2006 Vol. 24, No. 2
Display Method:
2006, 24(2): 153-164.
Abstract:
Chengdu basin developed ahead of Longmen Shan along the eastern margin of Tibetan Plateau, lying between the Longmen Shan and Longquan Shan, and extends from southwest to northeast with the long axis of the basin parallel to Longmen Shan. The filling in the basin with a maximum thickness of 541m include Dayi conglomerate, Yaan gravel layer and Late Pleistocene and Holocene gravel layer. In the transverse section of the basin(vertical to Longmen Shan), the wedge shaped sediments in the basin were derived from Longmen Shan and gradually northwestwards thickening, the depocenter is located in the northwestern part of the basin. As thrusting progressed southeastwards, the northwestern margin and the depocenter of the basin had been progressively migrated southeastwards. According to this evidence, it can be inferred that the direction of trusting and tectonic shorting was from NWSE and vertical to Longmen Shan. In the longitudinal section (parallel to Longmen Shan), there are many minor echelon depressions and uplifts, as dextral strikeslipping progressed northeastwards, the minor depression (rhombocham) and fan had been progressively migrated northeastwards. According to these lines of evidence, we can infer that the direction of dextral strikeslipping was from SWNE and parallel to Longmen Shan. So we draw a conclusion that the Chengdu basin is one of typical transpressional basin controlled by thrusting and strikeslipping along Longmen Shan since 3.6Ma.
Chengdu basin developed ahead of Longmen Shan along the eastern margin of Tibetan Plateau, lying between the Longmen Shan and Longquan Shan, and extends from southwest to northeast with the long axis of the basin parallel to Longmen Shan. The filling in the basin with a maximum thickness of 541m include Dayi conglomerate, Yaan gravel layer and Late Pleistocene and Holocene gravel layer. In the transverse section of the basin(vertical to Longmen Shan), the wedge shaped sediments in the basin were derived from Longmen Shan and gradually northwestwards thickening, the depocenter is located in the northwestern part of the basin. As thrusting progressed southeastwards, the northwestern margin and the depocenter of the basin had been progressively migrated southeastwards. According to this evidence, it can be inferred that the direction of trusting and tectonic shorting was from NWSE and vertical to Longmen Shan. In the longitudinal section (parallel to Longmen Shan), there are many minor echelon depressions and uplifts, as dextral strikeslipping progressed northeastwards, the minor depression (rhombocham) and fan had been progressively migrated northeastwards. According to these lines of evidence, we can infer that the direction of dextral strikeslipping was from SWNE and parallel to Longmen Shan. So we draw a conclusion that the Chengdu basin is one of typical transpressional basin controlled by thrusting and strikeslipping along Longmen Shan since 3.6Ma.
2006, 24(2): 175-184.
Abstract:
Cambrian System at Wangcun section, west Hunan Province, represents typical sedimentary successions on the Jiangnan Slop Belt. Traditionally, the Lower Cambrian Series at the Wangcun section is divided into Balang Formation, Qingxudong Formation; the Middle Cambrian is divided into Aoxi Formation as well as the lower member of Huqiao Formation, and the Upper Cambrian Series is divided into the upper member of Huqiao Formation and Zhuitun Formation. Formingstage of turbidity sediments within the Huqiao Formation can be attributed to seven longterm periods. The first turbidity succession in the Huqiao Formation includes 69 cycles that are attributed to 11 parasequences. The second turbidity succession in the Huaqiao Formation includes 37 cycles that are attributed to 7 parasequences. Lower part of each parasequence consists of initiated turbidity sediments, and the upper part of each parasequences consists of distal turbidity sediments. A gradual rise in sea level can be deduced based on the marine sediments within each parasequence. The first turbidity succession formed during the sealevel rising period consists of transgression system. However, the second turbidity succession deposited on the relatively steeper slope during the low sealevel period forms the low water system. The LowerMiddle Cambrian turbidity succession frequently deposited on the Jiangnan Slope Belt suggesting that periodic activities existed during the formation of deepfault along the margin of carbonate Platform.
Cambrian System at Wangcun section, west Hunan Province, represents typical sedimentary successions on the Jiangnan Slop Belt. Traditionally, the Lower Cambrian Series at the Wangcun section is divided into Balang Formation, Qingxudong Formation; the Middle Cambrian is divided into Aoxi Formation as well as the lower member of Huqiao Formation, and the Upper Cambrian Series is divided into the upper member of Huqiao Formation and Zhuitun Formation. Formingstage of turbidity sediments within the Huqiao Formation can be attributed to seven longterm periods. The first turbidity succession in the Huqiao Formation includes 69 cycles that are attributed to 11 parasequences. The second turbidity succession in the Huaqiao Formation includes 37 cycles that are attributed to 7 parasequences. Lower part of each parasequence consists of initiated turbidity sediments, and the upper part of each parasequences consists of distal turbidity sediments. A gradual rise in sea level can be deduced based on the marine sediments within each parasequence. The first turbidity succession formed during the sealevel rising period consists of transgression system. However, the second turbidity succession deposited on the relatively steeper slope during the low sealevel period forms the low water system. The LowerMiddle Cambrian turbidity succession frequently deposited on the Jiangnan Slope Belt suggesting that periodic activities existed during the formation of deepfault along the margin of carbonate Platform.
2006, 24(2): 185-192.
Abstract:
There exist three secondary porosity zones vertically in the Cenozoic reservoirs of the Southern Xibu Depression of the Bohaiwan Basin as revealed by the measured porosity data，thin sections，blue epoxy resinimpregnated thin sections and scanning electron microscopes. As a result，the highquality reservoirs are developed． Sedimentary microfacies and diageneses control the formations and occurrences of the highquality reservoirs， which are dominantly formed in the channel mouth bar， braided channel and channel bar deposits， located in the early diagenetic stage B～middle diagenetic stage A1〖KG*2〗and dissolution diagenetic facies． The diagenetic stages and diagenetic facies are predicted by modeling the paleotemperature， vitrinite reflectance， sterane isomerization rate and authigenic quartz concentration in space and time． The highquality reservoirs of the third middle member of Shahejie Formation are delineated by superposing the diagenetic facies map on the microfacies map． They are mainly in the middle part of the slop of the Southern Xibu Depression．
There exist three secondary porosity zones vertically in the Cenozoic reservoirs of the Southern Xibu Depression of the Bohaiwan Basin as revealed by the measured porosity data，thin sections，blue epoxy resinimpregnated thin sections and scanning electron microscopes. As a result，the highquality reservoirs are developed． Sedimentary microfacies and diageneses control the formations and occurrences of the highquality reservoirs， which are dominantly formed in the channel mouth bar， braided channel and channel bar deposits， located in the early diagenetic stage B～middle diagenetic stage A1〖KG*2〗and dissolution diagenetic facies． The diagenetic stages and diagenetic facies are predicted by modeling the paleotemperature， vitrinite reflectance， sterane isomerization rate and authigenic quartz concentration in space and time． The highquality reservoirs of the third middle member of Shahejie Formation are delineated by superposing the diagenetic facies map on the microfacies map． They are mainly in the middle part of the slop of the Southern Xibu Depression．
2006, 24(2): 202-209.
Abstract:
Breccia in Shulu depression was found in the middle and low of the third segment of Shahejie Formation, it is a breccia with carbonate fragment as its main constituent, and distributes skirt-shapely on slopes in the depression. Breccia and marlstone with breccia are familiar breccias in the area and the former is domestic. Grain and matrix in the breccia are mainly angular and subangular carbonate clastic particles, whose parent rock were carbonate stratum of Ordovician. Mainly grain support, massive structure, infrequent graded bedding and others bedding, un-sorting of detrital grains and thicker breccia layer are important features of carbonate breccia in Shulu depression. Characteristics of component, fabric, structure and geologic background all reveal that the breccia in the study area is inviscous debris flow sediment of terrestrial formation.
Breccia in Shulu depression was found in the middle and low of the third segment of Shahejie Formation, it is a breccia with carbonate fragment as its main constituent, and distributes skirt-shapely on slopes in the depression. Breccia and marlstone with breccia are familiar breccias in the area and the former is domestic. Grain and matrix in the breccia are mainly angular and subangular carbonate clastic particles, whose parent rock were carbonate stratum of Ordovician. Mainly grain support, massive structure, infrequent graded bedding and others bedding, un-sorting of detrital grains and thicker breccia layer are important features of carbonate breccia in Shulu depression. Characteristics of component, fabric, structure and geologic background all reveal that the breccia in the study area is inviscous debris flow sediment of terrestrial formation.
2006, 24(2): 217-222.
Abstract:
This research is systematically related to the characteristics and genetic analysis of algal limestones reservoirs, Nanyishan, Qaidam basin. The results show that: 1） Though the water environment of Nanyisan is more muddy than others, algal can still grow; 2) The composition and rock type of the algal limestone are complex, the main rock types include lettucelike stromatolites, algal reef, digitate stromatolies, wavelike stromatolites and so on; 3) The deposits of algal limestones were formed in lowenergy peritidal to subtidal highenergy environment of lakeshore slopes, sliding under the action of gravity and some other factors and become slump Mixosedimentite layers; 4) The physical property of algal limestones layers is better than others; 5)The genetic development of the sediment decides that the single deposit is small, distributive and thinlayed.
This research is systematically related to the characteristics and genetic analysis of algal limestones reservoirs, Nanyishan, Qaidam basin. The results show that: 1） Though the water environment of Nanyisan is more muddy than others, algal can still grow; 2) The composition and rock type of the algal limestone are complex, the main rock types include lettucelike stromatolites, algal reef, digitate stromatolies, wavelike stromatolites and so on; 3) The deposits of algal limestones were formed in lowenergy peritidal to subtidal highenergy environment of lakeshore slopes, sliding under the action of gravity and some other factors and become slump Mixosedimentite layers; 4) The physical property of algal limestones layers is better than others; 5)The genetic development of the sediment decides that the single deposit is small, distributive and thinlayed.
2006, 24(2): 229-234.
Abstract:
The calculation of mineral contents in rocks is an important basal work in geochemistry and petrology. The traditional methods mainly depend on microscopeobservation and programme calculation, which are useful when the mineral compositions are simple, but these methods will be inefficient when the mineral contents are complex. This paper presents the Nonnegative linear least square method of MATLAB-a quick and precise method of calculating mineral contents of detrital rocks with some examples. The results show that it's more accurate and quick to use MATLAB than other methods. Simultaneously, when use MATLAB, pay attention to choosing the appropriate data to ensure the authenticity of the results.
The calculation of mineral contents in rocks is an important basal work in geochemistry and petrology. The traditional methods mainly depend on microscopeobservation and programme calculation, which are useful when the mineral compositions are simple, but these methods will be inefficient when the mineral contents are complex. This paper presents the Nonnegative linear least square method of MATLAB-a quick and precise method of calculating mineral contents of detrital rocks with some examples. The results show that it's more accurate and quick to use MATLAB than other methods. Simultaneously, when use MATLAB, pay attention to choosing the appropriate data to ensure the authenticity of the results.
2006, 24(2): 242-250.
Abstract:
Based on studies of ecological characteristics of Ordovician Cephalopod from the southern China, Eighteen Cephalopod biofacies are recognized and described: 1.Open platform [WTBX]Proterocameroceras[WT] biofacies, 2. Restricted platform [WTBX]PseudoectenolitesXiadongoceras[WT] biofacies, 3. Open platform [WTBX]RetroclitendocerasPararetroclitendoceras[WT] biofacies, 4. Open platform [WTBX]Pronajaceras Mamagouceras[WT] biofacies, 5. Shelf slopebasin [WTBX]Cyclostomiceras[WT] biofacies, 6. Open platform [WTBX]CamerocerasCyrtovaginoceras
Based on studies of ecological characteristics of Ordovician Cephalopod from the southern China, Eighteen Cephalopod biofacies are recognized and described: 1.Open platform [WTBX]Proterocameroceras[WT] biofacies, 2. Restricted platform [WTBX]PseudoectenolitesXiadongoceras[WT] biofacies, 3. Open platform [WTBX]RetroclitendocerasPararetroclitendoceras[WT] biofacies, 4. Open platform [WTBX]Pronajaceras Mamagouceras[WT] biofacies, 5. Shelf slopebasin [WTBX]Cyclostomiceras[WT] biofacies, 6. Open platform [WTBX]CamerocerasCyrtovaginoceras
2006, 24(2): 251-258.
Abstract:
Highresolution sequence stratigraphy division of Shanxi Formation in northwestern part of Ordos basin has been put forward according to principle〖KG*2〗of base level cycle based on 4 outcrops and 35 core description and 305 well logs. As a component of longterm baselevel decreasing cycle, Shanxi Formation constitutes a mediumterm cycle, which can be subdivided into 5 shortterm cycles in ascending order(SSC1,SSC2,SSC3,SSC4,SSC5). Based on the sequence structure, and stack style and space variation, the highresolution sequence stratigraphy correlation framework〖KG*2〗is established to discuss sedimentary facies styles and controlling factors and physical〖KG*2〗property. The most favorable reservoir bodies were formed during early stage of semiascending cycle of short-term baselevel cycle. Reservoir bodies are mainly composed of delta plain distributary channel and delta front subaqueous channel. Here, the monofactor mapping method is adopted to study space distribution of the reservoir〖KG*2〗bed.
Highresolution sequence stratigraphy division of Shanxi Formation in northwestern part of Ordos basin has been put forward according to principle〖KG*2〗of base level cycle based on 4 outcrops and 35 core description and 305 well logs. As a component of longterm baselevel decreasing cycle, Shanxi Formation constitutes a mediumterm cycle, which can be subdivided into 5 shortterm cycles in ascending order(SSC1,SSC2,SSC3,SSC4,SSC5). Based on the sequence structure, and stack style and space variation, the highresolution sequence stratigraphy correlation framework〖KG*2〗is established to discuss sedimentary facies styles and controlling factors and physical〖KG*2〗property. The most favorable reservoir bodies were formed during early stage of semiascending cycle of short-term baselevel cycle. Reservoir bodies are mainly composed of delta plain distributary channel and delta front subaqueous channel. Here, the monofactor mapping method is adopted to study space distribution of the reservoir〖KG*2〗bed.
2006, 24(2): 267-275.
Abstract:
Sandy desertification in southeast Mo Us desert and its neighboring regions, according to their material origins〖KG*2〗and physiographic〖KG*2〗characteristics, can be classified into four types, sandy land insitu type, flow valley in situ type, weathered residual insitu type and finally the wind drifted type. The sands of sandy desertification of sandy land insitu type come from both palaeoaeolian〖KG*2〗sand and those of paleoor modern fluvial or lacustrine facies. Sands of this type of desertification have the characteristics such as coarse grain, of which mid grain size are between 200－300μｍ or even bigger than 1mm, lower standard〖KG*2〗deviation, and narrow and positive leaning distribution〖KG*2〗patterns. Researches on grain size parameters show that their formation environment is likely fluvial.
Sandy desertification of valley insitu type distributes mainly in river valleys and their neighbored regions, such as flood beds, terraces and nearby districts. Sands of this type may have varieties of sources, such as modern and paleo fluvial or flooded sediments Quaternary Epoch.
Sands of this type have the characteristics of broad range mid grain size (40-445μｍ), middle degree of sorting, narrow and positive leaning distribution patterns. These features suggest that the sands of river valley type desertification are mixtures of different geologic processes, mainly fluvial and aeolian.
Weathered residual insitu type desertification are formed by the erosion and separation by wind and fluvial forces of any sediments occurred in the region. During this process, fine grains become less and less, coarse grains remained. This type of sandy desertification mainly occurred in the north part of loess plateau. Their sands may come from paleoaeolian sands, sandy loess, paleosols as well as paleofluvial terrace sediments. Reactive paleoaeolian sands have the characteristics of both homogeneous in limited areas and features of different layers. Palaeoaeolian sands have twograin grades in the studied area, of which average grain size are between 23-60μm and 152－202μm respectively. They also have narrow, positive leaning distribution curves.
Wind drifted sandy desertification have the characteristics such as coarse grained sands (140－310μm), low clay contents ( <5% ), and very narrow and positive leaning distribution curves. This suggests that they are the products of modern windblown sands.
For the purpose of combating sandy desertification of different genetic type, it is important that different protect and renovate measurements should be used. It is strongly suggested that using the methods of seeding grasses and manpower projects to fix the drifting sands during combating sandy land insitu desertification. As for the river valley in situ desertification, the methods of reducing soil erosion, protecting terraces and flood beds should be firstly used.
To deal with the weathered residual desertification, methods of reducing water and wind erosion protecting finegrain materialsfrom losses can be used, such as reducing herding, vegetation and plantation. Finally, for combating wind drifted sandy desertification, manpower projects can be used to reduce wind harm and organic measurements to increase the percentage of coverage.
Sandy desertification in southeast Mo Us desert and its neighboring regions, according to their material origins〖KG*2〗and physiographic〖KG*2〗characteristics, can be classified into four types, sandy land insitu type, flow valley in situ type, weathered residual insitu type and finally the wind drifted type. The sands of sandy desertification of sandy land insitu type come from both palaeoaeolian〖KG*2〗sand and those of paleoor modern fluvial or lacustrine facies. Sands of this type of desertification have the characteristics such as coarse grain, of which mid grain size are between 200－300μｍ or even bigger than 1mm, lower standard〖KG*2〗deviation, and narrow and positive leaning distribution〖KG*2〗patterns. Researches on grain size parameters show that their formation environment is likely fluvial.
Sandy desertification of valley insitu type distributes mainly in river valleys and their neighbored regions, such as flood beds, terraces and nearby districts. Sands of this type may have varieties of sources, such as modern and paleo fluvial or flooded sediments Quaternary Epoch.
Sands of this type have the characteristics of broad range mid grain size (40-445μｍ), middle degree of sorting, narrow and positive leaning distribution patterns. These features suggest that the sands of river valley type desertification are mixtures of different geologic processes, mainly fluvial and aeolian.
Weathered residual insitu type desertification are formed by the erosion and separation by wind and fluvial forces of any sediments occurred in the region. During this process, fine grains become less and less, coarse grains remained. This type of sandy desertification mainly occurred in the north part of loess plateau. Their sands may come from paleoaeolian sands, sandy loess, paleosols as well as paleofluvial terrace sediments. Reactive paleoaeolian sands have the characteristics of both homogeneous in limited areas and features of different layers. Palaeoaeolian sands have twograin grades in the studied area, of which average grain size are between 23-60μm and 152－202μm respectively. They also have narrow, positive leaning distribution curves.
Wind drifted sandy desertification have the characteristics such as coarse grained sands (140－310μm), low clay contents ( <5% ), and very narrow and positive leaning distribution curves. This suggests that they are the products of modern windblown sands.
For the purpose of combating sandy desertification of different genetic type, it is important that different protect and renovate measurements should be used. It is strongly suggested that using the methods of seeding grasses and manpower projects to fix the drifting sands during combating sandy land insitu desertification. As for the river valley in situ desertification, the methods of reducing soil erosion, protecting terraces and flood beds should be firstly used.
To deal with the weathered residual desertification, methods of reducing water and wind erosion protecting finegrain materialsfrom losses can be used, such as reducing herding, vegetation and plantation. Finally, for combating wind drifted sandy desertification, manpower projects can be used to reduce wind harm and organic measurements to increase the percentage of coverage.
2006, 24(2): 282-288.
Abstract:
Four〖KG*2〗organic〖KG*2〗samples in〖KG*2〗Songliao basin〖KG*2〗are simultaneously tested〖KG*2〗in the closedsystem of autoclave isothermal hydrous pyrolysis experiment and opensystem of RockEval constant heating rate pyrolysis experiment, separately. Based on the latter experimental data, the chemical kinetic models are calibrated and then the generation rates of oil and gas under the same conditions as the former autoclave experiment are calculated from the models calibrated. The results show that it is more accurate to measure the liquid oil product by the online measurement of RockEval than the autoclave experiment that needs extraction and a constant weight because of no light hydrocarbons (C6—C13) missing in the constant heating rate experiment, and clearly, it provides an effective way to measure the light hydrocarbons (C6—C13) that are difficult to measure in the thermal simulation experiment but significant to evaluate the amount of hydrocarbon generation. Simultaneously, this method can avoid gas leakage influencing gas generation rate accuracy in the autoclave experiment. It is possibly indicated that it is not only feasible to use the chemical kinetic〖KG*2〗model calibrated by the experiment data to calculate〖KG*2〗the hydrocarbon generation rate, but also more accurate.
Four〖KG*2〗organic〖KG*2〗samples in〖KG*2〗Songliao basin〖KG*2〗are simultaneously tested〖KG*2〗in the closedsystem of autoclave isothermal hydrous pyrolysis experiment and opensystem of RockEval constant heating rate pyrolysis experiment, separately. Based on the latter experimental data, the chemical kinetic models are calibrated and then the generation rates of oil and gas under the same conditions as the former autoclave experiment are calculated from the models calibrated. The results show that it is more accurate to measure the liquid oil product by the online measurement of RockEval than the autoclave experiment that needs extraction and a constant weight because of no light hydrocarbons (C6—C13) missing in the constant heating rate experiment, and clearly, it provides an effective way to measure the light hydrocarbons (C6—C13) that are difficult to measure in the thermal simulation experiment but significant to evaluate the amount of hydrocarbon generation. Simultaneously, this method can avoid gas leakage influencing gas generation rate accuracy in the autoclave experiment. It is possibly indicated that it is not only feasible to use the chemical kinetic〖KG*2〗model calibrated by the experiment data to calculate〖KG*2〗the hydrocarbon generation rate, but also more accurate.
2006, 24(2): 294-299.
Abstract:
Biomarker is one of the most effective tools in the study of oilsource correlation gasoil maturity and gasoil migration. By using biomarker GC, GC—MS analysis techniques, the geochemical characters of steranes and hopanes from crude oils of Tahe oil field were investigated in this paper. The study shows〖KG*2〗Tahe oilfield is a compound oil reservoir, which is composed of later generated oils with high maturity lighter biodegradation and earlier〖KG*2〗generated oils with low maturity stronger biodegradation. The characters of C27—C29〖KG*2〗steranes and hopanes series indicate oils with varied maturities generated from the same sort of mother materials. The threedimensional diagram〖KG*2〗formed by Ts/(Tm+Ts),〖KG*2〗rearrangedsterane/sterane and ββ/(ββ+αα)C29〖KG*2〗shows that the migration direction of crude oil is from south to north, which confirms the opinion that oil and gas of Tahe oilfield mainly came from Manjiar Depression——an area to the south of Tahe oilfield.
Biomarker is one of the most effective tools in the study of oilsource correlation gasoil maturity and gasoil migration. By using biomarker GC, GC—MS analysis techniques, the geochemical characters of steranes and hopanes from crude oils of Tahe oil field were investigated in this paper. The study shows〖KG*2〗Tahe oilfield is a compound oil reservoir, which is composed of later generated oils with high maturity lighter biodegradation and earlier〖KG*2〗generated oils with low maturity stronger biodegradation. The characters of C27—C29〖KG*2〗steranes and hopanes series indicate oils with varied maturities generated from the same sort of mother materials. The threedimensional diagram〖KG*2〗formed by Ts/(Tm+Ts),〖KG*2〗rearrangedsterane/sterane and ββ/(ββ+αα)C29〖KG*2〗shows that the migration direction of crude oil is from south to north, which confirms the opinion that oil and gas of Tahe oilfield mainly came from Manjiar Depression——an area to the south of Tahe oilfield.
2006, 24(2): 165-174.
Abstract:
Onehundredandfiftyfour Mesozoic sandstone samples from the Qiangtang block (ca. 3３°~35°N, 85°~93°E) were conducted for analysis of detrital modes, in an attempt to evaluate their provenance and the type of tectonic setting in which they were deposited. The LowerMiddle Triassic sandstones (Q61±8F27±13L12±10, Qm59±8F28±13Lt13±9, Qp28±22Lvm72±22Lsm0±0) in central Qiangtang are characterized by complex derivations from both recycled orogen and continental block provenances. The most of the Upper Triassic (Q78±12F7±7L15±11, Qm77±12F7±7Lt16±11, Qp16±11Lvm30±35Lsm54±33), Lower Jurassic (Q83±20F2±2L15±22, Qm79±23F2±2Lt19±24, Qp35±19Lvm0±0 Lsm65±19), Middle Jurassic (Q69±22F6±6L24±25, Qm67±22F6±6Lt26±24, Qp14±22Lvm32±38Lsm54±38), and Upper Jurassic (Q80±17F6±4L14±17, Qm78±17F6±4Lt16±16, Qp17±23Lvm27±35Lsm56±34) sandstones are dominated by recycled orogen origin. However, the sandstones that were derived from continental block source also exist in the southern margin of southern Qiangtang and in the Lower Jurassic strata in the southern margin of northern Qiangtang. It could have contained abundant ophiolitic fragments and other readilydecomposed ferromagnesian minerals across the entire anticlinorium. These mafic minerals point to the presence of the Shuanghu suture along the entire central Qiangtang anticlinorium and the blueschistbearing metamorphic complexes in central Qiangtang could be accommodated in a largescale enclave in an irregular central Qiangtang continental margin. The distribution of Mesozoic recycled orogenderived sandstones on Qiangtang indicates a contraction background, supporting〖KG*2〗a tensile mechanism for backarc spreading along the BangongNujiang belt.
Onehundredandfiftyfour Mesozoic sandstone samples from the Qiangtang block (ca. 3３°~35°N, 85°~93°E) were conducted for analysis of detrital modes, in an attempt to evaluate their provenance and the type of tectonic setting in which they were deposited. The LowerMiddle Triassic sandstones (Q61±8F27±13L12±10, Qm59±8F28±13Lt13±9, Qp28±22Lvm72±22Lsm0±0) in central Qiangtang are characterized by complex derivations from both recycled orogen and continental block provenances. The most of the Upper Triassic (Q78±12F7±7L15±11, Qm77±12F7±7Lt16±11, Qp16±11Lvm30±35Lsm54±33), Lower Jurassic (Q83±20F2±2L15±22, Qm79±23F2±2Lt19±24, Qp35±19Lvm0±0 Lsm65±19), Middle Jurassic (Q69±22F6±6L24±25, Qm67±22F6±6Lt26±24, Qp14±22Lvm32±38Lsm54±38), and Upper Jurassic (Q80±17F6±4L14±17, Qm78±17F6±4Lt16±16, Qp17±23Lvm27±35Lsm56±34) sandstones are dominated by recycled orogen origin. However, the sandstones that were derived from continental block source also exist in the southern margin of southern Qiangtang and in the Lower Jurassic strata in the southern margin of northern Qiangtang. It could have contained abundant ophiolitic fragments and other readilydecomposed ferromagnesian minerals across the entire anticlinorium. These mafic minerals point to the presence of the Shuanghu suture along the entire central Qiangtang anticlinorium and the blueschistbearing metamorphic complexes in central Qiangtang could be accommodated in a largescale enclave in an irregular central Qiangtang continental margin. The distribution of Mesozoic recycled orogenderived sandstones on Qiangtang indicates a contraction background, supporting〖KG*2〗a tensile mechanism for backarc spreading along the BangongNujiang belt.
2006, 24(2): 193-201.
Abstract:
Origin and evolution of the hydrodynamics has important relationship with the migration and accumulation of petroleum in sedimentary basins. The hydrodynamics made of several hydrodynamic systems in the Songliao basin is asymmetrical obviously, with the characteristics of gravityinduced centripetal flow recharged by meteoric water mainly at its northern and northeastern regions, centrifugal flow and crossformational flow at the basin center area, as well as crossformational flowevaporation at its southern area. And every hydrodynamic unit of the hydrodynamics in the Songliao basin has its own characters in aspects of stratum pressure, the waterflow direction, potential level and vertical pressure grads. Meanwhile, the origin and evolution of the hydrodynamics is characterized by stages, and its intensity has the property of vertical zonation, with the depth increasing, strong, weak and stagnant waterzones could be divided.
Origin and evolution of the hydrodynamics has important relationship with the migration and accumulation of petroleum in sedimentary basins. The hydrodynamics made of several hydrodynamic systems in the Songliao basin is asymmetrical obviously, with the characteristics of gravityinduced centripetal flow recharged by meteoric water mainly at its northern and northeastern regions, centrifugal flow and crossformational flow at the basin center area, as well as crossformational flowevaporation at its southern area. And every hydrodynamic unit of the hydrodynamics in the Songliao basin has its own characters in aspects of stratum pressure, the waterflow direction, potential level and vertical pressure grads. Meanwhile, the origin and evolution of the hydrodynamics is characterized by stages, and its intensity has the property of vertical zonation, with the depth increasing, strong, weak and stagnant waterzones could be divided.
Analysis on the Lithofacies and Paleogeography of Fengtai Group in the Southeast North China Block
2006, 24(2): 210-216.
Abstract:
Fengtai Formation sedimented at the transition phase of Sinian and Cambrian has important meanings to confirm the sedimentary and tectonic circumstances of this transition phase by analyzing the lithofacies and paleogeography of this Formation. The lithofacies of Fengtai Formation mainly consist of silty mudstone facies contained phosphate concretions, blocky conglomerate facies, layered(coarsely layered) conglomerate facies, lens-shaped lithic greywacke facies contained gravels and arenaceous conglomerate facies, layered lithic greywacke (contained gravels)facies, rhythmically laminated lithic greywacke facies, which assembly bears the sedimentary model of submarine fan.The microfacies of Fengtai Formation mainly consist of conglomerate and lithic greywacke microfacies contained pyrites, lithic greywacke microfacies with neddle-like ring edge structure, breccias microfacies, lithic greywacke microfacies with reverse grading, which assembly bears the features of continental margin. Based on the above and the feature of sedimentary distribution，Fengtai Formation collectively is channel deposition of submarine fan which is similar to submarine canyon at high-angle continent edge probably generated by fault movement.
Fengtai Formation sedimented at the transition phase of Sinian and Cambrian has important meanings to confirm the sedimentary and tectonic circumstances of this transition phase by analyzing the lithofacies and paleogeography of this Formation. The lithofacies of Fengtai Formation mainly consist of silty mudstone facies contained phosphate concretions, blocky conglomerate facies, layered(coarsely layered) conglomerate facies, lens-shaped lithic greywacke facies contained gravels and arenaceous conglomerate facies, layered lithic greywacke (contained gravels)facies, rhythmically laminated lithic greywacke facies, which assembly bears the sedimentary model of submarine fan.The microfacies of Fengtai Formation mainly consist of conglomerate and lithic greywacke microfacies contained pyrites, lithic greywacke microfacies with neddle-like ring edge structure, breccias microfacies, lithic greywacke microfacies with reverse grading, which assembly bears the features of continental margin. Based on the above and the feature of sedimentary distribution，Fengtai Formation collectively is channel deposition of submarine fan which is similar to submarine canyon at high-angle continent edge probably generated by fault movement.
2006, 24(2): 223-228.
Abstract:
This paper overviews the sedimentary environment for the sandstonetype uranium deposits in China, analyzes the situation and significance of these researches in this field, types of Ubearing clastic sedimentary Formations, and favorable facies for the formation of sandstonetype uranium deposits as well. Several aspects, which should be paid attention to during the study of the sedimentary environment for sandstonetype uranium deposits, are put forward finally.
This paper overviews the sedimentary environment for the sandstonetype uranium deposits in China, analyzes the situation and significance of these researches in this field, types of Ubearing clastic sedimentary Formations, and favorable facies for the formation of sandstonetype uranium deposits as well. Several aspects, which should be paid attention to during the study of the sedimentary environment for sandstonetype uranium deposits, are put forward finally.
2006, 24(2): 235-241.
Abstract:
The Earth's most severe glaciation is considered to have occurred about 635 million years ago, in the late Neoproterozoic era, and is believed to have engulfed the entire earth under ice to create what came to be described as “Snowball Earth”. Carbonate rocks directly and ubiquitously overlie Neoproterozoic glacial diamicrites on almost every continent, and are commonly referred to as “cap carbonates”. Their unusual facies and strongly negative carbon isotopic signature stirred up considerable debates in the academic community, as they wonder how cap carbonates could have formed, thus “Snowball Earth” and “Methane Seep” were hypothesized. The “Snowball earth” hypothesis can explain many phenomena related to the Neoproterozoic glaciations, cap carbonates have been controversially ascribed to the aftermath of almost complete shutdown of the ocean ecosystems for millions of years during such ice ages.Conversely, it has also been suggested that these carbonate rocks were the result of destabilization of methane hydrates during deglaciation and concomitant flooding of continental shelves and interior basins. Recent carbon isotopic data of cap carbonates (δ13C as low as -41‰) provides direct evidence for methane-influenced process during deglaciation, strongly supported〖KG*2〗“Methane Seep” hypothesis.
The Earth's most severe glaciation is considered to have occurred about 635 million years ago, in the late Neoproterozoic era, and is believed to have engulfed the entire earth under ice to create what came to be described as “Snowball Earth”. Carbonate rocks directly and ubiquitously overlie Neoproterozoic glacial diamicrites on almost every continent, and are commonly referred to as “cap carbonates”. Their unusual facies and strongly negative carbon isotopic signature stirred up considerable debates in the academic community, as they wonder how cap carbonates could have formed, thus “Snowball Earth” and “Methane Seep” were hypothesized. The “Snowball earth” hypothesis can explain many phenomena related to the Neoproterozoic glaciations, cap carbonates have been controversially ascribed to the aftermath of almost complete shutdown of the ocean ecosystems for millions of years during such ice ages.Conversely, it has also been suggested that these carbonate rocks were the result of destabilization of methane hydrates during deglaciation and concomitant flooding of continental shelves and interior basins. Recent carbon isotopic data of cap carbonates (δ13C as low as -41‰) provides direct evidence for methane-influenced process during deglaciation, strongly supported〖KG*2〗“Methane Seep” hypothesis.
2006, 24(2): 259-266.
Abstract:
The highresolution sequence stratigraphy theories and technologies are widely used in the exploration and exploitation of subtle lithologic gas reservoir, taking it as a direction ,through dynamic analysis on baselevel cycle structure and stacking pattern , combined with the comprehensive studies of outcrops, cores and well logs,two longterm, five middleterm and fourteen shortterm cyclic sequences from the lower Shihezi Formation of Su 6 well area in Sulige gas field are classified. the structure types, sedimentary cycles, stacking patterns of shortterm, middleterm, longterm cyclic sequences and the relationship between cyclic sequences and distribution of favoring sand are discussed in detail. A chronostratigraghic framework is established by reference to the longterm and middleterm cycle sequences, in which the characteristics of different type of sand are discussed in detail. Based on the division and correlation of individualsandbody correspond to shortterm cyclic sequence,directing by the method of lithofaciespaleogeographical mapping, the sedimentary facies and sand distribution maps of the short or middleterm cyclic sequences come into being , the distribution of favoring sand reservoir can be predicted.
The highresolution sequence stratigraphy theories and technologies are widely used in the exploration and exploitation of subtle lithologic gas reservoir, taking it as a direction ,through dynamic analysis on baselevel cycle structure and stacking pattern , combined with the comprehensive studies of outcrops, cores and well logs,two longterm, five middleterm and fourteen shortterm cyclic sequences from the lower Shihezi Formation of Su 6 well area in Sulige gas field are classified. the structure types, sedimentary cycles, stacking patterns of shortterm, middleterm, longterm cyclic sequences and the relationship between cyclic sequences and distribution of favoring sand are discussed in detail. A chronostratigraghic framework is established by reference to the longterm and middleterm cycle sequences, in which the characteristics of different type of sand are discussed in detail. Based on the division and correlation of individualsandbody correspond to shortterm cyclic sequence,directing by the method of lithofaciespaleogeographical mapping, the sedimentary facies and sand distribution maps of the short or middleterm cyclic sequences come into being , the distribution of favoring sand reservoir can be predicted.
2006, 24(2): 276-281.
Abstract:
Based on the synthetic study on the correlations between magnetic susceptibility and the content of the different grain size〖KG*2〗of XH1# core in northern Jiangsu basin, this paper shows that the correlation is different〖KG*2〗in various depth: 350~247m, the mass susceptibility correlates negatively with〖KG*2〗mid-grain sizes, but correlates positively with the content〖KG*2〗of 4~12Φ; 234~0m, the mass susceptibility correlates positively with〖KG*2〗mid-grain sizes, and correlates positively with the content〖KG*2〗of 1~3Φ; The depth of 247~234m is the transition period of the transform of the correlations between magnetic susceptibility and the content of the different grain size.〖KG*2〗The results of environmental magnetism research〖KG*2〗show that the components〖KG*2〗of magnetic mineral are also different〖KG*2〗in the upper stratum(234~0m) and the lower stratum(350~247m). The difference〖KG*2〗of the correlations between magnetic susceptibility and the content of the different grain size,〖KG*2〗and the components〖KG*2〗of magnetic mineral in various depth reveal that, in the course〖KG*2〗of the sediment deposition in the depth 247~234m, one great event may have happened in Northern Jiangsu Basin, this event led to the change of detrital sediment〖KG*2〗origin.
Based on the synthetic study on the correlations between magnetic susceptibility and the content of the different grain size〖KG*2〗of XH1# core in northern Jiangsu basin, this paper shows that the correlation is different〖KG*2〗in various depth: 350~247m, the mass susceptibility correlates negatively with〖KG*2〗mid-grain sizes, but correlates positively with the content〖KG*2〗of 4~12Φ; 234~0m, the mass susceptibility correlates positively with〖KG*2〗mid-grain sizes, and correlates positively with the content〖KG*2〗of 1~3Φ; The depth of 247~234m is the transition period of the transform of the correlations between magnetic susceptibility and the content of the different grain size.〖KG*2〗The results of environmental magnetism research〖KG*2〗show that the components〖KG*2〗of magnetic mineral are also different〖KG*2〗in the upper stratum(234~0m) and the lower stratum(350~247m). The difference〖KG*2〗of the correlations between magnetic susceptibility and the content of the different grain size,〖KG*2〗and the components〖KG*2〗of magnetic mineral in various depth reveal that, in the course〖KG*2〗of the sediment deposition in the depth 247~234m, one great event may have happened in Northern Jiangsu Basin, this event led to the change of detrital sediment〖KG*2〗origin.
2006, 24(2): 289-293.
Abstract:
Linyi subsag have many faults in Paleogene and Neogene. Meanwhile, their sedimentary facies and depositional systems change frequently.〖KG*2〗Those provided avail qualification for forming the lithologic oil reservoir. The lithologic oil reservoirs in Paleogene〖KG*2〗in Linyi subsag include three kinds, such as oil charged in lensshaped sand body, lithologic upclined pinchout oil reservoir〖KG*2〗and oil charged in sand body that connected on the flanks of the faults. It was suggested that oil charged in lensshaped sand body will easily take place in deep sag belts and delta front〖KG*2〗in gentle slope belts. It was also suggested〖KG*2〗that lithologic upclined pinchout oil reservoirs will easily take place in gentle slope belts. And then, oil charged in sand body that connected on the flanks of the faults easily take place nearby the tectonic belts that faults relatively developed. The exploration practice〖KG*2〗in Linyin subsag revealed that it has abundant oil resources. The primary factor analysis of main controlling〖KG*2〗factors for〖KG*2〗the lithologic oil reservoir forming suggests that the most important controlling factors are the distribution of delta front sand body and fluxoturbidite body and lake sand body, the characteristics of the sealing and translocation of the fault block and unconformability and the characteristics of the valid cap rocks. Under their main control factors, it formed different types of lithologic oil reservoirs in different tectonic positions and different sedimentary facies in order.
Linyi subsag have many faults in Paleogene and Neogene. Meanwhile, their sedimentary facies and depositional systems change frequently.〖KG*2〗Those provided avail qualification for forming the lithologic oil reservoir. The lithologic oil reservoirs in Paleogene〖KG*2〗in Linyi subsag include three kinds, such as oil charged in lensshaped sand body, lithologic upclined pinchout oil reservoir〖KG*2〗and oil charged in sand body that connected on the flanks of the faults. It was suggested that oil charged in lensshaped sand body will easily take place in deep sag belts and delta front〖KG*2〗in gentle slope belts. It was also suggested〖KG*2〗that lithologic upclined pinchout oil reservoirs will easily take place in gentle slope belts. And then, oil charged in sand body that connected on the flanks of the faults easily take place nearby the tectonic belts that faults relatively developed. The exploration practice〖KG*2〗in Linyin subsag revealed that it has abundant oil resources. The primary factor analysis of main controlling〖KG*2〗factors for〖KG*2〗the lithologic oil reservoir forming suggests that the most important controlling factors are the distribution of delta front sand body and fluxoturbidite body and lake sand body, the characteristics of the sealing and translocation of the fault block and unconformability and the characteristics of the valid cap rocks. Under their main control factors, it formed different types of lithologic oil reservoirs in different tectonic positions and different sedimentary facies in order.
2006, 24(2): 300-308.
Abstract:
During the recent years, several medium and largescale gas fields, such as the Luojiazhai, Dukouhe, Tianshanpo and Puguang, etc, whose most remarkable features being the higher H2S contents, have been discovered in the northeastern Sichuan basin. Their H2S contents among the gas compositions account for 10 to 17 percent while the average being 14 percent. Based on the thorough study, it can be found that although these largescale oolitic shoal gas reservoirs usually have rich reserves along with high individualwell producing rate, their coefficients of fullness, which ranging from 25 to 91 percent, are generally rather low, also, their pressure coefficients are not high and mostly less than 1.2. According to their reservoir forming conditions, i.e., the abundant oolitic dissolution pores, the efficient reservoirs with huge thickness, the robust gas source, the welldeveloped transport systems, together with the excellent seal ability of the caprocks constituted by shale and gypsolyte, their lower coefficients of fullness were possibly due to a large quantity of hydrocarbons had been consumed or depleted within the traps. In the northeastern Sichuan basin, due to the H2S contained within the Feixianguan formation was generated from the TSR reactions, which occurred within reservoirs, between hydrocarbons and sulfate, there exist negative correlations between the H2S contents and the pressure coefficients, the reservoir water salinity together with the hydrocarbons contents, etc. Therefore, as far as the gas reservoirs with high H2S contents of the Feixianguan formation was concerned, their lower pressure coefficients and coefficients of fullness are likely caused by both the hydrocarbons had been consumed greatly due to TSR and the volume of reservoirs had been expanded.
During the recent years, several medium and largescale gas fields, such as the Luojiazhai, Dukouhe, Tianshanpo and Puguang, etc, whose most remarkable features being the higher H2S contents, have been discovered in the northeastern Sichuan basin. Their H2S contents among the gas compositions account for 10 to 17 percent while the average being 14 percent. Based on the thorough study, it can be found that although these largescale oolitic shoal gas reservoirs usually have rich reserves along with high individualwell producing rate, their coefficients of fullness, which ranging from 25 to 91 percent, are generally rather low, also, their pressure coefficients are not high and mostly less than 1.2. According to their reservoir forming conditions, i.e., the abundant oolitic dissolution pores, the efficient reservoirs with huge thickness, the robust gas source, the welldeveloped transport systems, together with the excellent seal ability of the caprocks constituted by shale and gypsolyte, their lower coefficients of fullness were possibly due to a large quantity of hydrocarbons had been consumed or depleted within the traps. In the northeastern Sichuan basin, due to the H2S contained within the Feixianguan formation was generated from the TSR reactions, which occurred within reservoirs, between hydrocarbons and sulfate, there exist negative correlations between the H2S contents and the pressure coefficients, the reservoir water salinity together with the hydrocarbons contents, etc. Therefore, as far as the gas reservoirs with high H2S contents of the Feixianguan formation was concerned, their lower pressure coefficients and coefficients of fullness are likely caused by both the hydrocarbons had been consumed greatly due to TSR and the volume of reservoirs had been expanded.
