1995 Vol. 13, No. 4
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Display Method:
1995, 13(4): 1-15.
Abstract:
Condensed sections (CS) are related to the maximum flooding stage (lag dePOsits) of a relative sea-level Change. They are present in each second and third order sequences in the Middle-Upper Cambrian strata.I. Main features of condensed sections(CS)1. Rock types and sub factes of condensed sections.CSs are composed of seven rock types which are distributed in three factes and five sub factes:Rock types:(1) Glauconitic siltstone-sandstone; (2) Glauconitic oolitic limestone 1 (3) Glauconitic Binclastic limestone; (4)Glauconitic micritic limestone; (5)Glauconitic storm calcirudite;(6)Glauconitic hardground; (7)Glauconitic clay.Three factes: inner shelf, middle shelf and outer shelf Five subfacies: (1) Quartz sandstone-siltstone and Glauconity; (2) Glauconitic oolitic limestome; (3) Glauconitic intraclastic muds; (4) Glauconitic muds and hardgrounds; (5) Deep water muds +phosphorus and manganese.2. Mineralogy and geochemistry of condensed sections.Glauconite, dolomite, pyrite, limonite and clays are the main mineral components of CSs.Chemical analyses of CSs have shown concentrations of some trace elements, such as Mn, lr,P,K and Ti, one of the most important features of condensed sections is the abundance of bingenic material.The potassium content and texture of glauconite permit the assessment of the evolutionary stage and duration of a condensed section. From this, it is apparent that the length of time for the development of CSs is in the range of 104～106 years. This is similar to the duration of the maximum flooding stage of second or third order sea level changes.Ⅱ. Conclusion1. A new concept of condensed section is given in this paper:A condensed section is a low--rate marine sedimentation unit which formed at the time maximum flooding close to the inflection-point from TST to HST during the long-term (2nd to 4th order cycle) global sea-level changes.2. Condensed sections are not only the products of maximum flooding and early highstand, but also the ties of TST and HST. They are the key stratigraphic units of sequence division and stratal correlation. Sea-level changes of the different orders result in the formation of condensed sediments. Studies of the maturity of glauconite can be used to distinguish different orders of sea-level changes.
Condensed sections (CS) are related to the maximum flooding stage (lag dePOsits) of a relative sea-level Change. They are present in each second and third order sequences in the Middle-Upper Cambrian strata.I. Main features of condensed sections(CS)1. Rock types and sub factes of condensed sections.CSs are composed of seven rock types which are distributed in three factes and five sub factes:Rock types:(1) Glauconitic siltstone-sandstone; (2) Glauconitic oolitic limestone 1 (3) Glauconitic Binclastic limestone; (4)Glauconitic micritic limestone; (5)Glauconitic storm calcirudite;(6)Glauconitic hardground; (7)Glauconitic clay.Three factes: inner shelf, middle shelf and outer shelf Five subfacies: (1) Quartz sandstone-siltstone and Glauconity; (2) Glauconitic oolitic limestome; (3) Glauconitic intraclastic muds; (4) Glauconitic muds and hardgrounds; (5) Deep water muds +phosphorus and manganese.2. Mineralogy and geochemistry of condensed sections.Glauconite, dolomite, pyrite, limonite and clays are the main mineral components of CSs.Chemical analyses of CSs have shown concentrations of some trace elements, such as Mn, lr,P,K and Ti, one of the most important features of condensed sections is the abundance of bingenic material.The potassium content and texture of glauconite permit the assessment of the evolutionary stage and duration of a condensed section. From this, it is apparent that the length of time for the development of CSs is in the range of 104～106 years. This is similar to the duration of the maximum flooding stage of second or third order sea level changes.Ⅱ. Conclusion1. A new concept of condensed section is given in this paper:A condensed section is a low--rate marine sedimentation unit which formed at the time maximum flooding close to the inflection-point from TST to HST during the long-term (2nd to 4th order cycle) global sea-level changes.2. Condensed sections are not only the products of maximum flooding and early highstand, but also the ties of TST and HST. They are the key stratigraphic units of sequence division and stratal correlation. Sea-level changes of the different orders result in the formation of condensed sediments. Studies of the maturity of glauconite can be used to distinguish different orders of sea-level changes.
1995, 13(4): 27-36.
Abstract:
The Llandoverian to Wenlockian storm-influenced siliciclastic and carbonate ramp environment has been recognized from the NW Sichuan area. The Early Silurian deposited on the NW margin of the S-China paleoplate tectonically and it has very thick sequences of shale, silty shale, mud and silty sandstone with some reefs, bioherms and stratigraphically discontinuous lenticular and irregular bioclastic tempestites, and multigenic nodular limestone beds.According to the different petrographic assemblages and paleoecology analysis, the authors have divided the sedimentary environment into littoral zone, shallow ramp, deep ramp and basin. The littoral zone is located at intertidal area with tidal flat carbonate deposits; the shallow ramp which is between the wave base and the storm wave base, has type A, B tempestites, pattern A, B nodular limestone, reef limestone and bindstone deposits; the deep ramp is below the storm wave base and above the maximal storm wave base and has type D, E tempestites, pattern C nodular limestone, dark shale deposits; the characteristics; the area below the maximal storm wave base is the basin area with black shale. From Lower Llandoverian to Lower Wenlockian, the sedimentary environment changed from basin to deep ramp, shallow ramp and littoral zone, the representative strata are Lungmachi Formation, Chuijiagou Formation, Wangjiawan Formation and Ningqian Formation, respectively.The authors also discuss the sea level change and its influence in this area. The global glaciation may be the main factor for the influence of the sea level change. Under the action of Tamadjert and Cananiri glaciation, the sea level changed from high to low in this area during the Llandoverian to Wenlockian.
The Llandoverian to Wenlockian storm-influenced siliciclastic and carbonate ramp environment has been recognized from the NW Sichuan area. The Early Silurian deposited on the NW margin of the S-China paleoplate tectonically and it has very thick sequences of shale, silty shale, mud and silty sandstone with some reefs, bioherms and stratigraphically discontinuous lenticular and irregular bioclastic tempestites, and multigenic nodular limestone beds.According to the different petrographic assemblages and paleoecology analysis, the authors have divided the sedimentary environment into littoral zone, shallow ramp, deep ramp and basin. The littoral zone is located at intertidal area with tidal flat carbonate deposits; the shallow ramp which is between the wave base and the storm wave base, has type A, B tempestites, pattern A, B nodular limestone, reef limestone and bindstone deposits; the deep ramp is below the storm wave base and above the maximal storm wave base and has type D, E tempestites, pattern C nodular limestone, dark shale deposits; the characteristics; the area below the maximal storm wave base is the basin area with black shale. From Lower Llandoverian to Lower Wenlockian, the sedimentary environment changed from basin to deep ramp, shallow ramp and littoral zone, the representative strata are Lungmachi Formation, Chuijiagou Formation, Wangjiawan Formation and Ningqian Formation, respectively.The authors also discuss the sea level change and its influence in this area. The global glaciation may be the main factor for the influence of the sea level change. Under the action of Tamadjert and Cananiri glaciation, the sea level changed from high to low in this area during the Llandoverian to Wenlockian.
1995, 13(4): 55-63.
Abstract:
Directed by the theory of the genetic stratigraphic analysis and basin analysis, simultaneously referring to the idea of seismic stratigraphy, the authors have reconstructed the stratigraphic sequence and its correlation, and further subdivided the coal measure(including Fuxian and Yan'an Formation) into five sedimentary episode, i. e.,Episode I (equivalent to Fuxian Formation) is composed of braided river deposits with provenance supply from west to east, and it is merely distributed in stripped shape in the middle part of the Huating area;Episode Ⅱ consists of pluvial and alluvial deposits with a provenance supply from south to north, and it is widely distributed in the Huating area. The main coal seam is found in the upper part of plurial alluvial deposits. Episode Ⅲ is a combination of distributary lacustrine delta deposits and shore to shallow lake deposits. Direction of provenance supply is from north to south;Episode Ⅳ is made up of lacustrine and swamp deposits;Episode Ⅴ is partly eroded,the direction of provenance supply of Episode Ⅳ and Ⅴ is not clear. The coal measure of the Huating coal-producing area underwent on evolutionary history i. e. first rifting and then depressing, in which Episode Ⅰ,Ⅱ and Ⅳ stand for a development period of rift basin, and Episode Ⅳ and Ⅴ indicate the stablely depressing period.Although there are more than ten coal seams in the Huating area, the workable seam is only No. 8 bed. Based on the research data of synsedimentary structure activity, anthraeology,depositional environment and coal-forming botany, the authors point out that the formation of coal seam with great thickness has a close relation to the special coal-forming conditions, and above all, the most favorable climate, together with synsedimentary structure activity, keeps a dynamic equilibrium between the accumumlation rate of a vast swamp and the swamp weather table in a long period.In addition, this paper has also discussed the problem of coal classification from the viewpoint of sedimentology, indicating that coal seams with great thickness in Huating area can be divided into two types; one is "aggradation type" coal that has a stable V/I ratio,implying the stability of water table during peat accumulation; and the other is "progradation type" coal that has an increasing V/I ratio, implying that the gradual rising of paleo-water table has changed peat accumulation.
Directed by the theory of the genetic stratigraphic analysis and basin analysis, simultaneously referring to the idea of seismic stratigraphy, the authors have reconstructed the stratigraphic sequence and its correlation, and further subdivided the coal measure(including Fuxian and Yan'an Formation) into five sedimentary episode, i. e.,Episode I (equivalent to Fuxian Formation) is composed of braided river deposits with provenance supply from west to east, and it is merely distributed in stripped shape in the middle part of the Huating area;Episode Ⅱ consists of pluvial and alluvial deposits with a provenance supply from south to north, and it is widely distributed in the Huating area. The main coal seam is found in the upper part of plurial alluvial deposits. Episode Ⅲ is a combination of distributary lacustrine delta deposits and shore to shallow lake deposits. Direction of provenance supply is from north to south;Episode Ⅳ is made up of lacustrine and swamp deposits;Episode Ⅴ is partly eroded,the direction of provenance supply of Episode Ⅳ and Ⅴ is not clear. The coal measure of the Huating coal-producing area underwent on evolutionary history i. e. first rifting and then depressing, in which Episode Ⅰ,Ⅱ and Ⅳ stand for a development period of rift basin, and Episode Ⅳ and Ⅴ indicate the stablely depressing period.Although there are more than ten coal seams in the Huating area, the workable seam is only No. 8 bed. Based on the research data of synsedimentary structure activity, anthraeology,depositional environment and coal-forming botany, the authors point out that the formation of coal seam with great thickness has a close relation to the special coal-forming conditions, and above all, the most favorable climate, together with synsedimentary structure activity, keeps a dynamic equilibrium between the accumumlation rate of a vast swamp and the swamp weather table in a long period.In addition, this paper has also discussed the problem of coal classification from the viewpoint of sedimentology, indicating that coal seams with great thickness in Huating area can be divided into two types; one is "aggradation type" coal that has a stable V/I ratio,implying the stability of water table during peat accumulation; and the other is "progradation type" coal that has an increasing V/I ratio, implying that the gradual rising of paleo-water table has changed peat accumulation.
1995, 13(4): 73-81.
Abstract:
Compounds derived from higher land plants in an immature brown coal extract are isotopically within ± 2%, of the bulk coal carbon isotopic composition (δ13C of - 27. 0‰), suggesting either that similar species contributed to these compounds or similar biosynthetic fractionations occurred in the plants from which this coal was formed. The terpenoid hydrocarbons form two isotopically distinct groups: the diterpenoids (δ13C of - 25. 0 ± 1. 4‰) and the sesguiterpenoids (δ13C of - 25. 9 ± 1. 5‰) are on average 1 ～ 2‰, enriched in 13C compared to the bulk coal, whereas the oleanane-ursane-lupane derivatives(δ13C of - 29. 0±0. 8‰) are on average 1～2‰, depleted in 13C compared to the bulk coal。 The n-alkanes, ranging from C15 to C35, have a mean δ13C value of - 32. 4± 0.6‰, whereby averages for the C17～C22, and C23～C33 n-alkanes do not significantly differ from the overall average. Hopane derivatives in this coal extract are depleted in 13C compared to the bulk coal by 8～34‰, suggesting that bacterial cycling of methane played a role during the formation of this coal.
Compounds derived from higher land plants in an immature brown coal extract are isotopically within ± 2%, of the bulk coal carbon isotopic composition (δ13C of - 27. 0‰), suggesting either that similar species contributed to these compounds or similar biosynthetic fractionations occurred in the plants from which this coal was formed. The terpenoid hydrocarbons form two isotopically distinct groups: the diterpenoids (δ13C of - 25. 0 ± 1. 4‰) and the sesguiterpenoids (δ13C of - 25. 9 ± 1. 5‰) are on average 1 ～ 2‰, enriched in 13C compared to the bulk coal, whereas the oleanane-ursane-lupane derivatives(δ13C of - 29. 0±0. 8‰) are on average 1～2‰, depleted in 13C compared to the bulk coal。 The n-alkanes, ranging from C15 to C35, have a mean δ13C value of - 32. 4± 0.6‰, whereby averages for the C17～C22, and C23～C33 n-alkanes do not significantly differ from the overall average. Hopane derivatives in this coal extract are depleted in 13C compared to the bulk coal by 8～34‰, suggesting that bacterial cycling of methane played a role during the formation of this coal.
1995, 13(4): 93-99.
Abstract:
Based on data acquired from a pressurized thermal simulation experiment (T = 270℃ ～390℃) in which both oil generation and expulsion from two brown coals are inspected, the characteristics of sterane and terpane products are studied in this paper. The results indicate:(1) The abnormal enrichment of C31 +components in hopane series may be related to a strong reducing environment, and their abnormal lack may have something to do with an oxidation environment. (2) Because the activation energy of isomerization of sterane and hopane is lower than that of vitrinite, the isomerization rates of sterane and hopane are much faster than that of vitrinite in geological low temperature, but the situation is converse in the condition of high temperature of laboratory. (3) Many ratios in sterane or terpane related to the difference of molecular size can be acted as migration parameters.
Based on data acquired from a pressurized thermal simulation experiment (T = 270℃ ～390℃) in which both oil generation and expulsion from two brown coals are inspected, the characteristics of sterane and terpane products are studied in this paper. The results indicate:(1) The abnormal enrichment of C31 +components in hopane series may be related to a strong reducing environment, and their abnormal lack may have something to do with an oxidation environment. (2) Because the activation energy of isomerization of sterane and hopane is lower than that of vitrinite, the isomerization rates of sterane and hopane are much faster than that of vitrinite in geological low temperature, but the situation is converse in the condition of high temperature of laboratory. (3) Many ratios in sterane or terpane related to the difference of molecular size can be acted as migration parameters.
1995, 13(4): 109-115.
Abstract:
By analysing GC/C/MS on line carbon isotopes of 14 condensate oil smples from different areas and measures in the Tarim basin, we get carbon isotopic compositions of monomeric molecules of the liquid hydrocarbon system. Based on the data, we have discussed the carbon isotopic characters of monomeric molecules in condensate oils with different ages, and made oiloil comparison and origin classification. It shows that there are the coal-type oil, oil type oil and mixing type oil in Tarim basin, in which oil type oil can be divided into three sub-types by the age of source rocks: the Ordovician (Cambrian), Carboniferous and Triassic. The source rocks of the coal- type oil is Jurassic coal measures, showing the Tarim basin has 4 sets of practical source rocks (Ordovician - Cambrian, Carboniferous, Triassic and Jurassic).
By analysing GC/C/MS on line carbon isotopes of 14 condensate oil smples from different areas and measures in the Tarim basin, we get carbon isotopic compositions of monomeric molecules of the liquid hydrocarbon system. Based on the data, we have discussed the carbon isotopic characters of monomeric molecules in condensate oils with different ages, and made oiloil comparison and origin classification. It shows that there are the coal-type oil, oil type oil and mixing type oil in Tarim basin, in which oil type oil can be divided into three sub-types by the age of source rocks: the Ordovician (Cambrian), Carboniferous and Triassic. The source rocks of the coal- type oil is Jurassic coal measures, showing the Tarim basin has 4 sets of practical source rocks (Ordovician - Cambrian, Carboniferous, Triassic and Jurassic).
1995, 13(4): 125-130.
Abstract:
It is well known that the strontium isotope is very useful not only for studying sedimentary history of palaeo-ocean but also for stratigraphic classification. So it is very important to research the geochemistry of strontium isotope. The paper, taking the Mouyang profile in Guizhou for example and through the analyses of the isotopic composition in marine carbonate,discusses in detail the evolution of strontium isotope and its geological significance. The results show the following facts:1. In general, the change of the isotopic composition of strontium in marine carbonate is between 0. 70722 and 0. 70767 from the begining to the end of the Permian period. 2. The change scale of the strontium isotope is similar to the results determined by B. N.Popp; And its evolution trend is very similar to the outcome published by W. H. Burk and B.N. Popp.3. The change of isotopic composition of strontium is controlled by the source of strontium, such as volcanic rock, crust silicate and old marine carbonate. From the study area, it is known that the change of 87Sr/86Sr ratio is related to sea level change, and there is a negtive conrelation between the 87Sr/86Sr ratio and sea level change.
It is well known that the strontium isotope is very useful not only for studying sedimentary history of palaeo-ocean but also for stratigraphic classification. So it is very important to research the geochemistry of strontium isotope. The paper, taking the Mouyang profile in Guizhou for example and through the analyses of the isotopic composition in marine carbonate,discusses in detail the evolution of strontium isotope and its geological significance. The results show the following facts:1. In general, the change of the isotopic composition of strontium in marine carbonate is between 0. 70722 and 0. 70767 from the begining to the end of the Permian period. 2. The change scale of the strontium isotope is similar to the results determined by B. N.Popp; And its evolution trend is very similar to the outcome published by W. H. Burk and B.N. Popp.3. The change of isotopic composition of strontium is controlled by the source of strontium, such as volcanic rock, crust silicate and old marine carbonate. From the study area, it is known that the change of 87Sr/86Sr ratio is related to sea level change, and there is a negtive conrelation between the 87Sr/86Sr ratio and sea level change.
1995, 13(4): 138-144.
Abstract:
In North Xingjiang, the Devonian-Carboniferous marine volcanic and sedimentary Formations are the main source rocks of solid mineral deposits. In this paper, lots of data such as satellite gravity anomaly, strata gravity and magnetic force features of different aged strata as well as spectral reflectance are used to further demonstrate this viewpoint. Meanwhile, the spectral reflectance features of gold bearing geological bodies such as igneous rock, silicalite, carbonatite, clay minerals and "iron hat" can be used as the theoretical base for directly detecting gold mine with remote sensing technology.
In North Xingjiang, the Devonian-Carboniferous marine volcanic and sedimentary Formations are the main source rocks of solid mineral deposits. In this paper, lots of data such as satellite gravity anomaly, strata gravity and magnetic force features of different aged strata as well as spectral reflectance are used to further demonstrate this viewpoint. Meanwhile, the spectral reflectance features of gold bearing geological bodies such as igneous rock, silicalite, carbonatite, clay minerals and "iron hat" can be used as the theoretical base for directly detecting gold mine with remote sensing technology.
1995, 13(4): 153-160.
Abstract:
The Paleozoic sequences are well developed in Kalpin Uplift. The lithostratigraphic sequences from Middle Ordovician to Lower Silurian have been effectively distinguished and correlated by using Landsat TM ratio composite imagery (3/1 (Y) 2/3 (M) 7/5 (C)). Lateral faices variation and spatial distribution of lithostratigraphic sequences can be also traced and delimited.The analysis of TM ratio composite imagery shows that the depocenter of Middle Ordovician series gradually migrated toward the southeast, and the lower part of Lower Silurian is red bed of marine factes in the western part, it becomes to green bed of marine factes in the eastern part. The results indicate that the differential elevation and subsidence movement occurred during the end of Early Ordovician to Early Silurian from the west to the east, and the relevant paleotopography is from high to low in the studied area.Yingan Formation has been first found that it not only distributes in the Yingan Mountain, but also distribute in the middle part of the Yimugantawu Mountain and the eastern part of the Kalpintage Mountain by the analysis of TM ratio composite imagery. We can infer that Shaergan and Yingan Formations, which are favourable source rocks in Tarim Basin, distribute widespreadly in the North Tarim Depression and North Tarim Uplift.The results of this study provide new data and evidence for the research of the Lower Paleozoic source rocks and petroleum exploration of Tarim Basin, and show that the remote sensing technology is a useful way for petroleum exploration in Northwestern China.
The Paleozoic sequences are well developed in Kalpin Uplift. The lithostratigraphic sequences from Middle Ordovician to Lower Silurian have been effectively distinguished and correlated by using Landsat TM ratio composite imagery (3/1 (Y) 2/3 (M) 7/5 (C)). Lateral faices variation and spatial distribution of lithostratigraphic sequences can be also traced and delimited.The analysis of TM ratio composite imagery shows that the depocenter of Middle Ordovician series gradually migrated toward the southeast, and the lower part of Lower Silurian is red bed of marine factes in the western part, it becomes to green bed of marine factes in the eastern part. The results indicate that the differential elevation and subsidence movement occurred during the end of Early Ordovician to Early Silurian from the west to the east, and the relevant paleotopography is from high to low in the studied area.Yingan Formation has been first found that it not only distributes in the Yingan Mountain, but also distribute in the middle part of the Yimugantawu Mountain and the eastern part of the Kalpintage Mountain by the analysis of TM ratio composite imagery. We can infer that Shaergan and Yingan Formations, which are favourable source rocks in Tarim Basin, distribute widespreadly in the North Tarim Depression and North Tarim Uplift.The results of this study provide new data and evidence for the research of the Lower Paleozoic source rocks and petroleum exploration of Tarim Basin, and show that the remote sensing technology is a useful way for petroleum exploration in Northwestern China.
1995, 13(4): 16-26.
Abstract:
The Middle Ordovician on the west margin of Ordos is represented by a succession of deep-water sediments in which contourites are well developed. According to grain-size and component, the contourites can be classified into: ①calcarenitic contourite, ②calcisiltitic contourite, ③calcilutitic contourite and ④ bioclastic contourite. Calcarenitic contourite is mainly composed of sparite calcarenite and is characterized by coarser grain, very irregular boundary plane, development of parallel stratification and ripple bedding. The laminae in ripple bedding imply a palaeocurrent direction of northwest, which is coincident with the strike of the regional palaeoslopes. Calcisiltitic contourite consists mainly of micrite calcisiltite and is always interbedded with calcilutitic contourite or present both below and above calcarenitic contourite. Parallel stratification or small-scale ripple bedding are common in calcisiltitic contourite and the laminae imply a palaeocurrent direction of northwest. On the whole, calcilutitic contourite comprises (muddy) micritic limestone, which commonly contains a variable proportion of calcisiltite and bioclastic materials and is a common occurence of bioturbational structures. Sometimes, some horizontal stratifications can be found in this contourite. Bioclastic contourite almost consists of a succession of echinederm fragment limestone with a thickness of 2m～5m and the thickest is near to 7m, which is composed of a series of single beds with a thickness of 20cm ～ 50cm where large-scale cross-stratifications are well developed, whose laminae imply a direction of northwest. The first three types are well developed in Guanzhuang, Pingliang, Gansu Province, and the fourth type is mainly found in the Zhuozishan mountain, Inner Mongolia.In the study area, some sequences of contourite are complete and similiar to the typical sequence of Gonthier (1984), and some sequences are incomplete and others are special, i. e.,only consisting of calcarenitic contourite. Ripples, cross stratification and texture have generally revealed a strong northward palaeoflow direction along the palaeoslope on the west margin of Ordos. The distribution of all kinds of contourites in the section confirms the existence of the Pingliang contourite drift.
The Middle Ordovician on the west margin of Ordos is represented by a succession of deep-water sediments in which contourites are well developed. According to grain-size and component, the contourites can be classified into: ①calcarenitic contourite, ②calcisiltitic contourite, ③calcilutitic contourite and ④ bioclastic contourite. Calcarenitic contourite is mainly composed of sparite calcarenite and is characterized by coarser grain, very irregular boundary plane, development of parallel stratification and ripple bedding. The laminae in ripple bedding imply a palaeocurrent direction of northwest, which is coincident with the strike of the regional palaeoslopes. Calcisiltitic contourite consists mainly of micrite calcisiltite and is always interbedded with calcilutitic contourite or present both below and above calcarenitic contourite. Parallel stratification or small-scale ripple bedding are common in calcisiltitic contourite and the laminae imply a palaeocurrent direction of northwest. On the whole, calcilutitic contourite comprises (muddy) micritic limestone, which commonly contains a variable proportion of calcisiltite and bioclastic materials and is a common occurence of bioturbational structures. Sometimes, some horizontal stratifications can be found in this contourite. Bioclastic contourite almost consists of a succession of echinederm fragment limestone with a thickness of 2m～5m and the thickest is near to 7m, which is composed of a series of single beds with a thickness of 20cm ～ 50cm where large-scale cross-stratifications are well developed, whose laminae imply a direction of northwest. The first three types are well developed in Guanzhuang, Pingliang, Gansu Province, and the fourth type is mainly found in the Zhuozishan mountain, Inner Mongolia.In the study area, some sequences of contourite are complete and similiar to the typical sequence of Gonthier (1984), and some sequences are incomplete and others are special, i. e.,only consisting of calcarenitic contourite. Ripples, cross stratification and texture have generally revealed a strong northward palaeoflow direction along the palaeoslope on the west margin of Ordos. The distribution of all kinds of contourites in the section confirms the existence of the Pingliang contourite drift.
1995, 13(4): 49-54.
Abstract:
Experiments of dissolution for carbonate with variable contents of calcite and dolomite have been performed under the temperature and pressure of epigenesis to burial diagenesis (40℃ ～ 100℃, normal atmospheric pressure ～ 25MPa). In the Experments under the condition of simulating epigenesis and relatively shallow burial (T75℃,P20MPa), calcite dissolved much more quickly than dolomite. With the increase of temperature and pressure, the difference of dissolution rate between the two minerals decreases. When temperature is more than 75℃ and pressure more than 20MPa, the dissolution rate of dolomite exceeds calcite.Under the conditions of 100℃, 25MPa, the dissolution rate of dolomite (dolomite/calcite= 98/2) is two times of limestone (dolomite/calcite=16/86). The reason is that the temperature and pressure effect on dolomite being greater than that on calcite. Based on the results of experiments, it can be predicated that under the conditions of epigensis and relatively shallow burial environment limestone dissolution must develope more greatly than that of dolomite, but under the deep burial conditions, dolomite must have dissolved more quickly than that of calcite. This is one of the most important reasons for that there are more dolomite reservoir with secondary porosity than limestone in the strata deeper than 2000m.
Experiments of dissolution for carbonate with variable contents of calcite and dolomite have been performed under the temperature and pressure of epigenesis to burial diagenesis (40℃ ～ 100℃, normal atmospheric pressure ～ 25MPa). In the Experments under the condition of simulating epigenesis and relatively shallow burial (T75℃,P20MPa), calcite dissolved much more quickly than dolomite. With the increase of temperature and pressure, the difference of dissolution rate between the two minerals decreases. When temperature is more than 75℃ and pressure more than 20MPa, the dissolution rate of dolomite exceeds calcite.Under the conditions of 100℃, 25MPa, the dissolution rate of dolomite (dolomite/calcite= 98/2) is two times of limestone (dolomite/calcite=16/86). The reason is that the temperature and pressure effect on dolomite being greater than that on calcite. Based on the results of experiments, it can be predicated that under the conditions of epigensis and relatively shallow burial environment limestone dissolution must develope more greatly than that of dolomite, but under the deep burial conditions, dolomite must have dissolved more quickly than that of calcite. This is one of the most important reasons for that there are more dolomite reservoir with secondary porosity than limestone in the strata deeper than 2000m.
1995, 13(4): 64-72.
Abstract:
This paper includes a systematic analysis and correlation study on the sporo-pollen assemblages, stratigraphic sequence and geochronology of the Zhuerzhuang Red Bed Sections in Yaone, Gansu. From the bottom to the top of the Zhuerzhuang section there are three sporopollen assemblages: ① Liqudambarpollenites - Meliaceoidites assemblage, which belongs to Early Mid Eocene; ② Saliaxipollenites-Celtis pollenites-Fraxinoipollenites assemblage, which may be assigned to Mid -Late Eocens; ③ Quercoidites - Saliaxipollenites- Fraxinoipollenits assemblage,which may belong to Late Eocene-Early Oligocene. The results of this study show that, the geological age of the Red Bed section belongs to Eocene-Early Oligocene; the Eocene sporopollen assemblages of Yaojie are approximately similar to those of the East region and the West region of China, which indicate subtropical broadleaved deciduous forest mainly composed of the subtropical and warm temperate taxa, and burning hot climate; from Late Eocene to Early Oligocene, the vegetation of Yaojie evolved to warm temperate mixed broadleaf and needleaf forests mainly composed of the warm broadleaf deciduous plant, presumably associated with warm and humid conditions.
This paper includes a systematic analysis and correlation study on the sporo-pollen assemblages, stratigraphic sequence and geochronology of the Zhuerzhuang Red Bed Sections in Yaone, Gansu. From the bottom to the top of the Zhuerzhuang section there are three sporopollen assemblages: ① Liqudambarpollenites - Meliaceoidites assemblage, which belongs to Early Mid Eocene; ② Saliaxipollenites-Celtis pollenites-Fraxinoipollenites assemblage, which may be assigned to Mid -Late Eocens; ③ Quercoidites - Saliaxipollenites- Fraxinoipollenits assemblage,which may belong to Late Eocene-Early Oligocene. The results of this study show that, the geological age of the Red Bed section belongs to Eocene-Early Oligocene; the Eocene sporopollen assemblages of Yaojie are approximately similar to those of the East region and the West region of China, which indicate subtropical broadleaved deciduous forest mainly composed of the subtropical and warm temperate taxa, and burning hot climate; from Late Eocene to Early Oligocene, the vegetation of Yaojie evolved to warm temperate mixed broadleaf and needleaf forests mainly composed of the warm broadleaf deciduous plant, presumably associated with warm and humid conditions.
1995, 13(4): 82-92.
Abstract:
The very abundant highly branched isoprenoid (HBI) alkenes (C20,C25 and C30) have been detected in four cores of Qinghai Lake recent sediments. This is the first report of these compounds in Chinese recent lake sediments. Diatoms may be the biological source of these sedimentary HBI alkenes.
The very abundant highly branched isoprenoid (HBI) alkenes (C20,C25 and C30) have been detected in four cores of Qinghai Lake recent sediments. This is the first report of these compounds in Chinese recent lake sediments. Diatoms may be the biological source of these sedimentary HBI alkenes.
1995, 13(4): 100-108.
Abstract:
There are a lot of gas-condensate reserviors bearing gas-caps or oil-rings found in the north of Tarim Basin. The calculated Ro data demonstrate that the natural gases possess much higher maturity (Ro2. 3%) than that of the associated oils and condensates (Ro1. 1 %),taking unfitable physical properties of the ring-oil into consideration, we concluded that the natural gas is a allochthonous one and the condensate is the product of vapor-liquid equilibrium between the all chthonous natural gas and the oils in reservior, in this physical-chemistry proccess, all light hydrocarbons, having distributed themselves according to their vepor-liquid equilibrium constants, would occur in different proportions in the vapor and liquid phases. On the basis of the above conclusion, we suggest that the separation of gas-cap from oil-ring once occured in the past geological time, there would be independent gas Condensate accumulation fromed in Tarim Basin, and meanwhile the light hydrocarbons of the primary reservior fractionated, which caused the unusual distribution of light hydrocarbons in Ordovician to Cretaceous reserviors.
There are a lot of gas-condensate reserviors bearing gas-caps or oil-rings found in the north of Tarim Basin. The calculated Ro data demonstrate that the natural gases possess much higher maturity (Ro2. 3%) than that of the associated oils and condensates (Ro1. 1 %),taking unfitable physical properties of the ring-oil into consideration, we concluded that the natural gas is a allochthonous one and the condensate is the product of vapor-liquid equilibrium between the all chthonous natural gas and the oils in reservior, in this physical-chemistry proccess, all light hydrocarbons, having distributed themselves according to their vepor-liquid equilibrium constants, would occur in different proportions in the vapor and liquid phases. On the basis of the above conclusion, we suggest that the separation of gas-cap from oil-ring once occured in the past geological time, there would be independent gas Condensate accumulation fromed in Tarim Basin, and meanwhile the light hydrocarbons of the primary reservior fractionated, which caused the unusual distribution of light hydrocarbons in Ordovician to Cretaceous reserviors.
1995, 13(4): 116-124.
Abstract:
By means of thermal modeling of compound samples which are composed of kaolinnes and modern pineal pollens, the thermometamorphic process of modern pineal pollens were succesively revealed, the products of solids, liquids and gases produced during the thermal degradation were quantitatively gathered, the geochemical characteristics of the products were primarily researched, and the shapes and colours of the pineal pollens during the thermometamorphic process were carefully observed.The gas products of the thermolysis of the pineal pollens included hydrocarbons and nonhydrocarbons. The products of hydrocarbon gases occoured at 200℃, clearly going up above 400℃, up to its maxium (247m3/t) at 600℃. The relative content of the hydrofarbon gases increased with the increase of tempratures, reaching its maxium (55. 77 %) at 500℃. The hydrocarbon gases were mainly composed of methane, ethane and propane with minor amount of butane。 The non-hydrocarbon gases predorminantly consisted of CO and H with certain amount of CO and N2 . The liquid products of the thermolysis are water, light hydrocarbon and extracts. The light hydrocarbons appeared at 250℃, their production went up with the increas of the tempretures, up to their maxium at 450℃ (66. 83kg/t), and then dropping rapidly. The components of light hydrocarbons were mainly satured hydrocarbons, monocyclic aromatic hydrocarbons and dicyclic aromatic hydrocarbons. The extracts were mainly produced at the tempretures below 400℃, the production of them reached its maxium (98. 4kg/t) at 300℃. The extracts contended higher quantities of non-hydrocarbons and alsphaltenes. The content of the satured hydrocarbons and aromatic hydrocarbons rose with the tempretures increasing, up to their highests of 37 % and 29 % respectively.During the thermometamorphic process of the pineal pollens the shapes of them mainly shrank and became small in the period of low tempretures, appearing fissures at 250℃, their sacs separating from their bodies at 300℃, and crushing completely at 350℃。 Their colours darkened with the tempretures rising, being yellow below the tempretures of 150℃, brown at the tempretures of 200℃ ～ 300℃, brown black at 350℃ ～450℃ and black above 500℃. The colour index and vitrinite reflectance of the pineal pollens also increased with the increasing of the tempretures.
By means of thermal modeling of compound samples which are composed of kaolinnes and modern pineal pollens, the thermometamorphic process of modern pineal pollens were succesively revealed, the products of solids, liquids and gases produced during the thermal degradation were quantitatively gathered, the geochemical characteristics of the products were primarily researched, and the shapes and colours of the pineal pollens during the thermometamorphic process were carefully observed.The gas products of the thermolysis of the pineal pollens included hydrocarbons and nonhydrocarbons. The products of hydrocarbon gases occoured at 200℃, clearly going up above 400℃, up to its maxium (247m3/t) at 600℃. The relative content of the hydrofarbon gases increased with the increase of tempratures, reaching its maxium (55. 77 %) at 500℃. The hydrocarbon gases were mainly composed of methane, ethane and propane with minor amount of butane。 The non-hydrocarbon gases predorminantly consisted of CO and H with certain amount of CO and N2 . The liquid products of the thermolysis are water, light hydrocarbon and extracts. The light hydrocarbons appeared at 250℃, their production went up with the increas of the tempretures, up to their maxium at 450℃ (66. 83kg/t), and then dropping rapidly. The components of light hydrocarbons were mainly satured hydrocarbons, monocyclic aromatic hydrocarbons and dicyclic aromatic hydrocarbons. The extracts were mainly produced at the tempretures below 400℃, the production of them reached its maxium (98. 4kg/t) at 300℃. The extracts contended higher quantities of non-hydrocarbons and alsphaltenes. The content of the satured hydrocarbons and aromatic hydrocarbons rose with the tempretures increasing, up to their highests of 37 % and 29 % respectively.During the thermometamorphic process of the pineal pollens the shapes of them mainly shrank and became small in the period of low tempretures, appearing fissures at 250℃, their sacs separating from their bodies at 300℃, and crushing completely at 350℃。 Their colours darkened with the tempretures rising, being yellow below the tempretures of 150℃, brown at the tempretures of 200℃ ～ 300℃, brown black at 350℃ ～450℃ and black above 500℃. The colour index and vitrinite reflectance of the pineal pollens also increased with the increasing of the tempretures.
1995, 13(4): 131-137.
Abstract:
We report REE (rare earth elements) data of 19 samples from Upper Sinian - Lower Cambrian chens by neutron activation analysis. The REE patterns with respect to an average shale show complicate changes and are preliminarily classified into different types, including "platform-type", "Red Sea-type", "seawater-type"and two distinctive types. The Ce depletion in the section exhibits a progressive increase from the lower to upper beds. The Ce anomaly,as an indicator of redox conditions, reveals that paleo-ocean bottom seawater in this area was anoxic during Late Precambrian and an oxidizing environment occurred in Early Cambrian.The occurrence of positive Eu anomaly may indicate submarine hydrothermal deposition.
We report REE (rare earth elements) data of 19 samples from Upper Sinian - Lower Cambrian chens by neutron activation analysis. The REE patterns with respect to an average shale show complicate changes and are preliminarily classified into different types, including "platform-type", "Red Sea-type", "seawater-type"and two distinctive types. The Ce depletion in the section exhibits a progressive increase from the lower to upper beds. The Ce anomaly,as an indicator of redox conditions, reveals that paleo-ocean bottom seawater in this area was anoxic during Late Precambrian and an oxidizing environment occurred in Early Cambrian.The occurrence of positive Eu anomaly may indicate submarine hydrothermal deposition.
1995, 13(4): 145-152.
Abstract:
The distribution of gold, geochemical features of trace elements in the Liba group goldbearing turbidite formation and their relationship with gold metalisation have been studied in detail. The results show that Liba group gold-bearing turbidite formation is rich in An, As,Sb, Bi and Cr, Ni, Co and V, and has high ratios of An/Ag and An/As, but it is depleted in Hg, Sr and Ba. Contents of As, Bi, Ni, Mn, Ti, Cr, V and ratios of Au/Ag, Au/ As and As/Sb gradually increase from D2Lb1 to D2Lb3, on the contrary, contents of Sb, Sb+Bi+Hg and ratios of Co/Ni and Cr/Ni reduce by degrees. R-type cluster analysis of trace elements in Liziyuan group, gold-bearing turbidite formation and Liba ore-bearing faults indicates that they have common elements association which are Ni, Co, Cr and V, and ore-forming elements in the Liba gold mine inherit obviously components in the Liba gold-bearing turbidite formation and Liziyuan group. The Liziyuan group is the primary gold-bearing formation which consists mainly of basic volcanic rocks with high gold abaundance. The Liba group goldbearing turbidite formation is a derivative gold-bearing formation. The Liba group gold-bearing formation is not main gold source rocks, but gold host rocks.
The distribution of gold, geochemical features of trace elements in the Liba group goldbearing turbidite formation and their relationship with gold metalisation have been studied in detail. The results show that Liba group gold-bearing turbidite formation is rich in An, As,Sb, Bi and Cr, Ni, Co and V, and has high ratios of An/Ag and An/As, but it is depleted in Hg, Sr and Ba. Contents of As, Bi, Ni, Mn, Ti, Cr, V and ratios of Au/Ag, Au/ As and As/Sb gradually increase from D2Lb1 to D2Lb3, on the contrary, contents of Sb, Sb+Bi+Hg and ratios of Co/Ni and Cr/Ni reduce by degrees. R-type cluster analysis of trace elements in Liziyuan group, gold-bearing turbidite formation and Liba ore-bearing faults indicates that they have common elements association which are Ni, Co, Cr and V, and ore-forming elements in the Liba gold mine inherit obviously components in the Liba gold-bearing turbidite formation and Liziyuan group. The Liziyuan group is the primary gold-bearing formation which consists mainly of basic volcanic rocks with high gold abaundance. The Liba group goldbearing turbidite formation is a derivative gold-bearing formation. The Liba group gold-bearing formation is not main gold source rocks, but gold host rocks.
1995, 13(4): 161-168.
Abstract:
The results of paleomagnetic research show that the Ordos Basin was located within the paleolatitude of 14°～20°N during the Cambrian and Early-middle Ordovician Periods with a warmer and moist climate, of which the littoral-neritic sedimentary strata in the north and south margins were very rich in organic materials, being favorable fields to find Early Paleozoic oil and gas. From the Late Ordovician to Early Carboniferous, the Ordos Basin may have a large-scale N-S horizontal tectonic displacement. In the Late Carboniferous and Permian Period, the location of Ordos Basin was at around 20°N with widespread limnogenic deposits,being important source rocks of Coal-oil and coal-gas. From the Triassic to Jurassic Period,the Ordos Basin was located at 24°～31°N. And the change of arid and humid climate and the differential tectonic rotations among the Ordos Block and other blocks resulted in favorable conditions for oil and gas formation and accumulation within the marginal areas of the basin. Thus, much more Mesozoic oil and gas reources should be found hopefully.
The results of paleomagnetic research show that the Ordos Basin was located within the paleolatitude of 14°～20°N during the Cambrian and Early-middle Ordovician Periods with a warmer and moist climate, of which the littoral-neritic sedimentary strata in the north and south margins were very rich in organic materials, being favorable fields to find Early Paleozoic oil and gas. From the Late Ordovician to Early Carboniferous, the Ordos Basin may have a large-scale N-S horizontal tectonic displacement. In the Late Carboniferous and Permian Period, the location of Ordos Basin was at around 20°N with widespread limnogenic deposits,being important source rocks of Coal-oil and coal-gas. From the Triassic to Jurassic Period,the Ordos Basin was located at 24°～31°N. And the change of arid and humid climate and the differential tectonic rotations among the Ordos Block and other blocks resulted in favorable conditions for oil and gas formation and accumulation within the marginal areas of the basin. Thus, much more Mesozoic oil and gas reources should be found hopefully.
