2010 Vol. 28, No. 2
Display Method:
2010, 28(2): 209-218.
Abstract:
In Tarim basin occurs a large amount of dolostone strata, in which contains plenty of good reservoir. In this paper, petrology and geochemistry methods were attempted to reveal the genesis of dolostones with different crystal characteristics and the subjects were the dolostones of the upper Cambrian in the centeral area of Tarim basin. According to the petrology, the studied dolostones can be divided into “Cloudy center with bright rim” type of euhedral dolomite (CBED),“clean and light” type of euhedral dolomite(CLED) and “dirty section” type of euhedral/subhedral dolomite (DED or DSD). The geochmical results show that the Mg/Ca of CBED,DSD and DED vary in 0.760.93, of the three types, the Mg/Ca value of DSD is the highest, which indicates DSD might have been on the highest evolving stage; There is a considerable coincidence between CBED and CLED, with Ca enriched in rim and Mg enriched in core, which indicates the meteoric water had taken part in at the late crystal stage. The order degrees of CBED, DED and DSD are 0.51, 0.6, 0.69 respectively, which suggests that the crystal speed of CBED is fast and the DSD might have been affected by thermal alternation resulting in the high order degree and high evolving stage. The Rb, Th, Ti enriched characteristics and the right inclined PAASnomalized REE patterns suggest that the CBED, DED and DSD might have derived Mg from evaporated seawater. The δ13C and δ18O values of CBED, DED and DSD range in -2.5‰-1.0‰ and -8.3‰ -5.4‰ respectively, and the δ18O values of CBED are lower than those of DED or DSD, which coincides with the joining of the meteoric water. The 87Sr/86Sr varies in 0.708 8350.709 204, coincident with paleoseawater. Therefore, conclusions were reached: 1) the crystallization of CBED can be divided into two stage, center stage and rim stage, of which the dolomitization fluid are evaporated seawater and mixed seawater and meteoric water, respectively; 2) CLED is results of mixed water dolomitization, however the different proportion of seawater and meteoric water lead to different composition of dolomite in core and rim; 3) DED and DSD are results of dolomitization by evaporated seawater, of which DSD had suffered thermal alternation, which may result in the higher order degree, higher 87Sr/86Sr values and higher evolving stage.
In Tarim basin occurs a large amount of dolostone strata, in which contains plenty of good reservoir. In this paper, petrology and geochemistry methods were attempted to reveal the genesis of dolostones with different crystal characteristics and the subjects were the dolostones of the upper Cambrian in the centeral area of Tarim basin. According to the petrology, the studied dolostones can be divided into “Cloudy center with bright rim” type of euhedral dolomite (CBED),“clean and light” type of euhedral dolomite(CLED) and “dirty section” type of euhedral/subhedral dolomite (DED or DSD). The geochmical results show that the Mg/Ca of CBED,DSD and DED vary in 0.760.93, of the three types, the Mg/Ca value of DSD is the highest, which indicates DSD might have been on the highest evolving stage; There is a considerable coincidence between CBED and CLED, with Ca enriched in rim and Mg enriched in core, which indicates the meteoric water had taken part in at the late crystal stage. The order degrees of CBED, DED and DSD are 0.51, 0.6, 0.69 respectively, which suggests that the crystal speed of CBED is fast and the DSD might have been affected by thermal alternation resulting in the high order degree and high evolving stage. The Rb, Th, Ti enriched characteristics and the right inclined PAASnomalized REE patterns suggest that the CBED, DED and DSD might have derived Mg from evaporated seawater. The δ13C and δ18O values of CBED, DED and DSD range in -2.5‰-1.0‰ and -8.3‰ -5.4‰ respectively, and the δ18O values of CBED are lower than those of DED or DSD, which coincides with the joining of the meteoric water. The 87Sr/86Sr varies in 0.708 8350.709 204, coincident with paleoseawater. Therefore, conclusions were reached: 1) the crystallization of CBED can be divided into two stage, center stage and rim stage, of which the dolomitization fluid are evaporated seawater and mixed seawater and meteoric water, respectively; 2) CLED is results of mixed water dolomitization, however the different proportion of seawater and meteoric water lead to different composition of dolomite in core and rim; 3) DED and DSD are results of dolomitization by evaporated seawater, of which DSD had suffered thermal alternation, which may result in the higher order degree, higher 87Sr/86Sr values and higher evolving stage.
2010, 28(2): 227-234.
Abstract:
Based on the theory of sequence stratigraphy, sequence stratigraphy framework of Nantun group in Huhehu Depression is established in this paper by comprehensively research of cores, logging data and seismic data. Nantu group in Huhehu Depression is divided into 2 3rdorder sequences:SQ1 sequence is equal to the first stage of Nantu group, and SQ2 is equal to the second stage of Nantun group. Neither sequences develops completely, which is composed of low stand system, transgressive system tract and high stand system. According to the characteristics of divide sequence development of target strate in researched area, and based on the division and comparison of sequence formation unit, this paper studies on sedimentary types and system, determined that fan delta, braided river delta, sublacustrine, lake and so on are very development. SQ1 sequence mainly develops braided river delta in the north of basin, and fan delta in the south of basin. SQ1 sequence mainly develops braided river delta in gentle slope belt, and fan delta in steep slope in local area. Compared with SQ1 sequence, SQ2 develops swamp facies. Comprehensive analysis of sedimentary characteristics and evolution law, this paper points out that sedimentary sand bodies in the south of Huhehu Depression is the favourable exploring area.
Based on the theory of sequence stratigraphy, sequence stratigraphy framework of Nantun group in Huhehu Depression is established in this paper by comprehensively research of cores, logging data and seismic data. Nantu group in Huhehu Depression is divided into 2 3rdorder sequences:SQ1 sequence is equal to the first stage of Nantu group, and SQ2 is equal to the second stage of Nantun group. Neither sequences develops completely, which is composed of low stand system, transgressive system tract and high stand system. According to the characteristics of divide sequence development of target strate in researched area, and based on the division and comparison of sequence formation unit, this paper studies on sedimentary types and system, determined that fan delta, braided river delta, sublacustrine, lake and so on are very development. SQ1 sequence mainly develops braided river delta in the north of basin, and fan delta in the south of basin. SQ1 sequence mainly develops braided river delta in gentle slope belt, and fan delta in steep slope in local area. Compared with SQ1 sequence, SQ2 develops swamp facies. Comprehensive analysis of sedimentary characteristics and evolution law, this paper points out that sedimentary sand bodies in the south of Huhehu Depression is the favourable exploring area.
2010, 28(2): 243-253.
Abstract:
Because of uplifting by Caledonian movement，most of the Silurian had been denuded and only its middle and lower series remained in the Northern GuizhouSoutheastern Sichuan. On the basis of the comprehensive study cores and log wells and outcrops, 8 sequences and 2 system tracts were divided by use of sequence stratigraphic method, there are two sequences (SSQ1~SSQ2)in Longmaxi Formation of the Lower Silurian，one sequence (SSQ3~SSQ4) in Xiaoheba Formation, four sequences(SSQ5~SSQ8) in middlelower Silurian Hanjiadian Formation. 3 depositional systems of delta, coastal and shelf were developed to explore the characteristics of the depositional systems and their planar distribution in isochronous stratigraphic framework. One is reef flat biolithite and granule limestone developed in the platform shallow facies and platform foreslope facies, mainly in highstand systematic tract of the third sequence SSQ3 and SSQ4 in the Shiniulan Age. The vertical distribution is in the middle and upper of the Shiniulan formation, and horizontal distribution in XuyongXishuiGuanyinqiao in the southern of the study area. The other is shallow continental shelf clasolite reservoir, mainly developed in highstand systems tract of the third sequence SSQ4 in the Xiaoheba Age, laterally distributed in NanchuanShizhuLichuan and other places.
Because of uplifting by Caledonian movement，most of the Silurian had been denuded and only its middle and lower series remained in the Northern GuizhouSoutheastern Sichuan. On the basis of the comprehensive study cores and log wells and outcrops, 8 sequences and 2 system tracts were divided by use of sequence stratigraphic method, there are two sequences (SSQ1~SSQ2)in Longmaxi Formation of the Lower Silurian，one sequence (SSQ3~SSQ4) in Xiaoheba Formation, four sequences(SSQ5~SSQ8) in middlelower Silurian Hanjiadian Formation. 3 depositional systems of delta, coastal and shelf were developed to explore the characteristics of the depositional systems and their planar distribution in isochronous stratigraphic framework. One is reef flat biolithite and granule limestone developed in the platform shallow facies and platform foreslope facies, mainly in highstand systematic tract of the third sequence SSQ3 and SSQ4 in the Shiniulan Age. The vertical distribution is in the middle and upper of the Shiniulan formation, and horizontal distribution in XuyongXishuiGuanyinqiao in the southern of the study area. The other is shallow continental shelf clasolite reservoir, mainly developed in highstand systems tract of the third sequence SSQ4 in the Xiaoheba Age, laterally distributed in NanchuanShizhuLichuan and other places.
2010, 28(2): 264-273.
Abstract:
On the basis of a careful analysis of thin section observation, scanning electron microscope and Xdiffraction data, the diagenetic stage of Yanchang Formation in Fuxian exploration area is the A stage of late diagenesis and the main diagenic metamorphism include mechanicalchemical compaction, consolidated fill and dissolution. The mechanicalchemical impact and consolidated fill are the main factors causing the loss of porosity for the sandstones. Carbonate, hydrosyalite and quartzfeldspar overgrowths are the main cements that reduced the reservoir quality of the sandstones．Thin chlorite film around detrital grains prevented from part of quartz and feldspar overgrowth and carbonate cement precipitation, which cause a part of primary pore preserved and hence caused a better reservoir quality. The main factor for the great quantity secondary pore is dissolution partly of detrital feldspars and laumonite cements developed in early stage by the acidic liquid related to decomposition of organic mater during hydrocarbon enrichment in the late diagenesis and meteoricowaters during epidiagenesis.
Laumonite cement developed mainly in Chang 3 Oilbeds which were owing to the high content of feldspar clastic and the alteration to feldspar at the diagenetic process. Kaolinite content is high in the Chang 2 and Change 3 Oilbeds which probably were owing to feldspar corrosion by fresh water in atmosphere and the kaolinite deposit at IndoChinese epoch.
The main pore types are residual intergranular pore and feldspardissolved pore and the porethroat structure can be divided into five types which are eyeletthin throat, eyeletmicro thin throat, eyelet micro throat, microthin pore microthin throat and microthin pore micro throat in which the last type is unavailabile reservoir.
On the basis of a careful analysis of thin section observation, scanning electron microscope and Xdiffraction data, the diagenetic stage of Yanchang Formation in Fuxian exploration area is the A stage of late diagenesis and the main diagenic metamorphism include mechanicalchemical compaction, consolidated fill and dissolution. The mechanicalchemical impact and consolidated fill are the main factors causing the loss of porosity for the sandstones. Carbonate, hydrosyalite and quartzfeldspar overgrowths are the main cements that reduced the reservoir quality of the sandstones．Thin chlorite film around detrital grains prevented from part of quartz and feldspar overgrowth and carbonate cement precipitation, which cause a part of primary pore preserved and hence caused a better reservoir quality. The main factor for the great quantity secondary pore is dissolution partly of detrital feldspars and laumonite cements developed in early stage by the acidic liquid related to decomposition of organic mater during hydrocarbon enrichment in the late diagenesis and meteoricowaters during epidiagenesis.
Laumonite cement developed mainly in Chang 3 Oilbeds which were owing to the high content of feldspar clastic and the alteration to feldspar at the diagenetic process. Kaolinite content is high in the Chang 2 and Change 3 Oilbeds which probably were owing to feldspar corrosion by fresh water in atmosphere and the kaolinite deposit at IndoChinese epoch.
The main pore types are residual intergranular pore and feldspardissolved pore and the porethroat structure can be divided into five types which are eyeletthin throat, eyeletmicro thin throat, eyelet micro throat, microthin pore microthin throat and microthin pore micro throat in which the last type is unavailabile reservoir.
2010, 28(2): 285-293.
Abstract:
Based on analyses of the samples in detail, the REE geochemical characteristics of the Middle Jurassic sandstone in Mohe Basin are described. The results indicate: (1)The LREE content obviously enriches compared with the HREE content and with negative Eu anomalies shown in the chondrite aerolite standard pattern of sandstone of Xiu Feng, E Muerhe and Kai Kukang Formations. However, Er Shierzhan Formation is obviously different frorm them. Little negative Eu anomalies is shown in the chondrite aerolite standard pattern of sandstone of Er Shierzhan Formation, which reflects the sandstone is from different provenance. (2) The provenance of the Middle Jurassic Sandstone in Mohe Basin may be felsic rocks of upper crust, including granites, metamorphic rocks and sediments. During the deposition of the Er Shierzhan Formation and E Muerhe Formation, some materials may be from the deep lower crust or mantle and leads to the great change of Provenance. (3)The tectonic settings of provenances of the Middle Jurassic Sandstone in Mohe Basin is the island arc of the margin of active continent.(4) The Ce/Ce* and Ceanom indexes indicate that the palaeoenvironment of the Middle Jurassic in Mohe Basin was a reduction environment and is profitable for the oil and gas formation.
Based on analyses of the samples in detail, the REE geochemical characteristics of the Middle Jurassic sandstone in Mohe Basin are described. The results indicate: (1)The LREE content obviously enriches compared with the HREE content and with negative Eu anomalies shown in the chondrite aerolite standard pattern of sandstone of Xiu Feng, E Muerhe and Kai Kukang Formations. However, Er Shierzhan Formation is obviously different frorm them. Little negative Eu anomalies is shown in the chondrite aerolite standard pattern of sandstone of Er Shierzhan Formation, which reflects the sandstone is from different provenance. (2) The provenance of the Middle Jurassic Sandstone in Mohe Basin may be felsic rocks of upper crust, including granites, metamorphic rocks and sediments. During the deposition of the Er Shierzhan Formation and E Muerhe Formation, some materials may be from the deep lower crust or mantle and leads to the great change of Provenance. (3)The tectonic settings of provenances of the Middle Jurassic Sandstone in Mohe Basin is the island arc of the margin of active continent.(4) The Ce/Ce* and Ceanom indexes indicate that the palaeoenvironment of the Middle Jurassic in Mohe Basin was a reduction environment and is profitable for the oil and gas formation.
2010, 28(2): 299-306.
Abstract:
At He 21 sedimentary stage, there appeared a lot of salt sediments while they all disappeared at the end of He_1 stage in Wuyang depression.Both of qualitative method and quantitative method are used in this paper, which can recover the relationship between salt sediment and tectonics effectively in this sag.Through this study, two results are as follows: (1) The sedimentary end of He 22 section is a very important tectonic activity stage, when the whole depression began uplift while the basal strikeslip tectonic started to reactivate.The He 3 and He 22 sedimentary stratum which deposited before the key stage have obvious difference with the ones of He 21 and He 1 that deposited after the key stage.(2)The response relation between salt sediment and tectonic activity is definite in Wuyang sag.The tectonic activity controlled the change of basin boundary, which made the study area a relatively closed depression, then decreased the provenance into the basin, the salt started to deposit.
At He 21 sedimentary stage, there appeared a lot of salt sediments while they all disappeared at the end of He_1 stage in Wuyang depression.Both of qualitative method and quantitative method are used in this paper, which can recover the relationship between salt sediment and tectonics effectively in this sag.Through this study, two results are as follows: (1) The sedimentary end of He 22 section is a very important tectonic activity stage, when the whole depression began uplift while the basal strikeslip tectonic started to reactivate.The He 3 and He 22 sedimentary stratum which deposited before the key stage have obvious difference with the ones of He 21 and He 1 that deposited after the key stage.(2)The response relation between salt sediment and tectonic activity is definite in Wuyang sag.The tectonic activity controlled the change of basin boundary, which made the study area a relatively closed depression, then decreased the provenance into the basin, the salt started to deposit.
2010, 28(2): 314-323.
Abstract:
After long term hotspot study about the endPermian mass extinction and relative catastrophic events, scientists recently focused on the aftermaths of mass extinction, such as ecosystems and sedimentary systems. The Early Triassic ecosystems immediately following the endPermian mass extinction were dominated by cosmopolitan members and opportunists, therefore, the importance of sediment records are obviously emerged, and "anachronistic facies" are becoming research foreland, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thinbedded limestone and zebra limestonemudstone.
As the aftermaths of geologic transition, the appearance of "anachronistic facies" sediment immediately following the mass extinction and the elimination from normal shallow marine setting in the early Middle Triassic with the final establishment of the Mesozoic ecosystems in the Late Anisian. The dramatic synchronization between the changes of sedimentary systems and the radiation of the Mesozoic biotas further demonstrates that there were the inevitable interrelations among the sedimentary systems, ecosystems, mass extinction and recovery and specific environment. The study of the "anachronistic facies" sediment in an absence of fossils record Lower Triassic strata provide valuable materials and new angle of view to seek the endPermian mass extinction and recovery.
After long term hotspot study about the endPermian mass extinction and relative catastrophic events, scientists recently focused on the aftermaths of mass extinction, such as ecosystems and sedimentary systems. The Early Triassic ecosystems immediately following the endPermian mass extinction were dominated by cosmopolitan members and opportunists, therefore, the importance of sediment records are obviously emerged, and "anachronistic facies" are becoming research foreland, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thinbedded limestone and zebra limestonemudstone.
As the aftermaths of geologic transition, the appearance of "anachronistic facies" sediment immediately following the mass extinction and the elimination from normal shallow marine setting in the early Middle Triassic with the final establishment of the Mesozoic ecosystems in the Late Anisian. The dramatic synchronization between the changes of sedimentary systems and the radiation of the Mesozoic biotas further demonstrates that there were the inevitable interrelations among the sedimentary systems, ecosystems, mass extinction and recovery and specific environment. The study of the "anachronistic facies" sediment in an absence of fossils record Lower Triassic strata provide valuable materials and new angle of view to seek the endPermian mass extinction and recovery.
2010, 28(2): 331-338.
Abstract:
Calcareous clastics in the tropical beaches are important fractions, which differ from the silicic constituents in the physical character. The beach sediments are chosen to study on the influence of calcareous clastics on the particle grain size distribution through different pretreatment procedures. After dissolving the calcareous clastics by hydrochloric acid, the main part of particle size distribution curve will be more peaky and move to the fine end. Because the calcareous clastics cement some finer terrigenous particles in the bodies, the dissolution may make the cemented finer particles (4～9) mix with silicic clastics in sediments. After removing the finer particles (4～9), the parameters of grain size of the insoluble residues show good correlations with the parameters of mixing sediment. The correlation coefficients of mean, sorting, skewness are 0.934, 0.890, 0.813. For more than 50% samples, the insoluble silicic sands are more fine, better sorted and more finely skew than the total samples. Because of great variability in the shape and species of calcareous clastics in the beach sands, knowing of the species and content of calcareous clastics is necessary to understand the grainsize parameters and studying the dynamic environment of beaches similar to those around Tongguling.
Calcareous clastics in the tropical beaches are important fractions, which differ from the silicic constituents in the physical character. The beach sediments are chosen to study on the influence of calcareous clastics on the particle grain size distribution through different pretreatment procedures. After dissolving the calcareous clastics by hydrochloric acid, the main part of particle size distribution curve will be more peaky and move to the fine end. Because the calcareous clastics cement some finer terrigenous particles in the bodies, the dissolution may make the cemented finer particles (4～9) mix with silicic clastics in sediments. After removing the finer particles (4～9), the parameters of grain size of the insoluble residues show good correlations with the parameters of mixing sediment. The correlation coefficients of mean, sorting, skewness are 0.934, 0.890, 0.813. For more than 50% samples, the insoluble silicic sands are more fine, better sorted and more finely skew than the total samples. Because of great variability in the shape and species of calcareous clastics in the beach sands, knowing of the species and content of calcareous clastics is necessary to understand the grainsize parameters and studying the dynamic environment of beaches similar to those around Tongguling.
2010, 28(2): 346-355.
Abstract:
As an important component of the Quaternary red earth, plinthitic red earth has special structures and is distributed over the red earth areas in south China widely. Plinthitic red earth can be divided into homogeneous plinthitic red earth and heterogenous plinthitic red earth according to its texture. Test results show that :(1)Silt(5～50 μm) and clay(<5 μm) are dominant components of homogeneous plinthitic red earth, sand(>50 μm) content is small, less than 3%; grainsize frequency curves are mostly single peak and opositiveskewed, the peak is between5.5 and 6.5, some samples’ grainsize frequency curves are the shape of two peak, peaks are at about 6 and 8 respectively; higher CIA values (84.31%~89.26%) and lower Ba values (0.19～0.30);rare earth element average value and distribution patterns of homogeneous plinthitic red earth are similar to aeolian deposition, 87Sr/86Sr values are close to Jiaxian Pliocene red clay; εNd(0) values are between 10.54 and 12.66, indicate that the genesis of heterogenous plinthitic red earth is stable basically; therefore ,homogeneous plinthitic red earth whose physical and chemical characteristics indicate aeolian genesis and significant impact of weathering could be considered as aggradation plinthitic red earth.(2)Heterogenous plinthitic red earth developed from alluvialflood sediments, slope wash or weathering crust red earth. Silt content of heterogenous plinthitic red earth declines significantly, no more than 50%, sand content increases highly, the coefficients of variation are high in sand (>50 μm) and medium coarse sand (>250 μm) components, all the grainsize results indicate obvious heterogenous features; most of heterogenous plinthitic red earth’s CIA values exceed 84% ,coefficients of variation of chemical elements and weathering indicators are less than 10%, all the chemical characteristics suggest a strong and stable weathering process as a whole.The formation of plinthitic red earth went through the process of weathering and formation of plinthitic in turn. The climate may be mainly humid in the formation period of plinthitic red earth in south China.
As an important component of the Quaternary red earth, plinthitic red earth has special structures and is distributed over the red earth areas in south China widely. Plinthitic red earth can be divided into homogeneous plinthitic red earth and heterogenous plinthitic red earth according to its texture. Test results show that :(1)Silt(5～50 μm) and clay(<5 μm) are dominant components of homogeneous plinthitic red earth, sand(>50 μm) content is small, less than 3%; grainsize frequency curves are mostly single peak and opositiveskewed, the peak is between5.5 and 6.5, some samples’ grainsize frequency curves are the shape of two peak, peaks are at about 6 and 8 respectively; higher CIA values (84.31%~89.26%) and lower Ba values (0.19～0.30);rare earth element average value and distribution patterns of homogeneous plinthitic red earth are similar to aeolian deposition, 87Sr/86Sr values are close to Jiaxian Pliocene red clay; εNd(0) values are between 10.54 and 12.66, indicate that the genesis of heterogenous plinthitic red earth is stable basically; therefore ,homogeneous plinthitic red earth whose physical and chemical characteristics indicate aeolian genesis and significant impact of weathering could be considered as aggradation plinthitic red earth.(2)Heterogenous plinthitic red earth developed from alluvialflood sediments, slope wash or weathering crust red earth. Silt content of heterogenous plinthitic red earth declines significantly, no more than 50%, sand content increases highly, the coefficients of variation are high in sand (>50 μm) and medium coarse sand (>250 μm) components, all the grainsize results indicate obvious heterogenous features; most of heterogenous plinthitic red earth’s CIA values exceed 84% ,coefficients of variation of chemical elements and weathering indicators are less than 10%, all the chemical characteristics suggest a strong and stable weathering process as a whole.The formation of plinthitic red earth went through the process of weathering and formation of plinthitic in turn. The climate may be mainly humid in the formation period of plinthitic red earth in south China.
2010, 28(2): 365-372.
Abstract:
Xingkai Lake, a transboundary lake by China and Russia, is the largest freshwater lake in Northeast Asia. A 269 m long continuous sediment core, approximately 28 kaold at the bottom, from Lake Xingkai, has been analyzed first in China for the stable isotopes of carbon, nitrogen, TOC and C/N ratios, in order to study the paleoclimatic and paleoenviromental changes in the area. The result showed that all δ13Corg values are well within the range of 24.56‰～27.67‰ derived from C3 vegetation, and the composition of δ13Corg in C3 plants increases with deceasing annual precipitation and temperature. So, sedimentary organic carbon in colddry periods is more enriched in 13C than that in warmwet periods. Low TOC, which are typical for lower temperatures, coincided with lower C/N ratios, reflecting that in cold period the sedimentary organic matters mainly derived from aquatic organic matters which have higher δ15N values than terraneous organic matters. These results enable us to reconstruct the evolution sequence of paleoclimate in Xingkai Lake region, 28 480～26 160cal.aBP, the climate was cold and dry;
26 160～22 880cal.aBP, the climate became warm and wet; 22 880～18 185cal.aBP correspond to the Last Glacial Maximum(LGM); 18 185～12 650cal.aBP, it was an frequent oscillation period corresponding to Blling/Older Dryas/Allerd warm period; Younger Dryas cold event occured at about 90~78 cm depth in the core; 11 500～4 570 cal.aBP, climate became wet and warm gradually, in which it was temperaturedry in early stage and temperaturewet in late stage, but 8 000～5 000 cal.aBP was Holocene Megathemal period(Holocene thermal optimum)in the area; During 4 570～1 470 cal.aBP, it was a colddry climate, and since 1 470 cal.aBP, climate became warmwet again.
Xingkai Lake, a transboundary lake by China and Russia, is the largest freshwater lake in Northeast Asia. A 269 m long continuous sediment core, approximately 28 kaold at the bottom, from Lake Xingkai, has been analyzed first in China for the stable isotopes of carbon, nitrogen, TOC and C/N ratios, in order to study the paleoclimatic and paleoenviromental changes in the area. The result showed that all δ13Corg values are well within the range of 24.56‰～27.67‰ derived from C3 vegetation, and the composition of δ13Corg in C3 plants increases with deceasing annual precipitation and temperature. So, sedimentary organic carbon in colddry periods is more enriched in 13C than that in warmwet periods. Low TOC, which are typical for lower temperatures, coincided with lower C/N ratios, reflecting that in cold period the sedimentary organic matters mainly derived from aquatic organic matters which have higher δ15N values than terraneous organic matters. These results enable us to reconstruct the evolution sequence of paleoclimate in Xingkai Lake region, 28 480～26 160cal.aBP, the climate was cold and dry;
26 160～22 880cal.aBP, the climate became warm and wet; 22 880～18 185cal.aBP correspond to the Last Glacial Maximum(LGM); 18 185～12 650cal.aBP, it was an frequent oscillation period corresponding to Blling/Older Dryas/Allerd warm period; Younger Dryas cold event occured at about 90~78 cm depth in the core; 11 500～4 570 cal.aBP, climate became wet and warm gradually, in which it was temperaturedry in early stage and temperaturewet in late stage, but 8 000～5 000 cal.aBP was Holocene Megathemal period(Holocene thermal optimum)in the area; During 4 570～1 470 cal.aBP, it was a colddry climate, and since 1 470 cal.aBP, climate became warmwet again.
2010, 28(2): 373-379.
Abstract:
As study proved, the oil and gas accumulation in the western Qaidam was mainly controlled by the late Himalayan tectonic events, and the effective source rocks led to oil and gas distributed around the five main hydrocarbon generation centers or along the relative nearby slope zones. The paleostructures and those structures with paleotectonic situation were the major areas of hydrocarbon accumulation, and faultsystems and their combinations with reservoirs controlled the lateral and longitudinal distribution of oil and gas. These conclusions on hydrocarbon distribution regularities establish the theoretical foundation for the future petroleum exploration, and imply the exploration directions for recent petroleum exploration.
As study proved, the oil and gas accumulation in the western Qaidam was mainly controlled by the late Himalayan tectonic events, and the effective source rocks led to oil and gas distributed around the five main hydrocarbon generation centers or along the relative nearby slope zones. The paleostructures and those structures with paleotectonic situation were the major areas of hydrocarbon accumulation, and faultsystems and their combinations with reservoirs controlled the lateral and longitudinal distribution of oil and gas. These conclusions on hydrocarbon distribution regularities establish the theoretical foundation for the future petroleum exploration, and imply the exploration directions for recent petroleum exploration.
2010, 28(2): 388-394.
Abstract:
Through statistics,it is concluded that the thickness and displacement pressure of cap rock, destroy degree of cap rock from fault, pressure of gas reservoir and gas viscosity are the main factors that influence the gas reservoir cap sealing ability of 46 large and medium gas fields in China. According to relationship between them and sealing and preservative ability of gas reservoirs, this paper has corrected an evaluation method of sealing and preservative ability of gas reservoirs, and evaluated for sealing and preservative ability of large and medium gas fields in China by the method. Finally it is concluded that sealing and preservative ability of 46 large and medium gas fields in China were bad in the main, followed by the middle, again best, and at least were better. Through the study of the sealing and preservative ability of cap rock and gas reserves abundance of 46 large and medium gas fields in China, this paper considered that there was a direct correlation between them. The average reserves abundance of gas fields sealed and perseverated by medium cap rock is the highest, followed by better cap rock. The minimum is best and bad cap rock. It indicates that sealing and preservative ability is not the only main factors controlling formation of large and medium gas fields with high reserve abundance in China. The reserve abundance of large and medium gas fields was yet controlled by other main factors.
Through statistics,it is concluded that the thickness and displacement pressure of cap rock, destroy degree of cap rock from fault, pressure of gas reservoir and gas viscosity are the main factors that influence the gas reservoir cap sealing ability of 46 large and medium gas fields in China. According to relationship between them and sealing and preservative ability of gas reservoirs, this paper has corrected an evaluation method of sealing and preservative ability of gas reservoirs, and evaluated for sealing and preservative ability of large and medium gas fields in China by the method. Finally it is concluded that sealing and preservative ability of 46 large and medium gas fields in China were bad in the main, followed by the middle, again best, and at least were better. Through the study of the sealing and preservative ability of cap rock and gas reserves abundance of 46 large and medium gas fields in China, this paper considered that there was a direct correlation between them. The average reserves abundance of gas fields sealed and perseverated by medium cap rock is the highest, followed by better cap rock. The minimum is best and bad cap rock. It indicates that sealing and preservative ability is not the only main factors controlling formation of large and medium gas fields with high reserve abundance in China. The reserve abundance of large and medium gas fields was yet controlled by other main factors.
2010, 28(2): 401-404.
Abstract:
Coal bed methane (CBM) accumulation models include continuous gas accumulation and staged gas accumulation. In this paper, the influence factors of carbon isotope of CBM formed by staged gas accumulation and carbon isotopic composition of CBM formed in different maturity intervals were researched by thermal simulation experiment. The results showed that the carbon isotopic composition of CBM formed by staged gas accumulation is related to initial Ro and final Ro values in the evolutionary stage. With the increase of initial Ro and final Ro values, carbon isotope of CBM became heavier. In some maturity intervals, the carbon isotopic composition of CBM formed at higher heating rate was lighter than that at lower heating rate. At the same time, nature of coal also affects carbon isotope of CBM. The carbon isotope of methane generated by peat was the lightest of all three samples. The carbon isotopic composition of CBM formed by coal parent material with Ro values of 1.2%, 1.6%, 2.0%, 2.4% and 2.8% rising to 3.0 and 4.0%, respectively, was determinated. This provides scientific evidence for studying the genesis of CBM generated in different maturity intervals. These results were used to study CBM from the southern Qinshui basin, and it is found that CBM from the southern Qinshui basin was accumulated after terminal Middle Jurassic (Ro >1.6%) and characterized by the staged gas accumulation.
Coal bed methane (CBM) accumulation models include continuous gas accumulation and staged gas accumulation. In this paper, the influence factors of carbon isotope of CBM formed by staged gas accumulation and carbon isotopic composition of CBM formed in different maturity intervals were researched by thermal simulation experiment. The results showed that the carbon isotopic composition of CBM formed by staged gas accumulation is related to initial Ro and final Ro values in the evolutionary stage. With the increase of initial Ro and final Ro values, carbon isotope of CBM became heavier. In some maturity intervals, the carbon isotopic composition of CBM formed at higher heating rate was lighter than that at lower heating rate. At the same time, nature of coal also affects carbon isotope of CBM. The carbon isotope of methane generated by peat was the lightest of all three samples. The carbon isotopic composition of CBM formed by coal parent material with Ro values of 1.2%, 1.6%, 2.0%, 2.4% and 2.8% rising to 3.0 and 4.0%, respectively, was determinated. This provides scientific evidence for studying the genesis of CBM generated in different maturity intervals. These results were used to study CBM from the southern Qinshui basin, and it is found that CBM from the southern Qinshui basin was accumulated after terminal Middle Jurassic (Ro >1.6%) and characterized by the staged gas accumulation.
2010, 28(2): 219-226.
Abstract:
Tubiphytes are widespread in reef strata of the Late Carboniferous in South Guizhou. They have a variety of morphological forms. The dense Tubiphytes construct the reef rock mainly by binding. They also form the reef with other reefbuilding organisms in the study area. The Tubiphytes reefs are relative smallsize and localized. In the study area, most of Tubiphytes form boundstone by encrusting the bioclasts and binding bioclastic grains and mud, except for forming reef. Tubiphytes boundstone can offer a stable substrate of coral reef by binding sediments. They can also bind the bioclastic grains that filled in the space of coral reefs framework to form a massive boundstone and enhance the stability of coral reefs. As the important component of the carbonate rocks, Tubiphytes also extensively occur in the strata with other bioclasts. Tubiphytes are the characteristic organism in reef strata of the Late Carboniferous in South Guizhou.
Tubiphytes are widespread in reef strata of the Late Carboniferous in South Guizhou. They have a variety of morphological forms. The dense Tubiphytes construct the reef rock mainly by binding. They also form the reef with other reefbuilding organisms in the study area. The Tubiphytes reefs are relative smallsize and localized. In the study area, most of Tubiphytes form boundstone by encrusting the bioclasts and binding bioclastic grains and mud, except for forming reef. Tubiphytes boundstone can offer a stable substrate of coral reef by binding sediments. They can also bind the bioclastic grains that filled in the space of coral reefs framework to form a massive boundstone and enhance the stability of coral reefs. As the important component of the carbonate rocks, Tubiphytes also extensively occur in the strata with other bioclasts. Tubiphytes are the characteristic organism in reef strata of the Late Carboniferous in South Guizhou.
2010, 28(2): 235-242.
Abstract:
The character of sequence boundary is summarized according to well log, seismic sections and rock cores in this paper. The distribution rules of sequence boundary and shortterm cycle in difference sedimentary facies are studied alone from west to east. From Qingshankou Formation to Yaojiazu Formation，can be divided into 4 long term base level cycles and 10 short term base level cycles. Based on the fundamental principle of sequence stratigraphy and sedimentary, the sequence stratigraphic framework of the middle oilbearing beds can server for future exploration and development.
The character of sequence boundary is summarized according to well log, seismic sections and rock cores in this paper. The distribution rules of sequence boundary and shortterm cycle in difference sedimentary facies are studied alone from west to east. From Qingshankou Formation to Yaojiazu Formation，can be divided into 4 long term base level cycles and 10 short term base level cycles. Based on the fundamental principle of sequence stratigraphy and sedimentary, the sequence stratigraphic framework of the middle oilbearing beds can server for future exploration and development.
2010, 28(2): 254-263.
Abstract:
The depositional stage of member 7 of Yanchang Formation in Triassic was the maximum of Mesozoic lake basin in Ordos basin, the subsidence of lake basin was the largest and the lake basin scope was extensive. it has been clarified that the source sediments were from five directions of basin circumference, the mainly source was located in the northeast and southwest area . In addition，there are three secondary source areas that was located in the west, south and northwest. The sedimentary facies of member 7 of Yanchang Formation are the delta and lacustrine facies, which can be further subdivided into five subfacies and ten microfacies. During the deposition of Member 73 of the Yanchang Formation, the lacustrine area was maximum, the turbidite of halfdeep lake and deep lake facies were not developed, but the dark and high resistance mudstone were developed, which were main high quality source rock of Mesozoic, the depositional area of halfdeep lake and deep lake facies were clearly reduced during the deposition of Member 72 of the Yanchang Formation, the turbidite were relatively developed; the lacustrine area and the depositional area of halfdeep lake and deep lake facies continually reduced during the deposition of Member 71 of the Yanchang Formation, the turbidite was extensively developed, which was the main reservoir of Member 7.
The depositional stage of member 7 of Yanchang Formation in Triassic was the maximum of Mesozoic lake basin in Ordos basin, the subsidence of lake basin was the largest and the lake basin scope was extensive. it has been clarified that the source sediments were from five directions of basin circumference, the mainly source was located in the northeast and southwest area . In addition，there are three secondary source areas that was located in the west, south and northwest. The sedimentary facies of member 7 of Yanchang Formation are the delta and lacustrine facies, which can be further subdivided into five subfacies and ten microfacies. During the deposition of Member 73 of the Yanchang Formation, the lacustrine area was maximum, the turbidite of halfdeep lake and deep lake facies were not developed, but the dark and high resistance mudstone were developed, which were main high quality source rock of Mesozoic, the depositional area of halfdeep lake and deep lake facies were clearly reduced during the deposition of Member 72 of the Yanchang Formation, the turbidite were relatively developed; the lacustrine area and the depositional area of halfdeep lake and deep lake facies continually reduced during the deposition of Member 71 of the Yanchang Formation, the turbidite was extensively developed, which was the main reservoir of Member 7.
2010, 28(2): 274-284.
Abstract:
Shoreshallow lacustrine beachbar sandbodies widely developed during the period of the upper submember of the fourth Member of the Shahejie Formation of Paleogene in the Western Dongying Depression. The environmentally sensitive grain size components of beachbar sandbodies have been studied using the method of grain sizestandard deviation according to the description of cores and other correlated analyses and tests. Combined with the analysis of grain size probability curves and the research of palaeotopography and palaeocurrent, there four kinds of environmentally sensitive grain size components were determined in the study area, which respectively represents suspension transportation, coastal current, wave and storm wave or gravity flow. Wave and coastal current are the main hydrodynamics of the four kinds of hydrodynamics which control the formation and development of beachbar sandbodies. Wave is the most important hydrodynamics that control the formation and development of beachbar sandbodies according to the calculation of the percentage of environmentally sensitive grain size components of wave and coastal current in the grain population. The energy of wave and its control degree to the formation and development of beachbar sandbodies decreases from the outer to the inner part of shoreshallow lacustrine. The effects of coastal current mainly exist in the inner part of shoreshallow lacustrine.
Shoreshallow lacustrine beachbar sandbodies widely developed during the period of the upper submember of the fourth Member of the Shahejie Formation of Paleogene in the Western Dongying Depression. The environmentally sensitive grain size components of beachbar sandbodies have been studied using the method of grain sizestandard deviation according to the description of cores and other correlated analyses and tests. Combined with the analysis of grain size probability curves and the research of palaeotopography and palaeocurrent, there four kinds of environmentally sensitive grain size components were determined in the study area, which respectively represents suspension transportation, coastal current, wave and storm wave or gravity flow. Wave and coastal current are the main hydrodynamics of the four kinds of hydrodynamics which control the formation and development of beachbar sandbodies. Wave is the most important hydrodynamics that control the formation and development of beachbar sandbodies according to the calculation of the percentage of environmentally sensitive grain size components of wave and coastal current in the grain population. The energy of wave and its control degree to the formation and development of beachbar sandbodies decreases from the outer to the inner part of shoreshallow lacustrine. The effects of coastal current mainly exist in the inner part of shoreshallow lacustrine.
2010, 28(2): 294-298.
Abstract:
Depressedtype slope breaks was developed in the southwest and northeast margin of the LateTriassic Ordos Basin. In the northeast margin, the slope breaks were characterized by multistage and gentle, with grade of 13 and width of 15~25 km; In the southwest margin, the slope breaks were characterized by monolithic and steep, with grade of 35 and width of 10~20 km. Variations of slope breaks distribution were partly affected by the shrinkage of lake basin. However, slope controls formation overlapping, lithologic association and distribution of sedimentary system. To build distribution modeling of slopenonstructural trap based on the research of slope break characteristics plays an important role in exploration activity of the LateTriassic Ordos Basin.
Depressedtype slope breaks was developed in the southwest and northeast margin of the LateTriassic Ordos Basin. In the northeast margin, the slope breaks were characterized by multistage and gentle, with grade of 13 and width of 15~25 km; In the southwest margin, the slope breaks were characterized by monolithic and steep, with grade of 35 and width of 10~20 km. Variations of slope breaks distribution were partly affected by the shrinkage of lake basin. However, slope controls formation overlapping, lithologic association and distribution of sedimentary system. To build distribution modeling of slopenonstructural trap based on the research of slope break characteristics plays an important role in exploration activity of the LateTriassic Ordos Basin.
2010, 28(2): 307-313.
Abstract:
There are braided, meandering and straight channel reaches along the lower Yellow River. The difference in channel planform certainly is influenced by different depositional dynamics. In this work, according to a series of data collected from the yearbook of the water and sediment of the Yellow River, the different indexes of representative channel depositional dynamics has analyzed. The results show that, there are evident differences in depositional dynamics among the braided, meandering and straight channel reaches in the lower Yellow River. The channel gradient is the maximum for the braided reach, which ranges 0.20.14, is moderate for the meandering reach, which ranges0.140.10 , and the minimum for the straight reach, which less than 0.10%. The flow velocity of the bankfull discharge is also larger for the braided, moderate for the meandering and least for the straight reaches. Its variational extent decreases downwards along the three channel patterns. The gross power of stream flow is decreases from the braiding via meandering to straight reaches and its ratio is 2.31∶〖KG-*2〗1.35∶〖KG-*2〗1. The specific power of stream flow is minimum for the braided, maximum for the meandering and moderate for the straight reaches and its ratio is 0.52∶〖KG-*2〗1.18∶〖KG-*2〗1. The channel bed sediment is relatively fine and generally lacks the roll component. The median grain size is 3.0, 3.2 and 3.67 for the braided, meandering and straight reaches, respectively, furthermore, the sediment sorting is also enhanced along the different channel reaches downwords. Be enslaved to the abovemationed depositional dynamics, the sedimentation rate on channel bed is different among the three channel pattern reaches. It is the minimum for the braided, maximum for the meandering and moderate for the straight reaches when discharge is moderate to large, and it is approximative among the three channel pattern reaches, but a decrease tendency downwards, when discharge is small. In addition, the sedimentation rate on braided channel bed evidently depends on the variation of discharge, and decreases with increasing discharge.
There are braided, meandering and straight channel reaches along the lower Yellow River. The difference in channel planform certainly is influenced by different depositional dynamics. In this work, according to a series of data collected from the yearbook of the water and sediment of the Yellow River, the different indexes of representative channel depositional dynamics has analyzed. The results show that, there are evident differences in depositional dynamics among the braided, meandering and straight channel reaches in the lower Yellow River. The channel gradient is the maximum for the braided reach, which ranges 0.20.14, is moderate for the meandering reach, which ranges0.140.10 , and the minimum for the straight reach, which less than 0.10%. The flow velocity of the bankfull discharge is also larger for the braided, moderate for the meandering and least for the straight reaches. Its variational extent decreases downwards along the three channel patterns. The gross power of stream flow is decreases from the braiding via meandering to straight reaches and its ratio is 2.31∶〖KG-*2〗1.35∶〖KG-*2〗1. The specific power of stream flow is minimum for the braided, maximum for the meandering and moderate for the straight reaches and its ratio is 0.52∶〖KG-*2〗1.18∶〖KG-*2〗1. The channel bed sediment is relatively fine and generally lacks the roll component. The median grain size is 3.0, 3.2 and 3.67 for the braided, meandering and straight reaches, respectively, furthermore, the sediment sorting is also enhanced along the different channel reaches downwords. Be enslaved to the abovemationed depositional dynamics, the sedimentation rate on channel bed is different among the three channel pattern reaches. It is the minimum for the braided, maximum for the meandering and moderate for the straight reaches when discharge is moderate to large, and it is approximative among the three channel pattern reaches, but a decrease tendency downwards, when discharge is small. In addition, the sedimentation rate on braided channel bed evidently depends on the variation of discharge, and decreases with increasing discharge.
2010, 28(2): 324-330.
Abstract:
Abundant plant fossils were found in the Upper Triassic Xujiahe Formation outcropped in the Western margin of Sichuan Basin. Based on the recent geological investigation，we discovered wellpreserved fossil woods with clear growth rings, which indicated that warm climate developed during the Xujiahe Formation deposited. The growth rings of fossil wood showed seasonal fluctuations. It was thought that the climate alternation was closely related to the megamonsoon which was prevalent from the Permian to the Triassic. Average sensitivity of the tree rings of fossil woods was calculated to less than 0.3,which showed the balanced water supply. The plant growth was strongly influenced by the magamonsoon developing during the Late Triassic.
Abundant plant fossils were found in the Upper Triassic Xujiahe Formation outcropped in the Western margin of Sichuan Basin. Based on the recent geological investigation，we discovered wellpreserved fossil woods with clear growth rings, which indicated that warm climate developed during the Xujiahe Formation deposited. The growth rings of fossil wood showed seasonal fluctuations. It was thought that the climate alternation was closely related to the megamonsoon which was prevalent from the Permian to the Triassic. Average sensitivity of the tree rings of fossil woods was calculated to less than 0.3,which showed the balanced water supply. The plant growth was strongly influenced by the magamonsoon developing during the Late Triassic.
2010, 28(2): 339-345.
Abstract:
Chenghu, a mediumsize and shallow lake, is situated in the central Taihu Plain of Lower Changjiang River, China. In its northcentral part, a temporal water pumped area from 2003~2007, there have developed a NNWSSE paleochannel filled up with deposits on the flat bottom. Sediment core (SC7) from this paleochannel near the central part of the lake was taken and the clay minerals were studied through Xray diffraction. Studies show that the main clay minerals, calculated by comparing major peak heights, are illite (70.0%~72.4%), kaolinite (10.0%~11.6%), 1.4 nm minerals (12.8%~14.6%), and small amounts of smectite (<5%). Compared with the bottom material ( hard clay') and lakeshore sediments, the sediments are characterized by higher content of illite, chlorite and better illite crystallinity, but lower content of kaolinite. These characteristics of clay minerals indicate that the sediments may come from both the lake catchment and the Changjiang River, and that the paleochannel (the ancient Dongjiang River) must have experienced frequent tidal upstream flow or Changjiang River's floods after entering the MidHolocene. As the Dongjiang River was filled up, the coastal development stage of Chenghu area ended.
Chenghu, a mediumsize and shallow lake, is situated in the central Taihu Plain of Lower Changjiang River, China. In its northcentral part, a temporal water pumped area from 2003~2007, there have developed a NNWSSE paleochannel filled up with deposits on the flat bottom. Sediment core (SC7) from this paleochannel near the central part of the lake was taken and the clay minerals were studied through Xray diffraction. Studies show that the main clay minerals, calculated by comparing major peak heights, are illite (70.0%~72.4%), kaolinite (10.0%~11.6%), 1.4 nm minerals (12.8%~14.6%), and small amounts of smectite (<5%). Compared with the bottom material ( hard clay') and lakeshore sediments, the sediments are characterized by higher content of illite, chlorite and better illite crystallinity, but lower content of kaolinite. These characteristics of clay minerals indicate that the sediments may come from both the lake catchment and the Changjiang River, and that the paleochannel (the ancient Dongjiang River) must have experienced frequent tidal upstream flow or Changjiang River's floods after entering the MidHolocene. As the Dongjiang River was filled up, the coastal development stage of Chenghu area ended.
2010, 28(2): 356-364.
Abstract:
Hierarchical clustering and factor analysis are respectively applied to grainsize and mineral analysis of sediment samples collected at 112 and 35 stations, respectively, in the Xiamen Bay. The results showed that the Xiamen Bay can be divided into three types of depositional environment areas corresponding to its' sedimentary dynamics properties. Fifty kinds of minerals were found in surface sediment samples, including 38 kinds of heavy minerals. The main heavy minerals include magnetite, ilmenite, limonite, hematite, epidote, hornblende, zircon, and so on. Surface sediments in the Xiamen Bay mainly included the suspended particles, discharged from the Jiulongjiang, and the particles materials of efflorescent rock around the Xiamen Bay, and partly came from the Taiwan Strait. Different source of particles was confirmed to be the mainly influencing factor of the characteristics of the minerals’ distribution.
Hierarchical clustering and factor analysis are respectively applied to grainsize and mineral analysis of sediment samples collected at 112 and 35 stations, respectively, in the Xiamen Bay. The results showed that the Xiamen Bay can be divided into three types of depositional environment areas corresponding to its' sedimentary dynamics properties. Fifty kinds of minerals were found in surface sediment samples, including 38 kinds of heavy minerals. The main heavy minerals include magnetite, ilmenite, limonite, hematite, epidote, hornblende, zircon, and so on. Surface sediments in the Xiamen Bay mainly included the suspended particles, discharged from the Jiulongjiang, and the particles materials of efflorescent rock around the Xiamen Bay, and partly came from the Taiwan Strait. Different source of particles was confirmed to be the mainly influencing factor of the characteristics of the minerals’ distribution.
2010, 28(2): 380-387.
Abstract:
Origin of oils in the MobeiMosuowan area of the central Junggar Basin is complex. In order to reveal this complexity, genetic types of the oils were classified in this paper, and their migration and accumulation was discussed. Based on artificial oil mixing experiments, it is found that some biomarker compositions of oils show regularities along with mixing ratios of oils. Thus, these representative biomarkers may be criteria for determining origin of mixed oils. According to the criteria, oils in the area were divided into four types. Migration and accumulation of the four type oils were further discussed, combined with geological backgrounds. Thus, this paper provides valuable information for the study of regional oil source and formation.
Origin of oils in the MobeiMosuowan area of the central Junggar Basin is complex. In order to reveal this complexity, genetic types of the oils were classified in this paper, and their migration and accumulation was discussed. Based on artificial oil mixing experiments, it is found that some biomarker compositions of oils show regularities along with mixing ratios of oils. Thus, these representative biomarkers may be criteria for determining origin of mixed oils. According to the criteria, oils in the area were divided into four types. Migration and accumulation of the four type oils were further discussed, combined with geological backgrounds. Thus, this paper provides valuable information for the study of regional oil source and formation.
2010, 28(2): 395-400.
Abstract:
Overpressure is widespread developed in the third member(Es3) and the forth member(Es4) of the Shahejie Formation of Dongying Depression. Es3 and Es4 are divided into two compartments(Es3Es4s compartment and Es4x compartment) by sealing of the Calcareous mudstone and dark mudstone transition zone at the bottom of the upper part and the middle part of Es3 and the salt gypsum formation at the top and bottom of the Lower part of Es4 (Es4x). Good Source Rock is developed respectively in the two compartments, so Es3 and Es4 can be divided into two mutually independent petroleum systems (Es3Es4s petroleum system and Es4x petroleum system). “Rootfan seeling, midfan accumulation, outerfan migration” is the characteristic of the hydrocarbon accumulation in deep layer of nearshore subaqueous fan of Es4 in the north zone of Minfeng Sag. Hydrocarbon from the contemporaneous source rocks accumulates in the middlefan and forms “selfgeneration and selfaccumulation” lithologic reservoir.
Overpressure is widespread developed in the third member(Es3) and the forth member(Es4) of the Shahejie Formation of Dongying Depression. Es3 and Es4 are divided into two compartments(Es3Es4s compartment and Es4x compartment) by sealing of the Calcareous mudstone and dark mudstone transition zone at the bottom of the upper part and the middle part of Es3 and the salt gypsum formation at the top and bottom of the Lower part of Es4 (Es4x). Good Source Rock is developed respectively in the two compartments, so Es3 and Es4 can be divided into two mutually independent petroleum systems (Es3Es4s petroleum system and Es4x petroleum system). “Rootfan seeling, midfan accumulation, outerfan migration” is the characteristic of the hydrocarbon accumulation in deep layer of nearshore subaqueous fan of Es4 in the north zone of Minfeng Sag. Hydrocarbon from the contemporaneous source rocks accumulates in the middlefan and forms “selfgeneration and selfaccumulation” lithologic reservoir.
