio(δ98Mo) of dissolved Mo in groundwater to arsenic mobilization in groundwater system for the very first time. The Mo isotope ratios (δ98Mo) in groundwater in Datong basin range from -0.12‰ to 2.17‰, which are relatively heavier than those reported in fresh waters. δ98Mo of Sanggan River shows a value of 0.72‰, comparable to the average δ98Mo of riverine Mo isotopic composition of 0.7‰.δ98Mo ratios of groundwater in Datong basin are positively correlated to dissolved sulfide, indicating that the formation of Mo-Fe-S complex preferentially co-precipitated the light Mo in groundwater resulting in the gradually increased δ98Mo values under certain condition. The formation of Mo-Fe-S complex might be competitive to the similar formation of As-Fe-S complex, as is further confirmed by the weak correlation between As and Mo concentrations and the positive relationship between As and δ98Mo ratios. This process leads to an elevation of As content in groundwater.The relatively heavier δ98Mo ratio of groundwater might be a consequence of the faster rate of adsorption of light Mo from groundwater than the rate of desorption of Mo from Fe-(hydr)oxides and the re-adsorption of dissolved Mo in groundwater.The progressive processes decrease Mo content and elevate δ98Mo ratio in groundwater, which is consistent with the observation in groundwater in Datong basin.The indicative δ98Mo ratio of groundwater indicates that the reductive dissolution of Fe-(hydr)oxides also has important influence on arsenic mobilization in groundwater.
Arsenic (AS) mobilization is closely linked to redox state in nature.In basin environment, the primary mechanism governing arsenic mobility is the reductive dissolution of Fe/Mn-(hydr)oxides which results in the subsequent As released into groundwater. Molybdenum (Mo) and Mo isotope can be informative of the redox conditions. Moreover, Mo isotope fractionation is mainly controlled by the adsorption and desorption onto/from Fe/Mn-(hydr)oxides. This study applies Mo isotope ratio(δ98Mo) of dissolved Mo in groundwater to arsenic mobilization in groundwater system for the very first time. The Mo isotope ratios (δ98Mo) in groundwater in Datong basin range from -0.12‰ to 2.17‰, which are relatively heavier than those reported in fresh waters. δ98Mo of Sanggan River shows a value of 0.72‰, comparable to the average δ98Mo of riverine Mo isotopic composition of 0.7‰.δ98Mo ratios of groundwater in Datong basin are positively correlated to dissolved sulfide, indicating that the formation of Mo-Fe-S complex preferentially co-precipitated the light Mo in groundwater resulting in the gradually increased δ98Mo values under certain condition. The formation of Mo-Fe-S complex might be competitive to the similar formation of As-Fe-S complex, as is further confirmed by the weak correlation between As and Mo concentrations and the positive relationship between As and δ98Mo ratios. This process leads to an elevation of As content in groundwater.The relatively heavier δ98Mo ratio of groundwater might be a consequence of the faster rate of adsorption of light Mo from groundwater than the rate of desorption of Mo from Fe-(hydr)oxides and the re-adsorption of dissolved Mo in groundwater.The progressive processes decrease Mo content and elevate δ98Mo ratio in groundwater, which is consistent with the observation in groundwater in Datong basin.The indicative δ98Mo ratio of groundwater indicates that the reductive dissolution of Fe-(hydr)oxides also has important influence on arsenic mobilization in groundwater.
2014, 39(1): 108-114.
doi: 10.3799/dqkx.2014.011
Abstract:
The fracture toughness of rock is of great significance in quantitative evaluation of engineering safety and stability. Rocks often destruct with water, so it is worthwhile to do study on the issue as how the rock fracture toughness and associated mechanical parameters change under long-term immersion of reservoir water. In this paper, a long-term immersion test is designed and carried out and a comprehensive analysis is done in aspects such as the fracture toughness, deformation failure characteristics and microstructure change characteristics. The results show that: (1) under the water-rock interaction, the fracture toughness has a significant deterioration trend, and the deterioration rate increased in prophase and lowered in anaphase; and the deterioration rate gradually becomes slow after 5 or 6 months' immersion. (2) The P-CMOD relation curves of the sandstone three-point bending test can be divided into three stages, namely elastic stage, yield stage, and crack development and damage phases; and with the immersion time, the elastic stage gradually becomes shorter, the yield stage gradually becomes longer, and the downward trend of crack development phase gradually becomes slow, meanwhile, the incision opening displacement which is corresponding to cracking peak load gradually increases. The sandstone brittleness gradually weakens, and plasticity gradually enhances. (3) Lubrication, softening and changes of sandstone's inner microscopic structure caused by water-rock interaction, especially the micro-cracks and the development of the cracks are the basic reasons which lead to the deterioration of the sandstone fracture toughness and other mechanical parameters. The research results facilitate the understanding of the degradation law of sandstone fracture toughness under long-term reservoir water immersion.
The fracture toughness of rock is of great significance in quantitative evaluation of engineering safety and stability. Rocks often destruct with water, so it is worthwhile to do study on the issue as how the rock fracture toughness and associated mechanical parameters change under long-term immersion of reservoir water. In this paper, a long-term immersion test is designed and carried out and a comprehensive analysis is done in aspects such as the fracture toughness, deformation failure characteristics and microstructure change characteristics. The results show that: (1) under the water-rock interaction, the fracture toughness has a significant deterioration trend, and the deterioration rate increased in prophase and lowered in anaphase; and the deterioration rate gradually becomes slow after 5 or 6 months' immersion. (2) The P-CMOD relation curves of the sandstone three-point bending test can be divided into three stages, namely elastic stage, yield stage, and crack development and damage phases; and with the immersion time, the elastic stage gradually becomes shorter, the yield stage gradually becomes longer, and the downward trend of crack development phase gradually becomes slow, meanwhile, the incision opening displacement which is corresponding to cracking peak load gradually increases. The sandstone brittleness gradually weakens, and plasticity gradually enhances. (3) Lubrication, softening and changes of sandstone's inner microscopic structure caused by water-rock interaction, especially the micro-cracks and the development of the cracks are the basic reasons which lead to the deterioration of the sandstone fracture toughness and other mechanical parameters. The research results facilitate the understanding of the degradation law of sandstone fracture toughness under long-term reservoir water immersion.
2014, 39(1): 115-122.
doi: 10.3799/dqkx.2014.012
Abstract:
The average low water level, water level change region, average flood level of natural river respectively exist many similar characteristics with the low water level, regulating water level (i.e. water level fluctuation band), the highest design flood level of reservoir operation period. Stable slope angles under low water level, in water level change region and above flood level in different rock-soil bodies have great significance to the prediction of bank collapse in reservoir operation period. Based on high-resolution aerial images in dry seasons and DEM (digital elevation model), using GIS component development technology, the paper developes a method to get stable slope angles of water level change region, which has some advantages such as high degree of automation and fast speed in achieving data in a large scale, therefore, underwater stable slope angles can be computed by discount, and the stable slope angles above water can be achieved through the similar method. Compared with the traditional method such as survey or statistical method, it greatly reduces the fieldwork, and according to the regions which human beings cannot reach in current conditions, it also can get detailed data, and it can get enough sample data for comparison and statistical analysis in different rock or soil bodies, so it can provide more dependable data for prediction of bank collapse of reservoir back zones.
The average low water level, water level change region, average flood level of natural river respectively exist many similar characteristics with the low water level, regulating water level (i.e. water level fluctuation band), the highest design flood level of reservoir operation period. Stable slope angles under low water level, in water level change region and above flood level in different rock-soil bodies have great significance to the prediction of bank collapse in reservoir operation period. Based on high-resolution aerial images in dry seasons and DEM (digital elevation model), using GIS component development technology, the paper developes a method to get stable slope angles of water level change region, which has some advantages such as high degree of automation and fast speed in achieving data in a large scale, therefore, underwater stable slope angles can be computed by discount, and the stable slope angles above water can be achieved through the similar method. Compared with the traditional method such as survey or statistical method, it greatly reduces the fieldwork, and according to the regions which human beings cannot reach in current conditions, it also can get detailed data, and it can get enough sample data for comparison and statistical analysis in different rock or soil bodies, so it can provide more dependable data for prediction of bank collapse of reservoir back zones.
