2009 Vol. 27, No. 6
Display Method:
2009, 27(6): 1027-1032.
Abstract:
Based on observation of core of the Middle and Lower Ordovician carbonate in Wells S85 and S79, a wide rangegeochemical methods has been used to characterize the diagenetic settings of paleocaves and fractures filling & vugs calcites and to decipher their origin, which includes Xray diffraction of crystal cell, carbon and oxygen isotope composition, fluid inclusion, hydrogen isotope of fluid inclusion and chemical elements analysis. Two diagenetic environments are defined and believed to be prevailing in the formation of paleocaves and fractures filling & vugs calcites. the first is diagenetic environment with prevailing hypergen fresh water, mostly related to phreatic zones in subaerial process and of characteristic of crystal cells c=17.057~17.062 and Fe2O3＝0.06%~0.07%，Sr=53.3×106~96.2×106,Ba=19×106~28×106，Mg/Ca(×103)＝1.94~5.14，Sr/Ba＝2.12~5.24 , the lowest values of δ18OPDB (15‰~17‰) , the considerable lower values of δ13C PDB (4‰~2‰) for calcites, without or with few hydrocarbon inclusions and δD PDB＝94.99~109.54‰ of its fluid inclusion; the second is believed to occur in freshwaterseawater mixing and formed during some degree of burial environment, and of features of crystal cell parameters (c)=17.064~17.065(exceptional for 17.212),the considerable high values Fe2O3＝0.06%~0.18%，Sr=111×106~208×106、Ba=215×106~479×106，the considerable lower ratios Mg/Ca(×103)＝1.53~1.76，Sr/Ba＝0.49~0.58 for calcites, the lower values of δ18OPDB (9.6‰~13.7‰)for calcites, the considerable higher δD PDB＝77.5‰~88.2‰ of fluid inclusion. In addition, the study also demonstrated that differential hydrogeochemical systems had been developed in the formation of the gigantic speleothem calcite crystal at the 5 960～5 966 m depth of burial with more than 6 m in height palaeocave in Well S85 in Tahe oil field.
Based on observation of core of the Middle and Lower Ordovician carbonate in Wells S85 and S79, a wide rangegeochemical methods has been used to characterize the diagenetic settings of paleocaves and fractures filling & vugs calcites and to decipher their origin, which includes Xray diffraction of crystal cell, carbon and oxygen isotope composition, fluid inclusion, hydrogen isotope of fluid inclusion and chemical elements analysis. Two diagenetic environments are defined and believed to be prevailing in the formation of paleocaves and fractures filling & vugs calcites. the first is diagenetic environment with prevailing hypergen fresh water, mostly related to phreatic zones in subaerial process and of characteristic of crystal cells c=17.057~17.062 and Fe2O3＝0.06%~0.07%，Sr=53.3×106~96.2×106,Ba=19×106~28×106，Mg/Ca(×103)＝1.94~5.14，Sr/Ba＝2.12~5.24 , the lowest values of δ18OPDB (15‰~17‰) , the considerable lower values of δ13C PDB (4‰~2‰) for calcites, without or with few hydrocarbon inclusions and δD PDB＝94.99~109.54‰ of its fluid inclusion; the second is believed to occur in freshwaterseawater mixing and formed during some degree of burial environment, and of features of crystal cell parameters (c)=17.064~17.065(exceptional for 17.212),the considerable high values Fe2O3＝0.06%~0.18%，Sr=111×106~208×106、Ba=215×106~479×106，the considerable lower ratios Mg/Ca(×103)＝1.53~1.76，Sr/Ba＝0.49~0.58 for calcites, the lower values of δ18OPDB (9.6‰~13.7‰)for calcites, the considerable higher δD PDB＝77.5‰~88.2‰ of fluid inclusion. In addition, the study also demonstrated that differential hydrogeochemical systems had been developed in the formation of the gigantic speleothem calcite crystal at the 5 960～5 966 m depth of burial with more than 6 m in height palaeocave in Well S85 in Tahe oil field.
2009, 27(6): 1043-1049.
Abstract:
The lower Triassic Feixianguan Formation is a shallow marine carbonate sequence with shale and evaporates. The edge of carbonate platform commonly developed some oolitic banks, which are dolomitized. The oolitic bank dolomites are the most important gas reservoir in Sichuan. Some researchers considered them as the origin of marinefresh water mixing model. However, petrography and chemistry of dolomite are not in consistence with origin of marinefresh water mixing dolomitization. Feixianguan oolitic dolomites included dullred cathodoluminescence, trace elements of 14×10-6~78×10-6 for Mn and 600×10-6~1 000×10-6 for Fe, stable isotopic oxygen composition of 6.73‰ ~ 3.65‰(PDB), the average is 4.89‰（PDB）, for matrix and vugfilling saddle dolomite and bright dolomite cement, stable isotopic strontium composition of 0.707 35 ~ 0.708 00 for 87Sr/86Sr. Dolomite replaced host rock along the fractures in section. These data about oolitic bank dolomite suggest that the dolomitization was formed in the buried condition.
The lower Triassic Feixianguan Formation is a shallow marine carbonate sequence with shale and evaporates. The edge of carbonate platform commonly developed some oolitic banks, which are dolomitized. The oolitic bank dolomites are the most important gas reservoir in Sichuan. Some researchers considered them as the origin of marinefresh water mixing model. However, petrography and chemistry of dolomite are not in consistence with origin of marinefresh water mixing dolomitization. Feixianguan oolitic dolomites included dullred cathodoluminescence, trace elements of 14×10-6~78×10-6 for Mn and 600×10-6~1 000×10-6 for Fe, stable isotopic oxygen composition of 6.73‰ ~ 3.65‰(PDB), the average is 4.89‰（PDB）, for matrix and vugfilling saddle dolomite and bright dolomite cement, stable isotopic strontium composition of 0.707 35 ~ 0.708 00 for 87Sr/86Sr. Dolomite replaced host rock along the fractures in section. These data about oolitic bank dolomite suggest that the dolomitization was formed in the buried condition.
2009, 27(6): 1057-1067.
Abstract:
Jiyuan area is in the middle of the western Ordos Basin and its sedimentary facies is controlled by provenance from northeast, northwest and south directions in Late Triassic epoch. Detailed studies have been made on the rock types, sedimentary structures, and direction of provenance, paleontology and sedimentary facies characteristics of Chang8 subsection of Yanchang Formation of Upper Triassic of Jiyuan area by an integrated analysis of cores, thin sections, well log and other data. During the deposition of the Chang8 subsection of Yanchang Formation, the topography was gentle and stream actions were weak and the depositional system of shallowwater delta facies was developed. The sedimentation and sandbodies distribution were controlled by the raise and fall of the lake level and the direction of provenance obviously which were significant for hydrocarbon accumulation. It can be summarized as follows: ①The shoreline moved to provenance directions quickly and stripshaped or birdfootshaped subaqueous distributary channel sandbodies developed in the periods of high water levels; ②The delta plain developed and the front sandbodies came from different provenance converged in the center of the study area in the periods of low water levels; ③The sandbodies deposited in the periods of high water levels were favorable to develop lithologic reservoirs than those deposited in low water levels because the former distributed as sheetshaped which formed lithologic barriers.
Jiyuan area is in the middle of the western Ordos Basin and its sedimentary facies is controlled by provenance from northeast, northwest and south directions in Late Triassic epoch. Detailed studies have been made on the rock types, sedimentary structures, and direction of provenance, paleontology and sedimentary facies characteristics of Chang8 subsection of Yanchang Formation of Upper Triassic of Jiyuan area by an integrated analysis of cores, thin sections, well log and other data. During the deposition of the Chang8 subsection of Yanchang Formation, the topography was gentle and stream actions were weak and the depositional system of shallowwater delta facies was developed. The sedimentation and sandbodies distribution were controlled by the raise and fall of the lake level and the direction of provenance obviously which were significant for hydrocarbon accumulation. It can be summarized as follows: ①The shoreline moved to provenance directions quickly and stripshaped or birdfootshaped subaqueous distributary channel sandbodies developed in the periods of high water levels; ②The delta plain developed and the front sandbodies came from different provenance converged in the center of the study area in the periods of low water levels; ③The sandbodies deposited in the periods of high water levels were favorable to develop lithologic reservoirs than those deposited in low water levels because the former distributed as sheetshaped which formed lithologic barriers.
2009, 27(6): 1076-1083.
Abstract:
Slope break belt is the most favorable setting for gravity flow development. Slope break belt can be developed in Lake basins and has the similar characteristics with one in continental slopes. Therefore, the study on depositional model and distribution regularity of gravity flow of slope breaks in large down warped lake basins is of important significance. The characteristic of slope break belt in LonghupaoDa'an terrace of Songliao Basin is distinctive, and it is a twolevel slope break. Sublacustrine fan is formed by sediment that carried by gravity flow. The sublacustrine fan of the south Songliao basin consists chiefly of clastics carried by landslide, debrisflow and turbidity current. Taking slope break of Songliao basin as an illustration, the paper elaborated depositional models of gravity flow in short gradual slope and long gradual slope setting. This study has shown that there are distinctly different features between two type models, especially the shape and distribution pattern of sublacustrine fan and incised waterway.
Slope break belt is the most favorable setting for gravity flow development. Slope break belt can be developed in Lake basins and has the similar characteristics with one in continental slopes. Therefore, the study on depositional model and distribution regularity of gravity flow of slope breaks in large down warped lake basins is of important significance. The characteristic of slope break belt in LonghupaoDa'an terrace of Songliao Basin is distinctive, and it is a twolevel slope break. Sublacustrine fan is formed by sediment that carried by gravity flow. The sublacustrine fan of the south Songliao basin consists chiefly of clastics carried by landslide, debrisflow and turbidity current. Taking slope break of Songliao basin as an illustration, the paper elaborated depositional models of gravity flow in short gradual slope and long gradual slope setting. This study has shown that there are distinctly different features between two type models, especially the shape and distribution pattern of sublacustrine fan and incised waterway.
2009, 27(6): 1093-1100.
Abstract:
The question about the deposition and the corresponding systems tract in forced regression is always the domestic and foreign focal point of argument. Integrated with sequence stratigraphic depositional model which was established by Exxon Corporation, forced regression deposition was corresponded to the early lowstand systems tract and the late highstand systems tract,the normal regression deposition was corresponded to progradation depositions of late lowstand systems tract, early highstand systems tract. Taking Zhujiang and Hanjiang Formations of Pearl River Mouth Basin as an example, they can be divided into 7 thirdorder relative sealevel change cycles, corresponding to 7 thirdorder sequence. The relative sealevel change is the external influence of the accommodate space change. The progradation depositions of late highstand systems tract distribute above the shelf slopebreak. The lowstand fans distribute on and under the slope. The lowstand wedges distribute on and under the slopebreak zone. The progradation depositions of early highstand systems tract distribute above the slopebreak zone. They are all the favorable reservoirs.
The question about the deposition and the corresponding systems tract in forced regression is always the domestic and foreign focal point of argument. Integrated with sequence stratigraphic depositional model which was established by Exxon Corporation, forced regression deposition was corresponded to the early lowstand systems tract and the late highstand systems tract,the normal regression deposition was corresponded to progradation depositions of late lowstand systems tract, early highstand systems tract. Taking Zhujiang and Hanjiang Formations of Pearl River Mouth Basin as an example, they can be divided into 7 thirdorder relative sealevel change cycles, corresponding to 7 thirdorder sequence. The relative sealevel change is the external influence of the accommodate space change. The progradation depositions of late highstand systems tract distribute above the shelf slopebreak. The lowstand fans distribute on and under the slope. The lowstand wedges distribute on and under the slopebreak zone. The progradation depositions of early highstand systems tract distribute above the slopebreak zone. They are all the favorable reservoirs.
2009, 27(6): 1109-1115.
Abstract:
On the basis of 106 kilometers measured sections and detailed research of sedimentary characteristics and evolution of Jiufotang Formation in Kazuo Basin,according to facies sequence relationship and the genetic significance of Calcium Carbonate and oil shale, Jiufotang Formation are divided into 1 longterm base level cycle and 7 midterm base level cycles. In longterm base level cycle, the midterm base level cycles on the rising period are mainly incomplete symmetry with the majority of uprising semicycle, the one on the transition period from rising to declining developed nearly complete symmetry, the one on the declining period mainly developed incomplete symmetry with the majority of subsiding semicycle. After detailed research of developmental characteristics and forming reason of midterm base level cycles and shortterm baselevel cycles, correlation of midterm base level cycles were carried out on representative profile.
On the basis of 106 kilometers measured sections and detailed research of sedimentary characteristics and evolution of Jiufotang Formation in Kazuo Basin,according to facies sequence relationship and the genetic significance of Calcium Carbonate and oil shale, Jiufotang Formation are divided into 1 longterm base level cycle and 7 midterm base level cycles. In longterm base level cycle, the midterm base level cycles on the rising period are mainly incomplete symmetry with the majority of uprising semicycle, the one on the transition period from rising to declining developed nearly complete symmetry, the one on the declining period mainly developed incomplete symmetry with the majority of subsiding semicycle. After detailed research of developmental characteristics and forming reason of midterm base level cycles and shortterm baselevel cycles, correlation of midterm base level cycles were carried out on representative profile.
2009, 27(6): 1124-1130.
Abstract:
Based on the study of sedimentary facies and sequence stratigraphy, Changxing Formation is a thirdorder of type Ⅱ sequence and subdivided into three systems tracts: SMST, TST, and HST. The lithofacies paleogeographic map based on systems tract as the timeequivalent of the stratigraphic units indicates that in Changxing stage of Late Permian in northeastern Sichuan basin a paleogeographic framework of platform alternating with basin (trough) was present. For instance, during the SMST sequence, from southwest to northeast of the study area KaijiangLiangping intraplatform trough and NortheastSichuan open platform facies successively developed. During the TST sequence, the sea water was aggressive from the northwest to the southeast, all kinds of sedimentary facies well developed. In the troughplatform transition belt fringing reefs and shoals occur often, and they are also the main favorable facies for reservoirs. During the development of HST sequence, the characteristics of sedimentary facies and distribution framework is basically the same with TST. However, because of the effect of structural uplifting and erosion at the end of Late Permian, the residual strata are very thin, and the fringing reefs and shoals almost are not absent.
Based on the study of sedimentary facies and sequence stratigraphy, Changxing Formation is a thirdorder of type Ⅱ sequence and subdivided into three systems tracts: SMST, TST, and HST. The lithofacies paleogeographic map based on systems tract as the timeequivalent of the stratigraphic units indicates that in Changxing stage of Late Permian in northeastern Sichuan basin a paleogeographic framework of platform alternating with basin (trough) was present. For instance, during the SMST sequence, from southwest to northeast of the study area KaijiangLiangping intraplatform trough and NortheastSichuan open platform facies successively developed. During the TST sequence, the sea water was aggressive from the northwest to the southeast, all kinds of sedimentary facies well developed. In the troughplatform transition belt fringing reefs and shoals occur often, and they are also the main favorable facies for reservoirs. During the development of HST sequence, the characteristics of sedimentary facies and distribution framework is basically the same with TST. However, because of the effect of structural uplifting and erosion at the end of Late Permian, the residual strata are very thin, and the fringing reefs and shoals almost are not absent.
2009, 27(6): 1138-1146.
Abstract:
Tuff interlayers distributing widely in Yanchang Formation in Ordos Basin, lots of cores which containing tuff interlayer were observed, then summarized the log curves characteristics of tuff, which represent by relatively low SP, high GR, R and AC, and usually lower than compacted mudstone; Single cores analysis of tuff interlayers suggest that the tuffs conformity contact with up and down rocks, which were typical sediments of volcanic ash carried by atmosphere then fall off, but there were perturbation structures that tuff accompanied with sandstone or mudstone, which underwent hydrodynamic reformation evidently; Welltie profiles analysis indicate that tuff occurred in form Chang 1 to Chang 9, there are four layers can be contrasted in lateral, which are Chang91, bottom of Chang 73, Chang 72 and Chang 71, and the tuff in Chang 73 is most; Tuff plane distributing characteristics is northwest trending, and from southwest to northeast the tuff gradually became thinner, which distributing characteristics are similar with source rock and radioactivity anomaly, So, the tuffs sediment process may induced elements migration and paleoenvironment change, which may play an important role in developing excellent source rock in Yanchang Formation.
Tuff interlayers distributing widely in Yanchang Formation in Ordos Basin, lots of cores which containing tuff interlayer were observed, then summarized the log curves characteristics of tuff, which represent by relatively low SP, high GR, R and AC, and usually lower than compacted mudstone; Single cores analysis of tuff interlayers suggest that the tuffs conformity contact with up and down rocks, which were typical sediments of volcanic ash carried by atmosphere then fall off, but there were perturbation structures that tuff accompanied with sandstone or mudstone, which underwent hydrodynamic reformation evidently; Welltie profiles analysis indicate that tuff occurred in form Chang 1 to Chang 9, there are four layers can be contrasted in lateral, which are Chang91, bottom of Chang 73, Chang 72 and Chang 71, and the tuff in Chang 73 is most; Tuff plane distributing characteristics is northwest trending, and from southwest to northeast the tuff gradually became thinner, which distributing characteristics are similar with source rock and radioactivity anomaly, So, the tuffs sediment process may induced elements migration and paleoenvironment change, which may play an important role in developing excellent source rock in Yanchang Formation.
2009, 27(6): 1155-1162.
Abstract:
The concentration of rare earth elements (REE) was determined in the Lower Paleogene core sedimentary rock from the Sanshui Basin. The ∑REE contents range from 7.06 to 230.01 μg/g, with an average value of 142.32 μg/g, close to that of Upper Continental Crust (UCC) and slightly depleted relative to North American Shale. Chondritenormalized REE patterns show little variation throughout the core and are consistent with the composition of UCC, with light REE enrichment, negative slopes, moderate Eu depletion and unobvious Ce anomaly. This indicates a relatively consistent sediment source and formation mechanism during the deposition of Lower Paleogene sediments in the Sanshui Basin. The REE records, combining with other geochemical proxies (Fe/Mn, Mg/Ca), suggest a general trend of getting more humidity during the core deposition and allow the recognition of four paleoclimate stages: stage Ⅰ(89~72.7 m) with drier condition, stage Ⅱ(72.7~51.8 m) with dominantly humid condition, stage Ⅲ(51.8 ( 30.6 m) with fluctuation of humid and dry condition and stage Ⅳ(30.6～0 m) with prevailing humid climate with intermittent dry condition.
The concentration of rare earth elements (REE) was determined in the Lower Paleogene core sedimentary rock from the Sanshui Basin. The ∑REE contents range from 7.06 to 230.01 μg/g, with an average value of 142.32 μg/g, close to that of Upper Continental Crust (UCC) and slightly depleted relative to North American Shale. Chondritenormalized REE patterns show little variation throughout the core and are consistent with the composition of UCC, with light REE enrichment, negative slopes, moderate Eu depletion and unobvious Ce anomaly. This indicates a relatively consistent sediment source and formation mechanism during the deposition of Lower Paleogene sediments in the Sanshui Basin. The REE records, combining with other geochemical proxies (Fe/Mn, Mg/Ca), suggest a general trend of getting more humidity during the core deposition and allow the recognition of four paleoclimate stages: stage Ⅰ(89~72.7 m) with drier condition, stage Ⅱ(72.7~51.8 m) with dominantly humid condition, stage Ⅲ(51.8 ( 30.6 m) with fluctuation of humid and dry condition and stage Ⅳ(30.6～0 m) with prevailing humid climate with intermittent dry condition.
2009, 27(6): 1163-1171.
Abstract:
It is an important science problem that braiding, meandering and straight channel patterns appeared in the lower Yellow River. Some researches have studied this problem in different aspects. However, some existent insufficiencies still need to study. In this work, it is mainly studied the water and sediment load effect to the different channel patterns in terms of discharge and sediment load evolution, crosssection form responding to discharge, channel crosssection evolution, depositional rate of channel bed, channel width evolution, and the channel gross power. The results show that the main dominant process of formation of the different channel patterns is gently channel gradient, fine materials of channel bed, alternation of low water and floodwater, a little of coarse sediment input to the channel, and restriction of the artificial levees. The formation of the straight channel pattern is induced by the artificial levee restriction. This channel pattern will be persistent with the decreasing suspended sediment load and mean discharge in recent decades and the restriction of the artificial levees. In the meandering reach the channel lateral migration is still evident, channel is narrowed gently, and the depositional rate on channel bed is the most among the three channel patterns. However, the higher depositional rate is unlikely to change the channel gradient of the lower Yellow River. The gross power of the braiding channel reach is higher than that of the other channel pattern reaches. Strong erosion and deposition occurred in braiding reach and lead to frequent change of the elevation and location of the channel bed and midchannel bars. It is evident the gross power of the braiding channel decreased in rent decades which must lead to the end reach of the braiding channel tend to meandering, namely, the meandering channel may be outspread upwards in limited length. In many management ways for the Yellow River basin the building of reservoirs and check dams in the upper and middle river basin is the effective work to hold up a great deal of coarse sediments and reduce the depositional rate in the lower channel bed. Of course, the building of artificial levees is necessary to avoid the bank crevasse but it needs to be adaptive with the different stability of the different channel patterns.
It is an important science problem that braiding, meandering and straight channel patterns appeared in the lower Yellow River. Some researches have studied this problem in different aspects. However, some existent insufficiencies still need to study. In this work, it is mainly studied the water and sediment load effect to the different channel patterns in terms of discharge and sediment load evolution, crosssection form responding to discharge, channel crosssection evolution, depositional rate of channel bed, channel width evolution, and the channel gross power. The results show that the main dominant process of formation of the different channel patterns is gently channel gradient, fine materials of channel bed, alternation of low water and floodwater, a little of coarse sediment input to the channel, and restriction of the artificial levees. The formation of the straight channel pattern is induced by the artificial levee restriction. This channel pattern will be persistent with the decreasing suspended sediment load and mean discharge in recent decades and the restriction of the artificial levees. In the meandering reach the channel lateral migration is still evident, channel is narrowed gently, and the depositional rate on channel bed is the most among the three channel patterns. However, the higher depositional rate is unlikely to change the channel gradient of the lower Yellow River. The gross power of the braiding channel reach is higher than that of the other channel pattern reaches. Strong erosion and deposition occurred in braiding reach and lead to frequent change of the elevation and location of the channel bed and midchannel bars. It is evident the gross power of the braiding channel decreased in rent decades which must lead to the end reach of the braiding channel tend to meandering, namely, the meandering channel may be outspread upwards in limited length. In many management ways for the Yellow River basin the building of reservoirs and check dams in the upper and middle river basin is the effective work to hold up a great deal of coarse sediments and reduce the depositional rate in the lower channel bed. Of course, the building of artificial levees is necessary to avoid the bank crevasse but it needs to be adaptive with the different stability of the different channel patterns.
2009, 27(6): 1178-1183.
Abstract:
The sequential extraction procedure was chosen for the study of speciation of Mercury in sediments of the Nanhai Lake. The fractions of watersoluble and exchangeable Hg are easy to release to the overlying water, and the sum of them account for 30.82 % of the total Hg. Furthermore, there exists positive correlation between these two fractions and the total Hg in overlying water, indicating high potential hazard to the Nanhai Lake. The content of humic acid Hg is the highest both in horizontal and vertical distribution and the correlation coefficient between humic acid Hg and organic matter is up to 0.72, indicating the contents of Hg and organic matter are highly correlated. Therefore, it is important that the organic matter is favor to immobilize Hg and reduce the potential Hg contamination of the Nanhai Lake.
The sequential extraction procedure was chosen for the study of speciation of Mercury in sediments of the Nanhai Lake. The fractions of watersoluble and exchangeable Hg are easy to release to the overlying water, and the sum of them account for 30.82 % of the total Hg. Furthermore, there exists positive correlation between these two fractions and the total Hg in overlying water, indicating high potential hazard to the Nanhai Lake. The content of humic acid Hg is the highest both in horizontal and vertical distribution and the correlation coefficient between humic acid Hg and organic matter is up to 0.72, indicating the contents of Hg and organic matter are highly correlated. Therefore, it is important that the organic matter is favor to immobilize Hg and reduce the potential Hg contamination of the Nanhai Lake.
2009, 27(6): 1191-1198.
Abstract:
Glycerol dialkyl glycerol tetraether lipids in the Lake Dianchi sediments were determinated based on bulk and molecular organic geochemical analyses of a lake sediment core (63 cm in length). The results indicate that the Lake Dianchi sediments have abundant GDGTs, and are dominated by the branched GDGTs from terrestrial soils. Methylation and cyclisation indices of branched tetraethers in this core samples reveal that 1) during the whole depositional stage of the core DC4, soil pH values of Lake Dianchi watershed are in the range of 7.5~8.2. Compared with the lower and middle section, the upper section has relatively low pH. 2）reconstructed mean annual air temperature of the Lake Dianchi watershed based on CBT/MBT displays a trend of changing from warm and moist climate in the early stage to cold and dry climate, and then become warm again lately. This variation can be used to explain the characteristics of bulk organic matter recorded in the lower and middle section of the core.
Glycerol dialkyl glycerol tetraether lipids in the Lake Dianchi sediments were determinated based on bulk and molecular organic geochemical analyses of a lake sediment core (63 cm in length). The results indicate that the Lake Dianchi sediments have abundant GDGTs, and are dominated by the branched GDGTs from terrestrial soils. Methylation and cyclisation indices of branched tetraethers in this core samples reveal that 1) during the whole depositional stage of the core DC4, soil pH values of Lake Dianchi watershed are in the range of 7.5~8.2. Compared with the lower and middle section, the upper section has relatively low pH. 2）reconstructed mean annual air temperature of the Lake Dianchi watershed based on CBT/MBT displays a trend of changing from warm and moist climate in the early stage to cold and dry climate, and then become warm again lately. This variation can be used to explain the characteristics of bulk organic matter recorded in the lower and middle section of the core.
2009, 27(6): 1199-1207.
Abstract:
Coqen Basin is the second largest marine basin in Tibet Plateau. Carbonate rocks of the Lower Cretaceous Langshan Formation is one of the most important hydrocarbon source rocks. Although having good conditions for petroleum preservation, Selincuo Sag has been got little petroleum study so far. A comprehensive study on biomarker of the extracts of sediments from the Langshan Formation at Xiongmei area by GC and GCMS, indicated that marine algae was main contribution to formation of its organic matters together with a few higher plants input. The organic matters were formed under anoxic environment having a little high salinity, and experienced high maturing and biodegradation ranked 12. Therefore, according to other organic geochemistry data, sedimentary and structural condition, carbonate rocks of the Langshan Formation have good source rocks potential considering weathering and should be of great importance to petroleum exploration.
Coqen Basin is the second largest marine basin in Tibet Plateau. Carbonate rocks of the Lower Cretaceous Langshan Formation is one of the most important hydrocarbon source rocks. Although having good conditions for petroleum preservation, Selincuo Sag has been got little petroleum study so far. A comprehensive study on biomarker of the extracts of sediments from the Langshan Formation at Xiongmei area by GC and GCMS, indicated that marine algae was main contribution to formation of its organic matters together with a few higher plants input. The organic matters were formed under anoxic environment having a little high salinity, and experienced high maturing and biodegradation ranked 12. Therefore, according to other organic geochemistry data, sedimentary and structural condition, carbonate rocks of the Langshan Formation have good source rocks potential considering weathering and should be of great importance to petroleum exploration.
2009, 27(6): 1033-1042.
Abstract:
Oolitic limestone is an crucial oil reservoir. Through dissolution kinetics experiment under normal temperature and pressure, this paper discussed dissolution kinetics characteristics and morphology evolution of oolitic limestone. The result indicates that oolitic limestone dissolution is main controlled by petrotextural features and chemical composition. Petrotextural feature control is characterized by selective dissolving textural weakness, such as tectonic microfracture, crack in ooid especially oolitic radiate crack, binding domain between grains and crystals and so on. Chemical composition control is characterized by prior dissolution of dolomitized particles and inhabitations of clay mineral and quartz. To dolomitized particles, they not only dissolve easer itself, but also could accelerate rock dissolution. However, to clay mineral and quartz, their inhabitations are more harmful to ooids and dolomitized particles' dissolution than to substrate. During oolitic limestone dissolution, firstly, it brought dissolved crack, intergranular pore, intercrystalliine pore after tectonic microfracture and crack in ooid. Secondly, it led to interpartide pore and intercrystalliine pore with dolomitized particles and calcite around them dissolved. Then, along with further dissolution, annular channel could be formed around ooids. Finally, it would form oolitic moldic pore in surface after ooids fell off substrate.
Oolitic limestone is an crucial oil reservoir. Through dissolution kinetics experiment under normal temperature and pressure, this paper discussed dissolution kinetics characteristics and morphology evolution of oolitic limestone. The result indicates that oolitic limestone dissolution is main controlled by petrotextural features and chemical composition. Petrotextural feature control is characterized by selective dissolving textural weakness, such as tectonic microfracture, crack in ooid especially oolitic radiate crack, binding domain between grains and crystals and so on. Chemical composition control is characterized by prior dissolution of dolomitized particles and inhabitations of clay mineral and quartz. To dolomitized particles, they not only dissolve easer itself, but also could accelerate rock dissolution. However, to clay mineral and quartz, their inhabitations are more harmful to ooids and dolomitized particles' dissolution than to substrate. During oolitic limestone dissolution, firstly, it brought dissolved crack, intergranular pore, intercrystalliine pore after tectonic microfracture and crack in ooid. Secondly, it led to interpartide pore and intercrystalliine pore with dolomitized particles and calcite around them dissolved. Then, along with further dissolution, annular channel could be formed around ooids. Finally, it would form oolitic moldic pore in surface after ooids fell off substrate.
2009, 27(6): 1050-1056.
Abstract:
The basal Doushantuo Formation in Qingzhen County, Guizhou Province, China, consists of mudstones, muddolostones, dolosandstones, thin dolostones and thick dolostones. The preservedwell and abundant carbon discform fossils, 2~15 mm in diameter, the carbon discform fossil was first discovered in dolostone in China. According to shape and feature of fossil, it may belong to algae fossil Chuarid. The cap dolostone of Doushantuo Formation in Qingzhen County, Guizhou Province, China, shows typical negative carbon isotopic composition of Marinoan Cap carbonate. Therefore, it reflects that abundant algae live in shallow lagoon after glaciation. Additionally, carbonate content rise gradually from glaciationend to carbonate (or dolostone) deposit in shallow lagoon, the feature shows that form of cap dolostone is gradually after glaciation, more than Hoffman et al .(1998) suggested that the cap dolostone is formed suddenly after glaciation.
The basal Doushantuo Formation in Qingzhen County, Guizhou Province, China, consists of mudstones, muddolostones, dolosandstones, thin dolostones and thick dolostones. The preservedwell and abundant carbon discform fossils, 2~15 mm in diameter, the carbon discform fossil was first discovered in dolostone in China. According to shape and feature of fossil, it may belong to algae fossil Chuarid. The cap dolostone of Doushantuo Formation in Qingzhen County, Guizhou Province, China, shows typical negative carbon isotopic composition of Marinoan Cap carbonate. Therefore, it reflects that abundant algae live in shallow lagoon after glaciation. Additionally, carbonate content rise gradually from glaciationend to carbonate (or dolostone) deposit in shallow lagoon, the feature shows that form of cap dolostone is gradually after glaciation, more than Hoffman et al .(1998) suggested that the cap dolostone is formed suddenly after glaciation.
2009, 27(6): 1068-1075.
Abstract:
The study of deep water sedimentation has developed fifty years. The misuse of term “turbidite” to deposits of deep water is common. Then the denial of Bouma sequence as the tubidite facies sequence and related fan depositional mode, the study on deepwater has undergone circle on cognition. The sandy debris theory is an innovation and negation to classical tubidity theory.The definition, experimentation, identification feature and sedimentation model were introduced in the passage. Applying the sandy debris theory to explain the reason why thick sand bodys could occur in the center of lacke in Ordos basin. By the way, the mechanism and characteristic of sand body at slope in terrestrial lacustrine basin could be revealed. The theory would be one of theoretical basis to continental exploration.
The study of deep water sedimentation has developed fifty years. The misuse of term “turbidite” to deposits of deep water is common. Then the denial of Bouma sequence as the tubidite facies sequence and related fan depositional mode, the study on deepwater has undergone circle on cognition. The sandy debris theory is an innovation and negation to classical tubidity theory.The definition, experimentation, identification feature and sedimentation model were introduced in the passage. Applying the sandy debris theory to explain the reason why thick sand bodys could occur in the center of lacke in Ordos basin. By the way, the mechanism and characteristic of sand body at slope in terrestrial lacustrine basin could be revealed. The theory would be one of theoretical basis to continental exploration.
2009, 27(6): 1084-1092.
Abstract:
The sandbody of Upper Triassic Xu 4 member in central Sichuan basin is thick，continuous sedimentation，and characterized by shoreshallow lacustrinedelta frontdelta plain which is proximal．During sedimentation, there were different accommodation space /sedimentary supply values，the Xu 4 member sandbody consists of three vertical superposed types which is regressive，channel and transgressive from bottom to top; and the channel sandbody composition on sequence boundary is the best genetic sandbody．Regressive sandbody mainly includes high energy truncation style channel，truncation style mouth bar and far bar sands；channel model sandbody mainly includes eroded style channel，high energy truncation style channel；transgressive sandbody mainly includes lowenergy channel，lowenergy truncation channel，complete mouth bar and lower part deletion mouth bar．Because the distribution of the different sand bodies combination，the different contributing sandbody formed different diagenetic facies and reservoir facies，the diagenesis of the channel sandbody is corrosion facies and lining chlorite facies，highporosity，so it is good reservoir；the diagenesis of the transgressive sandbody is compaction and binder facies，poor physical property； the diagenesis of the transgressive sandbody is corosion and binder facies，better physical property，so it is medium reservoir. Because the interface between channel model and regressive model is unconformity which constitutes the pathways for gas migration．In addition, the channel model sandbody is wideranging distribution，high energy truncation style channel sandbody stable depoition，and providing sufficient space for enrichment of oilgas．The transgressive model sandbody reservoir on the top becoming tight as favorable caprock，and promotes the channel model sandbody to become the favorable position of central Sichuan basin．
The sandbody of Upper Triassic Xu 4 member in central Sichuan basin is thick，continuous sedimentation，and characterized by shoreshallow lacustrinedelta frontdelta plain which is proximal．During sedimentation, there were different accommodation space /sedimentary supply values，the Xu 4 member sandbody consists of three vertical superposed types which is regressive，channel and transgressive from bottom to top; and the channel sandbody composition on sequence boundary is the best genetic sandbody．Regressive sandbody mainly includes high energy truncation style channel，truncation style mouth bar and far bar sands；channel model sandbody mainly includes eroded style channel，high energy truncation style channel；transgressive sandbody mainly includes lowenergy channel，lowenergy truncation channel，complete mouth bar and lower part deletion mouth bar．Because the distribution of the different sand bodies combination，the different contributing sandbody formed different diagenetic facies and reservoir facies，the diagenesis of the channel sandbody is corrosion facies and lining chlorite facies，highporosity，so it is good reservoir；the diagenesis of the transgressive sandbody is compaction and binder facies，poor physical property； the diagenesis of the transgressive sandbody is corosion and binder facies，better physical property，so it is medium reservoir. Because the interface between channel model and regressive model is unconformity which constitutes the pathways for gas migration．In addition, the channel model sandbody is wideranging distribution，high energy truncation style channel sandbody stable depoition，and providing sufficient space for enrichment of oilgas．The transgressive model sandbody reservoir on the top becoming tight as favorable caprock，and promotes the channel model sandbody to become the favorable position of central Sichuan basin．
2009, 27(6): 1101-1108.
Abstract:
The Kebai fault zone in the northwestern Junggar Basin is a largescale imbricate thrust system which originated in Permian. The tectonic activity played an important role in controlling the sedimentary process. Permian is a mixing accumulated formation which contains volcanics and clastic rocks. Through the analysis, it has been pointed that Permian is a laminar formation and has unconformities that are formed by the relative lake level change and can be regarded as the sequence boundary. Permian is divided into 5 secondorder sequences and 12 thirdorder sequences according the unconformities and the stratal surfaces. Lower Permian (PSQ1PSQ7) is characteristic as volcanic facies and sedimentary facies coexisting; the main sedimentary facies of MiddleUpper Permian are fluvial fan, fan delta and lacustrine facies. The main control actions of the tectonic activity to the sequence are tectonic subsidence, volcanic activity and features of palaeogeomorphic. The essence of the tectonic subsidence is flexural subsidence leaded by the thrusting orogenesis, which reflects the basinmountain coupling process between foreland thrusting action and the flexural subsidence. Flexural subsidence is the internal and dominating factor; the volcanic rock mass which is formed by the volcanic action and deposited fast had important impact on the formation and evolution of the sequence; the slope breaks that are formed by tectonic activity controlled sequence architecture and the sedimentary filling.
The Kebai fault zone in the northwestern Junggar Basin is a largescale imbricate thrust system which originated in Permian. The tectonic activity played an important role in controlling the sedimentary process. Permian is a mixing accumulated formation which contains volcanics and clastic rocks. Through the analysis, it has been pointed that Permian is a laminar formation and has unconformities that are formed by the relative lake level change and can be regarded as the sequence boundary. Permian is divided into 5 secondorder sequences and 12 thirdorder sequences according the unconformities and the stratal surfaces. Lower Permian (PSQ1PSQ7) is characteristic as volcanic facies and sedimentary facies coexisting; the main sedimentary facies of MiddleUpper Permian are fluvial fan, fan delta and lacustrine facies. The main control actions of the tectonic activity to the sequence are tectonic subsidence, volcanic activity and features of palaeogeomorphic. The essence of the tectonic subsidence is flexural subsidence leaded by the thrusting orogenesis, which reflects the basinmountain coupling process between foreland thrusting action and the flexural subsidence. Flexural subsidence is the internal and dominating factor; the volcanic rock mass which is formed by the volcanic action and deposited fast had important impact on the formation and evolution of the sequence; the slope breaks that are formed by tectonic activity controlled sequence architecture and the sedimentary filling.
2009, 27(6): 1116-1123.
Abstract:
On the basis of stratigraphic theory and the analysis of sedimentary facies, lithology and lithofacies and the changing of accommodation of field profile, sequence stratigraphy are researched to the upper Permian at Yanggudong profile in Dukou town, Xuanhan County, Northeastern of Sichuan Basin. Three types and six stratigraphic sequences boundary are discriminated. One 2order sequence and five 3order sequences in upper Permian , three 3order sequences in Wujiaping Formation and two 3order sequences in Changxing Formation are discriminated. We have constructed the sequence stratigraphic framework of upper Permian on the basis of sequence dividing. By the correlation of the change of accommodation curve and outcrop sequence stratigraphic dividing, there is a very well corresponding relation between the two curves. The relation not only verifies the correct of classification of the sequence stratigraphy but also shows the practicality and objectivity of cycle analysis technique of Fischer plot.
On the basis of stratigraphic theory and the analysis of sedimentary facies, lithology and lithofacies and the changing of accommodation of field profile, sequence stratigraphy are researched to the upper Permian at Yanggudong profile in Dukou town, Xuanhan County, Northeastern of Sichuan Basin. Three types and six stratigraphic sequences boundary are discriminated. One 2order sequence and five 3order sequences in upper Permian , three 3order sequences in Wujiaping Formation and two 3order sequences in Changxing Formation are discriminated. We have constructed the sequence stratigraphic framework of upper Permian on the basis of sequence dividing. By the correlation of the change of accommodation curve and outcrop sequence stratigraphic dividing, there is a very well corresponding relation between the two curves. The relation not only verifies the correct of classification of the sequence stratigraphy but also shows the practicality and objectivity of cycle analysis technique of Fischer plot.
2009, 27(6): 1131-1137.
Abstract:
Sedimentary facies indicators are the best effective criteria to identify seismites. In the flume experiments to simulate seismoturbidites, several typical facies indicators of seismites are found in soft sediments, such as synsedimentary faulting, microcorrugation, liquefied sandstone dike, liquefied uniform bed, syndepositional deformation, seismoturbidites, and so on. They formed in different periods of seismism and distribute regularly in the system of delta to seismoturbidites. At the same time, some facies indicators induced by other contributing factors are discovered, which is confused with facies indicators of seismites. So when analyzing seismites we should also consider the assemble characteristics of all kinds of facies indicators, their allocation relationship with depositional environment and regional tectonic setting. The distribution pattern of facies indicators of seismites can be derived from simulated experiments. According to analyzing the types and assemble characteristics of facies indicators of seismites, we can forecast the best zones that develop seismoturbidites and guide subtle reservoir exploration in faulted basin.
Sedimentary facies indicators are the best effective criteria to identify seismites. In the flume experiments to simulate seismoturbidites, several typical facies indicators of seismites are found in soft sediments, such as synsedimentary faulting, microcorrugation, liquefied sandstone dike, liquefied uniform bed, syndepositional deformation, seismoturbidites, and so on. They formed in different periods of seismism and distribute regularly in the system of delta to seismoturbidites. At the same time, some facies indicators induced by other contributing factors are discovered, which is confused with facies indicators of seismites. So when analyzing seismites we should also consider the assemble characteristics of all kinds of facies indicators, their allocation relationship with depositional environment and regional tectonic setting. The distribution pattern of facies indicators of seismites can be derived from simulated experiments. According to analyzing the types and assemble characteristics of facies indicators of seismites, we can forecast the best zones that develop seismoturbidites and guide subtle reservoir exploration in faulted basin.
2009, 27(6): 1147-1154.
Abstract:
A largescale transgression occured in early Jurassic in the eastern Guangdong Province, the continental margin of South China Sea. The sea level change is recorded by the variation of paleosalinity. The ratios of Sr/Ba and B/Ga reflecting the paleosalinity changes are coincident with the sea level changes, the former is a positive correlation and the latter is a negative correlation. In this area, the curves of m (m= MgO/ Al2O3 100)values and B/Ga are similar but different in ranges. According to variation of paleosalinity together with the filling succession, evolution of sedimentary environments and facies, two transgressions and one regression for sea level change are recognized in this area. The tectonic setting of the northern margin of the South China Sea in early Jurassic was active relatively. The recycled foreland orogenic belt or the foreland uplift became the source provenance, and the basin developed in this region including Haifeng area had some characteristics of the peripheral foreland basin. The sea level change of early Jurassic revealed by the records of paleosalinity variation may be affected by the paleotethys closure.
A largescale transgression occured in early Jurassic in the eastern Guangdong Province, the continental margin of South China Sea. The sea level change is recorded by the variation of paleosalinity. The ratios of Sr/Ba and B/Ga reflecting the paleosalinity changes are coincident with the sea level changes, the former is a positive correlation and the latter is a negative correlation. In this area, the curves of m (m= MgO/ Al2O3 100)values and B/Ga are similar but different in ranges. According to variation of paleosalinity together with the filling succession, evolution of sedimentary environments and facies, two transgressions and one regression for sea level change are recognized in this area. The tectonic setting of the northern margin of the South China Sea in early Jurassic was active relatively. The recycled foreland orogenic belt or the foreland uplift became the source provenance, and the basin developed in this region including Haifeng area had some characteristics of the peripheral foreland basin. The sea level change of early Jurassic revealed by the records of paleosalinity variation may be affected by the paleotethys closure.
2009, 27(6): 1172-1177.
Abstract:
Using the 210Pb dating methods in the sediment cores, the modern sedimentation rates in Prydz Bay (Antarctic) are estimated. The results show that the modern sedimentation rates are mainly controlled by marine primary productivity in upper water and benthos in surface sediment. Furthermore, the modern sedimentation rates are also controlled by water stability and submarine topography. The values are 0.47~1.88 mm/a and the average value is 1.06 mm/a. The sedimentation rate is higher than that in Ross Sea but lower than that in Weddell Sea. The highest value occurred in central area of the bay where the sea water is much more stability. The modern sedimentation rates in adjacent continental shelf are much lower.
Using the 210Pb dating methods in the sediment cores, the modern sedimentation rates in Prydz Bay (Antarctic) are estimated. The results show that the modern sedimentation rates are mainly controlled by marine primary productivity in upper water and benthos in surface sediment. Furthermore, the modern sedimentation rates are also controlled by water stability and submarine topography. The values are 0.47~1.88 mm/a and the average value is 1.06 mm/a. The sedimentation rate is higher than that in Ross Sea but lower than that in Weddell Sea. The highest value occurred in central area of the bay where the sea water is much more stability. The modern sedimentation rates in adjacent continental shelf are much lower.
2009, 27(6): 1184-1190.
Abstract:
A special aqueous gravel bed, which underlies the red clay and is mainly composed of red clay lumps and calcium nodules, was found at Weijiawa village of Liulin county in the west part of Lüliang Mountains. Sedimentological study shows that the clast（composed of the red clay and calcium nodule） in this bed are all with certain sorting and roundness, The calcium nodules did not show the anomalous ginger shape but process typical round or subround character, which is the product of fluviatile transport. Both sedimentary sequence's fining upward and fossil in certain beds are all typical features of aqueous deposit. The clast (red clay and calcium nodule) in the section indicate that some red clay deposited before the aqueous sediments. Magnetostratigraphic result reveals that the aqueous gravel bed is aged about 8.1Ma. The discovery of the special aqueous gravel bed can provide new information for the cause of red clay.
A special aqueous gravel bed, which underlies the red clay and is mainly composed of red clay lumps and calcium nodules, was found at Weijiawa village of Liulin county in the west part of Lüliang Mountains. Sedimentological study shows that the clast（composed of the red clay and calcium nodule） in this bed are all with certain sorting and roundness, The calcium nodules did not show the anomalous ginger shape but process typical round or subround character, which is the product of fluviatile transport. Both sedimentary sequence's fining upward and fossil in certain beds are all typical features of aqueous deposit. The clast (red clay and calcium nodule) in the section indicate that some red clay deposited before the aqueous sediments. Magnetostratigraphic result reveals that the aqueous gravel bed is aged about 8.1Ma. The discovery of the special aqueous gravel bed can provide new information for the cause of red clay.
2009, 27(6): 1208-1215.
Abstract:
Studying the geochemical characteristics and formation history of heavy oil from Well Tadong 2 is of great importance to clarify the oil accumulation of Tarim marine crude oil. The writer synthetically apply the isotope mass spectrogram, chromatogram and chromatogrammass spectrogram methods to the research of molecular fossil characteristic of heavy oil from Well Tadong 2 , and results reveal that heavy oil from Well Tadong 2 is characterized by high gammacerane , high C28 sterane ,low rearranged sterane and high C27triaromatic steroid, these characteristics are similar to that of CambrianLower Ordovician source rock , which demonstrate that Cambrian crude oil come from CambrianLower Ordovician source rock; condensed compounds (fluoranthene, pyrene, benzo\[a\]anthracene, bow, benzo fluoranthene, benzopyrene) with high abundance are detected in the heavy oil of Well Tadong 2, and carbon isotope value of whole oil evidently lean to heavier, all foregoing characteristics revealing that hydrocarbons in crude oil become densification by thermal alteration. Homogenization temperature of fluid inclusion and burialthermal evolution history imply that accumulation period of heavy oil from Well Tadong 2 may be at 450~440 Ma.
Studying the geochemical characteristics and formation history of heavy oil from Well Tadong 2 is of great importance to clarify the oil accumulation of Tarim marine crude oil. The writer synthetically apply the isotope mass spectrogram, chromatogram and chromatogrammass spectrogram methods to the research of molecular fossil characteristic of heavy oil from Well Tadong 2 , and results reveal that heavy oil from Well Tadong 2 is characterized by high gammacerane , high C28 sterane ,low rearranged sterane and high C27triaromatic steroid, these characteristics are similar to that of CambrianLower Ordovician source rock , which demonstrate that Cambrian crude oil come from CambrianLower Ordovician source rock; condensed compounds (fluoranthene, pyrene, benzo\[a\]anthracene, bow, benzo fluoranthene, benzopyrene) with high abundance are detected in the heavy oil of Well Tadong 2, and carbon isotope value of whole oil evidently lean to heavier, all foregoing characteristics revealing that hydrocarbons in crude oil become densification by thermal alteration. Homogenization temperature of fluid inclusion and burialthermal evolution history imply that accumulation period of heavy oil from Well Tadong 2 may be at 450~440 Ma.
