1999 Vol. 17, No. 2
column
Display Method:
1999, 17(2): 167-175.
Abstract:
The Yangtze area during the Late-Sinian and Early Cambrian is the typical passiv e c ontinental margin basin, which is the ideal basin type for us to study the sedim entary crust and recovery the eustatic curve. Black shales are widely distribute d in the Upper Sinian and Lower Cambrian of the western Hunan, which belongs to the southeastern margin of the Yangtze Platform. The strata of the Upper Sinian - Lower Cambrian can be divided as two super-sequences and three sequences. The sequence of Upper-Sinian and Lower Cambrian is as follows (in ascending order): Upper Sinian-dolostone, black slate and siliceous slate, lenticular barite, blac k slate, phosphorite, black siliceous slate; Lower Cambrian-black slate, concret ionary phosphorites, barite, stone coal, V-Ni-Mo deposits, black slate, black sa ndstone, K-shale, limestone. The series of ore bearing are the black shale-phosp hate-silicalite of Upper Sinian and phosphate-barite-stone coal-metals rich of L ower Cambrian. Advances presented in this thesis can be summarized as follows: 1. There are six types of black shales: black shale, chert, coal stone, phosphor ite, barite and carbonate rich in organic matter. They exhibit different regiona l characteristics in time and space; 2. The geological evidence suggest that the black shales were formed in a platfo rm marginal trough on southeastern margins of the upper Yangtze-Exi Platform, wh ich belongs to a shallow water shelf reductive environment with water depth less than 250 meters. The environment evolved gradually from shallow water during la te Sinian to deeper, and more open during early Cambrian. 3. Many organisms have been discovered in the black shales, including radiolaria s, spicules, and bacteria-algae, which indicate that they have played an importa nt role in the formation of the black shale series. 4. Bio-sedimentation and bio-geochemical processes play a certain leading role. Resulted from the reworked benthos, the organic carbon in the sediments (especia lly in Xinhuang region) is rather abundant. As the upper layer (surface) seawate r is abundant nutrient and rather high biotic productivity, the biomass influx is relatively large. The biologic processes cause the enrichment of metal elemen ts, minor elements and REE, and locally change the pH and Eh values as to form a weak reduction condition resulting in the leaching of the Fe and Mn and remigra tion and re-distribution of metal elements. 5. The rate of sedimentation is very slow and discontinuous. The bottom current eroded and reworked the sediments and hence restrained the accumulation. Therefo re，the sedimentation rate in the area is very low and even some segments witho ut sediments. On the above, the black shale of the Upper Sinian-Lower Cambrian generated from the anoxic event, and the organic matter source is algae and fungal (Thallophy ta). After the organisms degrade slowly, the organic matter absorbed and complex ed many elements. At the early diagenesis stage, the organic matter decomposed, and some element relaxed, i.e.，the element accumulated by many stages, so the e l ements exist in many styles.The generation of Ni-Mo, coal stone, barite and pho sphorite deposits are controlled by the sea-level change, and the ore-bearing se ts developed in the transgressive systems tract and condensed section. Finally, the author concluded that the ore-bearing characteristics controlled by the two aspects of the abundant source of organic matter from algae and fungi and the pr eserved and transverse conditions of the organic matter in the anoxic environmen t.
The Yangtze area during the Late-Sinian and Early Cambrian is the typical passiv e c ontinental margin basin, which is the ideal basin type for us to study the sedim entary crust and recovery the eustatic curve. Black shales are widely distribute d in the Upper Sinian and Lower Cambrian of the western Hunan, which belongs to the southeastern margin of the Yangtze Platform. The strata of the Upper Sinian - Lower Cambrian can be divided as two super-sequences and three sequences. The sequence of Upper-Sinian and Lower Cambrian is as follows (in ascending order): Upper Sinian-dolostone, black slate and siliceous slate, lenticular barite, blac k slate, phosphorite, black siliceous slate; Lower Cambrian-black slate, concret ionary phosphorites, barite, stone coal, V-Ni-Mo deposits, black slate, black sa ndstone, K-shale, limestone. The series of ore bearing are the black shale-phosp hate-silicalite of Upper Sinian and phosphate-barite-stone coal-metals rich of L ower Cambrian. Advances presented in this thesis can be summarized as follows: 1. There are six types of black shales: black shale, chert, coal stone, phosphor ite, barite and carbonate rich in organic matter. They exhibit different regiona l characteristics in time and space; 2. The geological evidence suggest that the black shales were formed in a platfo rm marginal trough on southeastern margins of the upper Yangtze-Exi Platform, wh ich belongs to a shallow water shelf reductive environment with water depth less than 250 meters. The environment evolved gradually from shallow water during la te Sinian to deeper, and more open during early Cambrian. 3. Many organisms have been discovered in the black shales, including radiolaria s, spicules, and bacteria-algae, which indicate that they have played an importa nt role in the formation of the black shale series. 4. Bio-sedimentation and bio-geochemical processes play a certain leading role. Resulted from the reworked benthos, the organic carbon in the sediments (especia lly in Xinhuang region) is rather abundant. As the upper layer (surface) seawate r is abundant nutrient and rather high biotic productivity, the biomass influx is relatively large. The biologic processes cause the enrichment of metal elemen ts, minor elements and REE, and locally change the pH and Eh values as to form a weak reduction condition resulting in the leaching of the Fe and Mn and remigra tion and re-distribution of metal elements. 5. The rate of sedimentation is very slow and discontinuous. The bottom current eroded and reworked the sediments and hence restrained the accumulation. Therefo re，the sedimentation rate in the area is very low and even some segments witho ut sediments. On the above, the black shale of the Upper Sinian-Lower Cambrian generated from the anoxic event, and the organic matter source is algae and fungal (Thallophy ta). After the organisms degrade slowly, the organic matter absorbed and complex ed many elements. At the early diagenesis stage, the organic matter decomposed, and some element relaxed, i.e.，the element accumulated by many stages, so the e l ements exist in many styles.The generation of Ni-Mo, coal stone, barite and pho sphorite deposits are controlled by the sea-level change, and the ore-bearing se ts developed in the transgressive systems tract and condensed section. Finally, the author concluded that the ore-bearing characteristics controlled by the two aspects of the abundant source of organic matter from algae and fungi and the pr eserved and transverse conditions of the organic matter in the anoxic environmen t.
1999, 17(2): 192-197.
Abstract:
The Cambrian-Ordovician sequences are the most widespread ones in Tarim basin.More and more results of explorations and exploitations indicate that they are most important source and reservoir rocks in the basin. It is a set of shallow-bathyal deposits of carbonate and clastic rocks. The sedimentary facies of the study area were a kind of local platform in Cambrian,and platform-open sea shelf in Early-Middle Ordovician,at the same period,it was shelf facies in Keping area and open platform facies in Bachu area.In late Ordovician,the bulk areas were rapidly uplifted and changed into land by the influences of Caledonian orogeny. So the Upper Ordovician was hiatus or truncation in most areas of the basin. The variations of sea level had varying scales or orders during the long geological history and it led to formation of various sedimemtary characteristics in which it were objectively recorded in sedimentary rocks and sequences.For this reason,by means of studying the sedimentary features,sequences and boundary characters in the rocks and strata,it is able to estimate the laws of sea level changes during the period of sedimentation,analyse the conditions of paleogeography and paleoclimatology,and provide some scientific basis for exploration of oil and gas.Through study on the deposition characteristics,sequence stratigraphic framework and sea level changes,two second-order cyclic sequences,four third-order cyclic sequeces and nine fouth-order cyclic sequences have been recognized.Detailed analysis has focussed on the third-order cyclic sequences. The study shows that the formation of every cyclic sequence is caused by the relatively rapid rise,slowly rise,stagnant,slowly fall and rapid fall of the sea-level,in which the maximun sea-level rise occured during late Qioulitage period-early Tumuxiouke Period and,thereafter,for the sake of tectonic activity and global sea-level fall,the sea water withdrawed rapidly from the study area,resulting in the loss of the Upper Ordovician deposition. In brief,according to the evolutionary history of sea level changes and cyclic-sequence,there were two times large scale transgression-regression during the period,and it was the Early-Middle Cambrian and Late Cambrian-Orovician,in which the period of maximum transgression was the Middle Ordovician in the Tarim basin.In the long period(Ⅲ-order) of sea level changes,it contained many high-frequency short-period variations of sea level that it was named composite sea level change.
The Cambrian-Ordovician sequences are the most widespread ones in Tarim basin.More and more results of explorations and exploitations indicate that they are most important source and reservoir rocks in the basin. It is a set of shallow-bathyal deposits of carbonate and clastic rocks. The sedimentary facies of the study area were a kind of local platform in Cambrian,and platform-open sea shelf in Early-Middle Ordovician,at the same period,it was shelf facies in Keping area and open platform facies in Bachu area.In late Ordovician,the bulk areas were rapidly uplifted and changed into land by the influences of Caledonian orogeny. So the Upper Ordovician was hiatus or truncation in most areas of the basin. The variations of sea level had varying scales or orders during the long geological history and it led to formation of various sedimemtary characteristics in which it were objectively recorded in sedimentary rocks and sequences.For this reason,by means of studying the sedimentary features,sequences and boundary characters in the rocks and strata,it is able to estimate the laws of sea level changes during the period of sedimentation,analyse the conditions of paleogeography and paleoclimatology,and provide some scientific basis for exploration of oil and gas.Through study on the deposition characteristics,sequence stratigraphic framework and sea level changes,two second-order cyclic sequences,four third-order cyclic sequeces and nine fouth-order cyclic sequences have been recognized.Detailed analysis has focussed on the third-order cyclic sequences. The study shows that the formation of every cyclic sequence is caused by the relatively rapid rise,slowly rise,stagnant,slowly fall and rapid fall of the sea-level,in which the maximun sea-level rise occured during late Qioulitage period-early Tumuxiouke Period and,thereafter,for the sake of tectonic activity and global sea-level fall,the sea water withdrawed rapidly from the study area,resulting in the loss of the Upper Ordovician deposition. In brief,according to the evolutionary history of sea level changes and cyclic-sequence,there were two times large scale transgression-regression during the period,and it was the Early-Middle Cambrian and Late Cambrian-Orovician,in which the period of maximum transgression was the Middle Ordovician in the Tarim basin.In the long period(Ⅲ-order) of sea level changes,it contained many high-frequency short-period variations of sea level that it was named composite sea level change.
1999, 17(2): 204-208.
Abstract:
The sediment samples of Core 1787,which is 810 cm in the length was colle cted from the esat Pacific Ocean.The present water depth is 5073 m.Their clastic components,distributions and sources were studied,and an attempt was made to ex tract paleooceanogrphic information from the clastic components in late Cenozice ra. For the mineral analyses,the 0.063～0.25 mm fraction was separated from the sedi ment samples by wet sieving,heavy components were extracted using tribromomethan e(density 2.89).All the minerals were identified using a petrographic microscope,when necessary,immersion oils.The results shows that the heavy components are m ainly micro-manganese nodules,biogenous apatite,limonte,magnetite and pyroxene; and the light components are mainly biogenous opal(the tests of siliceous organi sms,such as radiolaria and sponge-spicule),clay aggregates and volcanic glass.W ith the depth increasing,the abundance of these components varies regularly.It i s revealed that,in Cenozoic era,there are 11 times of valcano actvity and 9 time s of activity of antarctic bottom water(AABW),and the AABW led to at least 8 tim es of hiatuses.In the periods of valcano erruption,the abundnce of volcanic clas ts are appearently increased.In the periods of AABW,the abundance of limonite,mi cro-manganese nodules are high,bioturbation in sediments are strong,and the oxi gen isotope values are lighter.AABW is the main factor to lead to hiatuses and o xidative enviroment.The supposed periods of AABW coincided well with the hitu ses infered by magnetostraitigraphy,sediments structure and DSDP data.It is sugg seted that clastic components and their assemblages can provide mineral evidence s to reconstruct sedimentary environment.
The sediment samples of Core 1787,which is 810 cm in the length was colle cted from the esat Pacific Ocean.The present water depth is 5073 m.Their clastic components,distributions and sources were studied,and an attempt was made to ex tract paleooceanogrphic information from the clastic components in late Cenozice ra. For the mineral analyses,the 0.063～0.25 mm fraction was separated from the sedi ment samples by wet sieving,heavy components were extracted using tribromomethan e(density 2.89).All the minerals were identified using a petrographic microscope,when necessary,immersion oils.The results shows that the heavy components are m ainly micro-manganese nodules,biogenous apatite,limonte,magnetite and pyroxene; and the light components are mainly biogenous opal(the tests of siliceous organi sms,such as radiolaria and sponge-spicule),clay aggregates and volcanic glass.W ith the depth increasing,the abundance of these components varies regularly.It i s revealed that,in Cenozoic era,there are 11 times of valcano actvity and 9 time s of activity of antarctic bottom water(AABW),and the AABW led to at least 8 tim es of hiatuses.In the periods of valcano erruption,the abundnce of volcanic clas ts are appearently increased.In the periods of AABW,the abundance of limonite,mi cro-manganese nodules are high,bioturbation in sediments are strong,and the oxi gen isotope values are lighter.AABW is the main factor to lead to hiatuses and o xidative enviroment.The supposed periods of AABW coincided well with the hitu ses infered by magnetostraitigraphy,sediments structure and DSDP data.It is sugg seted that clastic components and their assemblages can provide mineral evidence s to reconstruct sedimentary environment.
1999, 17(2): 214-220.
Abstract:
The reasonably interpretation of the genesis of the Late Neogene red clay has attracted increasingly attention due to its importance for better understan ding of problems such as the evolution of the Quaternary paleoclimate and the Pa leomonsoon.Several opinions have been documented.But a more systematic petrologi c study on red clay has not been reported. Recently we have made a careful field observation and conducted a systematic stu dy on petrology,microtexture and morphology,geochemistry on several red clay sec tions in different parts in the middle reaches of the Yellow River,using thin se ction,SEM,X-ray diffraction,particle size and geochemical analysis.Field and lab oratory studies show that the pedostratigraphic structure in different red clay sections can be fairly well correlated although they are located over far distan ces and the texture,mineral components exhibit an obvious homogeneity in differe nt places.Our studies also found that preferentially oriented optical clay films are common in red clay.They mainly occur along the walls of pores and cracks a s flowing colloid or as rim films around framents. They were formed during soil -forming process and fheir development is controlled by paleoclimate.The develo ped optical caly films in red clay indicate a warm,wet forest climate accompanie d by an intensely leaching process,while undeveloped ones imply an arid or semia rid prairie environment coupled with slight leaching.Our studies also show that calcareous concretion layer beneath the red clay horizon is an illuvial horizon which was resulted from eluviation of calc form the upper clay and by its migr ation and reperecipitation during pedogenic process of the red clay,impluing a w arm and wet climate with intensely leaching. The Hipparion red clay was formed domintly under an arid-semiarid pr airie environment with subhumid-humid forest climate alternative.This climatic p attern was probably related with the paleogeographic pattern that Qing-Zang Plat eau had elevated to a height that could blocked the warm and wet paleomonsoon bl owing from the Indian Ocean to northe China.The variation of the climate and di fferentiation of temperature among red clay layers became greater after about 6. 0Ma,this also attributed to the deteriorated climate resulted in accelerating el evation rate of Qing-Zang Plateau.Taking the Hipparion red clay in R idge Wangdaifu,Fugu,norther Shaanxi province as an example,its formation experi enced four main climatic cycles,according to the petrology,texture and micromor phological features as well as geochemical characteristics of the red clay.Each cycle initiated with arid or semiarid climate and ended with humid or subhumid c limate.
The reasonably interpretation of the genesis of the Late Neogene red clay has attracted increasingly attention due to its importance for better understan ding of problems such as the evolution of the Quaternary paleoclimate and the Pa leomonsoon.Several opinions have been documented.But a more systematic petrologi c study on red clay has not been reported. Recently we have made a careful field observation and conducted a systematic stu dy on petrology,microtexture and morphology,geochemistry on several red clay sec tions in different parts in the middle reaches of the Yellow River,using thin se ction,SEM,X-ray diffraction,particle size and geochemical analysis.Field and lab oratory studies show that the pedostratigraphic structure in different red clay sections can be fairly well correlated although they are located over far distan ces and the texture,mineral components exhibit an obvious homogeneity in differe nt places.Our studies also found that preferentially oriented optical clay films are common in red clay.They mainly occur along the walls of pores and cracks a s flowing colloid or as rim films around framents. They were formed during soil -forming process and fheir development is controlled by paleoclimate.The develo ped optical caly films in red clay indicate a warm,wet forest climate accompanie d by an intensely leaching process,while undeveloped ones imply an arid or semia rid prairie environment coupled with slight leaching.Our studies also show that calcareous concretion layer beneath the red clay horizon is an illuvial horizon which was resulted from eluviation of calc form the upper clay and by its migr ation and reperecipitation during pedogenic process of the red clay,impluing a w arm and wet climate with intensely leaching. The Hipparion red clay was formed domintly under an arid-semiarid pr airie environment with subhumid-humid forest climate alternative.This climatic p attern was probably related with the paleogeographic pattern that Qing-Zang Plat eau had elevated to a height that could blocked the warm and wet paleomonsoon bl owing from the Indian Ocean to northe China.The variation of the climate and di fferentiation of temperature among red clay layers became greater after about 6. 0Ma,this also attributed to the deteriorated climate resulted in accelerating el evation rate of Qing-Zang Plateau.Taking the Hipparion red clay in R idge Wangdaifu,Fugu,norther Shaanxi province as an example,its formation experi enced four main climatic cycles,according to the petrology,texture and micromor phological features as well as geochemical characteristics of the red clay.Each cycle initiated with arid or semiarid climate and ended with humid or subhumid c limate.
1999, 17(2): 226-232.
Abstract:
Red clay, a predominant deposit in Chinese loess plateau during the late Tertiary,is regarded as a good record of paleoclimate changes during the Late Mi ocen e and Pliocene.Some fossils have been found in this deposit and a number of samp les have been measured for magnetic susceptibility,grain size etc.In order to ob tain climatic information in the past several million years,however,it's deposit ion process and origin are still discrepant.In this paper,a detail grain size d istribution of the Late Tertiary red clay deposit in North China is presented,c omparisons of grain size distribution of red clay with that of typical Quaternar y aeolian loess-paleosol deposit in this region demonstrate both sediments are s imilar origin.And a specific difference between their grain size distributions a lso exist.It implies that some different transportation media and depositional e nvironments to form these sediments.Our detailed grain size distribution compari sons demonstrate that the dust to form the red clay deposit was transported by w eaker wind system than that in Quaternary.A unification of the grain size distri bution of red clay may infer that red clay has strongly been weathered. Climate was progressively cold and dry in the Late Tertiary in the North Chian and t errestrial sediments were dominated in this region.The red clay is not lacustrin e and weathering materials origin because:(1) it was impossible there existed a l ake as big as several hundred thousand kilometers in this region since the clima te was quite dry at that time,(2) evidence from chemical element analysis are bi g different from that underlying bedrock,demonstrating that its heterogeneous or igin was from bedrock.In addition,a very good unification of grain size distribu tion from top to bottom of the red clay sequence has also verified that it was n ot weathering origin. Noticeable differences of grain size distributions of red clay and fluvial sediments have corroborated that it was not fluvial origin, als o this conclusion can be proved by that there are no laminations and multi inter calation of calcium carbonate in the red clay sequence by field observations. A very good similarity of grain s ize distribution of red clay and its overlying loess-paleosol sediments should b e strong evidences showing their similar origin. Detailed comparisons of granulo metry characteristic of C-M, L-M,L-M and A-M plots Q1-Md-Q3 fluctua tions empirical judging equation and vector analysis supported this conclusion.M ore specific analyis shows that grain size characterisitcs of red clay are more close to that of paleosol than that of loess.Finer particle size distribution,st rong we athering and pedogenesis and more reddish color of red clay may indicate that th e wind system was weaker, climate was much drier and warmer,and stronger oxidati on in the Late Tertiary than that in Quaternary. However,some red clay removed b y water was involved. From above evidences we conclude that the red clay deposit in North China are ae olian origin.The dust to form the red clay deposits was transported by the wind system which was weaker than that of loess-paleosol formed during Quaternary.The dust may has been strongly weathered by weathering and pedogensis p rocess.
Red clay, a predominant deposit in Chinese loess plateau during the late Tertiary,is regarded as a good record of paleoclimate changes during the Late Mi ocen e and Pliocene.Some fossils have been found in this deposit and a number of samp les have been measured for magnetic susceptibility,grain size etc.In order to ob tain climatic information in the past several million years,however,it's deposit ion process and origin are still discrepant.In this paper,a detail grain size d istribution of the Late Tertiary red clay deposit in North China is presented,c omparisons of grain size distribution of red clay with that of typical Quaternar y aeolian loess-paleosol deposit in this region demonstrate both sediments are s imilar origin.And a specific difference between their grain size distributions a lso exist.It implies that some different transportation media and depositional e nvironments to form these sediments.Our detailed grain size distribution compari sons demonstrate that the dust to form the red clay deposit was transported by w eaker wind system than that in Quaternary.A unification of the grain size distri bution of red clay may infer that red clay has strongly been weathered. Climate was progressively cold and dry in the Late Tertiary in the North Chian and t errestrial sediments were dominated in this region.The red clay is not lacustrin e and weathering materials origin because:(1) it was impossible there existed a l ake as big as several hundred thousand kilometers in this region since the clima te was quite dry at that time,(2) evidence from chemical element analysis are bi g different from that underlying bedrock,demonstrating that its heterogeneous or igin was from bedrock.In addition,a very good unification of grain size distribu tion from top to bottom of the red clay sequence has also verified that it was n ot weathering origin. Noticeable differences of grain size distributions of red clay and fluvial sediments have corroborated that it was not fluvial origin, als o this conclusion can be proved by that there are no laminations and multi inter calation of calcium carbonate in the red clay sequence by field observations. A very good similarity of grain s ize distribution of red clay and its overlying loess-paleosol sediments should b e strong evidences showing their similar origin. Detailed comparisons of granulo metry characteristic of C-M, L-M,L-M and A-M plots Q1-Md-Q3 fluctua tions empirical judging equation and vector analysis supported this conclusion.M ore specific analyis shows that grain size characterisitcs of red clay are more close to that of paleosol than that of loess.Finer particle size distribution,st rong we athering and pedogenesis and more reddish color of red clay may indicate that th e wind system was weaker, climate was much drier and warmer,and stronger oxidati on in the Late Tertiary than that in Quaternary. However,some red clay removed b y water was involved. From above evidences we conclude that the red clay deposit in North China are ae olian origin.The dust to form the red clay deposits was transported by the wind system which was weaker than that of loess-paleosol formed during Quaternary.The dust may has been strongly weathered by weathering and pedogensis p rocess.
1999, 17(2): 240-246.
Abstract:
There are many fluvial clsaaifications in the world.S ome of them mainly are concerned with the relationship be tween river process and geotectonic evolution.Some of them are impressed the co mbination of predominant mode of sediment transport and channel stability .Some of them are classified only according to channel planforms.Some classifications are considered the relative rates of channel and interchannel accumulations,and so on.However,many of the classification schemes have more or less defects.Furth ermore,some classifications derived by the research workers of one subject can n ot applied in other subjects. Two classification schemes of fluvial rivers derived by Rust〔12〕 and Qia n〔17〕 according to channel planform are applied widely in the world.The classification scheme derived by Rust〔12〕 is given extensive attention b y many sedimentologists,while the other derived by Qian〔17〕 is given mor e attention by many water engineers and geomorphologists.The former includes bra ided,meandering,anastomosing and straight fluvial channel patterns and the later includes braided,meandiering,anabranched and straight channel patterns.Some wat er engineers and geomorphologists think that the anastomosing and the anabranche d fluvial rivers are the same river types because the other river types in the t wo schemes are the same respectively.So,they consider that the two classificatio n schemes are equivalent.More studies indicate that the anastomosing and the ana branched aren't the same channel type. The definitions and the interchannel subsurface deposits of anastomosing and ana dranched channel patterns are compared in detail,The anastomosing river is stab le,low bedload,multiple channel systems with low gradicnt and moderate sinuosity separated by vegetated islands.The anabranched river is alternation of single a nd double (or mulitple) channels in flow orientation.The former banks are very s table.Mud and silt are the main sediments of its interchannels and floodplains a nd no channel sand bodies exist in these areas.The banks of the later are very stable in the single channel reaches and are unstable in the double (or multiple ) channel reaches.Mud and silt are the main sediments in the floodplains of sin gle channel reaches and the upper mud-silt floodplains of double (or multiple)channel reaches.The autho rs think that the two classification schemes above aren't equivalent because t he anastomosing and the anabranched are the different channel patterns.Thus the study achievements of fluvial systems in one field are difficult to be applied i n other fields.For the sake of convenience to exchange the achievements in diffe rent fields,a new classification scheme of fluvial revers is needed. After discussing the imperfection of some representative river classification sc hemes,a new classification of fluvial rivers is derived according to the planfor m and stability of channels and the sediment characteristics of interchannnels. Fluvial rivers are divided into braided.meandering,anabranched,anastomosing and straight channel patterns in this new classification.The definitions of anastomo sing and anabranched rivers are defined above.The definitions of braided,meander ing and straight rivers are respectively similar to that of defined by Rust in 1978.The main characteristics of the five fluvial channle patterns are compared in fig.1 and table 3.The new classification may be applied in fluvial sedimento logy,fluvial geomorphology and fluvial hydraulics. It is necessary and useful fo r the study of fluvial systems.
There are many fluvial clsaaifications in the world.S ome of them mainly are concerned with the relationship be tween river process and geotectonic evolution.Some of them are impressed the co mbination of predominant mode of sediment transport and channel stability .Some of them are classified only according to channel planforms.Some classifications are considered the relative rates of channel and interchannel accumulations,and so on.However,many of the classification schemes have more or less defects.Furth ermore,some classifications derived by the research workers of one subject can n ot applied in other subjects. Two classification schemes of fluvial rivers derived by Rust〔12〕 and Qia n〔17〕 according to channel planform are applied widely in the world.The classification scheme derived by Rust〔12〕 is given extensive attention b y many sedimentologists,while the other derived by Qian〔17〕 is given mor e attention by many water engineers and geomorphologists.The former includes bra ided,meandering,anastomosing and straight fluvial channel patterns and the later includes braided,meandiering,anabranched and straight channel patterns.Some wat er engineers and geomorphologists think that the anastomosing and the anabranche d fluvial rivers are the same river types because the other river types in the t wo schemes are the same respectively.So,they consider that the two classificatio n schemes are equivalent.More studies indicate that the anastomosing and the ana branched aren't the same channel type. The definitions and the interchannel subsurface deposits of anastomosing and ana dranched channel patterns are compared in detail,The anastomosing river is stab le,low bedload,multiple channel systems with low gradicnt and moderate sinuosity separated by vegetated islands.The anabranched river is alternation of single a nd double (or mulitple) channels in flow orientation.The former banks are very s table.Mud and silt are the main sediments of its interchannels and floodplains a nd no channel sand bodies exist in these areas.The banks of the later are very stable in the single channel reaches and are unstable in the double (or multiple ) channel reaches.Mud and silt are the main sediments in the floodplains of sin gle channel reaches and the upper mud-silt floodplains of double (or multiple)channel reaches.The autho rs think that the two classification schemes above aren't equivalent because t he anastomosing and the anabranched are the different channel patterns.Thus the study achievements of fluvial systems in one field are difficult to be applied i n other fields.For the sake of convenience to exchange the achievements in diffe rent fields,a new classification scheme of fluvial revers is needed. After discussing the imperfection of some representative river classification sc hemes,a new classification of fluvial rivers is derived according to the planfor m and stability of channels and the sediment characteristics of interchannnels. Fluvial rivers are divided into braided.meandering,anabranched,anastomosing and straight channel patterns in this new classification.The definitions of anastomo sing and anabranched rivers are defined above.The definitions of braided,meander ing and straight rivers are respectively similar to that of defined by Rust in 1978.The main characteristics of the five fluvial channle patterns are compared in fig.1 and table 3.The new classification may be applied in fluvial sedimento logy,fluvial geomorphology and fluvial hydraulics. It is necessary and useful fo r the study of fluvial systems.
1999, 17(2): 258-262.
Abstract:
Braided river sandstones are widely distributed in Chinese continental ba sins;however,development for these reservoirs is not very satisfactory.The most important reason is the heavy heterogeneity of braided sandstones.This paper tak es the outcrop in the Zhangjiakou region,Hebei province as an example,which was densely sampled.Geological models are established based on the heterogeneity ana lysis of the sandstone,and then methods of modeling are probed.Kriging models a nd conditional simulation models are built based on porosity and permeability va riogram.Hurst indexes are calculated based on spectral analysis and rescale rang e analysis,which vary at the level of 0.8.One fractional permeability model is b uilt based on fractional geometry interpolation principles.The results suggest t hat Kriging models could reflect the macroscopic change of reservoir physical pr operties,conditional simulation models could reveal the reservoir heterogeneity, and the fractional model could reveal both the macroscopic physical properties a nd microscopic heterogeneity.Comparison of these models show that the fractional model is relatively the most effective model,which could be used in reservoir i n early development of oil fields.
Braided river sandstones are widely distributed in Chinese continental ba sins;however,development for these reservoirs is not very satisfactory.The most important reason is the heavy heterogeneity of braided sandstones.This paper tak es the outcrop in the Zhangjiakou region,Hebei province as an example,which was densely sampled.Geological models are established based on the heterogeneity ana lysis of the sandstone,and then methods of modeling are probed.Kriging models a nd conditional simulation models are built based on porosity and permeability va riogram.Hurst indexes are calculated based on spectral analysis and rescale rang e analysis,which vary at the level of 0.8.One fractional permeability model is b uilt based on fractional geometry interpolation principles.The results suggest t hat Kriging models could reflect the macroscopic change of reservoir physical pr operties,conditional simulation models could reveal the reservoir heterogeneity, and the fractional model could reveal both the macroscopic physical properties a nd microscopic heterogeneity.Comparison of these models show that the fractional model is relatively the most effective model,which could be used in reservoir i n early development of oil fields.
1999, 17(2): 269-272.
Abstract:
Based on the microscopic features of pore structure,this article quantita tively discusses several essential problems about hydrocarbon migration principl e in petroleum geology.It mainly investigates the primary pore structure charact eristics,fluid properties and direction of hydrocarbon migration as well as the hydrocarbon migration behaviors in the reservoir of the homogeneous pore structu re and in the reservoir which has the various combinations of heterogeneous pore structure.The conclusion could enrich and supplement the theories of petroleum geology (1) Only under certain condition can the hydrocarbon migrate.It includes pore s tructure and fluid condition.The former is the coordination number is bigger tha n or equal to 2 and the pore throat which the hydrocarbon immigrant by.The latte r is fluid number reaching saturation of hydrocarbon migration. (2) The diversification of microscopic pore structure in reservoir cause that th e hydrocarbon migrates in multi-direetion.The trend of the hydrocarbon migratio n is upward,but when the coordination number is bigger than 2,it may migrate upw ard as well as updip. (3) The hydrocarbon migration show heterogeneity of the hydrocarbon migration d irection,saturation and height of oil column in heterogenous reservoir which por e structure is complex.
Based on the microscopic features of pore structure,this article quantita tively discusses several essential problems about hydrocarbon migration principl e in petroleum geology.It mainly investigates the primary pore structure charact eristics,fluid properties and direction of hydrocarbon migration as well as the hydrocarbon migration behaviors in the reservoir of the homogeneous pore structu re and in the reservoir which has the various combinations of heterogeneous pore structure.The conclusion could enrich and supplement the theories of petroleum geology (1) Only under certain condition can the hydrocarbon migrate.It includes pore s tructure and fluid condition.The former is the coordination number is bigger tha n or equal to 2 and the pore throat which the hydrocarbon immigrant by.The latte r is fluid number reaching saturation of hydrocarbon migration. (2) The diversification of microscopic pore structure in reservoir cause that th e hydrocarbon migrates in multi-direetion.The trend of the hydrocarbon migratio n is upward,but when the coordination number is bigger than 2,it may migrate upw ard as well as updip. (3) The hydrocarbon migration show heterogeneity of the hydrocarbon migration d irection,saturation and height of oil column in heterogenous reservoir which por e structure is complex.
1999, 17(2): 285-290.
Abstract:
Tricyclic diterpanes such as pimarane, dehydrabieatane and simonelli te and tetracyclic diterpanes such as phyllocladene are most common biomarkers i n coal and other terrestrial source rocks and oils, but in most case they are no t high in abundance. In this study we examined some Chinese coals and terrestria l sediments for the highly presence of tricyclic and tetracyclic diterpenoid hyd rocarbons, and have assigned structures to the diterpanes by mass spectra. The s amples were collected from the third Member of Shahejie Formation, Low-Eogene, E astern Depression, Liaohe Basin. The sedimentary environments for the samples ar e fresh water lacustrine bog and flood plain facies. Organic petrologic analyses show that the organic macerales for the coal measure source rocks are mainly co mposed of vitrinite, contented up to 70% or even high to 90 %, while the content s of exinite, inertinite and sapropelic material are very low. The Ro for the sa mples under study varies from 0.475%to 0.539%, so the organic matters from those samples are generally in immature and lower thermal evolution stages. Fo r all of the samples, C20+ n-alkanes predominate over C15～ C19 n-alkanes and the nC29 or nC31 n-alkanes are the prominent peaks . All of the OEP values for the samples are large than 7 and the CPI values are larger than 3. Therefore the alkanes also show an obviously immatures to low-mature thermal evolution. In all of the samples pristane is the most abun dant alkane of the saturated hydrocarbon fractions. Pristane/phytane ratios all are larger than 2. This is also the typical isoprenoid hydrocarbon distribution characteristic for coal measure source rocks. High abundance tricyclic diterpane s such as pimarane and dehydrabieatane and tetracyclic diterpanes such as phyllo cladene are detected from the samples. Besides, some special biomarkers such as oleanene, ursene and other pentacyclic triterpenoids are also detected from thos e samples. Although thre kinds of biomarkers are detected in the same strata, t hey come from different plants. Tricyclic diterpanes and tetracyclic diterpanes mainly come from gymnosperm (in particular the conifer), petridophyte, bryophyte and pteridophyte respectively, whereas pentacyclic triterpenoids mainly come fr om angiosperm. show that the input of organic matter in the coal source rocks, the third Member of Shahejie Formation, Low-Eogene, Eastern Depression, Liaohe Ba sin,is of obvions diversification and complexity.
Tricyclic diterpanes such as pimarane, dehydrabieatane and simonelli te and tetracyclic diterpanes such as phyllocladene are most common biomarkers i n coal and other terrestrial source rocks and oils, but in most case they are no t high in abundance. In this study we examined some Chinese coals and terrestria l sediments for the highly presence of tricyclic and tetracyclic diterpenoid hyd rocarbons, and have assigned structures to the diterpanes by mass spectra. The s amples were collected from the third Member of Shahejie Formation, Low-Eogene, E astern Depression, Liaohe Basin. The sedimentary environments for the samples ar e fresh water lacustrine bog and flood plain facies. Organic petrologic analyses show that the organic macerales for the coal measure source rocks are mainly co mposed of vitrinite, contented up to 70% or even high to 90 %, while the content s of exinite, inertinite and sapropelic material are very low. The Ro for the sa mples under study varies from 0.475%to 0.539%, so the organic matters from those samples are generally in immature and lower thermal evolution stages. Fo r all of the samples, C20+ n-alkanes predominate over C15～ C19 n-alkanes and the nC29 or nC31 n-alkanes are the prominent peaks . All of the OEP values for the samples are large than 7 and the CPI values are larger than 3. Therefore the alkanes also show an obviously immatures to low-mature thermal evolution. In all of the samples pristane is the most abun dant alkane of the saturated hydrocarbon fractions. Pristane/phytane ratios all are larger than 2. This is also the typical isoprenoid hydrocarbon distribution characteristic for coal measure source rocks. High abundance tricyclic diterpane s such as pimarane and dehydrabieatane and tetracyclic diterpanes such as phyllo cladene are detected from the samples. Besides, some special biomarkers such as oleanene, ursene and other pentacyclic triterpenoids are also detected from thos e samples. Although thre kinds of biomarkers are detected in the same strata, t hey come from different plants. Tricyclic diterpanes and tetracyclic diterpanes mainly come from gymnosperm (in particular the conifer), petridophyte, bryophyte and pteridophyte respectively, whereas pentacyclic triterpenoids mainly come fr om angiosperm. show that the input of organic matter in the coal source rocks, the third Member of Shahejie Formation, Low-Eogene, Eastern Depression, Liaohe Ba sin,is of obvions diversification and complexity.
1999, 17(2): 301-305.
Abstract:
To understand the thermal evolution process and hydrocarbon-forming mech anism of organic matter, the researchers have done lots of hydrocarbon-generatio n experiments on the sediment and rock-containing organic matter. In this paper we have adopted the method DTA coupled with chromatography to simulate the gener ation of gaseous hydrocarbon from the standard coal samples of different ranks a nd oth er source rocks. The method is of the following advantages: (1) rapid temperatur e-rising speed and without influence of pressure; (2) continuous sampling; (3) o nly gaseous hydrocarbon analysed; (4) directly comparing gas-forming state of so urce rock with DTA and weight loss features; (5) less human-induced influence on experiment results. By use of the new analysis method, we have concluded that the low-mature c oal has the strongest exothermic reaction and weight loss in relatively lower th e first temperature of exothemic reaction and weight loss temperature. And the c oal sample with low rank has much stronger hydrocarbon-generating capacity than those with high rank in the course of the themal simulation. The generation amou nt and features of the gaseous hydrocarbon are dependent not only on the abundan ce of organic matter,but also rock types,kerogen types,maturation degree and so on. Source rocks with higher maturation degree belongs to the exhausted rock of the weaker hydrocarbon-generating capacity. Gaseous hydrocarbon produced from th e source rock containing Ⅰ and Ⅱ-type kerogens is generally of the high conten t of heavy components, whereas those formed from the source rock bearing Ⅲ-type kerogen is mainly composed of the light components such as methane and ethane. Carbonate source rocks have weaker hydrocarbon-generating capacity in the proces s of the thermal simulation due to their low content of organic carbon, but the much higher temperature can increase the internal pressure of the inclusion in c arbonate crystals resulting in explosion to release "effective hydrocarbon". Thus, carbonate source rock can usually produce large amounts of gaseous hydroc arbon at the higher temperature stage during thermal simulation.
To understand the thermal evolution process and hydrocarbon-forming mech anism of organic matter, the researchers have done lots of hydrocarbon-generatio n experiments on the sediment and rock-containing organic matter. In this paper we have adopted the method DTA coupled with chromatography to simulate the gener ation of gaseous hydrocarbon from the standard coal samples of different ranks a nd oth er source rocks. The method is of the following advantages: (1) rapid temperatur e-rising speed and without influence of pressure; (2) continuous sampling; (3) o nly gaseous hydrocarbon analysed; (4) directly comparing gas-forming state of so urce rock with DTA and weight loss features; (5) less human-induced influence on experiment results. By use of the new analysis method, we have concluded that the low-mature c oal has the strongest exothermic reaction and weight loss in relatively lower th e first temperature of exothemic reaction and weight loss temperature. And the c oal sample with low rank has much stronger hydrocarbon-generating capacity than those with high rank in the course of the themal simulation. The generation amou nt and features of the gaseous hydrocarbon are dependent not only on the abundan ce of organic matter,but also rock types,kerogen types,maturation degree and so on. Source rocks with higher maturation degree belongs to the exhausted rock of the weaker hydrocarbon-generating capacity. Gaseous hydrocarbon produced from th e source rock containing Ⅰ and Ⅱ-type kerogens is generally of the high conten t of heavy components, whereas those formed from the source rock bearing Ⅲ-type kerogen is mainly composed of the light components such as methane and ethane. Carbonate source rocks have weaker hydrocarbon-generating capacity in the proces s of the thermal simulation due to their low content of organic carbon, but the much higher temperature can increase the internal pressure of the inclusion in c arbonate crystals resulting in explosion to release "effective hydrocarbon". Thus, carbonate source rock can usually produce large amounts of gaseous hydroc arbon at the higher temperature stage during thermal simulation.
1999, 17(2): 312-317.
Abstract:
The behaviour of pyrrolic compounds in oils from Lunnan area,Tarim Basin,Xingzhang and Chaochang oil-fields,Songliao Basin,and Gasikuke oil-field,Chaidamu Basin are investigated,which are representive of marin,fresh lake,fresh to half salt lake and salt lake origin correspondingly.It wsa founded that there are abviously differences among the oils of different genetic type in both richness and relative distribution.Several geochemical factors which may have influence on the compounds are also discussed,such as paleoenvironment thermal maturity,original source materical and oil migration.The results indicated that the content and distribution of pyrrolic compounds are controled by several factors,and oil fractionation during migration,paleoenvironment are possibly the main factors,furthermore,maturity and original source material are also have effects on the compounds.It was determinedthat pyrrolic nitrogen compounds have potential significance in evaluating oil migration,paleoenvironment and thermal maturity.
The behaviour of pyrrolic compounds in oils from Lunnan area,Tarim Basin,Xingzhang and Chaochang oil-fields,Songliao Basin,and Gasikuke oil-field,Chaidamu Basin are investigated,which are representive of marin,fresh lake,fresh to half salt lake and salt lake origin correspondingly.It wsa founded that there are abviously differences among the oils of different genetic type in both richness and relative distribution.Several geochemical factors which may have influence on the compounds are also discussed,such as paleoenvironment thermal maturity,original source materical and oil migration.The results indicated that the content and distribution of pyrrolic compounds are controled by several factors,and oil fractionation during migration,paleoenvironment are possibly the main factors,furthermore,maturity and original source material are also have effects on the compounds.It was determinedthat pyrrolic nitrogen compounds have potential significance in evaluating oil migration,paleoenvironment and thermal maturity.
1999, 17(2): 325-329.
Abstract:
Global change become a world wide concerned problem in the recent years. The study of plant carbon isotopic composition become an important field in the research of global change,in which a fundamental goal is to determine the contro ling factors of plant carbon isotope discrimination and composition. The paper gives an analysis on the carbon isotope composition of modern plants ( all are C3 species) in Qinghai-Tibet plateau(NE)and a detailed discussion on t he various factors that can influence it. The value of δ13C of 61 samples varies from -23.5‰ to -30.8‰，with an average of -26.6‰. Analysis shows that with the same plant the δ13C value increases with the increase of altitu de and decresases with the increase of latitude.The result of this study shows t hat precipitation,air moisture and pressure are the most important environmental factors to the change of δ13C. The less the amount of precipitation, the more positive the plant δ13C values are. On the other hand,the higher th e air pressure the more negative the δ13C values are. It is now clear tha t plant δ13C value relates directly to the assimilation of leaf to CO2( A),leaf stomatic conductance(g) and intercellular/ambient partial pressure ratio (Pi/Pa). A(cording to) their effect on A, g and Pi/Pa,it is clear that the precipitation, air moisture and pressure cause the change of plant δ13C value. The study suggests that a lot of information reflecting the change of nature env ironmental can be recorded in plants.So it is completely possible to extract cli matic information from plant δ13C.
Global change become a world wide concerned problem in the recent years. The study of plant carbon isotopic composition become an important field in the research of global change,in which a fundamental goal is to determine the contro ling factors of plant carbon isotope discrimination and composition. The paper gives an analysis on the carbon isotope composition of modern plants ( all are C3 species) in Qinghai-Tibet plateau(NE)and a detailed discussion on t he various factors that can influence it. The value of δ13C of 61 samples varies from -23.5‰ to -30.8‰，with an average of -26.6‰. Analysis shows that with the same plant the δ13C value increases with the increase of altitu de and decresases with the increase of latitude.The result of this study shows t hat precipitation,air moisture and pressure are the most important environmental factors to the change of δ13C. The less the amount of precipitation, the more positive the plant δ13C values are. On the other hand,the higher th e air pressure the more negative the δ13C values are. It is now clear tha t plant δ13C value relates directly to the assimilation of leaf to CO2( A),leaf stomatic conductance(g) and intercellular/ambient partial pressure ratio (Pi/Pa). A(cording to) their effect on A, g and Pi/Pa,it is clear that the precipitation, air moisture and pressure cause the change of plant δ13C value. The study suggests that a lot of information reflecting the change of nature env ironmental can be recorded in plants.So it is completely possible to extract cli matic information from plant δ13C.
1999, 17(2): 176-182.
Abstract:
The Changning-Menglian Belt, located in the western Yunnan,Himalayan tect onic region of Palaeo-Tethys,is one of the important areas of studing and resolv ing m any significant geological problems in which the nature and scale of Changning-M englian ocean are very key question,but now there are some arguments too.Some re searchers believe that there is a late paleozoic great ocean and a set o f complete oceanic sedimentary sequence,that is Lalei Group(D-P) of Changning-Men glian Belt, and this group consists of siliceous rock,mudstone and sandstone,the im portant and main evidences are deepsea radiolarian fossils combination in silic eous rock and δ Ce＜-1 of siliceous rock.Others think that there is no a great ocean, in Changning-Menglian Belt but a intercontinental rift and so on. In the paper some new evidences and idea are proposed on the base of the study for three sets of siliceous rock system, which are Lalei Group,Nanpihe Gro up and La ba Group. The common characteristics of Laba Group and Nanpihe Group is consist of sand stone,mudstone,siliceous rcoks and a few grain limestone,in which there are epib enthos fossils or their debris,oscillation ripple cross bedding composed of gra in limesto ne,graded bedding composed of radiolaria fossils.Their radiolaria fossils combination belong to the combination of shallow sea deep shelf to continental s lope subabyss environment. They are undoubtably continental margin deposition.L alei Group consists of three parts. The Upper is the interbed of sandstone,muds ton e,siliceous rock,and includes a few tuffite,continental tholeiite (P1) and and esite-basalt-welded tuff (P2),and so on,which represents the volcanic eruption of continental basement.The Middle is pure siliceous rocks and few mudstone.The Lower is the interbed of sandstone,shale and siliceous rocks.There are graded bedding composed of radiolaria fossils,eroding appearance and lack of burrows or bioturbation in silliceous rocks of Lalei Group.The radiolaria fossils combination in siliceous rocks belong to the combination of continental slope to slope margin basin envi ronment. The geochemical character of siliceous rock is Fe203＜＜FeO,Fe=16 800～17 100 ppm,Mn=120～290 ppm, Co=9～15 ppm, Ni=18～24 ppm,Zn=27.7～121 ppm,M nO/TiO=0.1～0.29,δCe=0.996～1.345,δCe*=(shale standard)=1.02～1.39,δEu=0.53 ～0.67,δEu*=0.83～1.04,REE shale standardization model curve is nearly hori zontal,but spherulite aerolite standardization model curve obviously incline t o right,they are entirely different from oceanic geochemical characteristics.In addition,there is a mixture of Gondwana and Laurasia spore and pollen in Laba G roup,Nanpihe Group and Lalei Group,at the same time,which containes also fusulinid fossils that reflect warm water condition. The above characteristics appear that Lalei Group,Laba Group and Nanpihe Group are all formed in closer neritic continental ma rgin deep shelf to continental slope subabyss environment.Therefore, Changning -Menglian ocean is not a late paleozoic great ocean,and not the boundary between Gondwana and Laurasia,too.
The Changning-Menglian Belt, located in the western Yunnan,Himalayan tect onic region of Palaeo-Tethys,is one of the important areas of studing and resolv ing m any significant geological problems in which the nature and scale of Changning-M englian ocean are very key question,but now there are some arguments too.Some re searchers believe that there is a late paleozoic great ocean and a set o f complete oceanic sedimentary sequence,that is Lalei Group(D-P) of Changning-Men glian Belt, and this group consists of siliceous rock,mudstone and sandstone,the im portant and main evidences are deepsea radiolarian fossils combination in silic eous rock and δ Ce＜-1 of siliceous rock.Others think that there is no a great ocean, in Changning-Menglian Belt but a intercontinental rift and so on. In the paper some new evidences and idea are proposed on the base of the study for three sets of siliceous rock system, which are Lalei Group,Nanpihe Gro up and La ba Group. The common characteristics of Laba Group and Nanpihe Group is consist of sand stone,mudstone,siliceous rcoks and a few grain limestone,in which there are epib enthos fossils or their debris,oscillation ripple cross bedding composed of gra in limesto ne,graded bedding composed of radiolaria fossils.Their radiolaria fossils combination belong to the combination of shallow sea deep shelf to continental s lope subabyss environment. They are undoubtably continental margin deposition.L alei Group consists of three parts. The Upper is the interbed of sandstone,muds ton e,siliceous rock,and includes a few tuffite,continental tholeiite (P1) and and esite-basalt-welded tuff (P2),and so on,which represents the volcanic eruption of continental basement.The Middle is pure siliceous rocks and few mudstone.The Lower is the interbed of sandstone,shale and siliceous rocks.There are graded bedding composed of radiolaria fossils,eroding appearance and lack of burrows or bioturbation in silliceous rocks of Lalei Group.The radiolaria fossils combination in siliceous rocks belong to the combination of continental slope to slope margin basin envi ronment. The geochemical character of siliceous rock is Fe203＜＜FeO,Fe=16 800～17 100 ppm,Mn=120～290 ppm, Co=9～15 ppm, Ni=18～24 ppm,Zn=27.7～121 ppm,M nO/TiO=0.1～0.29,δCe=0.996～1.345,δCe*=(shale standard)=1.02～1.39,δEu=0.53 ～0.67,δEu*=0.83～1.04,REE shale standardization model curve is nearly hori zontal,but spherulite aerolite standardization model curve obviously incline t o right,they are entirely different from oceanic geochemical characteristics.In addition,there is a mixture of Gondwana and Laurasia spore and pollen in Laba G roup,Nanpihe Group and Lalei Group,at the same time,which containes also fusulinid fossils that reflect warm water condition. The above characteristics appear that Lalei Group,Laba Group and Nanpihe Group are all formed in closer neritic continental ma rgin deep shelf to continental slope subabyss environment.Therefore, Changning -Menglian ocean is not a late paleozoic great ocean,and not the boundary between Gondwana and Laurasia,too.
1999, 17(2): 188-191.
Abstract:
The left-oblique depocenter,the oval enclosed isopsach,sedimentary and v olcanic basins controlled and influenced by three sets of strike-slip faults,th e rhombus basins where the circular extentional structure with respect to the st rata young inside and old outside,all of them prove that from the Jurassic Perio d to the Early Creatceous Epoch the transextensional basin was formed in the Lo wer Yangtse Region.Further research showed that its evolution can be divided int o 2 stages,i.e.,early stage(J1＋2) featured by clastic sedimentation and t he later stage (J3-K1) in the property of intensely magmatic activity. In the extensional background of Mesozoic in Eastern China,three sets of strike -slip faults were developed.They are:1)Yangtse Fault,also as zigzag fault,2)bra nch faults obliquely jointed with Tanlu Fault,which cut the main part of the Low er Yangtse Region into wedge-shaped blocks;3)the horse tail-shaped faults taki ng the Qingyang-Guangde Fault as its main component,the later also as the south ern limit of the Lower Yangtse Region.The faults controlled the formation and ev olution of basins. In the Lower Yangtse Region,the basins were classified into 3 types.They involve :1)sedimentary basin, e.g. Susong Basin, Caohan Basin， 2)sedimentary-volcanic basin, e.g.Ningwu Basin,Luzong Basin，3)volcanic basin formed laterly,e.g.Lishu i Basin,Liyang Basin and Fanchang Basin.Among them,Luzong Basin and Ningwu Basin were proved to be typical pull-apart basins,where the strata were arranged seq uentially,i.e.from center to margin,they become older.The basin is of circular e xtensional structure in plane.The laterly formed volcanic basins as rhombus are strike-slip basins. The sedimentary center of J1＋2 were left-obliquely arranged in equal spa cing intervals.The main sedimentary centers were just above the NNE parts of Yan gtse Fault.The concordance of sedimentation with structure revealed that the fau lt controlling the distribution of sub-lift and sub-settlement in basins.
The left-oblique depocenter,the oval enclosed isopsach,sedimentary and v olcanic basins controlled and influenced by three sets of strike-slip faults,th e rhombus basins where the circular extentional structure with respect to the st rata young inside and old outside,all of them prove that from the Jurassic Perio d to the Early Creatceous Epoch the transextensional basin was formed in the Lo wer Yangtse Region.Further research showed that its evolution can be divided int o 2 stages,i.e.,early stage(J1＋2) featured by clastic sedimentation and t he later stage (J3-K1) in the property of intensely magmatic activity. In the extensional background of Mesozoic in Eastern China,three sets of strike -slip faults were developed.They are:1)Yangtse Fault,also as zigzag fault,2)bra nch faults obliquely jointed with Tanlu Fault,which cut the main part of the Low er Yangtse Region into wedge-shaped blocks;3)the horse tail-shaped faults taki ng the Qingyang-Guangde Fault as its main component,the later also as the south ern limit of the Lower Yangtse Region.The faults controlled the formation and ev olution of basins. In the Lower Yangtse Region,the basins were classified into 3 types.They involve :1)sedimentary basin, e.g. Susong Basin, Caohan Basin， 2)sedimentary-volcanic basin, e.g.Ningwu Basin,Luzong Basin，3)volcanic basin formed laterly,e.g.Lishu i Basin,Liyang Basin and Fanchang Basin.Among them,Luzong Basin and Ningwu Basin were proved to be typical pull-apart basins,where the strata were arranged seq uentially,i.e.from center to margin,they become older.The basin is of circular e xtensional structure in plane.The laterly formed volcanic basins as rhombus are strike-slip basins. The sedimentary center of J1＋2 were left-obliquely arranged in equal spa cing intervals.The main sedimentary centers were just above the NNE parts of Yan gtse Fault.The concordance of sedimentation with structure revealed that the fau lt controlling the distribution of sub-lift and sub-settlement in basins.
1999, 17(2): 198-203.
Abstract:
Carbonate mud-mounds of Middle-Late Ordovician age in Tazhong area grew and developed on an old carbonate platform when it was progressively sinking b elow the sea level.Those laterally climbed up the slope toward high position of the platform,and vertically are the multiple superimposed mud-mound.The main mu d-mound-building organisms are bacterium and algae,such as ortonella and its k ind genus.The secondary organisms are Tabulati,Btyozoa,stromatoproids,spongea,an d so on .It is considered that the rock types of the mud-mounds are dominantly micrite-thromoblites framestone,micrite-thrombolites baffle-framestone,algal micrite-thrombolites bindstone. Mud-mound facies may be divided into three sub facies such as mud-mound centre,mud-mound talus and intermud mound-deposit. Th e evolution of mud-mound was controlled by the relationship between the rate of transgressive and the rate of mud-mounds growth,and by the change of water dep th and turbidity.
Carbonate mud-mounds of Middle-Late Ordovician age in Tazhong area grew and developed on an old carbonate platform when it was progressively sinking b elow the sea level.Those laterally climbed up the slope toward high position of the platform,and vertically are the multiple superimposed mud-mound.The main mu d-mound-building organisms are bacterium and algae,such as ortonella and its k ind genus.The secondary organisms are Tabulati,Btyozoa,stromatoproids,spongea,an d so on .It is considered that the rock types of the mud-mounds are dominantly micrite-thromoblites framestone,micrite-thrombolites baffle-framestone,algal micrite-thrombolites bindstone. Mud-mound facies may be divided into three sub facies such as mud-mound centre,mud-mound talus and intermud mound-deposit. Th e evolution of mud-mound was controlled by the relationship between the rate of transgressive and the rate of mud-mounds growth,and by the change of water dep th and turbidity.
1999, 17(2): 209-213.
Abstract:
The Yily Basin,developed in the central Tianshan orogenid belt,accommodat es a huge thickness(about 5 000～9 000 m) of continental Permian strata.The Upper Permian is chiefly composed of lacustrine clastic sedimentary rocks interbedded with limestone 2 700 m in total thickn ess.including units Xiaoshansayi Formation,Hamist Formation,Tiemulike Formation and Bakaluesayi Formation in ascending order.Ophiomorpha is amp l y produced in the Lower part of Xiaoshansayi Formation which consists of thin-be dded limestones interbedded with massive sandstones.Graded pebble-bearing sandst onaes,cross-bedded sandstones and rippled fine sandstones often constitute cycli c fining-upward deposits in section,showing mountainy river fan deposits.The lime stone usually contains sands,bioclastics and mud with few plant and freshwater b ivalve fossils in them revealing shallow lacustrine deposits.It is absent in bla ck laminar limestone and shales of Tiemulike Formation and Bakaluesayi Formation because this lithology represents an exaerobic condition. Ophiomorpha exists in limestone beds without laminae in them,pre served as a set of different burrows in diameter from 0.6 to 1.6 cm,probably rep resenting developing stages of the burrow-maker.The burrow wall,0.5～2.5 cm in thickness,is made up of dark or black pellets ovoid,or irregular in shape,but it is conspicuously double-layered.Their maximum length observed in the section ca n reach 35 cm .They are tube-like or caecum-like,predominantly horizontal and obli que in level,neither showing divergent branching pattern of typical Oph iomorpha So,they are similar to Ophiomorpha nodosa Lu ndgren in size and pellet wall,but different in wall texture and branching patte rn.Infill is passive and its composition is like country rocks. Ophiomorpha was once accepted as a marine indicator(Kennedy and Sellwood,1970),and afterwards documented in continental strata(Stewart,1978;Bown,1982; Merill,1984).But Goldering and Pollard (1995) thought that the continenta l appearance of Ophiomorpha is questionable.Samples in this stud y are collected in absolutely lacustrine sedimentary rocks,This supports the poi nt of view that Ophiomorpha can occur in nonmarine environments. Some samples possess upward grading fill (Plate I-E),reflecting a rapi d depositional condition. It could be also used as top-indicating structure.Abov e characteristics demonstrate that the burrow-maker is inclined to penetrate sof t sedimentary floor where there are relatively a high rate of deposition and a h igh level of oxygen content,and they are scarcely controlled by composition of the substrate,water-depth and salinity.
The Yily Basin,developed in the central Tianshan orogenid belt,accommodat es a huge thickness(about 5 000～9 000 m) of continental Permian strata.The Upper Permian is chiefly composed of lacustrine clastic sedimentary rocks interbedded with limestone 2 700 m in total thickn ess.including units Xiaoshansayi Formation,Hamist Formation,Tiemulike Formation and Bakaluesayi Formation in ascending order.Ophiomorpha is amp l y produced in the Lower part of Xiaoshansayi Formation which consists of thin-be dded limestones interbedded with massive sandstones.Graded pebble-bearing sandst onaes,cross-bedded sandstones and rippled fine sandstones often constitute cycli c fining-upward deposits in section,showing mountainy river fan deposits.The lime stone usually contains sands,bioclastics and mud with few plant and freshwater b ivalve fossils in them revealing shallow lacustrine deposits.It is absent in bla ck laminar limestone and shales of Tiemulike Formation and Bakaluesayi Formation because this lithology represents an exaerobic condition. Ophiomorpha exists in limestone beds without laminae in them,pre served as a set of different burrows in diameter from 0.6 to 1.6 cm,probably rep resenting developing stages of the burrow-maker.The burrow wall,0.5～2.5 cm in thickness,is made up of dark or black pellets ovoid,or irregular in shape,but it is conspicuously double-layered.Their maximum length observed in the section ca n reach 35 cm .They are tube-like or caecum-like,predominantly horizontal and obli que in level,neither showing divergent branching pattern of typical Oph iomorpha So,they are similar to Ophiomorpha nodosa Lu ndgren in size and pellet wall,but different in wall texture and branching patte rn.Infill is passive and its composition is like country rocks. Ophiomorpha was once accepted as a marine indicator(Kennedy and Sellwood,1970),and afterwards documented in continental strata(Stewart,1978;Bown,1982; Merill,1984).But Goldering and Pollard (1995) thought that the continenta l appearance of Ophiomorpha is questionable.Samples in this stud y are collected in absolutely lacustrine sedimentary rocks,This supports the poi nt of view that Ophiomorpha can occur in nonmarine environments. Some samples possess upward grading fill (Plate I-E),reflecting a rapi d depositional condition. It could be also used as top-indicating structure.Abov e characteristics demonstrate that the burrow-maker is inclined to penetrate sof t sedimentary floor where there are relatively a high rate of deposition and a h igh level of oxygen content,and they are scarcely controlled by composition of the substrate,water-depth and salinity.
1999, 17(2): 221-225.
Abstract:
It has been proved that quartz grains of different sources are characte rized with different surface textures and features,which has been successfully applied in d istinguishing the original source of Chinese loess.Seven groups of loess samples were retrieved from Dadunling loess section in Xining basin,Qinghai Province,No rhtwest China. Quartz grains were seperated by chemical processes and their surf ace texures and features were observed under SEM in this study to discover the o riginal source of loess on the Qinghai-Tibet plateau. It is found that the quartz grains in Xining loess since 1.2 Ma are mainly angul ar and subangular in features which are different form those of ordinary desert sands. Besides, these quartz grains display a distinct set of surface features including typical sheering fractures(with a frequency of 31%),big conchoidal br eakages(occurred on 50% of grains that are ＞1μm) and oriented striations(3%),w hich is generally considered to be the markers of glacial actions.At the same ti me,the sub-rounded quartz sands with typical V-shaped pits(12% in frequency)and polishe d surface(21%)under water environment are also found in the samples.All the abov e information indicates that the Xining loess material is not mainly originated from desert but from glacial and periglacial environment of the Tibetan plateau. It could be explained that a quantity of detrital material was formed by glacial grindings and freezing and melting processes when the Qinghai-Tibet Plateau rea ched an average altitude of 3 000 m 1.1Ma～0.7Ma ago,when most of the Plateau re ached the cryosphere.Under the Plateau winter monsoon or the westerly,the fine g rains were transported eastward and deposited in relatively lower basins such as Xining Basin.The quartz grains in Xining loess have documented not only the inf o rmation of global change but also the history of glacial actions on the Qinghai- Tibet Plateau.
It has been proved that quartz grains of different sources are characte rized with different surface textures and features,which has been successfully applied in d istinguishing the original source of Chinese loess.Seven groups of loess samples were retrieved from Dadunling loess section in Xining basin,Qinghai Province,No rhtwest China. Quartz grains were seperated by chemical processes and their surf ace texures and features were observed under SEM in this study to discover the o riginal source of loess on the Qinghai-Tibet plateau. It is found that the quartz grains in Xining loess since 1.2 Ma are mainly angul ar and subangular in features which are different form those of ordinary desert sands. Besides, these quartz grains display a distinct set of surface features including typical sheering fractures(with a frequency of 31%),big conchoidal br eakages(occurred on 50% of grains that are ＞1μm) and oriented striations(3%),w hich is generally considered to be the markers of glacial actions.At the same ti me,the sub-rounded quartz sands with typical V-shaped pits(12% in frequency)and polishe d surface(21%)under water environment are also found in the samples.All the abov e information indicates that the Xining loess material is not mainly originated from desert but from glacial and periglacial environment of the Tibetan plateau. It could be explained that a quantity of detrital material was formed by glacial grindings and freezing and melting processes when the Qinghai-Tibet Plateau rea ched an average altitude of 3 000 m 1.1Ma～0.7Ma ago,when most of the Plateau re ached the cryosphere.Under the Plateau winter monsoon or the westerly,the fine g rains were transported eastward and deposited in relatively lower basins such as Xining Basin.The quartz grains in Xining loess have documented not only the inf o rmation of global change but also the history of glacial actions on the Qinghai- Tibet Plateau.
1999, 17(2): 233-239.
Abstract:
Stalagmites in cave are a better carrier of karst environment record,and the mature methods of the various datings and testing of the index showing environment has possessed at present for the re construction paleoenvironment using the preserved information of stalagmites in cave is one of the most popular project in recent 20 years.Under the forecast s t udy of the global climatic changes,the high resolution dating and the regular ch ange of carbon and oxygen isotopic component of stalagmites in cave have made a greater contribution for the breakthrough and filling in the gaps in the field. The sedimentary characteristics and the trend changes of paleo-drip records in stalagmite from Shuinan cave,Guilin are studied by examing composition of calcite,rock chemistry,content of the trace element,texture,bedding-stucture, as well as typical marks of depositional break or weathering crust ect.By dating U series along the axis cores of the stalagmite,the age of the stalagmite is fr om the late period of Middle Pleistocene to the early period of Late Pleistocene,i.e.,from 80.7×103a to 229.1×103a.The growth rate of the stalagmite varies from 2.08mm/100a to 2.82mm/100a.
Stalagmites in cave are a better carrier of karst environment record,and the mature methods of the various datings and testing of the index showing environment has possessed at present for the re construction paleoenvironment using the preserved information of stalagmites in cave is one of the most popular project in recent 20 years.Under the forecast s t udy of the global climatic changes,the high resolution dating and the regular ch ange of carbon and oxygen isotopic component of stalagmites in cave have made a greater contribution for the breakthrough and filling in the gaps in the field. The sedimentary characteristics and the trend changes of paleo-drip records in stalagmite from Shuinan cave,Guilin are studied by examing composition of calcite,rock chemistry,content of the trace element,texture,bedding-stucture, as well as typical marks of depositional break or weathering crust ect.By dating U series along the axis cores of the stalagmite,the age of the stalagmite is fr om the late period of Middle Pleistocene to the early period of Late Pleistocene,i.e.,from 80.7×103a to 229.1×103a.The growth rate of the stalagmite varies from 2.08mm/100a to 2.82mm/100a.
1999, 17(2): 247-251.
Abstract:
The Huangxian Paleogene faulted basin is located at the northwestern marg in o f the Jiaobei faulted uplift,the Eastern Shandong faulted block,east to the Tanl u Fracture zone.It is a terrestrial depositional basin,belong to the coal,oil an d gas faulted basin in uplifted block.Two kinds of sequence boundaries are recog nized in the basin filling succession.One is regional tectonic boundary,displayi ng as the regional unconformity.The other is the tectonic-depositional mechanics -transforming boundary,that is the basin water expand or shrink due to the basin tectonics transformation (tectonic stress field change).The upper part of the te ctonic-depositional mechanics boundary is different from the lower part in depos itional association. Three tectonic-depositional cycles can be distinguished in the basin filling suc cession,which were controlled by the activity of the marginal faults of the basi n,According to the tectonic-depositional cycles,the sequences boundaries and the analysis to the evolution of the basin,three sequences can be divided,that is, sequence Ⅰ，Ⅱ and Ⅲ from bottom to top.The sequence Ⅱ and Ⅲ are complete th ird-order sequences,with lowstand,transgressive and highstand systems tracts,con taining coal,oil and gas deposits,Five genetic stratigraphic units can be identi fied.The sequence Ⅰ is mainly fluvial depositional system,forming the first gen etic stratigraphic unit,The lowstand and transgressive systems tracts in sequenc e Ⅱ and Ⅲ constitute four genetic units respectively.The evolution of the faul ted basin was controlled by the tectonic activity in the basin.The lake level ch anges were expressed as integral water expansion or shrink,not in a single direc tion. Study shows that the coal accumulation occurred in both the lowstand and transgr essive systems tracts,stronger in the lowstand systems tracts.The centers of the coal accumulation migrated with the evolution of the sequences.The coal accumul a ted mainly in the transitional belt from the basin's center to margin,also in th e center of the basin.The coal accumulation centers migrated toward the basin's margin in the transgressive systems tracts,with smaller scopes.There was only sm all-scaled coal accumulation in the highstand systems tracts,occurring in the ce nter part of the basin. The activity of the basin's marginal faults was relative ly stable in the lowstand periods.In despite of fluvial-braided river system dev el oped in the basin.the blocks outside the basin uplifted in a small scale.The coa rse sediment supply was not abundant.The lake basin with shallow water beneaped and gradually became swamp,further transmulated to peat swamp,forming large-scal ed coalbeds. The oil shales and the oil-bearing shales in the basin's filling succession cont ain a lot of animal remains and animal fragments distributed in the top of the l owstand systems tracts,which,the authors believe,may be the condensed interval i n the basin's sequence.They are important ore-bearing layers,playing key roles i n the sequence division.
The Huangxian Paleogene faulted basin is located at the northwestern marg in o f the Jiaobei faulted uplift,the Eastern Shandong faulted block,east to the Tanl u Fracture zone.It is a terrestrial depositional basin,belong to the coal,oil an d gas faulted basin in uplifted block.Two kinds of sequence boundaries are recog nized in the basin filling succession.One is regional tectonic boundary,displayi ng as the regional unconformity.The other is the tectonic-depositional mechanics -transforming boundary,that is the basin water expand or shrink due to the basin tectonics transformation (tectonic stress field change).The upper part of the te ctonic-depositional mechanics boundary is different from the lower part in depos itional association. Three tectonic-depositional cycles can be distinguished in the basin filling suc cession,which were controlled by the activity of the marginal faults of the basi n,According to the tectonic-depositional cycles,the sequences boundaries and the analysis to the evolution of the basin,three sequences can be divided,that is, sequence Ⅰ，Ⅱ and Ⅲ from bottom to top.The sequence Ⅱ and Ⅲ are complete th ird-order sequences,with lowstand,transgressive and highstand systems tracts,con taining coal,oil and gas deposits,Five genetic stratigraphic units can be identi fied.The sequence Ⅰ is mainly fluvial depositional system,forming the first gen etic stratigraphic unit,The lowstand and transgressive systems tracts in sequenc e Ⅱ and Ⅲ constitute four genetic units respectively.The evolution of the faul ted basin was controlled by the tectonic activity in the basin.The lake level ch anges were expressed as integral water expansion or shrink,not in a single direc tion. Study shows that the coal accumulation occurred in both the lowstand and transgr essive systems tracts,stronger in the lowstand systems tracts.The centers of the coal accumulation migrated with the evolution of the sequences.The coal accumul a ted mainly in the transitional belt from the basin's center to margin,also in th e center of the basin.The coal accumulation centers migrated toward the basin's margin in the transgressive systems tracts,with smaller scopes.There was only sm all-scaled coal accumulation in the highstand systems tracts,occurring in the ce nter part of the basin. The activity of the basin's marginal faults was relative ly stable in the lowstand periods.In despite of fluvial-braided river system dev el oped in the basin.the blocks outside the basin uplifted in a small scale.The coa rse sediment supply was not abundant.The lake basin with shallow water beneaped and gradually became swamp,further transmulated to peat swamp,forming large-scal ed coalbeds. The oil shales and the oil-bearing shales in the basin's filling succession cont ain a lot of animal remains and animal fragments distributed in the top of the l owstand systems tracts,which,the authors believe,may be the condensed interval i n the basin's sequence.They are important ore-bearing layers,playing key roles i n the sequence division.
1999, 17(2): 273-279.
Abstract:
Based on the actual situation of the Bohai Gulf Basin,its deep zone is the reali stic new exploration region at present.Although it has the characteristics of l ow porosity ad permeability,large depth and some difficulty,its oil and gas reso urces potential is large in the deep zone of Bohai Gulf Basin,and there is good exploration prospects. In the deep zone of Bohai Gulf Basin,there are three series of source rocks,the fourth member dark mudstone of Shahejie Formation and Kongdian Formation,the thi rd and first member dark mudstone Shahejie Formation.The source rock of the thi rd m ember of Shahejie formation is the major source rock for the deep zone of Basin. It has the character of large thickness of black mudstone,good hydrocarbon gener ation indicators,high thermal evolution degree and large hydrocarbon generation potential. Reservoir condition is one of the major controlling factors to the formation of oil and gas pools in the deep zone of Bohai Gulf Basin.There are multi－type res ervoir rocks,but the sandstone is the major reservoir type,including sandstone a nd conglomerate of alluvial fan,fan-delta and delta as weu as,gravity flow san dstone.In add ition,the buried－hill reservoir is the another important type in the deep zone exploration.Based on the research results,diagenesis,sandstone thickness,supper －pressure abnormal belt and secondary porosity development belt are the major controlling factors to the reservoir property in the deep zone of Bohai Gulf Bas in. There is good seal condition in the deep zone of Bohai Gulf Basin,and the self－ source,self-reservoir and self－seal is the major combination type of oil and poo l formation.In the deep zone of Bohai Gulf Basin,the play is characterized by mu lti－types,early formation and large scale traps. In general,in the deep zone of Bohai Gulf Basin,there are good formation conditi on of oil-gas pools,and rich in resources.Without doubt,in the future,i t will be the most important new exploration region in Bohai Gulf Basin.
Based on the actual situation of the Bohai Gulf Basin,its deep zone is the reali stic new exploration region at present.Although it has the characteristics of l ow porosity ad permeability,large depth and some difficulty,its oil and gas reso urces potential is large in the deep zone of Bohai Gulf Basin,and there is good exploration prospects. In the deep zone of Bohai Gulf Basin,there are three series of source rocks,the fourth member dark mudstone of Shahejie Formation and Kongdian Formation,the thi rd and first member dark mudstone Shahejie Formation.The source rock of the thi rd m ember of Shahejie formation is the major source rock for the deep zone of Basin. It has the character of large thickness of black mudstone,good hydrocarbon gener ation indicators,high thermal evolution degree and large hydrocarbon generation potential. Reservoir condition is one of the major controlling factors to the formation of oil and gas pools in the deep zone of Bohai Gulf Basin.There are multi－type res ervoir rocks,but the sandstone is the major reservoir type,including sandstone a nd conglomerate of alluvial fan,fan-delta and delta as weu as,gravity flow san dstone.In add ition,the buried－hill reservoir is the another important type in the deep zone exploration.Based on the research results,diagenesis,sandstone thickness,supper －pressure abnormal belt and secondary porosity development belt are the major controlling factors to the reservoir property in the deep zone of Bohai Gulf Bas in. There is good seal condition in the deep zone of Bohai Gulf Basin,and the self－ source,self-reservoir and self－seal is the major combination type of oil and poo l formation.In the deep zone of Bohai Gulf Basin,the play is characterized by mu lti－types,early formation and large scale traps. In general,in the deep zone of Bohai Gulf Basin,there are good formation conditi on of oil-gas pools,and rich in resources.Without doubt,in the future,i t will be the most important new exploration region in Bohai Gulf Basin.
1999, 17(2): 291-300.
Abstract:
It is still a disputing problem whether the Jurassic coal measure are the another oil source rock or not.Some coal petrologists believe that there may be oils from coal based on the higher content of liptinites contained in it.Others don't agree because the chemical structure of crude oils can't be related to maceral composition dominated by liptinites from coals. In this paper, the three sites,respectively Lingwu-yanchi area lying in the northern basin,Longdong area in the middle basin and HuanLing-Tongchuan area in the southern basin,are selected to collect coal samples. The coal macrotype,microtype,macerals and their oil-generating potential are studied in detail and then discussed.The research results indicate that the principal macerals are vitrinite and inertinite in the coal of Yan'an Formation,and the coal contains liptinites less than 5% and it's petroleum potential will be very low when it only depends on the minor content of liptinites it contains.Thus,it is very important if vitrinite group became oil-pron macerals,especially desmocollinite.The desmocollinites can be drvided into three subtypes A, B and C according to the genesis and hydrocarbon-generating nature,only desmocollinite B and C have moderate to high petroleum potential,whereas desmocollinite A is not oil-prone maceral which is the main type in desmocollinite.In general,the coal of Yan'an Formation is of poor petroleum potential.However,the cannel coal and bright coal contain the large amount of sporinites in the middle and south of the basin,where content the sporinites is about 10%,the maximum oil-generated period of sporinite corresponds to 0.9%～1.1% vitrinite reflectance,whereas above coal reflectance is only 0.6%～0.7% and bright coal volume is less than 2% in all coals.The cannel coals and bright coals may generate minor amount oil.So the Yan'an Formation coal measure can't become the commercial oils source rocks in Ordos basin.
It is still a disputing problem whether the Jurassic coal measure are the another oil source rock or not.Some coal petrologists believe that there may be oils from coal based on the higher content of liptinites contained in it.Others don't agree because the chemical structure of crude oils can't be related to maceral composition dominated by liptinites from coals. In this paper, the three sites,respectively Lingwu-yanchi area lying in the northern basin,Longdong area in the middle basin and HuanLing-Tongchuan area in the southern basin,are selected to collect coal samples. The coal macrotype,microtype,macerals and their oil-generating potential are studied in detail and then discussed.The research results indicate that the principal macerals are vitrinite and inertinite in the coal of Yan'an Formation,and the coal contains liptinites less than 5% and it's petroleum potential will be very low when it only depends on the minor content of liptinites it contains.Thus,it is very important if vitrinite group became oil-pron macerals,especially desmocollinite.The desmocollinites can be drvided into three subtypes A, B and C according to the genesis and hydrocarbon-generating nature,only desmocollinite B and C have moderate to high petroleum potential,whereas desmocollinite A is not oil-prone maceral which is the main type in desmocollinite.In general,the coal of Yan'an Formation is of poor petroleum potential.However,the cannel coal and bright coal contain the large amount of sporinites in the middle and south of the basin,where content the sporinites is about 10%,the maximum oil-generated period of sporinite corresponds to 0.9%～1.1% vitrinite reflectance,whereas above coal reflectance is only 0.6%～0.7% and bright coal volume is less than 2% in all coals.The cannel coals and bright coals may generate minor amount oil.So the Yan'an Formation coal measure can't become the commercial oils source rocks in Ordos basin.
1999, 17(2): 306-311.
Abstract:
Carbon isotope distribution among the C1 to C4 hydrocarbon is one of the most important criteria to identify the genesis of natural gas.Generally,bio genic natural gases possess a “normal distribution ”in carbon isotopes of C 1 to C4 hydrocarbons and abiogenic natual gases a “reversal distribution”in carbon isotopes of C1 to C4 hydrocarbons.Some scholars consider that “isot opic reversals”can result from the mixture of two kinds of biogenic natural gas with “normal distribution” in carbon isotope.However,prevenient numerical sim ulation did not confim the viewpoint.By means of numerical simulation,the possib ility of “isotopic reversals” in C1 to C4 hydrocarbons resulted from the mixture of two kinds of biogenic natural gas was discussed in this paper. Computation in this article shows that a complete reverse carbon isotopic distri bution among C1 to C4 hydrocarbons (i.e. δ13C methane >δ13 C propane >δ13C n-butane) can be produced by the mixture of two kinds of biogenic gas with a normal carbon isotopic distribution (i.e. δ13C m ethane <δ13C ethane <δ13 propane <δ13C n-butane). While a normal carbon isotopic distribution in natural gas can also be produced by two e ndmembers with reverse distributions. As for the first case, the two endmembers should be of different source, different formation, or of different evolutional stage. It is unreasonable to explain the isotopic reverse distribution of the gas sampl es from several wells of the Changde pool, Songliao Basin by the mixture model, because the isotopically higher endmember needed to form this real gas is not fo und in Songliao Basin. So a better explanation to the isotopic reversal in this gas pool is to consider it to be abiogenic.
Carbon isotope distribution among the C1 to C4 hydrocarbon is one of the most important criteria to identify the genesis of natural gas.Generally,bio genic natural gases possess a “normal distribution ”in carbon isotopes of C 1 to C4 hydrocarbons and abiogenic natual gases a “reversal distribution”in carbon isotopes of C1 to C4 hydrocarbons.Some scholars consider that “isot opic reversals”can result from the mixture of two kinds of biogenic natural gas with “normal distribution” in carbon isotope.However,prevenient numerical sim ulation did not confim the viewpoint.By means of numerical simulation,the possib ility of “isotopic reversals” in C1 to C4 hydrocarbons resulted from the mixture of two kinds of biogenic natural gas was discussed in this paper. Computation in this article shows that a complete reverse carbon isotopic distri bution among C1 to C4 hydrocarbons (i.e. δ13C methane >δ13 C propane >δ13C n-butane) can be produced by the mixture of two kinds of biogenic gas with a normal carbon isotopic distribution (i.e. δ13C m ethane <δ13C ethane <δ13 propane <δ13C n-butane). While a normal carbon isotopic distribution in natural gas can also be produced by two e ndmembers with reverse distributions. As for the first case, the two endmembers should be of different source, different formation, or of different evolutional stage. It is unreasonable to explain the isotopic reverse distribution of the gas sampl es from several wells of the Changde pool, Songliao Basin by the mixture model, because the isotopically higher endmember needed to form this real gas is not fo und in Songliao Basin. So a better explanation to the isotopic reversal in this gas pool is to consider it to be abiogenic.
