2012 Vol. 30, No. 5
Display Method:
2012, 30(5): 787-794.
Abstract:
Storm deposits with typical features of were found in the Qingxudong Formation, Lower Cambrian（corresponding to Series 2 of Cambrian）in Zhenyuan area, eastern Guizhou Province. Based on field observation on the Jinpen Section and Liushaguan Section and laboratory analysis, sedimentary structures of storm deposit, such as erosion surface, coarse lag deposits, graded bedding, ripple beddings and rhythmic lamination, are present in the succession, excluding hummocky crossstratification. Particularly, the lagsuspension deposit couple is evident, winnowed coarse lag deposits occur in the below with an overlying fine laminated bed. Three types of storm deposit sequences with different vertical stacking patterns were identified. Sequence Ⅰconsists of the coarse lag deposits, ripple beddings and rhythmic lamination upwards. The coarse lag deposits which are composed of gravels, intraclasts and ooids are the predominant parts. Sequence Ⅱconsists of the graded bedding and ripple beddings, and including wavy erosion surface in the bottom. Sequence Ⅲ is responsible for multistage small scale storm, including lag deposits and ripple beddings. The background deposit is gray laminated limestone, with ripple bedding, bird's eye structure, indicating tidal flat environment. In summary, the storm deposits in Zhenyuan is attributed to tidal flat storm deposit, that enrich the style of storm deposits of Qingxudong Formation, early Cambrian, in eastern Guizhou and western Hunan. The distribution pattern of storm deposit of Qingxudong Formation, in eastern Guizhou and western Hunan was preliminarily summarized based on the previous work and this study. The discovery of storm deposits reflects indirectly the study area should be located in the low latitudes near the equator during the Early Cambrian.
Storm deposits with typical features of were found in the Qingxudong Formation, Lower Cambrian（corresponding to Series 2 of Cambrian）in Zhenyuan area, eastern Guizhou Province. Based on field observation on the Jinpen Section and Liushaguan Section and laboratory analysis, sedimentary structures of storm deposit, such as erosion surface, coarse lag deposits, graded bedding, ripple beddings and rhythmic lamination, are present in the succession, excluding hummocky crossstratification. Particularly, the lagsuspension deposit couple is evident, winnowed coarse lag deposits occur in the below with an overlying fine laminated bed. Three types of storm deposit sequences with different vertical stacking patterns were identified. Sequence Ⅰconsists of the coarse lag deposits, ripple beddings and rhythmic lamination upwards. The coarse lag deposits which are composed of gravels, intraclasts and ooids are the predominant parts. Sequence Ⅱconsists of the graded bedding and ripple beddings, and including wavy erosion surface in the bottom. Sequence Ⅲ is responsible for multistage small scale storm, including lag deposits and ripple beddings. The background deposit is gray laminated limestone, with ripple bedding, bird's eye structure, indicating tidal flat environment. In summary, the storm deposits in Zhenyuan is attributed to tidal flat storm deposit, that enrich the style of storm deposits of Qingxudong Formation, early Cambrian, in eastern Guizhou and western Hunan. The distribution pattern of storm deposit of Qingxudong Formation, in eastern Guizhou and western Hunan was preliminarily summarized based on the previous work and this study. The discovery of storm deposits reflects indirectly the study area should be located in the low latitudes near the equator during the Early Cambrian.
2012, 30(5): 795-805.
Abstract:
Soft sediment deformation is one of the key indicators identifying the existence of paleoearthquake. Based on the standard as the sediments suffer the earthquake,fliud pressure changing degree and the strength of the liquefied. Through three horizons of soft sediment deformation events with earthquakedriven on the Cambrian Dachenling Formation in the Tongcun village in Zhejiang province, the abundant soft sediment deformation are seismic microfractures, microfolding and liquefied structures. They reflect the extent of the fliud pressure changing and the strength of the liquefaction, when the sediments suffer from the earthquake. The microfoldings in the profile of Tongcun village always place there, and are symmetrical folds and uniform liquid layer. Its tectonic features do not match significantly to the landslide deformation, and the author and other measure the microfolding axial plane randomly in the profile of Tongcun village, and get total of 39 sets of data, and then correct in level for statistical analysis. After all the work, the author rules out the possibility of landslide. Liquefied structure is a kind of the geological phenomenon of conservation of matter and transfer of form, and it shows the flow structure when liquefaction invades. The formation of liquefied form caused by three reasons, which represent the diffferent stages of devolatilization. The auther researchs by contrasting among the liquefied structures by means of four aspects of section characteristics, surface features, contrasting with surrrounding rock, and symbiotic construction. By observing and counting about special characteristics and properties of event horizons of the soft sediment deformation, and distinguishing the similar structures without earthquakedriven, these indicate that earthquake was the driven force. The discovery of three seismite events layers indicated that the deposition period of Dachenling formation is the period of paleoseimic occuring frequently.Paleoseismic induces the formation of KaihuaChun'an major deslocation, so the author and other consider deposition time of the event layer Ⅱ is the strong activing period of the formation of KaihuaChun’an major deslocation. Counting the seismic disturbance and epicentral distance in the three events layer estimate the layer Ⅱ and layer Ⅲ magnitude are 67 level and about 6 level, and the autherand other preliminary view that the layers without the earthquake zone maybe exist molan tooth. So, the identification mark and lithological sequence of seismite get perfect, the understanding get deepening about the sedinentation of cambrian Dachenling formation resulting from seismic events in the west of Zhejiang province.
Soft sediment deformation is one of the key indicators identifying the existence of paleoearthquake. Based on the standard as the sediments suffer the earthquake,fliud pressure changing degree and the strength of the liquefied. Through three horizons of soft sediment deformation events with earthquakedriven on the Cambrian Dachenling Formation in the Tongcun village in Zhejiang province, the abundant soft sediment deformation are seismic microfractures, microfolding and liquefied structures. They reflect the extent of the fliud pressure changing and the strength of the liquefaction, when the sediments suffer from the earthquake. The microfoldings in the profile of Tongcun village always place there, and are symmetrical folds and uniform liquid layer. Its tectonic features do not match significantly to the landslide deformation, and the author and other measure the microfolding axial plane randomly in the profile of Tongcun village, and get total of 39 sets of data, and then correct in level for statistical analysis. After all the work, the author rules out the possibility of landslide. Liquefied structure is a kind of the geological phenomenon of conservation of matter and transfer of form, and it shows the flow structure when liquefaction invades. The formation of liquefied form caused by three reasons, which represent the diffferent stages of devolatilization. The auther researchs by contrasting among the liquefied structures by means of four aspects of section characteristics, surface features, contrasting with surrrounding rock, and symbiotic construction. By observing and counting about special characteristics and properties of event horizons of the soft sediment deformation, and distinguishing the similar structures without earthquakedriven, these indicate that earthquake was the driven force. The discovery of three seismite events layers indicated that the deposition period of Dachenling formation is the period of paleoseimic occuring frequently.Paleoseismic induces the formation of KaihuaChun'an major deslocation, so the author and other consider deposition time of the event layer Ⅱ is the strong activing period of the formation of KaihuaChun’an major deslocation. Counting the seismic disturbance and epicentral distance in the three events layer estimate the layer Ⅱ and layer Ⅲ magnitude are 67 level and about 6 level, and the autherand other preliminary view that the layers without the earthquake zone maybe exist molan tooth. So, the identification mark and lithological sequence of seismite get perfect, the understanding get deepening about the sedinentation of cambrian Dachenling formation resulting from seismic events in the west of Zhejiang province.
2012, 30(5): 806-816.
Abstract:
The fraction of organic carbon burial(forg) is calculated on the basis of the carbon cycle model with the records of carbon isotope composition on both carbonate and organic matter in the late Permian at Xinmin section, and the abundance of acritachs, algae and microbes which represents marine primary paleoproductivity is examined. We discuss the relationship among forg, marine paleoproductivity and the content of residual TOC in details. Residual TOC is determined by the combinations of the primary productivity, organic carbon burial fraction(forg) and burial redox conditions. But the data in Xinmin section and Meishan section show that the paleoproductivity plays a dominant role on the value of residual TOC. But this conclusion still needs further proof: we found that forg is mainly controlled by δ13Ccarb by Kump’s model, in which it concluded increased volcanism leads to only small changes in δ13Ccarb, and set the carbon isotope value of volcanic activity and weathering as δw =5‰. That is to say, a series of secondary environmental effects caused by volcanism were ignored, such as "volcanic winter", ocean acidification, smoke and other toxic substances and so on, all of which had great impact on the marine environment. However, largesized volcanism in the Late Permian could result in serious perturbation to marine carbon cycle. Therefore, the model still need to be further improved on calculating organic carbon burial fraction quantitatively or semiquantitatively during this special geological period.
The fraction of organic carbon burial(forg) is calculated on the basis of the carbon cycle model with the records of carbon isotope composition on both carbonate and organic matter in the late Permian at Xinmin section, and the abundance of acritachs, algae and microbes which represents marine primary paleoproductivity is examined. We discuss the relationship among forg, marine paleoproductivity and the content of residual TOC in details. Residual TOC is determined by the combinations of the primary productivity, organic carbon burial fraction(forg) and burial redox conditions. But the data in Xinmin section and Meishan section show that the paleoproductivity plays a dominant role on the value of residual TOC. But this conclusion still needs further proof: we found that forg is mainly controlled by δ13Ccarb by Kump’s model, in which it concluded increased volcanism leads to only small changes in δ13Ccarb, and set the carbon isotope value of volcanic activity and weathering as δw =5‰. That is to say, a series of secondary environmental effects caused by volcanism were ignored, such as "volcanic winter", ocean acidification, smoke and other toxic substances and so on, all of which had great impact on the marine environment. However, largesized volcanism in the Late Permian could result in serious perturbation to marine carbon cycle. Therefore, the model still need to be further improved on calculating organic carbon burial fraction quantitatively or semiquantitatively during this special geological period.
2012, 30(5): 817-824.
Abstract:
Magnetic susceptibility results from Xinmin section in Anshun, Guizhou indicate that the Permian Dalong Formation is with low values(6.4×108 m3/kg in average) and that their values increase significantly across the PT boundary and are high, about 1.3×107 m3/kg, in the Triassic Luolou Formation, which shows the same variation trend with that across other PT boundary sections in South China. A good positive correlation with both terrestrial sporopollen abundance and TiO2 variations proves that terrestrial influx attributes most of the magnetic susceptibility at Xinmin section. 3 paleoclimatic stages in the source area were figured out based on the variations of magnetic susceptibility and geochemical climatic proxies: StageⅠ(bed 1 to the middle of bed 2) is characterized by a warm/humid climate with strong chemical weathering; while a hot/humid climate with stronger chemical weathering dominates stageⅡ(top of bed 2 to the PT boundary), the climate condition change rapidly between much milder climate and humid climate; after a short transitional period, the climate in stageⅢ(above the PT boundary) turns into a relatively hot/dry climate with obvious much stronger physical weathering and weaker chemical weathering.
Magnetic susceptibility results from Xinmin section in Anshun, Guizhou indicate that the Permian Dalong Formation is with low values(6.4×108 m3/kg in average) and that their values increase significantly across the PT boundary and are high, about 1.3×107 m3/kg, in the Triassic Luolou Formation, which shows the same variation trend with that across other PT boundary sections in South China. A good positive correlation with both terrestrial sporopollen abundance and TiO2 variations proves that terrestrial influx attributes most of the magnetic susceptibility at Xinmin section. 3 paleoclimatic stages in the source area were figured out based on the variations of magnetic susceptibility and geochemical climatic proxies: StageⅠ(bed 1 to the middle of bed 2) is characterized by a warm/humid climate with strong chemical weathering; while a hot/humid climate with stronger chemical weathering dominates stageⅡ(top of bed 2 to the PT boundary), the climate condition change rapidly between much milder climate and humid climate; after a short transitional period, the climate in stageⅢ(above the PT boundary) turns into a relatively hot/dry climate with obvious much stronger physical weathering and weaker chemical weathering.
2012, 30(5): 825-833.
Abstract:
In the Late Jurassic period, Qiangtang basin has experienced an obvious tectonic uplift and turned into a terrestrial basin. Most of the region has undergone erosion in the Cretaceous, which results in the lack of Lower Cretaceous. Therefore, to confirm the existence of the Early Cretaceous marine sediments in the Qiangtang basin, this paper conducted a research on ShengliheTuonamu region preliminarily judged as Late JurassicEarly Cretaceous marine strata era, which is based on the Nadigangri section and combined with the Shenglihe, Tuonamu, Changsheshan sections which are preliminary judged on the Early Cretaceous era oil shale formation on the auxiliary sections, with the adoption of paleontological fossils and isotopic chronology to judge the era of each formation of the section from the top to the bottom and rejudge the era of the Original Suowa formation. The results show that original Suowa Formation is in the Late JurassicEarly Cretaceous, Suowa formation is in the Late Jurassic, Weimingming formation is in the Early Cretaceous, and Xueshan formation is in the Late Early CretaceousEarly Late Cretaceous. The formation comparison show that the era which was initially judged as Late JurassicEarly Cretaceous shale limestonegypsum marine strata should be Early Cretaceous. In the Early Cretaceous period, Early Cretaceous marine strata are widely distributed in ShengliheTuonamu region, lithology formations of which are different in different regions. This stratum is oil shale and the thickest in ShengliheChangsheshan region, which gradually becomes thinner along the east and transits into shale sediment, and into limestone sediment in the west. Regionally, the existence of the Early Cretaceous strata is important to the conditions of the underlying oil and gas storage.
In the Late Jurassic period, Qiangtang basin has experienced an obvious tectonic uplift and turned into a terrestrial basin. Most of the region has undergone erosion in the Cretaceous, which results in the lack of Lower Cretaceous. Therefore, to confirm the existence of the Early Cretaceous marine sediments in the Qiangtang basin, this paper conducted a research on ShengliheTuonamu region preliminarily judged as Late JurassicEarly Cretaceous marine strata era, which is based on the Nadigangri section and combined with the Shenglihe, Tuonamu, Changsheshan sections which are preliminary judged on the Early Cretaceous era oil shale formation on the auxiliary sections, with the adoption of paleontological fossils and isotopic chronology to judge the era of each formation of the section from the top to the bottom and rejudge the era of the Original Suowa formation. The results show that original Suowa Formation is in the Late JurassicEarly Cretaceous, Suowa formation is in the Late Jurassic, Weimingming formation is in the Early Cretaceous, and Xueshan formation is in the Late Early CretaceousEarly Late Cretaceous. The formation comparison show that the era which was initially judged as Late JurassicEarly Cretaceous shale limestonegypsum marine strata should be Early Cretaceous. In the Early Cretaceous period, Early Cretaceous marine strata are widely distributed in ShengliheTuonamu region, lithology formations of which are different in different regions. This stratum is oil shale and the thickest in ShengliheChangsheshan region, which gradually becomes thinner along the east and transits into shale sediment, and into limestone sediment in the west. Regionally, the existence of the Early Cretaceous strata is important to the conditions of the underlying oil and gas storage.
2012, 30(5): 834-846.
Abstract:
The JiangyouGuangyuan area, which is located in the north margin of the Longmen Mountain Nappe Structural Belts, is one of the classic areas for the upper Carboniferous researches in Sichuan Basin and even in the upper Yangtze Plate. The upper Carboniferous was deposited in semienclosed gulfs of the western Yangtze Block, which characterized by slight thickness, light color, many fossils and several fuchsia mudstone and containing gravels bioclastic limestone as a set of semirestricted platform and open platform carbonate rocks in this area. The strata are revised according to sedimentary types, sedimentary structures, lithological characters, and paleontological combinations. The upper Zongchanggou Formation, which was considered as one part of the lower Carboniferous, is amended to the upper Carboniferous Huanglong Formation in this paper. The upper Carboniferous is divided into four parts, as lower Huanglong Formation, middle Huanglong Formation, upper Huanglong Formation and lower Chuanshan Formation.Fifteen microfacies can be divided according to field observation, laboratory microanalysis and classification of carbonate rocks by Dunham, as Unfossiliferous mudstones (MF11), Clastizoic mudstones (MF12), Calcareous green algae wackestones (MF21), Bioclastic wackestones (MF22), BirdseyesFenestral pelletoid packstones (MF3), Bivalve wackestones (MF41), Bivalve packstones (MF42), Calcareous green algae packstones (MF51), Fusulinid packstones (MF52), Bioclastic wackestones with oncoids (MF53), Bioclastic wackestones (MF54), Fine-grained peloid grainstones (MF6), Bioclastic grainstones (MF71), Fusulinid grainstones (MF72), Worn foraminiferal grainstones (MF73), Coated bioclastic grainstones (MF8), Bahamite peloids grainstones (MF91), BioclasticBahamite peloids grainstones (MF92), Ooid grainstones with radial ooids(MF101), Ooid grainstones with micritizatal concentric ooids (MF102), Lithoclasts grainstones with micrite ooids (MF11), BioclasticOncoid grainstones (MF121), Oncoid grainstones (MF122), Aggregategrain grainstones (MF13), Conglomerates grainstones (MF14), Crystal powder secondary dolomites (MF151) and Fine secondary dolomites (MF152). Based on these microfacies in the features of the vertical and horizontal combination , four sedimentary facies belts can be summarized according to the microfacies combination as winnowed platform edge sands (FZ6), open platforms (FZ7), restricted platforms (FZ8) and platform evaporates (FZ9). The combination characteristics of the depositional facies belts indicate that several transgression to regression occurred during the late Carboniferous and the maximum transgression occurred the late Huanglong Formation with Carbonate deposit in the northwest Sichuan and eastern Sichuan. 〖JP〗The studied special layer in JiangyouGuangyuan area have shown that four storm layers and storm sedimentary combinations are formed in the upper shelf environment as proximal storms rocks in Huanglong Formation, such as storm shell limestones, storm calcirudites, storm nodular limestones, storm calcarenites, scouring structures, graded beddings, knottylike structures, scale beddings, horizontal beddings, current beddings, bioturbate structures and so on.ICPMS is used to determine REE contents of oncolite carbonate rocks of the Chuanshan Formatiom in these area. The analyses of the REEs are related to their depositional environments, especially ΣREE, LREE, HREE, δCe, δEu and Y/Ho are displayed regularly. The LREE patterns are a little rightward heeling, and the HREE patterns are flat. δCe vary from 0.43 to 0.74, and the average of all samples is 0.59. They all have obviously negative δCe anomalies, as indicated strong Oxidation environments during the Chuanshan Stage. Some samples have negative δEu anomalies and some have positive δEu anomalies. As indicate that REE characteristics are affected by ancient climate cycles （glacialinterglacial cycle） and the periodical sea level changes in the Late Carboniferous.
The JiangyouGuangyuan area, which is located in the north margin of the Longmen Mountain Nappe Structural Belts, is one of the classic areas for the upper Carboniferous researches in Sichuan Basin and even in the upper Yangtze Plate. The upper Carboniferous was deposited in semienclosed gulfs of the western Yangtze Block, which characterized by slight thickness, light color, many fossils and several fuchsia mudstone and containing gravels bioclastic limestone as a set of semirestricted platform and open platform carbonate rocks in this area. The strata are revised according to sedimentary types, sedimentary structures, lithological characters, and paleontological combinations. The upper Zongchanggou Formation, which was considered as one part of the lower Carboniferous, is amended to the upper Carboniferous Huanglong Formation in this paper. The upper Carboniferous is divided into four parts, as lower Huanglong Formation, middle Huanglong Formation, upper Huanglong Formation and lower Chuanshan Formation.Fifteen microfacies can be divided according to field observation, laboratory microanalysis and classification of carbonate rocks by Dunham, as Unfossiliferous mudstones (MF11), Clastizoic mudstones (MF12), Calcareous green algae wackestones (MF21), Bioclastic wackestones (MF22), BirdseyesFenestral pelletoid packstones (MF3), Bivalve wackestones (MF41), Bivalve packstones (MF42), Calcareous green algae packstones (MF51), Fusulinid packstones (MF52), Bioclastic wackestones with oncoids (MF53), Bioclastic wackestones (MF54), Fine-grained peloid grainstones (MF6), Bioclastic grainstones (MF71), Fusulinid grainstones (MF72), Worn foraminiferal grainstones (MF73), Coated bioclastic grainstones (MF8), Bahamite peloids grainstones (MF91), BioclasticBahamite peloids grainstones (MF92), Ooid grainstones with radial ooids(MF101), Ooid grainstones with micritizatal concentric ooids (MF102), Lithoclasts grainstones with micrite ooids (MF11), BioclasticOncoid grainstones (MF121), Oncoid grainstones (MF122), Aggregategrain grainstones (MF13), Conglomerates grainstones (MF14), Crystal powder secondary dolomites (MF151) and Fine secondary dolomites (MF152). Based on these microfacies in the features of the vertical and horizontal combination , four sedimentary facies belts can be summarized according to the microfacies combination as winnowed platform edge sands (FZ6), open platforms (FZ7), restricted platforms (FZ8) and platform evaporates (FZ9). The combination characteristics of the depositional facies belts indicate that several transgression to regression occurred during the late Carboniferous and the maximum transgression occurred the late Huanglong Formation with Carbonate deposit in the northwest Sichuan and eastern Sichuan. 〖JP〗The studied special layer in JiangyouGuangyuan area have shown that four storm layers and storm sedimentary combinations are formed in the upper shelf environment as proximal storms rocks in Huanglong Formation, such as storm shell limestones, storm calcirudites, storm nodular limestones, storm calcarenites, scouring structures, graded beddings, knottylike structures, scale beddings, horizontal beddings, current beddings, bioturbate structures and so on.ICPMS is used to determine REE contents of oncolite carbonate rocks of the Chuanshan Formatiom in these area. The analyses of the REEs are related to their depositional environments, especially ΣREE, LREE, HREE, δCe, δEu and Y/Ho are displayed regularly. The LREE patterns are a little rightward heeling, and the HREE patterns are flat. δCe vary from 0.43 to 0.74, and the average of all samples is 0.59. They all have obviously negative δCe anomalies, as indicated strong Oxidation environments during the Chuanshan Stage. Some samples have negative δEu anomalies and some have positive δEu anomalies. As indicate that REE characteristics are affected by ancient climate cycles （glacialinterglacial cycle） and the periodical sea level changes in the Late Carboniferous.
2012, 30(5): 847-858.
Abstract:
The Strata of Qixia Formation is well developed in ChaohuNanling Area of Anhui Province, with constant thickness, high content of organic matter and the porosity. Previousy study of the carbonate Qixia Formation in this area is essentially qualitative. Therefore, quantitative microfacies analysis of the carbonate in Qixia Formation is significant to confirm the sedimentary facies, predict and explore the gas and oil. In Qixia Formation, the first member deposits in the middle carbonate slope, with the highest grain, opensea biota content and grain/matrix ratio, which are 35.65%, 0.43% and 0.70, respectively; The second member deposits in lower carbonate slope, with the lowest grain content, grain/matrix ratio, which are 24.69% and 0.38, and also highest opensea biota content, that is 0.43%; The third member deposits in open carbonate platform, with higher grain and the lowest opensea biota contents, which are 32.68% and 0.34%, respectively. The fourth member deposits in middleupper slope, with higer grain content and grain/matrix ratio, which are 29.91% and 0.52, respectively, and the content of opensea biota is 2.39%. This conclusion is consistent with the previous one, further supporting the previous research.
The Strata of Qixia Formation is well developed in ChaohuNanling Area of Anhui Province, with constant thickness, high content of organic matter and the porosity. Previousy study of the carbonate Qixia Formation in this area is essentially qualitative. Therefore, quantitative microfacies analysis of the carbonate in Qixia Formation is significant to confirm the sedimentary facies, predict and explore the gas and oil. In Qixia Formation, the first member deposits in the middle carbonate slope, with the highest grain, opensea biota content and grain/matrix ratio, which are 35.65%, 0.43% and 0.70, respectively; The second member deposits in lower carbonate slope, with the lowest grain content, grain/matrix ratio, which are 24.69% and 0.38, and also highest opensea biota content, that is 0.43%; The third member deposits in open carbonate platform, with higher grain and the lowest opensea biota contents, which are 32.68% and 0.34%, respectively. The fourth member deposits in middleupper slope, with higer grain content and grain/matrix ratio, which are 29.91% and 0.52, respectively, and the content of opensea biota is 2.39%. This conclusion is consistent with the previous one, further supporting the previous research.
2012, 30(5): 859-868.
Abstract:
In order to analyze the dolomite origin of Permian(Fengcheng Formation) in the northwest edge of Junggar basin. This article take the rockmineral analysis, thinsection analysis and geochemical analysis, and systematically analyzed this set of dolomite geochemistry characteristics and their origin. The research indicated that the dolomite mainly could divide into muddy dolostone, dolomitic tuff and dolomitic mudstones. The crystal size of dolomite greatly varies, mainly consisting of powder crystal, fine or micrite dolomites, which crystals are euhedral or subhedral. Dolomite fills in bedding or cracks or distribute in rocks with patterns of strip belts, laminated structure or gobbets. Dolomitization is not incompletely, residual calcite still be found in rocks. Dolostone commonly show ribbon, crumb, sausage or lens shapes in rocks, partly laminate and satellite. Sr content varies greatly between 95.9~783.6 μg/g with an average of 447 μg/g because of replenishment of freshwater and intense evaporation. Conclusion can be reached that sedimentary environment is mainly salt water with little amount of freshwater supplement and related to evaporative lake. V/Ni ratio varies greatly,and largely distribute in an range of 1.2~2.9. It refers to dolomitic rocks form in brackish lacustrine environment with complex setting and various salinity. Mn content is relatively low, varies between 133~985 μg/g with an average of 579 μg/g. From Mn data, we can conclude that aragonite forms in relatively deep water. In studying area, δ13C is low and distributes in an range of 1.6‰~5.2‰(PDB) with an average of 2.9‰(PDB).δ18O data still be low, and varies between 14.8‰~3.2 with average of 3.01 .The characteristics of petromineralogy and the data of geochemical analyzation in Fengcheng Formation show that the dolomite in this area mainly formed in a peaceful, deep and high salinity semiclosed bay environment. Permian periods climate is hot, speedy evaporation and frequent volcanic, besides, short of fresh water supply, those factors provide favourable source of magnesium ions and hydrodynamic condition to form dolomite. In this period, the bays deposit tuff or mudstones which are rich in aragonite or high magnesian calcite, during the early diagenesis ,the rocks convert to plenty of dolomitic tuff and dolomitic mudstones infiltration and circumfluence effect. In the middle and late diagenesis, compaction and mesothermal and micro thermal processes, in the study areas mainly consist of fine or medium dolomites, in which crystals are euhedral or subhedral.
In order to analyze the dolomite origin of Permian(Fengcheng Formation) in the northwest edge of Junggar basin. This article take the rockmineral analysis, thinsection analysis and geochemical analysis, and systematically analyzed this set of dolomite geochemistry characteristics and their origin. The research indicated that the dolomite mainly could divide into muddy dolostone, dolomitic tuff and dolomitic mudstones. The crystal size of dolomite greatly varies, mainly consisting of powder crystal, fine or micrite dolomites, which crystals are euhedral or subhedral. Dolomite fills in bedding or cracks or distribute in rocks with patterns of strip belts, laminated structure or gobbets. Dolomitization is not incompletely, residual calcite still be found in rocks. Dolostone commonly show ribbon, crumb, sausage or lens shapes in rocks, partly laminate and satellite. Sr content varies greatly between 95.9~783.6 μg/g with an average of 447 μg/g because of replenishment of freshwater and intense evaporation. Conclusion can be reached that sedimentary environment is mainly salt water with little amount of freshwater supplement and related to evaporative lake. V/Ni ratio varies greatly,and largely distribute in an range of 1.2~2.9. It refers to dolomitic rocks form in brackish lacustrine environment with complex setting and various salinity. Mn content is relatively low, varies between 133~985 μg/g with an average of 579 μg/g. From Mn data, we can conclude that aragonite forms in relatively deep water. In studying area, δ13C is low and distributes in an range of 1.6‰~5.2‰(PDB) with an average of 2.9‰(PDB).δ18O data still be low, and varies between 14.8‰~3.2 with average of 3.01 .The characteristics of petromineralogy and the data of geochemical analyzation in Fengcheng Formation show that the dolomite in this area mainly formed in a peaceful, deep and high salinity semiclosed bay environment. Permian periods climate is hot, speedy evaporation and frequent volcanic, besides, short of fresh water supply, those factors provide favourable source of magnesium ions and hydrodynamic condition to form dolomite. In this period, the bays deposit tuff or mudstones which are rich in aragonite or high magnesian calcite, during the early diagenesis ,the rocks convert to plenty of dolomitic tuff and dolomitic mudstones infiltration and circumfluence effect. In the middle and late diagenesis, compaction and mesothermal and micro thermal processes, in the study areas mainly consist of fine or medium dolomites, in which crystals are euhedral or subhedral.
2012, 30(5): 869-878.
Abstract:
The existing methods for establishing geological knowledge database include dense well pattern anatomy, outcrop anatomy, modern sedimentation anatomy, sedimentary simulation experiment, and so on. The advantages and disadvantages of these methods are firstly analyzed in this article. Then the method of building geological knowledge database by using the Google Earth software is proposed combined with the basic geological idea of "the present being a key to the past". Google Earth is a virtual globe, map and geographic information program that were created by Keyhole, Inc, a company acquired by Google in 2004. It maps the Earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS 3D globe. The steps and basic principals for measuring the meandering channel by Google Earth are introduced, and a series of fundamental data which consist of channel width, pointbar length and its arc length of different areas and different curvatures are measured. The data sheets are made based on the measurements. Furthermore, both the existing empirical formula and the formula obtained by fitting measurement data are analyzed integratedly. The database established by the Google Earth method proposed here is mainly composed of three parts basic measurement data sheets, the macro images and the empirical formulas. Each part has its functions: the basic data provide quantitative modeling data; the macro images provide development features of meandering rivers; while the empirical formulas provide directly available algorithm reference formulas. Case studies of typical meandering rivers in areas of South America and Hailar, and the point bars of lowcurvature meandering river of middle stream and downstream Pearl River are shown here. Results of the case studies demonstrated the feasibility of this method of using Google Earth to establish the geological knowledge database. Statistical analysis of the measured data shows that there are different positive correlations between channel width and point bar length of meandering rivers of different areas and different curvatures. According to the statistical data of meandering rivers in South America and Pearl River, and combined with previous studies, similar positive correlations between channel width and point bar length are found. Fitting correlation coefficient can reach as high as 0.92, indicating that the correlation between channel width and point bar length is universal. According to the fitting of all measured data, correlations under different curvatures are different. There are obvious correlation between channel width and point bar length of meandering rivers when their curvatures are above 1.7, with correlation coefficients higher than 0.85. While the curvature of the meandering river is between 1.4~1.7, the correlation coefficient is around 0.75, and declines when curvature is under 1.4. The result of our research shows that development of point bars is controlled by the curvature of the meandering river. As the curvature declines, the correlation between channel width and point bar length of meandering rivers weakens. The bigger curvature, the easier for large and typical point bars to develop. As we found that not all underground reservoirs are developed in large or typical point bars, we suggest geologists strengthen the study about meandering rivers with curvatures smaller than 1.7, so as to get better prediction of reservoirs, and achieve reservoir geological modeling. Different quantitative formulas are needed for correlations between channel width and point bar length of meandering rivers from different areas and different curvatures. This reflects the "differences in common" characteristic of geological models of meandering rivers. Borrowing ideas from the thought of "training image library" in multiplepoint geostatistics algorithms, we suggest that a meandering river model database should be included within a meandering river geological knowledge database, instead of establishing a single simple geological model. Only by this way, better comparison and prediction of underground reservoir modeling can be achieved. Restricted by data amount and dispersion of all data, correlation coefficients between channel width and point bar length of meandering rivers in South America area are mostly relatively low. The correlation coefficients of meandering rivers don't change very much as curvatures vary among 1.4~1.7 and below 1.4. So the laws of statistics are not only affected by the amount of data, but also influenced by the dispersion of the data. Because the lack of modern sedimentation study or depth measurement tools such as groundpenetrating radars, no empirical formulas of width/ depth ratio are given here. Actually, each method has got its limitations in application. Although the approach proposed in this article can provide good supplement in quantitative and macro holistic aspects of existing database establishing methods, with plenty of quantitative data of meandering channels from different regions and different curvatures, depicted observations of abandoned channels, detailed morphological classifications and numerical fitting of abandoned channels, and instructional prediction of unmeasured point bars, it has limitations of establishing three dimensional models. That is why we finally suggest that comprehensive study of a variety of methods to establish the geological knowledge base should be adopted in practical reservoir modeling.
The existing methods for establishing geological knowledge database include dense well pattern anatomy, outcrop anatomy, modern sedimentation anatomy, sedimentary simulation experiment, and so on. The advantages and disadvantages of these methods are firstly analyzed in this article. Then the method of building geological knowledge database by using the Google Earth software is proposed combined with the basic geological idea of "the present being a key to the past". Google Earth is a virtual globe, map and geographic information program that were created by Keyhole, Inc, a company acquired by Google in 2004. It maps the Earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS 3D globe. The steps and basic principals for measuring the meandering channel by Google Earth are introduced, and a series of fundamental data which consist of channel width, pointbar length and its arc length of different areas and different curvatures are measured. The data sheets are made based on the measurements. Furthermore, both the existing empirical formula and the formula obtained by fitting measurement data are analyzed integratedly. The database established by the Google Earth method proposed here is mainly composed of three parts basic measurement data sheets, the macro images and the empirical formulas. Each part has its functions: the basic data provide quantitative modeling data; the macro images provide development features of meandering rivers; while the empirical formulas provide directly available algorithm reference formulas. Case studies of typical meandering rivers in areas of South America and Hailar, and the point bars of lowcurvature meandering river of middle stream and downstream Pearl River are shown here. Results of the case studies demonstrated the feasibility of this method of using Google Earth to establish the geological knowledge database. Statistical analysis of the measured data shows that there are different positive correlations between channel width and point bar length of meandering rivers of different areas and different curvatures. According to the statistical data of meandering rivers in South America and Pearl River, and combined with previous studies, similar positive correlations between channel width and point bar length are found. Fitting correlation coefficient can reach as high as 0.92, indicating that the correlation between channel width and point bar length is universal. According to the fitting of all measured data, correlations under different curvatures are different. There are obvious correlation between channel width and point bar length of meandering rivers when their curvatures are above 1.7, with correlation coefficients higher than 0.85. While the curvature of the meandering river is between 1.4~1.7, the correlation coefficient is around 0.75, and declines when curvature is under 1.4. The result of our research shows that development of point bars is controlled by the curvature of the meandering river. As the curvature declines, the correlation between channel width and point bar length of meandering rivers weakens. The bigger curvature, the easier for large and typical point bars to develop. As we found that not all underground reservoirs are developed in large or typical point bars, we suggest geologists strengthen the study about meandering rivers with curvatures smaller than 1.7, so as to get better prediction of reservoirs, and achieve reservoir geological modeling. Different quantitative formulas are needed for correlations between channel width and point bar length of meandering rivers from different areas and different curvatures. This reflects the "differences in common" characteristic of geological models of meandering rivers. Borrowing ideas from the thought of "training image library" in multiplepoint geostatistics algorithms, we suggest that a meandering river model database should be included within a meandering river geological knowledge database, instead of establishing a single simple geological model. Only by this way, better comparison and prediction of underground reservoir modeling can be achieved. Restricted by data amount and dispersion of all data, correlation coefficients between channel width and point bar length of meandering rivers in South America area are mostly relatively low. The correlation coefficients of meandering rivers don't change very much as curvatures vary among 1.4~1.7 and below 1.4. So the laws of statistics are not only affected by the amount of data, but also influenced by the dispersion of the data. Because the lack of modern sedimentation study or depth measurement tools such as groundpenetrating radars, no empirical formulas of width/ depth ratio are given here. Actually, each method has got its limitations in application. Although the approach proposed in this article can provide good supplement in quantitative and macro holistic aspects of existing database establishing methods, with plenty of quantitative data of meandering channels from different regions and different curvatures, depicted observations of abandoned channels, detailed morphological classifications and numerical fitting of abandoned channels, and instructional prediction of unmeasured point bars, it has limitations of establishing three dimensional models. That is why we finally suggest that comprehensive study of a variety of methods to establish the geological knowledge base should be adopted in practical reservoir modeling.
2012, 30(5): 879-890.
Abstract:
Dawuzhuang oyster reef is the deeply studied one in the recent years while Konggang oyster reef is a new one on the northwest coast of Bohai Bay. Diatom analysis of the muddy sediments filling into the oyster shells, between the shells and in the overlying muddy layers all contained the Auliscus caelatus which indicated that the late development of the reef and the early stage of the overlying muddy layers are all belonging to the intertidal zone environment. However, the reefmud conversion was not the same in these two reefs. (1) The Auliscus caelatus in Dawuzhuang oyster reef decreased gradually from the top of the reef to the overlying muddy layers, which indicated an environment change from the middle to upper parts of intertidal zone, upper parts of intertidal zone to supratidal zone. (2) The Achnanches brevipes, indicating estuary environment, with the percentage of 6%~23% were found only in the overlying muddy layers of Konggang oyseter reef. It showed estuary influence in the muddy layers. The above differences revealed the reefmud conversion was not the same in the two reefs. The Dawuzhuang oyster reef grew up to the middle to upper parts of intertidal zone in the year 5 520 cal BP, and development stopped with the gradual disappearance of the marine influence. The Konggang oyster reef grew up to the intertidal zone in the year 4 000 cal BP and was suddenly buried by the muddy and sandy sediments which maybe from the Yellow River. Therefore, the "reefmud conversion" periods, which the oyster reefs stopped growing up and began overlaid by the mud layers, are 5 520 cal BP and 4 000 cal BP in Dawuzhuang and Tianjin Konggang, respectively. The seawater didn't quickly exit when the two reefs stop growing, and then 1.2m thick intertidal zone sediments and 2.9 thick lagoonintertidal zone sediments respectively deposited in the two locations. The author speculated that the seawater completely withdraw from the two reefs were later than 4 700 and 1 100 years ago. The altitudes of the maximum marine layers are -1.44 m in Dawuzhuang and 0m in Konggang profiles. It was speculated that the relative sea level were 2.95 m under the modern sea level in 4 700a ago and 1.5m under the modern sea level in 1 100a ago. This is due to the crust decline and compaction which indicated that the earlier of the regression, the lower position of the upper limit of the marine layer in the west Bohai Bay. The ancient Yellow River diverged and into the sea from Tianjin in 4 000 years ago. At the same time, the large number of the sediments into the sea and made the coastline constantly advanced seaward which lead to the subsequent oyster reefs developed seaward.
Dawuzhuang oyster reef is the deeply studied one in the recent years while Konggang oyster reef is a new one on the northwest coast of Bohai Bay. Diatom analysis of the muddy sediments filling into the oyster shells, between the shells and in the overlying muddy layers all contained the Auliscus caelatus which indicated that the late development of the reef and the early stage of the overlying muddy layers are all belonging to the intertidal zone environment. However, the reefmud conversion was not the same in these two reefs. (1) The Auliscus caelatus in Dawuzhuang oyster reef decreased gradually from the top of the reef to the overlying muddy layers, which indicated an environment change from the middle to upper parts of intertidal zone, upper parts of intertidal zone to supratidal zone. (2) The Achnanches brevipes, indicating estuary environment, with the percentage of 6%~23% were found only in the overlying muddy layers of Konggang oyseter reef. It showed estuary influence in the muddy layers. The above differences revealed the reefmud conversion was not the same in the two reefs. The Dawuzhuang oyster reef grew up to the middle to upper parts of intertidal zone in the year 5 520 cal BP, and development stopped with the gradual disappearance of the marine influence. The Konggang oyster reef grew up to the intertidal zone in the year 4 000 cal BP and was suddenly buried by the muddy and sandy sediments which maybe from the Yellow River. Therefore, the "reefmud conversion" periods, which the oyster reefs stopped growing up and began overlaid by the mud layers, are 5 520 cal BP and 4 000 cal BP in Dawuzhuang and Tianjin Konggang, respectively. The seawater didn't quickly exit when the two reefs stop growing, and then 1.2m thick intertidal zone sediments and 2.9 thick lagoonintertidal zone sediments respectively deposited in the two locations. The author speculated that the seawater completely withdraw from the two reefs were later than 4 700 and 1 100 years ago. The altitudes of the maximum marine layers are -1.44 m in Dawuzhuang and 0m in Konggang profiles. It was speculated that the relative sea level were 2.95 m under the modern sea level in 4 700a ago and 1.5m under the modern sea level in 1 100a ago. This is due to the crust decline and compaction which indicated that the earlier of the regression, the lower position of the upper limit of the marine layer in the west Bohai Bay. The ancient Yellow River diverged and into the sea from Tianjin in 4 000 years ago. At the same time, the large number of the sediments into the sea and made the coastline constantly advanced seaward which lead to the subsequent oyster reefs developed seaward.
2012, 30(5): 891-899.
Abstract:
The material basis of the coast includes water, rock, sediment and organisms. Biodetritus which come from organisms have certain effect on grain size of beach sediment. By adding excess acid and hydrogen peroxide in the beach surface sediment samples from the Gaolong Bay, Hainan Island, the difference of their grain size distribution with and without biodetritus was discussed, and the analysis was made with the height of the beach. It can be seen from the results that (1) Biodetritus content on beach is mainly determined by marine dynamic, and the biodetritus which have coarse sizes and large mass is brought to the beach by waves during high tidal period. (2) The distribution of biodetritus in the beach sediment is influenced by landform and main wave direction, biodetritus produced by beach breeding as well as coral reefs flat offcoast. (3) Biodetritus content in the beach sediment changes with the seasons. The biodetritus supplied by sea water would be reduced and further decomposed from winter to spring, which makes biodetritus content decrease in the north area, but the stable supply of coral debris and strong wave dynamics in spring increase the biodetritus content in the south area of the beach. (4) Coarse particles in surface beach sediment in Gaolong Bay contain more biodetritus than that fine particles contain. Grain size of biodetritus is mostly 1~2, namely coarse sand to gravel. The more biodetritus sediment contains the larger changer grain size parameters have.
The material basis of the coast includes water, rock, sediment and organisms. Biodetritus which come from organisms have certain effect on grain size of beach sediment. By adding excess acid and hydrogen peroxide in the beach surface sediment samples from the Gaolong Bay, Hainan Island, the difference of their grain size distribution with and without biodetritus was discussed, and the analysis was made with the height of the beach. It can be seen from the results that (1) Biodetritus content on beach is mainly determined by marine dynamic, and the biodetritus which have coarse sizes and large mass is brought to the beach by waves during high tidal period. (2) The distribution of biodetritus in the beach sediment is influenced by landform and main wave direction, biodetritus produced by beach breeding as well as coral reefs flat offcoast. (3) Biodetritus content in the beach sediment changes with the seasons. The biodetritus supplied by sea water would be reduced and further decomposed from winter to spring, which makes biodetritus content decrease in the north area, but the stable supply of coral debris and strong wave dynamics in spring increase the biodetritus content in the south area of the beach. (4) Coarse particles in surface beach sediment in Gaolong Bay contain more biodetritus than that fine particles contain. Grain size of biodetritus is mostly 1~2, namely coarse sand to gravel. The more biodetritus sediment contains the larger changer grain size parameters have.
2012, 30(5): 900-908.
Abstract:
Through widespread field survey along the Jinghe River valley, a Holocene loesssoil profile with interbedded flood slackwater deposits (SWD) was found at the YGZ site at the riverbank near the Yangguanzhai village. Samples were collected systematically and the chemical elements, grainsize distribution and magnetic susceptibility were measured in the laboratory. All of these indexes showed that there are two bedsets of palaeoflood slackwater deposits in the profile. They have recorded the extraordinary palaeoflood events occurred during 4200－4000aB.P. and 3200－2800aB.P., respectively. The comparative study of the geochemical difference between palaeoflood slackwater deposits and the eolian loess and soil showed that: (1) The concentrations of major elements Fe2O3, Al2O3. K2O, MgO are higher in the palaeosol (S0) and lower in the loess (L1, Lt, L0). The abundances of elements CaO and Na2O showed a reversed change, indicating that these elements were affected by weathering and pedogenesis along with the Holocene climatic change. The abundances of trace elements including Zr, Hf, Ti, Cr, Y and they are very stable and close to the averages in the Earth's crust. This is because these trace elements are connected with the coarse fraction and heavy minerals. They have stable chemical properties and are not much affected by weathering and pedogenesis. (2) In a single palaeoflood slackwater deposit (SWD) bed, the sorted deposition in floodwater resulted in a concentration of the coarse fraction and heavy minerals at the bottom of the SWD bed. Thus, Zr, Hf, Ti, Cr, Y and other trace elements show a prominent peak. However, the increased abundance of clay minerals resulted in an increase in the major elements including Fe2O3, Al2O3, K2O, MgO in the top of a SWD bed. This change is well consistent with the change of sandsized particles and magnetic susceptibility in a SWD bed. These physicochemical features are very useful in identifying palaeoflood slackwater deposits in the eolian sediment profiles. These findings are of great importance in palaeoflood hydrology.
Through widespread field survey along the Jinghe River valley, a Holocene loesssoil profile with interbedded flood slackwater deposits (SWD) was found at the YGZ site at the riverbank near the Yangguanzhai village. Samples were collected systematically and the chemical elements, grainsize distribution and magnetic susceptibility were measured in the laboratory. All of these indexes showed that there are two bedsets of palaeoflood slackwater deposits in the profile. They have recorded the extraordinary palaeoflood events occurred during 4200－4000aB.P. and 3200－2800aB.P., respectively. The comparative study of the geochemical difference between palaeoflood slackwater deposits and the eolian loess and soil showed that: (1) The concentrations of major elements Fe2O3, Al2O3. K2O, MgO are higher in the palaeosol (S0) and lower in the loess (L1, Lt, L0). The abundances of elements CaO and Na2O showed a reversed change, indicating that these elements were affected by weathering and pedogenesis along with the Holocene climatic change. The abundances of trace elements including Zr, Hf, Ti, Cr, Y and they are very stable and close to the averages in the Earth's crust. This is because these trace elements are connected with the coarse fraction and heavy minerals. They have stable chemical properties and are not much affected by weathering and pedogenesis. (2) In a single palaeoflood slackwater deposit (SWD) bed, the sorted deposition in floodwater resulted in a concentration of the coarse fraction and heavy minerals at the bottom of the SWD bed. Thus, Zr, Hf, Ti, Cr, Y and other trace elements show a prominent peak. However, the increased abundance of clay minerals resulted in an increase in the major elements including Fe2O3, Al2O3, K2O, MgO in the top of a SWD bed. This change is well consistent with the change of sandsized particles and magnetic susceptibility in a SWD bed. These physicochemical features are very useful in identifying palaeoflood slackwater deposits in the eolian sediment profiles. These findings are of great importance in palaeoflood hydrology.
2012, 30(5): 909-918.
Abstract:
Base on the study of the bauxite and Sc of Shenjiping mine in southern Chongqing,The A12O3 was found distribut mainly in the middleupper and middle place,the main type of bauxite are argillaceous, pisolitic, ruditel and tight.The Sc was found distribut mainly in the middleunder and under place, the main type of bauxite are claystone and bauxite. The average of correlation coefficient r =-0.62 between Sc and A12O3,it is a moderate negative correlation.The average of correlation coefficient r =-0.44 between Sc and A/S, it is a low negative correlation. The REE distribution patterns suggest that the bauxite of Shenjiping mine has some characteristics as follows: enriched LREE, Ce positive anomalies and Eu negative anomalies.The dependence relation between Sc and ΣREE of each drill hole is remarkable, and the average is a low degree of positive correlation. Bauxite and Sc may come from the aluminosilicate rocks, The migration, enrichment and evolution of bauxite and Sc have been confinemented by the environment of sedimentation, likely there are two types of Sc in bauxite: one is isomorph,the other is ion adsorption.
Base on the study of the bauxite and Sc of Shenjiping mine in southern Chongqing,The A12O3 was found distribut mainly in the middleupper and middle place,the main type of bauxite are argillaceous, pisolitic, ruditel and tight.The Sc was found distribut mainly in the middleunder and under place, the main type of bauxite are claystone and bauxite. The average of correlation coefficient r =-0.62 between Sc and A12O3,it is a moderate negative correlation.The average of correlation coefficient r =-0.44 between Sc and A/S, it is a low negative correlation. The REE distribution patterns suggest that the bauxite of Shenjiping mine has some characteristics as follows: enriched LREE, Ce positive anomalies and Eu negative anomalies.The dependence relation between Sc and ΣREE of each drill hole is remarkable, and the average is a low degree of positive correlation. Bauxite and Sc may come from the aluminosilicate rocks, The migration, enrichment and evolution of bauxite and Sc have been confinemented by the environment of sedimentation, likely there are two types of Sc in bauxite: one is isomorph,the other is ion adsorption.
2012, 30(5): 919-927.
Abstract:
We have carried out an rock magnetism investigation and thermal demagnetization for the Late Cretaceous to Early Miocene sediments on Kuzigongsu section from the Northwestern Tarim basin, Western China. The results indicate that thermal demagnetization and rock magnetic characteristics of rocks can be divided into three types specifically. Rocks from sublittoral zone, shallow of platform edge are dominated by the pseudosingle domain (PSD) magnetite with a little amount of goethite and maghematite. Its natural remanence intensity is smaller than 1×10-2A/m generally, and the characteristic remanent magnetism (ChRM) are carried by magnetite and can be isolated from 250℃~500℃. Rocks from intertidal zone and supratidal zone are dominated by pseudosingle domain and multidomain(PSD﹢MD) magnetite generally, with a little amount of goethite,maghematite and hematite. It’s natural remanence intensity is between 1×10-2~1A/m,and the characteristic remanent magnetism (ChRM) are carried by magnetite and can be isolated from 250℃~580℃.Rocks from the fluvial and lacustrine facies are dominated by the pseudosingle domain(PSD) magnetite, the hematite, with a little amount of maghemite, the goethite, Its natural remanence intensity is greater than 1 101A/m generally, and the characteristic remanent magnetism (ChRM) are carried by hematite in most samples,and carried by magnetite and hematite in some samples. So investigation of rock magnetism on sediments from different sedimentary environments is important for the paloemagnetic research.
We have carried out an rock magnetism investigation and thermal demagnetization for the Late Cretaceous to Early Miocene sediments on Kuzigongsu section from the Northwestern Tarim basin, Western China. The results indicate that thermal demagnetization and rock magnetic characteristics of rocks can be divided into three types specifically. Rocks from sublittoral zone, shallow of platform edge are dominated by the pseudosingle domain (PSD) magnetite with a little amount of goethite and maghematite. Its natural remanence intensity is smaller than 1×10-2A/m generally, and the characteristic remanent magnetism (ChRM) are carried by magnetite and can be isolated from 250℃~500℃. Rocks from intertidal zone and supratidal zone are dominated by pseudosingle domain and multidomain(PSD﹢MD) magnetite generally, with a little amount of goethite,maghematite and hematite. It’s natural remanence intensity is between 1×10-2~1A/m,and the characteristic remanent magnetism (ChRM) are carried by magnetite and can be isolated from 250℃~580℃.Rocks from the fluvial and lacustrine facies are dominated by the pseudosingle domain(PSD) magnetite, the hematite, with a little amount of maghemite, the goethite, Its natural remanence intensity is greater than 1 101A/m generally, and the characteristic remanent magnetism (ChRM) are carried by hematite in most samples,and carried by magnetite and hematite in some samples. So investigation of rock magnetism on sediments from different sedimentary environments is important for the paloemagnetic research.
2012, 30(5): 928-936.
Abstract:
By studying on correlation between magnetic susceptibility,TOC,CaCO3,Fe2O3 and grainsize component of 73 samples from the paleosandpaleosol sedimentary section of Xinjiang Takermohuer desert,according to OSL date,we discussed mechanism of magnetic susceptibility change and paleoclimate significance.The results were that:The correlation between χlf and percent content of 16~250 μm component was positive,coarse component percent content affected the change of χlf.In the section, χlf of paleosand is higher than χlf of paleosol,this characteristic is opposite to magnetic susceptibility of monsoon desert sediment in China.According to magnetic susceptibility and other paleoclimate indexes of section sediment,we divided 5 paleoclimate stages of study area from 3.71 ka BP:3.71~3.06 kaBP,the climate was cool and wet,from 3.06 kaBP to 2.78 kaBP was cold and dry,2.78~2.10 kaBP was cool wet,2.10~0.50 kaBP was cold and wet,0.50 kaBP to now was warm and dry.Climate change of research area is simliar to the other regiones during late holocene,and it was related to the temperature change events of surface seawater in north Alantic Ocean.The climate change was typical westerly climate model,warmdry or coolwet.
By studying on correlation between magnetic susceptibility,TOC,CaCO3,Fe2O3 and grainsize component of 73 samples from the paleosandpaleosol sedimentary section of Xinjiang Takermohuer desert,according to OSL date,we discussed mechanism of magnetic susceptibility change and paleoclimate significance.The results were that:The correlation between χlf and percent content of 16~250 μm component was positive,coarse component percent content affected the change of χlf.In the section, χlf of paleosand is higher than χlf of paleosol,this characteristic is opposite to magnetic susceptibility of monsoon desert sediment in China.According to magnetic susceptibility and other paleoclimate indexes of section sediment,we divided 5 paleoclimate stages of study area from 3.71 ka BP:3.71~3.06 kaBP,the climate was cool and wet,from 3.06 kaBP to 2.78 kaBP was cold and dry,2.78~2.10 kaBP was cool wet,2.10~0.50 kaBP was cold and wet,0.50 kaBP to now was warm and dry.Climate change of research area is simliar to the other regiones during late holocene,and it was related to the temperature change events of surface seawater in north Alantic Ocean.The climate change was typical westerly climate model,warmdry or coolwet.
2012, 30(5): 937-944.
Abstract:
Choosing two parabolic dunes with different morphology on the Southern Fringe of Hobq Desert, we conducted sampling analysis on surface sediments both 05cm and 5~10 cm collected along typical transects. The results showed that grain size parameters and their distribution on parabolic dune were affected by dune morphology, vegetation cover, dune developmental stage, as well as their distance from the sand source. The parabolic dunes were characterized by concave stoss slope and convex lee slope, and dune apex was in a subenvironment which was eroded all the time. In the windward transects, particle size gradually became coarser from stoss slope toe to dune crest, and then became finer until lee slope toe. The higher the dune is, the more obvious the grain size varies with dune morphology. Sorting was moderate and good in the windward slope, poor on the dune top, and then became moderate and good until lee slope toe. Frequency curve of particle size was symmetrically unimodal except that dune apex was positively skewed and bimodal as well as stoss slope toe was positively skewed. In the two wings' transect normal to wind direction, average grain diameter became finer from wing apex to bilateral slope in the mature dune, whereas no significant trends in the less mature dune. Compared with the body and two wings of parabolic dunes, the vegetation belt between arms received finer or more silty sand subsided by suspension, whereas sorting was poor for being mixed up with gravels. The frequency curve was bimodal and positively skewed. The grain size pattern on the less developed parabolic dune was more easily redistributed than the dune with a longer period development, which leads to differences in grain size parameters between 05cm and 510cm on the less mature dune.
Choosing two parabolic dunes with different morphology on the Southern Fringe of Hobq Desert, we conducted sampling analysis on surface sediments both 05cm and 5~10 cm collected along typical transects. The results showed that grain size parameters and their distribution on parabolic dune were affected by dune morphology, vegetation cover, dune developmental stage, as well as their distance from the sand source. The parabolic dunes were characterized by concave stoss slope and convex lee slope, and dune apex was in a subenvironment which was eroded all the time. In the windward transects, particle size gradually became coarser from stoss slope toe to dune crest, and then became finer until lee slope toe. The higher the dune is, the more obvious the grain size varies with dune morphology. Sorting was moderate and good in the windward slope, poor on the dune top, and then became moderate and good until lee slope toe. Frequency curve of particle size was symmetrically unimodal except that dune apex was positively skewed and bimodal as well as stoss slope toe was positively skewed. In the two wings' transect normal to wind direction, average grain diameter became finer from wing apex to bilateral slope in the mature dune, whereas no significant trends in the less mature dune. Compared with the body and two wings of parabolic dunes, the vegetation belt between arms received finer or more silty sand subsided by suspension, whereas sorting was poor for being mixed up with gravels. The frequency curve was bimodal and positively skewed. The grain size pattern on the less developed parabolic dune was more easily redistributed than the dune with a longer period development, which leads to differences in grain size parameters between 05cm and 510cm on the less mature dune.
2012, 30(5): 945-954.
Abstract:
Grainsize analysis of a sediment core CW02 and surface sediments of the drainage area, retrieved from Chaiwopu Lake of Xinjiang, were carried out using a Malvern 2 000 grainsize analyzer. Combining with 137Cs dating, a continuous highresolution record of environmental changes was studied over the past 150 years. Firstly, according to primary components analysis of the contents of different grainsize, the material source of lake sediment was discussed. It showed that the large particle fraction of lake sediment was from the drainage surface sediment. And then, environmentally sensitive grainsize components were extracted by the variations of the grainsize standard deviation. The results indicated that the content/meansize of sensitive grainsize component (20~209 μm) is sensitive to the regional sanddust storm events in Chaiwopu lake basin. During the last 150 years, the strong sanddust storm occurred during 1910—1930AD and 1980—2000AD. Historical documents also recorded the strong dust storms around 1910s and 1980s. Based on the analysis of the abrupt change points, the sediment grainsize increased abruptly around 1910AD, which indicated an abrupt environmental event.
Grainsize analysis of a sediment core CW02 and surface sediments of the drainage area, retrieved from Chaiwopu Lake of Xinjiang, were carried out using a Malvern 2 000 grainsize analyzer. Combining with 137Cs dating, a continuous highresolution record of environmental changes was studied over the past 150 years. Firstly, according to primary components analysis of the contents of different grainsize, the material source of lake sediment was discussed. It showed that the large particle fraction of lake sediment was from the drainage surface sediment. And then, environmentally sensitive grainsize components were extracted by the variations of the grainsize standard deviation. The results indicated that the content/meansize of sensitive grainsize component (20~209 μm) is sensitive to the regional sanddust storm events in Chaiwopu lake basin. During the last 150 years, the strong sanddust storm occurred during 1910—1930AD and 1980—2000AD. Historical documents also recorded the strong dust storms around 1910s and 1980s. Based on the analysis of the abrupt change points, the sediment grainsize increased abruptly around 1910AD, which indicated an abrupt environmental event.
2012, 30(5): 955-963.
Abstract:
Hydrocarbon generation was occurred in the pore space of source rock under high hydrostatic pressure and high fluid pressure. However, due to the limited experimental device and conditions, most of the generation and expulsion simulation experiment were carried out in a lowpressure and relatively large reaction space, quite different with the actual geological conditions. Through the same source rock, the authors have simulated hydrocarbon generation in finite spaces and conventional autoclave method. It can be seen: (1) the gaseous products of the simulation in finite spaces are closer to geological reality. Gas component in possession of a greater proportion of hydrocarbon gas; heavy hydrocarbon gas lower than conventional analog preservation, delayed the reconversion of hydrocarbon gas to methane; olefin content less than the conventional simulated conditions, basically undetectable. (2) The limited space constraints in the water medium into the enhanced role of hydrocarbons, and its limited space, high fluid pressure delayed the conversion of oil to the process of hydrocarbon gas, liquid oil is conducive to the formation and preservation. (3) Limited space, highpressure liquid medium under conditions conducive to the discharge of hydrocarbons.
Hydrocarbon generation was occurred in the pore space of source rock under high hydrostatic pressure and high fluid pressure. However, due to the limited experimental device and conditions, most of the generation and expulsion simulation experiment were carried out in a lowpressure and relatively large reaction space, quite different with the actual geological conditions. Through the same source rock, the authors have simulated hydrocarbon generation in finite spaces and conventional autoclave method. It can be seen: (1) the gaseous products of the simulation in finite spaces are closer to geological reality. Gas component in possession of a greater proportion of hydrocarbon gas; heavy hydrocarbon gas lower than conventional analog preservation, delayed the reconversion of hydrocarbon gas to methane; olefin content less than the conventional simulated conditions, basically undetectable. (2) The limited space constraints in the water medium into the enhanced role of hydrocarbons, and its limited space, high fluid pressure delayed the conversion of oil to the process of hydrocarbon gas, liquid oil is conducive to the formation and preservation. (3) Limited space, highpressure liquid medium under conditions conducive to the discharge of hydrocarbons.
2012, 30(5): 964-974.
Abstract:
:Ordos Basin is the typical inland depression lake basin of Mesozoic. Yanchang Formation of Upper Triassic and Yan'an Formation of Jurassic are the main oilbearing strata. Chang 7 high quality source rocks are the principal source rocks of Mesozoic oil reservoir, abnormal high pressure is the principal migration force of Mesozoic low permeability reservoir, porosity sandstone and fracture system are the main migration pathway of mesozoic hydrocarbon, the effective combination of several carrier system and abnormal high pressure controlled the reservoir distribution. By using the methods of the diagenetic fluid inclusion of reservoirs, authigenic illite dating and bitumen with different periods, analysis of the petroleum accumulation period, considered that the formation of Mesozoic oil reservoir is oil migration and accumulation. The accumulation poriod can be divided into early stage, middle stage and late stage, respectively corresponded to early period, middle period and late period of early cretaceous, The main accumulation stage is the middle stage of accumulation poriod in middle period of early Cretaceous. The formation rule for low permeability lithologic reservoir of Mesozoic in Ordos Basin has been summrized. Under the effect of abnormal high pressure which was generated by low compaction and hydrocarbongenerating pressurization of Chang 7 source rocks, hydrocarbon migrated up and down by overlying high permeability sandstone, formed largescale lithologic reservoir in Chang 4+5, Chang 6 and Chang 8, and by the passage system of micro fracture and anterior Jurassic paleoriver sand, formed structural lithologic reservoir in Chang 2 and Jurassic reservoir.
:Ordos Basin is the typical inland depression lake basin of Mesozoic. Yanchang Formation of Upper Triassic and Yan'an Formation of Jurassic are the main oilbearing strata. Chang 7 high quality source rocks are the principal source rocks of Mesozoic oil reservoir, abnormal high pressure is the principal migration force of Mesozoic low permeability reservoir, porosity sandstone and fracture system are the main migration pathway of mesozoic hydrocarbon, the effective combination of several carrier system and abnormal high pressure controlled the reservoir distribution. By using the methods of the diagenetic fluid inclusion of reservoirs, authigenic illite dating and bitumen with different periods, analysis of the petroleum accumulation period, considered that the formation of Mesozoic oil reservoir is oil migration and accumulation. The accumulation poriod can be divided into early stage, middle stage and late stage, respectively corresponded to early period, middle period and late period of early cretaceous, The main accumulation stage is the middle stage of accumulation poriod in middle period of early Cretaceous. The formation rule for low permeability lithologic reservoir of Mesozoic in Ordos Basin has been summrized. Under the effect of abnormal high pressure which was generated by low compaction and hydrocarbongenerating pressurization of Chang 7 source rocks, hydrocarbon migrated up and down by overlying high permeability sandstone, formed largescale lithologic reservoir in Chang 4+5, Chang 6 and Chang 8, and by the passage system of micro fracture and anterior Jurassic paleoriver sand, formed structural lithologic reservoir in Chang 2 and Jurassic reservoir.
2012, 30(5): 975-982.
Abstract:
Upper Permian Lucaogou Formation of Santanghu Basin with a wide distribution, large thickness, high organic carbon content, and good hydrocarbon potential, was the main source rocks in the basin. Soluble organic matter from rock samples contains rich carbonyl compounds such as fatty acids, fatty acid esters, etc. Saturated hydrocarbons and aromatics content increasing along with the depth increase, but nonhydrocarbon content and organic carbon decreasing, showed these carbonyl compounds in the source rocks have made a greater contribution to hydrocarbon generation. The indicators of saturated hydrocarbon showed that the depositional environment of source rocks was the salinity lake, reduction conditions. The input of the parent material dominated by aquatic organisms, terrestrial input less. A lot of evidence indicated that bacteria entered the organic matter deposition during the early diagenesis stages and formed part of the original organic matter; bacteria transformed the original organic matter and produced the aforementioned carbonyl compounds, hydrocarbons could be generated in the thermal effect and affection of microorganisms.
Upper Permian Lucaogou Formation of Santanghu Basin with a wide distribution, large thickness, high organic carbon content, and good hydrocarbon potential, was the main source rocks in the basin. Soluble organic matter from rock samples contains rich carbonyl compounds such as fatty acids, fatty acid esters, etc. Saturated hydrocarbons and aromatics content increasing along with the depth increase, but nonhydrocarbon content and organic carbon decreasing, showed these carbonyl compounds in the source rocks have made a greater contribution to hydrocarbon generation. The indicators of saturated hydrocarbon showed that the depositional environment of source rocks was the salinity lake, reduction conditions. The input of the parent material dominated by aquatic organisms, terrestrial input less. A lot of evidence indicated that bacteria entered the organic matter deposition during the early diagenesis stages and formed part of the original organic matter; bacteria transformed the original organic matter and produced the aforementioned carbonyl compounds, hydrocarbons could be generated in the thermal effect and affection of microorganisms.
2012, 30(5): 983-990.
Abstract:
Using GC/C/MS online carbon isotope analysis technique, we obtained the carbon and hydrogen isotopic composition of individual nalkanes for crude oil from different tectonic belts of the north margin of Qaidam Basin. The carbon and hydrogen isotopic composition of nalkanes for crude oil samples can be used to analyze genetic type of crude oil and oilsource correlation. The analytical results indicate that the δ13C and δD values of nalkanes in soluble organic matter ranging between 36‰～25‰ and 180‰～110‰, respectively. Through comparing, it is found that there exist significant differences between the carbon and hydrogen isotopic composition of nalkanes for crude oil from different tectonic belts. By the combination of δ13Cnalkanes (30‰), δDnalkanes (140‰), and distribution pattern isotopic curve, the carbon and hydrogen isotopic composition can be divided into different distribution patterns. Using these patterns can discriminate hydrocarbon generation material and sedimentary environment.
Using GC/C/MS online carbon isotope analysis technique, we obtained the carbon and hydrogen isotopic composition of individual nalkanes for crude oil from different tectonic belts of the north margin of Qaidam Basin. The carbon and hydrogen isotopic composition of nalkanes for crude oil samples can be used to analyze genetic type of crude oil and oilsource correlation. The analytical results indicate that the δ13C and δD values of nalkanes in soluble organic matter ranging between 36‰～25‰ and 180‰～110‰, respectively. Through comparing, it is found that there exist significant differences between the carbon and hydrogen isotopic composition of nalkanes for crude oil from different tectonic belts. By the combination of δ13Cnalkanes (30‰), δDnalkanes (140‰), and distribution pattern isotopic curve, the carbon and hydrogen isotopic composition can be divided into different distribution patterns. Using these patterns can discriminate hydrocarbon generation material and sedimentary environment.
