1994 Vol. 12, No. 4
column
Display Method:
1994, 12(4): 1-10.
Abstract:
ABSTRACT-Four glaciations can be recognized，in Pleistocene of Mt. Xixabangma Region，from old to new named, Xixabangma, Nyanyaxungla, Qomolangma I (Jilong Temple) and Qomolangma Ⅱ (Rongbu Temple),equivalent to Nebraskan，Kansan，Illinolian and Wisconsinian Glaciation in Mountain region in North America. Nyanyaxungla Glaciation was the maximum in glacial extent in this region. At the time glaciers covered over the whole of the Fuqu valley，which destructed the glacial deposits in Xixabangma Glaciation almost completely. There is only glacial traces from the last three glaciations since the Middle Pleistocene, and a series of end moraines is in the Holocene they are Nyalam，Fuqu and Pulou Glaciations, which each glaciation can be also divided into two substages.^higher moraine plateform is extended in south of Nyalam，which is 1. 5km wide, 3. 5km long and 300m above Nyalam，with yellow brown soil on the surface overlying a red paleosol layer, the till about 200m thick，The moraine plateform is the great valley glacier deposits of Nyalam ( Nyanyaxangla)Glaciation of the Middle Pieistocene, A several kilometers moraine section is exposed at the end of the platform because of the Chinese-Nepal Highway cut over, and may be observed complex deposits faGise and glaciotectonics, including superglacial and subglacial meltout tills, flow till，logement till，dump till, englacial-subglacial meltwater channel deposits, glacial lacutrine sediments, droping boulders of floating ice, deformation till. The glaciotectonic and depositional structures，such as thrust plane, collapse structure, sliding plane and so on, are also very clearly. All these composites reflect the large scale of glacier, rapid movement of glacier, strong ablation，developing of glacial lakes and subglacial channels and avalancheing of ice bodies, all which generally occour at warm or martime glaciers. The glacial facies and glaciotectonic marks respressent a martime (warm )glacial depositional process and thermal sitiuaion. The moraine plateform section is one of the most ideal field for research on glaciotectonice in China.
ABSTRACT-Four glaciations can be recognized，in Pleistocene of Mt. Xixabangma Region，from old to new named, Xixabangma, Nyanyaxungla, Qomolangma I (Jilong Temple) and Qomolangma Ⅱ (Rongbu Temple),equivalent to Nebraskan，Kansan，Illinolian and Wisconsinian Glaciation in Mountain region in North America. Nyanyaxungla Glaciation was the maximum in glacial extent in this region. At the time glaciers covered over the whole of the Fuqu valley，which destructed the glacial deposits in Xixabangma Glaciation almost completely. There is only glacial traces from the last three glaciations since the Middle Pleistocene, and a series of end moraines is in the Holocene they are Nyalam，Fuqu and Pulou Glaciations, which each glaciation can be also divided into two substages.^higher moraine plateform is extended in south of Nyalam，which is 1. 5km wide, 3. 5km long and 300m above Nyalam，with yellow brown soil on the surface overlying a red paleosol layer, the till about 200m thick，The moraine plateform is the great valley glacier deposits of Nyalam ( Nyanyaxangla)Glaciation of the Middle Pieistocene, A several kilometers moraine section is exposed at the end of the platform because of the Chinese-Nepal Highway cut over, and may be observed complex deposits faGise and glaciotectonics, including superglacial and subglacial meltout tills, flow till，logement till，dump till, englacial-subglacial meltwater channel deposits, glacial lacutrine sediments, droping boulders of floating ice, deformation till. The glaciotectonic and depositional structures，such as thrust plane, collapse structure, sliding plane and so on, are also very clearly. All these composites reflect the large scale of glacier, rapid movement of glacier, strong ablation，developing of glacial lakes and subglacial channels and avalancheing of ice bodies, all which generally occour at warm or martime glaciers. The glacial facies and glaciotectonic marks respressent a martime (warm )glacial depositional process and thermal sitiuaion. The moraine plateform section is one of the most ideal field for research on glaciotectonice in China.
1994, 12(4): 22-30.
Abstract:
The generative kerogen，although recognized as the most important quantitative index of fossil organic matter before，has new been frequently dealt with in a descriptive or bulk geochemical manner by organic petrographers and petroleum geochemists. This was sufficient，however，to stimulate progress in the understanding of many of the gross factors influencing on the accumulation and transormation of organic matter in the geosphere[1]. In particular，it was helpful fw the application of organic geochemical techniques in petroleum exploration. A true integration of organic geochemistry in modern petroleum exploration strategies aiming at an understanding of generation，migration and accumulation of hydrocarbons as interrelated processes on a geological time scale[2]. Situ study of the micro Forier Transform Infra-Red(FTIR) spectrum (by Nicolet NIC-Plan Microscope)on the generative kerogen and bitumen-free in sedimentary rock (Fig. 6) shows a strong contribution of hydroxyl groups (absorption centered at 3400cm-1).The band is at 2920 and 2850cm-1(CH2 stretching frequencies).Further information on the branching level can be derived from the ratio of the 1375 cm-1band(C-CH3 symmetric bending)and of the 14 5 Ocm-1one (CH2and CH3, asymmetric bending). The presence of aromatic carbons is indicated by the absorption at 1600cm-1 and by broad absorptions centered at 830 and 750cm-1. The 1600cm-1 band is a shoulder of a beoad band centered at 1620cm-1. The latter absorption may be due to olefinic C=C stretching vibrations but its intensity indicates that it does not chiefly correspond to simple non-conjugated olefinic groups. The presence of non-conjugated caroyl is indicated by the intense 1700cm-1band and the small band at 720cm-1$ assigned to long chain alkyl groups with four or more carbon atoms. And it can be also used in studying characters of types, shapes and molecular structure of kerogen and bitumen in the sedimentary rocks. The silo micro-FT'IR spectrometry is a new technique for petroleum geology. Therefore, this suggests that it is very possible to messure in situ kerogen in the sedimentary rock，as very exciting possibility for the petroleum geology and molecular geochemical investigations.
The generative kerogen，although recognized as the most important quantitative index of fossil organic matter before，has new been frequently dealt with in a descriptive or bulk geochemical manner by organic petrographers and petroleum geochemists. This was sufficient，however，to stimulate progress in the understanding of many of the gross factors influencing on the accumulation and transormation of organic matter in the geosphere[1]. In particular，it was helpful fw the application of organic geochemical techniques in petroleum exploration. A true integration of organic geochemistry in modern petroleum exploration strategies aiming at an understanding of generation，migration and accumulation of hydrocarbons as interrelated processes on a geological time scale[2]. Situ study of the micro Forier Transform Infra-Red(FTIR) spectrum (by Nicolet NIC-Plan Microscope)on the generative kerogen and bitumen-free in sedimentary rock (Fig. 6) shows a strong contribution of hydroxyl groups (absorption centered at 3400cm-1).The band is at 2920 and 2850cm-1(CH2 stretching frequencies).Further information on the branching level can be derived from the ratio of the 1375 cm-1band(C-CH3 symmetric bending)and of the 14 5 Ocm-1one (CH2and CH3, asymmetric bending). The presence of aromatic carbons is indicated by the absorption at 1600cm-1 and by broad absorptions centered at 830 and 750cm-1. The 1600cm-1 band is a shoulder of a beoad band centered at 1620cm-1. The latter absorption may be due to olefinic C=C stretching vibrations but its intensity indicates that it does not chiefly correspond to simple non-conjugated olefinic groups. The presence of non-conjugated caroyl is indicated by the intense 1700cm-1band and the small band at 720cm-1$ assigned to long chain alkyl groups with four or more carbon atoms. And it can be also used in studying characters of types, shapes and molecular structure of kerogen and bitumen in the sedimentary rocks. The silo micro-FT'IR spectrometry is a new technique for petroleum geology. Therefore, this suggests that it is very possible to messure in situ kerogen in the sedimentary rock，as very exciting possibility for the petroleum geology and molecular geochemical investigations.
1994, 12(4): 40-50.
Abstract:
The academic circles have considered Turpan-Hami Basin is a compressional one by plate collision, but the research of this paper shower Turpan-Harm Basin is similar to the extensional basins of East China in many ways, such as sedimental evolution，structural deformation，basin texture and crust-mantle texture reflected by the similar geophysic fields and so on. From the Late Permian Period，Turpan-Hami Basin began developing and kept up a steady spreading two cycles for a very long time(P2-J2,K2-N2). Two compressional tectogenesis (Huoyanshan and Xiyu) took place and the two spreading and sedimentary cycles were checked by the two movements in the Late Jurassic and the end of the Tertiary Period，respectivelly，and the extensional structure of the basin was reformed at the same times. The basin extension is a result of the mantle diapirism. Due to the basin extension，the adjacent regions (Tianshan Orogenic Belt) north and south to the basin had been compressed and deformed plastically (folding and upwarping). The stress accumulated with the plastic deformation in the rocks was so stronger that faulting took place, releasing the stress. The compressional movements occured when the faulting reacted on the basin，and the sedimentation discontinued. Combining the geological features with experimental results, we propose a new viewpoint that Turpan-Hami Basin is a extensional basin. Thus a new theory or model about the dynamics and kinematics of continental inner plate is described as follows; mantal diapirism- basin extension- folding and accumulating stress in adjacent regions(orogenic belts)-releasing the stress-basin lifting and sedimentation discontinuance.
The academic circles have considered Turpan-Hami Basin is a compressional one by plate collision, but the research of this paper shower Turpan-Harm Basin is similar to the extensional basins of East China in many ways, such as sedimental evolution，structural deformation，basin texture and crust-mantle texture reflected by the similar geophysic fields and so on. From the Late Permian Period，Turpan-Hami Basin began developing and kept up a steady spreading two cycles for a very long time(P2-J2,K2-N2). Two compressional tectogenesis (Huoyanshan and Xiyu) took place and the two spreading and sedimentary cycles were checked by the two movements in the Late Jurassic and the end of the Tertiary Period，respectivelly，and the extensional structure of the basin was reformed at the same times. The basin extension is a result of the mantle diapirism. Due to the basin extension，the adjacent regions (Tianshan Orogenic Belt) north and south to the basin had been compressed and deformed plastically (folding and upwarping). The stress accumulated with the plastic deformation in the rocks was so stronger that faulting took place, releasing the stress. The compressional movements occured when the faulting reacted on the basin，and the sedimentation discontinued. Combining the geological features with experimental results, we propose a new viewpoint that Turpan-Hami Basin is a extensional basin. Thus a new theory or model about the dynamics and kinematics of continental inner plate is described as follows; mantal diapirism- basin extension- folding and accumulating stress in adjacent regions(orogenic belts)-releasing the stress-basin lifting and sedimentation discontinuance.
1994, 12(4): 58-65.
Abstract:
Eogene System in East Depression of the Liaohe basin is at the diagenesis stage. The correlation between the Extractable Organic Matter (EOM)，kerogen and the Bio-thermocatalytic Transition Zone Gases (BTZG) in the source rocks has been discussed m this paper. It is discovered that there exist different organic source materials in the EOM and kerogen of the same sample. A higher carbon -number preference of the saturated hydrocarbons, and a significant distribution of land plant-derived biomarkers, i. e.，C29 sterane , pimarane , abietane , r-lupane and oleanane in the EOM show that the EOM is characterized by organic matter of type Ⅱb-Ⅲ.However，the carbon isotopic composition of the kerogen indicate that it mainly consists of organic matter of type I-Ⅱa.The difference in organic compositions between the EOM and kerogen at the diagenesis stage can be explained by the selective accumulation of sedimentary organic matter. Specific 1R absorption spectra and corresponding parameters of bitumen A, non-hydrocarbons and asphaltene show the same pattern of variation in the depth of 1850^-3060m. Three evolution stages have been determined in this study. The EOM are rapidly degradated in about 2200~2770m，i. e.，the second stage，and highest at about 2500m，which results in forming BTZG. Although kerogens are characteristic of deoxygen and delipidic groups at the stage, they have no direct relations to the formation of BTZG because they mainly produce depolymeric betumen at the stage. Therefore the EOM，especially non-hycrocarbons and asphaltene, could be considered as the most important source materials of BTZG in East Depression of the Liaohe basin.
Eogene System in East Depression of the Liaohe basin is at the diagenesis stage. The correlation between the Extractable Organic Matter (EOM)，kerogen and the Bio-thermocatalytic Transition Zone Gases (BTZG) in the source rocks has been discussed m this paper. It is discovered that there exist different organic source materials in the EOM and kerogen of the same sample. A higher carbon -number preference of the saturated hydrocarbons, and a significant distribution of land plant-derived biomarkers, i. e.，C29 sterane , pimarane , abietane , r-lupane and oleanane in the EOM show that the EOM is characterized by organic matter of type Ⅱb-Ⅲ.However，the carbon isotopic composition of the kerogen indicate that it mainly consists of organic matter of type I-Ⅱa.The difference in organic compositions between the EOM and kerogen at the diagenesis stage can be explained by the selective accumulation of sedimentary organic matter. Specific 1R absorption spectra and corresponding parameters of bitumen A, non-hydrocarbons and asphaltene show the same pattern of variation in the depth of 1850^-3060m. Three evolution stages have been determined in this study. The EOM are rapidly degradated in about 2200~2770m，i. e.，the second stage，and highest at about 2500m，which results in forming BTZG. Although kerogens are characteristic of deoxygen and delipidic groups at the stage, they have no direct relations to the formation of BTZG because they mainly produce depolymeric betumen at the stage. Therefore the EOM，especially non-hycrocarbons and asphaltene, could be considered as the most important source materials of BTZG in East Depression of the Liaohe basin.
1994, 12(4): 77-86.
Abstract:
An organic facies is defined as a mappable stratigraphic unit containing organic matter (OM)of a particular genetic type in cartaain abundance. A new organic facies classification，which is based on indicative genetic kerogen(OM)type。is proposed. The improved definition and classification makes organic facies capable of reflecting the origin，diagenetic alternation of organic matter comprehensively, and，the organic facies thus defined and classified，which must be identified on the basis of synthetical parameters other than by atomic H/C ratios and/or Rock-Eval Hydrogen Index values merely. Several new concepts concerning organic facies such as Vertical Organic Facies Sequence ( VOFS )，Organic Facies Association ( OFA ) and Organic Basin-fill Sequence ( OBFS ) are advanced, and their significance in basin analysis is discussed in detail.Several cases are presented in this paper which confirm that organic facies, especially VOFS，OFA and OBFS analysis can not only become a very usefull tool for prediction and three-dimensional mapping of petroleum source rocks, but also make up for some shortcomings of sedimentological studies that put the stress on coarse rocks, and therefore may play a distinctive role in identifying and accurately locating unconformities or sequence/ systems tract boundaries as well as in reconstructing the tectonic subsidence and sedimentary fill histories of sedimentary basins.
An organic facies is defined as a mappable stratigraphic unit containing organic matter (OM)of a particular genetic type in cartaain abundance. A new organic facies classification，which is based on indicative genetic kerogen(OM)type。is proposed. The improved definition and classification makes organic facies capable of reflecting the origin，diagenetic alternation of organic matter comprehensively, and，the organic facies thus defined and classified，which must be identified on the basis of synthetical parameters other than by atomic H/C ratios and/or Rock-Eval Hydrogen Index values merely. Several new concepts concerning organic facies such as Vertical Organic Facies Sequence ( VOFS )，Organic Facies Association ( OFA ) and Organic Basin-fill Sequence ( OBFS ) are advanced, and their significance in basin analysis is discussed in detail.Several cases are presented in this paper which confirm that organic facies, especially VOFS，OFA and OBFS analysis can not only become a very usefull tool for prediction and three-dimensional mapping of petroleum source rocks, but also make up for some shortcomings of sedimentological studies that put the stress on coarse rocks, and therefore may play a distinctive role in identifying and accurately locating unconformities or sequence/ systems tract boundaries as well as in reconstructing the tectonic subsidence and sedimentary fill histories of sedimentary basins.
1994, 12(4): 95-100.
Abstract:
The research results of laboratory thermal infrared emissivity spectra of some typical clastic rocks, argillacous rocks, carbonate rocks and evaporite collected from ICalpin Uplift in Tarim Basin，integrated with the results of chemical anelysis, X-ray diffraction and thin section identification of rocks indcate that clastic rocks and argillaceous rocks with quartz have restrahlen band between 8 and l0μm，which results from interatomic stretching vibrations of silicon and oxygen bound in the crystal lattice. The band center has been shown to move to longer wavelengths and decrease in intensity with decreasing quartz content,Carbonate rocks exhibit low emissivity band at 11. 3μm due to C-O bending modes, the band center shown to move to shorter wavelengths with increasing Mg2+ content, and gypsum has an intense low emissity band near 8. 56μm caused by fundmental stretching motions of sulfate ion.The rock type, mineralogical composition and content of sedimentary rocks can be determined according to these features. The analyses of thermal infrared spectra features of sedimentary rocks provide a theoretical basis for thermal infrared multispectral remote sensing. According to the center wavelengths of restrahlen band (or low emissivity band)of sedimentary rocks, the relevant bands can be selected for airborne and spaceborne thermal infrared multispectral scanners(TIMS)to extract and distinguish the lithologic and mineralogic information. For example, 8. 13μm，9. 17μm，11. 3μm and 8. 56μm,etc. are the best band center for TIMS scanner. The TIMS will become a powerful new geologic remote sensing tool that can provide rich lithologic and mineralogic information in the future.
The research results of laboratory thermal infrared emissivity spectra of some typical clastic rocks, argillacous rocks, carbonate rocks and evaporite collected from ICalpin Uplift in Tarim Basin，integrated with the results of chemical anelysis, X-ray diffraction and thin section identification of rocks indcate that clastic rocks and argillaceous rocks with quartz have restrahlen band between 8 and l0μm，which results from interatomic stretching vibrations of silicon and oxygen bound in the crystal lattice. The band center has been shown to move to longer wavelengths and decrease in intensity with decreasing quartz content,Carbonate rocks exhibit low emissivity band at 11. 3μm due to C-O bending modes, the band center shown to move to shorter wavelengths with increasing Mg2+ content, and gypsum has an intense low emissity band near 8. 56μm caused by fundmental stretching motions of sulfate ion.The rock type, mineralogical composition and content of sedimentary rocks can be determined according to these features. The analyses of thermal infrared spectra features of sedimentary rocks provide a theoretical basis for thermal infrared multispectral remote sensing. According to the center wavelengths of restrahlen band (or low emissivity band)of sedimentary rocks, the relevant bands can be selected for airborne and spaceborne thermal infrared multispectral scanners(TIMS)to extract and distinguish the lithologic and mineralogic information. For example, 8. 13μm，9. 17μm，11. 3μm and 8. 56μm,etc. are the best band center for TIMS scanner. The TIMS will become a powerful new geologic remote sensing tool that can provide rich lithologic and mineralogic information in the future.
1994, 12(4): 110-117.
Abstract:
Ordos basin is a large sedimentary basin in the eastern China. In the inner of the basin，faults donut develop and strata are flat(the angle of inclination is less than one degree)，so the possibility that oil and gas can migrate along faults should be ruled out, and then oll and gas microleapage through the fractures and pores in strata should be main form for oil and gas vertical migration. A deep gas-producing well, which is located in the central ancient rift in the inner of the basin，is chosen for study. According to the characteristics of the vertical evolution of organic matter and the change of acidolysis hydrocarbon compositions in different clastic rock layers from the deep well， the chromatographic fractional effect of vertical oil-gas microleapage has been discussed. Owing to the chemical and physical difference among methane and its homologes in mass number，molecular diameter, and the solubility in water, etc.，methane and i-butane preferentially migrate to heavier hydrocarbon and n- butane，respectively. Because the concentation of organic matter is low and the amount of hydrocarbon generated in situ is accordingly little in the two sections which range from 0 to 1020m and 3080m to 3560m in depth，so the above chromatographic effect can be recorded. 1. In the section from 0 to 1020m depth, the result shows that the ratios of C1/C2+，C1/Ctal, and iC4/nC4, of acidolysis hydrocarbon gases in sandstone are less than those in mudstone. It mainly results from the chromatographic fractional effect, i. e.，methane and i-butane are relativeiy easier to go through poorly permeabie mudstone barrier bed than heavier hydrocarbon and n- butane respectively. 2. In the section from 3080m to 3560m depth，the maturity of organic matter is in condensate to high mature stage，the composition of gas generated by such matter should be increasingly drier and therefore the ratios of C1/C2+，C1/Ctal,tend to rise with depth. However, the change of the ratios shows a controversial tendency and an obvious inconsistence with the composition characteristics of gas generated by thermolization，suggesting that methane preferentially migrates to heavier hydrocarbon. In addition，the changing characteristics of C1/C2+，C1/Ctal and C2/C3 ratios of the acidolysis hydrocarbon in the layers rich in organic matter ( the depth from 1020m to 3080m)，which decreases firstly and increases consequently with depth，is controlled by the generation of hydrocarbon in situ and hence the chromatographic fractional effect is concealed.
Ordos basin is a large sedimentary basin in the eastern China. In the inner of the basin，faults donut develop and strata are flat(the angle of inclination is less than one degree)，so the possibility that oil and gas can migrate along faults should be ruled out, and then oll and gas microleapage through the fractures and pores in strata should be main form for oil and gas vertical migration. A deep gas-producing well, which is located in the central ancient rift in the inner of the basin，is chosen for study. According to the characteristics of the vertical evolution of organic matter and the change of acidolysis hydrocarbon compositions in different clastic rock layers from the deep well， the chromatographic fractional effect of vertical oil-gas microleapage has been discussed. Owing to the chemical and physical difference among methane and its homologes in mass number，molecular diameter, and the solubility in water, etc.，methane and i-butane preferentially migrate to heavier hydrocarbon and n- butane，respectively. Because the concentation of organic matter is low and the amount of hydrocarbon generated in situ is accordingly little in the two sections which range from 0 to 1020m and 3080m to 3560m in depth，so the above chromatographic effect can be recorded. 1. In the section from 0 to 1020m depth, the result shows that the ratios of C1/C2+，C1/Ctal, and iC4/nC4, of acidolysis hydrocarbon gases in sandstone are less than those in mudstone. It mainly results from the chromatographic fractional effect, i. e.，methane and i-butane are relativeiy easier to go through poorly permeabie mudstone barrier bed than heavier hydrocarbon and n- butane respectively. 2. In the section from 3080m to 3560m depth，the maturity of organic matter is in condensate to high mature stage，the composition of gas generated by such matter should be increasingly drier and therefore the ratios of C1/C2+，C1/Ctal,tend to rise with depth. However, the change of the ratios shows a controversial tendency and an obvious inconsistence with the composition characteristics of gas generated by thermolization，suggesting that methane preferentially migrates to heavier hydrocarbon. In addition，the changing characteristics of C1/C2+，C1/Ctal and C2/C3 ratios of the acidolysis hydrocarbon in the layers rich in organic matter ( the depth from 1020m to 3080m)，which decreases firstly and increases consequently with depth，is controlled by the generation of hydrocarbon in situ and hence the chromatographic fractional effect is concealed.
1994, 12(4): 124-131.
Abstract:
For a long time, ripple marks were often regarded as one of sedimentary indicators of shallow water, but large quantities of them were also found in bathyal terrigenous elastic turbidites of Upper Triassic of west Qinling Mts. The ripple marks characterize that(1)they occour on the surface of Tc of Bouma sequence, which means that they were formed by tractive currents derived from turbidity flows, ( 2 ) they exist in the lobe facies associations of seafloor fan sequences, which indicates that the most favourable hydrodynamic }rtditions to form them appeared in outer fans,(3)they are all symmetrical，which shows that tractfve currents to form them were unidirectional, ( 4 ) They are smal l-scale，which proves that the veIocIty of tractive currents and the grain size of bottom bed sands varied in a certain extend,(5)their wavelengths and heights are directly proportional to the thickness of turbidites, which means that the strength of tractive currents was controlled by the scale and strength of turbidity flows, (6)the shapes of wave crests and troughs are smooth and the shapes of ripple ridges are regularly changeable , ( 7 ) their shapes and scales are closely related with those of ripple laminations in Tc intervals of Bouma sequences, which reflects that they were two forms of expression produced by the same tractive currents,(8 ) The flow directions determined by ripple marks are consistent with those determined by bottom marks,which reflects that the flow directions of tractive currents were controlled by those of turbidity flows. The characteristics above reflect that ripple marks occoured not only in shallow-water enviroments but also in deep water enviroments.
For a long time, ripple marks were often regarded as one of sedimentary indicators of shallow water, but large quantities of them were also found in bathyal terrigenous elastic turbidites of Upper Triassic of west Qinling Mts. The ripple marks characterize that(1)they occour on the surface of Tc of Bouma sequence, which means that they were formed by tractive currents derived from turbidity flows, ( 2 ) they exist in the lobe facies associations of seafloor fan sequences, which indicates that the most favourable hydrodynamic }rtditions to form them appeared in outer fans,(3)they are all symmetrical，which shows that tractfve currents to form them were unidirectional, ( 4 ) They are smal l-scale，which proves that the veIocIty of tractive currents and the grain size of bottom bed sands varied in a certain extend,(5)their wavelengths and heights are directly proportional to the thickness of turbidites, which means that the strength of tractive currents was controlled by the scale and strength of turbidity flows, (6)the shapes of wave crests and troughs are smooth and the shapes of ripple ridges are regularly changeable , ( 7 ) their shapes and scales are closely related with those of ripple laminations in Tc intervals of Bouma sequences, which reflects that they were two forms of expression produced by the same tractive currents,(8 ) The flow directions determined by ripple marks are consistent with those determined by bottom marks,which reflects that the flow directions of tractive currents were controlled by those of turbidity flows. The characteristics above reflect that ripple marks occoured not only in shallow-water enviroments but also in deep water enviroments.
1994, 12(4): 11-21.
Abstract:
It is a method which needs to be improved using the component of oxygen and carbon isotope to study and judge the diagenetic environment and the intensity of diagenesis. However, many lab data of samples and the analyzing results of Cambrian and Ordovician in Yichang area，Hu Bei Province;the 110. 3 Ren Well and the NO. 1 Bu Well in Ordos area proved that this method is very effective and practical. The research result indicates that the δ18O and δ13C values shift towards the higher negative values in meteoric diagenetic environment. The δ18O and δ13C values shift towards obviously higher positive values in marine diagenetic environment. The Z value which was calculated using δ18O and δ13C are all more than 122. In buried diagenetic environment, especially deeply buried environment, the 8'80 value shift towards relatively higher negative values. The more the depth, the lower the δ18O value. However, the δ13C value has not changed obviously in the process of burial. All the conclusion above are consistent with the achievement of foreign countries. There are many factors influencing the values of oxygen and carbon isotopes，and the procedures of the buried diagenesis are very complex. So the method metioned above is not absolute. It must be connected with the other research work of petrology and many lab methods.
It is a method which needs to be improved using the component of oxygen and carbon isotope to study and judge the diagenetic environment and the intensity of diagenesis. However, many lab data of samples and the analyzing results of Cambrian and Ordovician in Yichang area，Hu Bei Province;the 110. 3 Ren Well and the NO. 1 Bu Well in Ordos area proved that this method is very effective and practical. The research result indicates that the δ18O and δ13C values shift towards the higher negative values in meteoric diagenetic environment. The δ18O and δ13C values shift towards obviously higher positive values in marine diagenetic environment. The Z value which was calculated using δ18O and δ13C are all more than 122. In buried diagenetic environment, especially deeply buried environment, the 8'80 value shift towards relatively higher negative values. The more the depth, the lower the δ18O value. However, the δ13C value has not changed obviously in the process of burial. All the conclusion above are consistent with the achievement of foreign countries. There are many factors influencing the values of oxygen and carbon isotopes，and the procedures of the buried diagenesis are very complex. So the method metioned above is not absolute. It must be connected with the other research work of petrology and many lab methods.
1994, 12(4): 31-39.
Abstract:
Kerogen is the direct original material of oil-forming. To determine the type and the mature degree of kerogen is one of the important works in petroleum geology. While studing the clay minerals of Baise Basin，Guangxi，the authors made some detailed work on the kerogen of this of‘-forming region. The type，mature degree，and the evolution process of kerogen was determined through X-ray diffraction and micro-region analysis method，and also by microscopic，atom distribution and infrared work. According to the results of X-ray analysis, the aliphatic degree(Fa) of the kerogen in this region is 0. 28 to 0. 37. On increasing of the depth in the same geological section，the Fa becomes higher，that is ,the kerogen evoluted to mature. By calculation，the height of aliphatic nuclei (Lc ) is between 16. 60 and 20. 76人，the layer number (n) of them is 5 to 6. These are the characteristics of type if kerogen. The evolution process of the kerogen in this region was studied using micro- region method，and also using some routine methods. The lower matured kerogen was photoed by microscope，and the distribution of the atoms in it was analyzed by electronic probe. It is shown that the carbon atom in this kind of lower mature kerogen is not homogeneous, normally higher in the center，lower in the outer part. Iron and silica are also concentrated to the center. Most of the Kerogen have FeS2 nuclei, and around the nuclei mainly are clay minerals. The evolution trent of the mature degree of the kerogen is consistent with the evolution trend of the clay minerals，that is，montmorillonite evoluted to illite/ montmorillonite. The combining patterns of organic molecules and clay minerals were also discussed. According to the thermodynamics data and some experiments of transforming clay minerals, we quantitatively calculated the water and heat that produced by the montmorillonite to illite. It will let out 30 to 40 grams of water and 100 kal of heat by 1 mol montmorillonite transforming to illite. This may be the medium and dynamic power source of the formdtion，evolution，and decomposition of kerogen. It is concluded that the clay minerals were the catalytic promoter for organic material to eveoute to hydrocarbon.
Kerogen is the direct original material of oil-forming. To determine the type and the mature degree of kerogen is one of the important works in petroleum geology. While studing the clay minerals of Baise Basin，Guangxi，the authors made some detailed work on the kerogen of this of‘-forming region. The type，mature degree，and the evolution process of kerogen was determined through X-ray diffraction and micro-region analysis method，and also by microscopic，atom distribution and infrared work. According to the results of X-ray analysis, the aliphatic degree(Fa) of the kerogen in this region is 0. 28 to 0. 37. On increasing of the depth in the same geological section，the Fa becomes higher，that is ,the kerogen evoluted to mature. By calculation，the height of aliphatic nuclei (Lc ) is between 16. 60 and 20. 76人，the layer number (n) of them is 5 to 6. These are the characteristics of type if kerogen. The evolution process of the kerogen in this region was studied using micro- region method，and also using some routine methods. The lower matured kerogen was photoed by microscope，and the distribution of the atoms in it was analyzed by electronic probe. It is shown that the carbon atom in this kind of lower mature kerogen is not homogeneous, normally higher in the center，lower in the outer part. Iron and silica are also concentrated to the center. Most of the Kerogen have FeS2 nuclei, and around the nuclei mainly are clay minerals. The evolution trent of the mature degree of the kerogen is consistent with the evolution trend of the clay minerals，that is，montmorillonite evoluted to illite/ montmorillonite. The combining patterns of organic molecules and clay minerals were also discussed. According to the thermodynamics data and some experiments of transforming clay minerals, we quantitatively calculated the water and heat that produced by the montmorillonite to illite. It will let out 30 to 40 grams of water and 100 kal of heat by 1 mol montmorillonite transforming to illite. This may be the medium and dynamic power source of the formdtion，evolution，and decomposition of kerogen. It is concluded that the clay minerals were the catalytic promoter for organic material to eveoute to hydrocarbon.
1994, 12(4): 51-57.
Abstract:
Between Guangyuan. Sichuan to Ningqiang. Shaanxi province, Within giant-thick dead color mudstones of lower Silurian there are hundreds of reefs developed，including barrier reef, patch reef, barrier-like patch reefs, biohorm，Limemud mound and bed-rock mound. All of them are out Groped well and a great disparity in size. The reefs developed on the bases of the mudrock facies of the shallower shelf. The reef-building organism are mainly Halysites. Favorites, subalveotella,paleaofavosites, and clathrodictyon, Rosenella. The basesment rock on which reefs grooved is mainly mudbasis-knollenakalk and some are on the bioclast bank，the proximal tempestites and sumerged tidal flat stratifera limestones. Many of the reefs declimed and fell because of drove and a few of them died for drought. The reef is over 50 meters thick in the Hoshen 1 well and Ho 15 well in Guangyuan. North-west Sichuan，and a litter gas was gotten in it. Also, the reef was found in many wells in the southern Sichuan. In addition，the reefs is distributed over the eastern Sichuan，Northern Guizhou and western Hebui, the character of reef Complex is similar to that of the studied area. Bitumen filling crack and vug is often found. The organic carbon content in dead color mudstone which wraped up the reefs is high. There for. It is hope for the reef of the lower Silurian to be the exploration bojective formation in the Sichuan basin.
Between Guangyuan. Sichuan to Ningqiang. Shaanxi province, Within giant-thick dead color mudstones of lower Silurian there are hundreds of reefs developed，including barrier reef, patch reef, barrier-like patch reefs, biohorm，Limemud mound and bed-rock mound. All of them are out Groped well and a great disparity in size. The reefs developed on the bases of the mudrock facies of the shallower shelf. The reef-building organism are mainly Halysites. Favorites, subalveotella,paleaofavosites, and clathrodictyon, Rosenella. The basesment rock on which reefs grooved is mainly mudbasis-knollenakalk and some are on the bioclast bank，the proximal tempestites and sumerged tidal flat stratifera limestones. Many of the reefs declimed and fell because of drove and a few of them died for drought. The reef is over 50 meters thick in the Hoshen 1 well and Ho 15 well in Guangyuan. North-west Sichuan，and a litter gas was gotten in it. Also, the reef was found in many wells in the southern Sichuan. In addition，the reefs is distributed over the eastern Sichuan，Northern Guizhou and western Hebui, the character of reef Complex is similar to that of the studied area. Bitumen filling crack and vug is often found. The organic carbon content in dead color mudstone which wraped up the reefs is high. There for. It is hope for the reef of the lower Silurian to be the exploration bojective formation in the Sichuan basin.
1994, 12(4): 66-76.
Abstract:
C27 ,C28, C29sterols, including△5,22,△22,△5and △5,22(28)，and 5a-stanols have been identified in the three recent sediment cores of Qinghai Lake [QH core (near Heima River mouth, water depth : 0. 5m，core length:30cm )，QG core ( in Gahai，water depth:9m, core lengths 230cm，water salinity:33‰) and QE core (in Erhai，water depth:4m , core length:30cm, fresh water)].C29 sterols, especially 24-ethylcholesta-5, 22E-then-3β-ol and 24-ethylcholest-5-en-3β-ol, preponderate in all sections of the three sediment cores. Three C30 sterols (4α, 23, 24-trimethy-5α-chelest-22E-en -3β-ol(dinosterol ) , 4α-methy-24-ethyl- 5α-chokest- 22E- 3β-ol and its saturated analog(4α-methyl-24-ethyl-5α-chelestan-3β-ol) are also detected at low concentrations in the QE and QG sediment cores of the lake. The parallelism between the C27-C29△5-sterol and 5a-stanol in sections of 0~10cm and 20~30cm of QH core, and 0~20cm and 40~60cm of QG core provide indirect evidence for a sterol hydrogenation process in the sediment rather than a sediment input of both saturated and unsaturated sterols. The fact that the changes of saturated sterols/unsaturated sterols ratios(C27-C29 5a-stanol/△5-sterol and △22-/△5,22ratios) are most pronounced in near-surface and the -uppermost sediment layers of QG and QH cores suggests that microorganisms are involved in the hydrogenation process. The sterols initially incorporated into the lake sediments mainly originate from abundant higher plants in the lake area and algae etc. in the lake water. An considerable increase in concentration of 5a-chelestanol in 80~100cm and 120~140cm sections of QG sediment core may reflect special organism ( ostracodes)contribution to the two section sediments.
C27 ,C28, C29sterols, including△5,22,△22,△5and △5,22(28)，and 5a-stanols have been identified in the three recent sediment cores of Qinghai Lake [QH core (near Heima River mouth, water depth : 0. 5m，core length:30cm )，QG core ( in Gahai，water depth:9m, core lengths 230cm，water salinity:33‰) and QE core (in Erhai，water depth:4m , core length:30cm, fresh water)].C29 sterols, especially 24-ethylcholesta-5, 22E-then-3β-ol and 24-ethylcholest-5-en-3β-ol, preponderate in all sections of the three sediment cores. Three C30 sterols (4α, 23, 24-trimethy-5α-chelest-22E-en -3β-ol(dinosterol ) , 4α-methy-24-ethyl- 5α-chokest- 22E- 3β-ol and its saturated analog(4α-methyl-24-ethyl-5α-chelestan-3β-ol) are also detected at low concentrations in the QE and QG sediment cores of the lake. The parallelism between the C27-C29△5-sterol and 5a-stanol in sections of 0~10cm and 20~30cm of QH core, and 0~20cm and 40~60cm of QG core provide indirect evidence for a sterol hydrogenation process in the sediment rather than a sediment input of both saturated and unsaturated sterols. The fact that the changes of saturated sterols/unsaturated sterols ratios(C27-C29 5a-stanol/△5-sterol and △22-/△5,22ratios) are most pronounced in near-surface and the -uppermost sediment layers of QG and QH cores suggests that microorganisms are involved in the hydrogenation process. The sterols initially incorporated into the lake sediments mainly originate from abundant higher plants in the lake area and algae etc. in the lake water. An considerable increase in concentration of 5a-chelestanol in 80~100cm and 120~140cm sections of QG sediment core may reflect special organism ( ostracodes)contribution to the two section sediments.
1994, 12(4): 87-94.
Abstract:
The question on oil generation in the coal and coal-bearing deposit has attracted ever more geologists attention already, with the strengthening of oil exploration. Jurassic strata are widespread in the Junggar Basin，being characterized by a large sedimentary area and a high percentage of coal. Until now，Known oil and gas fields formed from coal measures include the Qigu field and some high-yielding.wells. In the southern margin of the basin，the total thickness of the lower and middle Jurassic series is about 2500m，of which the largest thickness of coal seams is 160~238m，and that of individual coal layer reaches 40~70. 47m Most. of coal layer numbers are more than 50. To this end, the authors collected Jurassic coal samples there,microscopic analysis indicates that they contain Higher hydrogen-rich macerals and vitrinite. By using the flash pyrolysis method, the hydrocarbon potential of coal macerals and whole coals is studied. These results show:(1)the 350-450℃phrolysates have the largest peak area (S2)which matches for oil-generating peak stage. (2) in samples of high hydrogen macerals, pyrolysis products have n-alkane and n-alkene as the predominant constituents, with aromatics next in abundance. ( 3 ) in vitrinite or vitrinite-rich coal samples, some of aromatics becomes major peak ranging from C8 to C15 for pyrolysis products. ( 4 ) the hydrocarbon-generating possiblity for the initinite is the lowest, at the higher temperature state, a low content of n-alkane and n-alkene or a trace amount of hydrocarbon was formed in the gas-state range，or pyrolysis products were not generated. ( 5 ) with the increasing of the heating time or sample evolutional level , the alkene content decreases or lusts. Remnant hydrogen occured in kerogen transforming process can serve as the hydrogen source for hydrogenation of the alkene, leading to the transformation of alkene to alkane.
The question on oil generation in the coal and coal-bearing deposit has attracted ever more geologists attention already, with the strengthening of oil exploration. Jurassic strata are widespread in the Junggar Basin，being characterized by a large sedimentary area and a high percentage of coal. Until now，Known oil and gas fields formed from coal measures include the Qigu field and some high-yielding.wells. In the southern margin of the basin，the total thickness of the lower and middle Jurassic series is about 2500m，of which the largest thickness of coal seams is 160~238m，and that of individual coal layer reaches 40~70. 47m Most. of coal layer numbers are more than 50. To this end, the authors collected Jurassic coal samples there,microscopic analysis indicates that they contain Higher hydrogen-rich macerals and vitrinite. By using the flash pyrolysis method, the hydrocarbon potential of coal macerals and whole coals is studied. These results show:(1)the 350-450℃phrolysates have the largest peak area (S2)which matches for oil-generating peak stage. (2) in samples of high hydrogen macerals, pyrolysis products have n-alkane and n-alkene as the predominant constituents, with aromatics next in abundance. ( 3 ) in vitrinite or vitrinite-rich coal samples, some of aromatics becomes major peak ranging from C8 to C15 for pyrolysis products. ( 4 ) the hydrocarbon-generating possiblity for the initinite is the lowest, at the higher temperature state, a low content of n-alkane and n-alkene or a trace amount of hydrocarbon was formed in the gas-state range，or pyrolysis products were not generated. ( 5 ) with the increasing of the heating time or sample evolutional level , the alkene content decreases or lusts. Remnant hydrogen occured in kerogen transforming process can serve as the hydrogen source for hydrogenation of the alkene, leading to the transformation of alkene to alkane.
1994, 12(4): 101-109.
Abstract:
The climate change between 800^-150Ka B. P. reflected by pollen record from RH-core in Zoige Basin，located in the northeastern part of Qinghai-Xizang ( Tibet)Plateau, is in close relationship with that showed by oxygen isotope record of deep sea，loess records in central China，and organic carbon content and hydrogen index records in this core. According to the concentration，amounts and types of pollen and spores, the pollen assemblage of RH-core can be divided into 19 zones, which indicates the unstability of climate and shows the sensitivity to climatic changes in the region. According to the pollen record，there were two bigger colder stages ( glaciation)and one warmer stage (interglaciation) between 800-150Ka. B. P. in this region. Earlier glaciation, i. e.，the third glaciation from the last took place about 710^-529Ka B. P. corresponding to MIS-18 to 16，later one ( i. e. the Penulitimate glaciation ) occured about 298~128Ka B. P.，corresponding to M1S-8 to 6. During the glaciations, the pollen concentration was very lower，there are fewer.4Ttemisia presented. A big warmer stage (big interglaction) took place about 480^-298Ka B. P.，and the contents of pollen were mainly Abees, PiQea，Be}la，Craminene Cyperacese and Arte>nisia，which reflects warm and little dry climate. In these stages，there were geomorphological and lithological changes stongly on the earth surface. The pollen record RH-core shows that the climatic changes since 800Ka B. P. are frequent in Zoige Basin，and the ranges are bigger，but in general，the cold are dominated. Meanwhile, the frequent fluctuation of pollen assemblage reflects that the ecosystem of the regiion is weaker，when suffering from environmental forcing it will be changed soon.
The climate change between 800^-150Ka B. P. reflected by pollen record from RH-core in Zoige Basin，located in the northeastern part of Qinghai-Xizang ( Tibet)Plateau, is in close relationship with that showed by oxygen isotope record of deep sea，loess records in central China，and organic carbon content and hydrogen index records in this core. According to the concentration，amounts and types of pollen and spores, the pollen assemblage of RH-core can be divided into 19 zones, which indicates the unstability of climate and shows the sensitivity to climatic changes in the region. According to the pollen record，there were two bigger colder stages ( glaciation)and one warmer stage (interglaciation) between 800-150Ka. B. P. in this region. Earlier glaciation, i. e.，the third glaciation from the last took place about 710^-529Ka B. P. corresponding to MIS-18 to 16，later one ( i. e. the Penulitimate glaciation ) occured about 298~128Ka B. P.，corresponding to M1S-8 to 6. During the glaciations, the pollen concentration was very lower，there are fewer.4Ttemisia presented. A big warmer stage (big interglaction) took place about 480^-298Ka B. P.，and the contents of pollen were mainly Abees, PiQea，Be}la，Craminene Cyperacese and Arte>nisia，which reflects warm and little dry climate. In these stages，there were geomorphological and lithological changes stongly on the earth surface. The pollen record RH-core shows that the climatic changes since 800Ka B. P. are frequent in Zoige Basin，and the ranges are bigger，but in general，the cold are dominated. Meanwhile, the frequent fluctuation of pollen assemblage reflects that the ecosystem of the regiion is weaker，when suffering from environmental forcing it will be changed soon.
1994, 12(4): 118-123.
Abstract:
The marginal listric fault, planar kink fault and Domino faults were found in the analysis of the tectonic lithofacies in the Southeastern part of the Dongpu Depression，which was one of typical half-graben basins in China. These faults impressed significantly on the evolution of the basin itself, on the development of the depositional systems and the distribution of hydrocarbons. The crest -cut faults of the east border of the Dongpu Depression consist of the listric faults with NE trend and the panar kink faults with NNE trend, which have controlled the formation and evolution of the Depression. The listric faults were formed by the regionally extensional stress field. They were long-active ones, and the deep sags or oil source centers were developed along the listric faults. The longer fault strike and longer active time the listric faults, the larger and deeper the sags. There are three listric faults in the tan-liao fault at the eastern margin of the Southeastern Dongpu Depression，and three oil source centers along the faults, which are respectively;the Geganji North，the Gegan扛South Sag and the Guyan Sag. The listric fault in the middle was the longest in its strike and throw，consequently, the Geganji South Sag was the largest one of the three. The marginal planar kink faults were also formed in regionally extensional stress field, but their bases of the upfaulted block were broken into several parts to form the step-planar kink faults, in which the rising bases evolved into buried h}71s. Although the planar kink faults and the listric faults influenced on the evolution of the Dongpu Depression, the down-faulted blocks the planar kink faults often conducted as the seperating zones by large volumes of sediments of allovial fan，delta-fan and subaqueous fan. Because there are a lot of reservoir sandbodies and various fault traps or lithological traps with in the down-fault block sediments, the blocks are significant hydrocarbon accumulation areas in the half-graben basins. The Baimiao Structure located on the down-fault block of the Lan-liao fault was formed under the setting mentioned above and was rich in oil and gas. Similar situations were found in the other two planar kink faults. The Domino faults were produced by the local extensional stress field under the influence of the marginal faults, and commonly distributed on the central uplift belt and the gentle slop belt of the half-graben basins. The Domino faults consisted of a few of parallel faults with about equal distances, and led the sediments and traps into linear arrangement. For example, the Domino faults formed on the central uplift belt in the Southern part of the Dongpu Depression introduced the delta sediments and turbidites into the deeper area of the basin，which produced a number of linear sandbodies and traps along the fault troughs and were the most important hydrocarbon accumulation areas. In the end，this paper put forward the listric lake-filling model, which affected the development of oil source centers and the hydrocarbon potential of the basin;the planar kink fan-filling model and the Domino delta-turbidite-filling model which controlled petroleum accumulations in the basin. These models are of significance in basin analysis and evaluation.
The marginal listric fault, planar kink fault and Domino faults were found in the analysis of the tectonic lithofacies in the Southeastern part of the Dongpu Depression，which was one of typical half-graben basins in China. These faults impressed significantly on the evolution of the basin itself, on the development of the depositional systems and the distribution of hydrocarbons. The crest -cut faults of the east border of the Dongpu Depression consist of the listric faults with NE trend and the panar kink faults with NNE trend, which have controlled the formation and evolution of the Depression. The listric faults were formed by the regionally extensional stress field. They were long-active ones, and the deep sags or oil source centers were developed along the listric faults. The longer fault strike and longer active time the listric faults, the larger and deeper the sags. There are three listric faults in the tan-liao fault at the eastern margin of the Southeastern Dongpu Depression，and three oil source centers along the faults, which are respectively;the Geganji North，the Gegan扛South Sag and the Guyan Sag. The listric fault in the middle was the longest in its strike and throw，consequently, the Geganji South Sag was the largest one of the three. The marginal planar kink faults were also formed in regionally extensional stress field, but their bases of the upfaulted block were broken into several parts to form the step-planar kink faults, in which the rising bases evolved into buried h}71s. Although the planar kink faults and the listric faults influenced on the evolution of the Dongpu Depression, the down-faulted blocks the planar kink faults often conducted as the seperating zones by large volumes of sediments of allovial fan，delta-fan and subaqueous fan. Because there are a lot of reservoir sandbodies and various fault traps or lithological traps with in the down-fault block sediments, the blocks are significant hydrocarbon accumulation areas in the half-graben basins. The Baimiao Structure located on the down-fault block of the Lan-liao fault was formed under the setting mentioned above and was rich in oil and gas. Similar situations were found in the other two planar kink faults. The Domino faults were produced by the local extensional stress field under the influence of the marginal faults, and commonly distributed on the central uplift belt and the gentle slop belt of the half-graben basins. The Domino faults consisted of a few of parallel faults with about equal distances, and led the sediments and traps into linear arrangement. For example, the Domino faults formed on the central uplift belt in the Southern part of the Dongpu Depression introduced the delta sediments and turbidites into the deeper area of the basin，which produced a number of linear sandbodies and traps along the fault troughs and were the most important hydrocarbon accumulation areas. In the end，this paper put forward the listric lake-filling model, which affected the development of oil source centers and the hydrocarbon potential of the basin;the planar kink fan-filling model and the Domino delta-turbidite-filling model which controlled petroleum accumulations in the basin. These models are of significance in basin analysis and evaluation.
1994, 12(4): 132-139.
Abstract:
Late Permian Xuanwei Formation(corresponding to Longtan and Changxing Formations) in the eastern Yunnan and western Guizhou consists of coal-bearing clastic sequences. Some thick bedded basalt conglomerates were developed at the bottom of the sequence ( Lower Member of Xuanwei Formation).In this paper, the distribution and the depositional environments of the conglomerates are investigated and their relations to the coal-accumulation are discussed. The cotlglomerates are distributed to the east of Xiaojiang Fault (S-N trend ) along the east side of the Kangdian paleocontinent and they are displayed in four E-W trend belts. Our researches are focused on the Xundian-Fuyuan-Panxian conglomerate belt. Gravels of conglomerates are 5cm to 25cm in size, well rounded, middle to well sorted and gravel supported. The contents of gravels are mainly basalt fragments and occasionally siliceous rocks, tufaceous rocks and agates. The matrix consists of fine sands, plant debris and siliceous, calcareous and glauconitic cements.Sometimes marine algae fossils can be found in martix. These conglomerates are believed to be the deposits of braided delta depositional system. The main facies are pebbly braided channel conglmerates with erosional bottom and unidirectional imbricated structures. sandy braided channel sandstones with trough cross stratification and many erosional bases，pebbly mouth bar conglomerates with evident bidirectional grain orientation，and sandy mouth bar sandstones and siltstones with upward coarsening sequence and many tidal flat muddy pebble and tidal lamination.During the activation of marginal fault(Xiao jiang Fault)，the progradation of each braided delta will produce an irregular upward-coarsening delta front sequence. But in some areas, the basal conglomerate beds directly cover on the paleoweathering surface on the top of Lower Permian. These basal conglomerates are probably the results of the rapid progradation of braided channel and the tidal winnowing during the initial strong activity stage of marginal fault. The coal accumulation were controlled by the braided-delta. During progradation of delta，the coal-accumulation mainly occured at the inter-channel areas on the delta plain. During retrogradation of braided delta，the coal-accumulation occured on the gradully abandoned delta lobes. As a result,at the lower part of the Lower Member of Xuanwei Formation，which was formed during the progradation of delta, the coal seams are restrictly distributed，thin and discontinuous. At the upper part, which was formed during the retrogradation of delta, the coal seams are generally thick and continuously distributed. In the inter-delta lobe areas, the coal seams are well developed both at the lower part and upper part. It can be concluded that the coa-accumulation is favored in the inter-delta areas and on the declined delta lobe.
Late Permian Xuanwei Formation(corresponding to Longtan and Changxing Formations) in the eastern Yunnan and western Guizhou consists of coal-bearing clastic sequences. Some thick bedded basalt conglomerates were developed at the bottom of the sequence ( Lower Member of Xuanwei Formation).In this paper, the distribution and the depositional environments of the conglomerates are investigated and their relations to the coal-accumulation are discussed. The cotlglomerates are distributed to the east of Xiaojiang Fault (S-N trend ) along the east side of the Kangdian paleocontinent and they are displayed in four E-W trend belts. Our researches are focused on the Xundian-Fuyuan-Panxian conglomerate belt. Gravels of conglomerates are 5cm to 25cm in size, well rounded, middle to well sorted and gravel supported. The contents of gravels are mainly basalt fragments and occasionally siliceous rocks, tufaceous rocks and agates. The matrix consists of fine sands, plant debris and siliceous, calcareous and glauconitic cements.Sometimes marine algae fossils can be found in martix. These conglomerates are believed to be the deposits of braided delta depositional system. The main facies are pebbly braided channel conglmerates with erosional bottom and unidirectional imbricated structures. sandy braided channel sandstones with trough cross stratification and many erosional bases，pebbly mouth bar conglomerates with evident bidirectional grain orientation，and sandy mouth bar sandstones and siltstones with upward coarsening sequence and many tidal flat muddy pebble and tidal lamination.During the activation of marginal fault(Xiao jiang Fault)，the progradation of each braided delta will produce an irregular upward-coarsening delta front sequence. But in some areas, the basal conglomerate beds directly cover on the paleoweathering surface on the top of Lower Permian. These basal conglomerates are probably the results of the rapid progradation of braided channel and the tidal winnowing during the initial strong activity stage of marginal fault. The coal accumulation were controlled by the braided-delta. During progradation of delta，the coal-accumulation mainly occured at the inter-channel areas on the delta plain. During retrogradation of braided delta，the coal-accumulation occured on the gradully abandoned delta lobes. As a result,at the lower part of the Lower Member of Xuanwei Formation，which was formed during the progradation of delta, the coal seams are restrictly distributed，thin and discontinuous. At the upper part, which was formed during the retrogradation of delta, the coal seams are generally thick and continuously distributed. In the inter-delta lobe areas, the coal seams are well developed both at the lower part and upper part. It can be concluded that the coa-accumulation is favored in the inter-delta areas and on the declined delta lobe.
