1995 Vol. 13, No. 3
column
Display Method:
1995, 13(3): 13-22.
Abstract:
The Devonian strain are developed on the north margin of the West Kunlun Mt. They are the oldest Paleozoic sedimentary rocks in this region and overlapped on the Middle-Upper Proterozoic strata. To the south of Monk, the Middle-Upper Devonian is well developed in the Keziyangluk area.According to the lithological features and rock associations, they can be divided into two members. The lower one is a tuffaceous graywacke carbonate rock formation, composed of tuffaceous graywacke, tuffaceous shale, pebble-bearing sandy slate and carbonate rock. The upper member is a terrigenous sandy conglomerate graywacke formation, composed of conglomerate,sandy conglomerate, lithic graywacke,quartzose graywacke, silstone, etc. The lower member is characterized by laminar bedding and horizontal bedding, indicating a steady hydrodynamic sedimentary environment. The upper member comprises torrigenous sand and Pebble sediments with clear cyclicity. Its different horizons show different sedimentary structures, such as horizontal bedding, various cross-bedding and interference ripple, indicating an unstable sedimentary water body and unsteady sedimentary factes.The studies on sedimentary structures and lithological grain features of the Middle Upper Devonian strata suggest that the lower member is formed in a bathyal-neritic sedimentary environment. and that the upper member is developed in an littoral beach inshore deltufluvial sedimentary environment.
The Devonian strain are developed on the north margin of the West Kunlun Mt. They are the oldest Paleozoic sedimentary rocks in this region and overlapped on the Middle-Upper Proterozoic strata. To the south of Monk, the Middle-Upper Devonian is well developed in the Keziyangluk area.According to the lithological features and rock associations, they can be divided into two members. The lower one is a tuffaceous graywacke carbonate rock formation, composed of tuffaceous graywacke, tuffaceous shale, pebble-bearing sandy slate and carbonate rock. The upper member is a terrigenous sandy conglomerate graywacke formation, composed of conglomerate,sandy conglomerate, lithic graywacke,quartzose graywacke, silstone, etc. The lower member is characterized by laminar bedding and horizontal bedding, indicating a steady hydrodynamic sedimentary environment. The upper member comprises torrigenous sand and Pebble sediments with clear cyclicity. Its different horizons show different sedimentary structures, such as horizontal bedding, various cross-bedding and interference ripple, indicating an unstable sedimentary water body and unsteady sedimentary factes.The studies on sedimentary structures and lithological grain features of the Middle Upper Devonian strata suggest that the lower member is formed in a bathyal-neritic sedimentary environment. and that the upper member is developed in an littoral beach inshore deltufluvial sedimentary environment.
1995, 13(3): 32-38.
Abstract:
Shallowing-upward sequences in the Majiagou carbonates in the Luuliang-Northen Shaanxi area consist of a great number of small-scale sequences. The small-scale sequences (1.2-5min thickness) are the fundamental units of the Majiagou sedimentary deposit. The small-scale sequences have obvious boundaries of abrupt change tO deeper facies, and are of internally regressive deposits,containing little or no transgressive deposits. The small-scale sequences are vertically stucked and laterally extensive asymmetry cycles for tens of kilometers (independent of lateral facies). These sequences appear to occur in the depositional facies of most environments.Six types of small-scale sequences Can be recognized, i. e., A: trace-fossil cycles in deeper open sea subtidal facies; B:dilution cycles of hypersaline brine in deeper lagoon factes; C:intertidel to supratidal overprinting of shallow subtidal factes:D: intertidal to supratldal ovetprining of shallow brackish subtidal factes, ofen associated with early dolomitization; E: Sabkha sequences; F:terrestrial overprinting of intertidal factes. The characteristics and distribution of small- scale sequences were formed during high-frequency but low-amplitude sea level variations superimposedon the third order transgressive - cycles. The types of the small-scale sequences depend on the position of high- frequency sea level variations within the third order cycles and the palaeotopography of sedimentary environments. During the high sea level of long-term cycles periodically changed the physical-chemical conditions of water body in deeper open sea subtidal racies. Thus small-scale sequences recorded the benthic and in fauna response to trasgressiveregressive cycles. In shallow peritidal environments during the longer-term sea level fall, highfrequency sea level variations made the ralative sea level reach the critical water depth. Consequently, C. D. E. F small-scale sequences were formed. In local depressions, the highfrequency sea level rise provided the punctuated supplement of sea water for the evaporation and caused the dilution cycles of hypersaline brine which formed B small- scale sequences. Highfrequency small-scale sea level variations seem to be related to Milankovitch climatic cycles caused by the Earth's orbital cycles. identification and correlation of sequence boundaries make it possible to set up a framework of isochronous surfaces, and thus to interpret in derail the palaeographic,sedimentological evolution of the Majiagou carbonate environments and to predict the distribution of oil-gas reservoirs in the sedimentary basin.
Shallowing-upward sequences in the Majiagou carbonates in the Luuliang-Northen Shaanxi area consist of a great number of small-scale sequences. The small-scale sequences (1.2-5min thickness) are the fundamental units of the Majiagou sedimentary deposit. The small-scale sequences have obvious boundaries of abrupt change tO deeper facies, and are of internally regressive deposits,containing little or no transgressive deposits. The small-scale sequences are vertically stucked and laterally extensive asymmetry cycles for tens of kilometers (independent of lateral facies). These sequences appear to occur in the depositional facies of most environments.Six types of small-scale sequences Can be recognized, i. e., A: trace-fossil cycles in deeper open sea subtidal facies; B:dilution cycles of hypersaline brine in deeper lagoon factes; C:intertidel to supratidal overprinting of shallow subtidal factes:D: intertidal to supratldal ovetprining of shallow brackish subtidal factes, ofen associated with early dolomitization; E: Sabkha sequences; F:terrestrial overprinting of intertidal factes. The characteristics and distribution of small- scale sequences were formed during high-frequency but low-amplitude sea level variations superimposedon the third order transgressive - cycles. The types of the small-scale sequences depend on the position of high- frequency sea level variations within the third order cycles and the palaeotopography of sedimentary environments. During the high sea level of long-term cycles periodically changed the physical-chemical conditions of water body in deeper open sea subtidal racies. Thus small-scale sequences recorded the benthic and in fauna response to trasgressiveregressive cycles. In shallow peritidal environments during the longer-term sea level fall, highfrequency sea level variations made the ralative sea level reach the critical water depth. Consequently, C. D. E. F small-scale sequences were formed. In local depressions, the highfrequency sea level rise provided the punctuated supplement of sea water for the evaporation and caused the dilution cycles of hypersaline brine which formed B small- scale sequences. Highfrequency small-scale sea level variations seem to be related to Milankovitch climatic cycles caused by the Earth's orbital cycles. identification and correlation of sequence boundaries make it possible to set up a framework of isochronous surfaces, and thus to interpret in derail the palaeographic,sedimentological evolution of the Majiagou carbonate environments and to predict the distribution of oil-gas reservoirs in the sedimentary basin.
1995, 13(3): 46-53.
Abstract:
The Middle-Upper Proterozoic Eon in Jixian County, Tianjin, is a sedimentary series measured for 3000m in thickness. The middle- ower part of which is mainly composed of primary sedimentary dolostone, while the upper Part mostly of limestone. Seventeen dolostone and calcite samples were selected to determine the oxygen and carbon isotope in order to analyse the diagenesis and paleosalinity, then to discuss the genesis of the dolomite accumulated there 1) DiagenesisWhen plentiful rains fare present on land-surface, a vadose zone, where the 18O.12C Contents would be plantiful would appear. Yangzhuang Formation shows larger negative values of δ18O and δ13C. From these analytic data, it can be seen that the carbonate rocks of Yangzhuang Formation and Tuaneshanzi Formation have a δ13C Value of -3.53‰, and the other δ13C value of carbonate rocks of stratigraphic formations varies in the range from+1‰, to-1‰, The δ18O value has the similar changes. It is interesting in Wumishan FOrmation that the oxygen and carbon isotopes of carbonate rocks in sedimentary micro factes reflect that fresh water perticipated in the course of diagenesis, and from this point of view it can be seen that greater part of carbonate rocks of the Upper-Middle Proterozoic in Jixian is of primarily sedimentary origin.2) Paleosalinity The value of δ18O in seawater is increasing with the increase of salinity, and the δ18O value may be applied as an indicator for peleosalinity. The increase of its value may reflect the augment o f Paleosalinity. The carbonate rocks of Wumishan Formation may reflect such a change that indirectly shows the primary depositional properties of dolostone in situ, this may provide the quantitative signs for sedimentary factes.
The Middle-Upper Proterozoic Eon in Jixian County, Tianjin, is a sedimentary series measured for 3000m in thickness. The middle- ower part of which is mainly composed of primary sedimentary dolostone, while the upper Part mostly of limestone. Seventeen dolostone and calcite samples were selected to determine the oxygen and carbon isotope in order to analyse the diagenesis and paleosalinity, then to discuss the genesis of the dolomite accumulated there 1) DiagenesisWhen plentiful rains fare present on land-surface, a vadose zone, where the 18O.12C Contents would be plantiful would appear. Yangzhuang Formation shows larger negative values of δ18O and δ13C. From these analytic data, it can be seen that the carbonate rocks of Yangzhuang Formation and Tuaneshanzi Formation have a δ13C Value of -3.53‰, and the other δ13C value of carbonate rocks of stratigraphic formations varies in the range from+1‰, to-1‰, The δ18O value has the similar changes. It is interesting in Wumishan FOrmation that the oxygen and carbon isotopes of carbonate rocks in sedimentary micro factes reflect that fresh water perticipated in the course of diagenesis, and from this point of view it can be seen that greater part of carbonate rocks of the Upper-Middle Proterozoic in Jixian is of primarily sedimentary origin.2) Paleosalinity The value of δ18O in seawater is increasing with the increase of salinity, and the δ18O value may be applied as an indicator for peleosalinity. The increase of its value may reflect the augment o f Paleosalinity. The carbonate rocks of Wumishan Formation may reflect such a change that indirectly shows the primary depositional properties of dolostone in situ, this may provide the quantitative signs for sedimentary factes.
1995, 13(3): 83-88.
Abstract:
Experiment for dolomite dissolution by acetic acid has been run under the conditions of temperature and pressure of burial diagenesis (75-130 ℃, 20-30MPa). The result shows that Dissolution rate of dolomite increases quickly with the increase of temperature and pressure. From 75℃. 20MPa to 130℃, 30MPa, the total releasing quantity of Ca2+ and Mg2+ increases from 32.98 mg/L to 337.9 mg/L, increasing more than 10 times. The temperature of 100℃ and pressure of 25 MPa are the best condition for dolomite dissolution.According to the result of experiment, We can predict that the secondary porosity formed by dolomite dissolution under deep burial diagenesis environment should be more common than that under epigenesis and shallow burial environment. So dolomite reservoir of deep burial strain should be more popular than that of shallow burial strain.
Experiment for dolomite dissolution by acetic acid has been run under the conditions of temperature and pressure of burial diagenesis (75-130 ℃, 20-30MPa). The result shows that Dissolution rate of dolomite increases quickly with the increase of temperature and pressure. From 75℃. 20MPa to 130℃, 30MPa, the total releasing quantity of Ca2+ and Mg2+ increases from 32.98 mg/L to 337.9 mg/L, increasing more than 10 times. The temperature of 100℃ and pressure of 25 MPa are the best condition for dolomite dissolution.According to the result of experiment, We can predict that the secondary porosity formed by dolomite dissolution under deep burial diagenesis environment should be more common than that under epigenesis and shallow burial environment. So dolomite reservoir of deep burial strain should be more popular than that of shallow burial strain.
1995, 13(3): 98-106.
Abstract:
Commercial oils drilled in most parts of the North Tarim Uplift and Central Tarim Uplift have been characterized and corn firmed as oils derived from marine Lower Paleozoic source rocks. The marine oils might have, however, originated from blask shale beds or carbonate sequences of the same age. That brings difficulties in oil-source correlation by biomaker approaches. In this paper, dibenzothiophene distributions of typical marine carbonate-sourced oils and siliciclanic sourced oils with different maturity have been studied in detail. It is revealed that the dibenzothiophene demethylation index(DDI) and dibenzothiophene methyl-isomeration index(DMI) could distinguish two types of oils effectively and suffer from little influence of maturity. According to the relative amounts of DBTS and DDI vs DMI values of Tarim oils, the major source rocks in Tarim Basin are identified as the dark and black laminated micrite and marlite deposited in the Ordovician continental shelf zone.
Commercial oils drilled in most parts of the North Tarim Uplift and Central Tarim Uplift have been characterized and corn firmed as oils derived from marine Lower Paleozoic source rocks. The marine oils might have, however, originated from blask shale beds or carbonate sequences of the same age. That brings difficulties in oil-source correlation by biomaker approaches. In this paper, dibenzothiophene distributions of typical marine carbonate-sourced oils and siliciclanic sourced oils with different maturity have been studied in detail. It is revealed that the dibenzothiophene demethylation index(DDI) and dibenzothiophene methyl-isomeration index(DMI) could distinguish two types of oils effectively and suffer from little influence of maturity. According to the relative amounts of DBTS and DDI vs DMI values of Tarim oils, the major source rocks in Tarim Basin are identified as the dark and black laminated micrite and marlite deposited in the Ordovician continental shelf zone.
1995, 13(3): 117-125.
Abstract:
A10 samples were collected from the Jurassic system of the Mazhuang gas reservoir in the Junggar Basin. Formed in a swamp- shallow shore depositional environment, they consist of rich TypeⅡ B and Ⅲ organic matter with R0 values less than 0.74% at the low evolutionary stage. This paper mainly discusses questions on the amount of anerobic fermenting bacteria, the type and distribution of methanogen, and the methane yield of per gram organic carbon in the process of the simulahng fermentation experiment and so on. The numbers of permenting bacteria are from 5×102/g rock to 2.3×104/g rock. At 35℃-65℃,Methanococcus is found in all samples, at 55℃, Methanobocterium is found in No. 7 sample. Simulating experiment results show: (1 )methane accumulation yields are the most at 35℃, from 29.48ml to 39.41 ml, over 80% in the total gas-producing yield. (2)in the gas product, methane is the major, secondly carbon dioxide, and only a trace of ethane and profane is present. (3)from the methane-producing yield of per gram organic carbon, it can be seen that most of samples produce 50ml/g org. to 200ml/g org. gas, and the highest reaches to 568ml/g org. gas. (4)the methaneproducing ability is different at different temperature, 35 ℃ 65 ℃ 55 ℃. (5 )under the condition of the same sample and temprature, with the increase of the methane yield the carbon dioxide yield is also increasing. (6)the δ13C values of methane are - 40.12‰, to - 43.98‰, at 35℃, - 56.82‰ to - 60.10‰, at 55℃, -58.06‰ to - 65.11‰, at 65℃, and the median value of the carbon isotopic ratio of methane at 35℃ to 55 ℃ is nearly similar to the δ13C value of methane from the Mazhuang natural gas reservoir.This poper provides some evidence for that methanogen and other anaerobic microbes still have activity beneath over 2000m sediments and also it gives many significant scientific information to the study on geomicrobiology and some of of natural gas-forming mechnism.
A10 samples were collected from the Jurassic system of the Mazhuang gas reservoir in the Junggar Basin. Formed in a swamp- shallow shore depositional environment, they consist of rich TypeⅡ B and Ⅲ organic matter with R0 values less than 0.74% at the low evolutionary stage. This paper mainly discusses questions on the amount of anerobic fermenting bacteria, the type and distribution of methanogen, and the methane yield of per gram organic carbon in the process of the simulahng fermentation experiment and so on. The numbers of permenting bacteria are from 5×102/g rock to 2.3×104/g rock. At 35℃-65℃,Methanococcus is found in all samples, at 55℃, Methanobocterium is found in No. 7 sample. Simulating experiment results show: (1 )methane accumulation yields are the most at 35℃, from 29.48ml to 39.41 ml, over 80% in the total gas-producing yield. (2)in the gas product, methane is the major, secondly carbon dioxide, and only a trace of ethane and profane is present. (3)from the methane-producing yield of per gram organic carbon, it can be seen that most of samples produce 50ml/g org. to 200ml/g org. gas, and the highest reaches to 568ml/g org. gas. (4)the methaneproducing ability is different at different temperature, 35 ℃ 65 ℃ 55 ℃. (5 )under the condition of the same sample and temprature, with the increase of the methane yield the carbon dioxide yield is also increasing. (6)the δ13C values of methane are - 40.12‰, to - 43.98‰, at 35℃, - 56.82‰ to - 60.10‰, at 55℃, -58.06‰ to - 65.11‰, at 65℃, and the median value of the carbon isotopic ratio of methane at 35℃ to 55 ℃ is nearly similar to the δ13C value of methane from the Mazhuang natural gas reservoir.This poper provides some evidence for that methanogen and other anaerobic microbes still have activity beneath over 2000m sediments and also it gives many significant scientific information to the study on geomicrobiology and some of of natural gas-forming mechnism.
1995, 13(3): 132-136.
Abstract:
To draw a computer plotted cumulative curve by an interPolation function, it is essential to Possess the characters of monotonicity and smoothness. Based on a method to construct a sort of monotone and smooth interpolation function, the computer drawing of the cumulative curve of the tgrain size data has been realized with the monotonicity and the first or more than first order of smoothness of the cumulative curve. By the derivative function of the interpolation function, the homologous frequency curve has been plotted in the computer as well with its smoothness corresponding to that of the cumulative curve. Because the grain siza distribution (in phi scale ) of sediments follows the normal distribution and Rosin's distribution, while as an approximating function, the cubic spline interpolation function can satisfy (with some restriction) the monotonicity of the probability distribution functions of these two sorts of distribution in an interval, in which there is more than 90% of the area under the probability density curve, so in the method introduced in this paper, the cubic spline function is taken to be the interpolation function in the main part of the data interval [a,b]. In those subintervals in which there exist points of s' (x)0,two classes of the elementary functions are assigned to be the interpolation functions with the character of monotonicity and at least first order of smoothness at all knots. By this interpolation function.besides plotting the monotone and smooth cumulative curve and corresponding frequency curve,grain size parameters of moment and graphic measures can be calculated through the interpolation and percentiles computation. From the information revealed by the frequency curve, such as number of the peaks, location of each Peak, the Peak values, correlation among the peaks, and so on, the further studies could be taken out on the characteristics of the dynamics, environment,source and transportation of the sediment. The method has provided a basis for developing a software of the grain size analysis data processing to treat the data effectively and with high quality.And it is of benefit to remedy the defect of other means in exptessing grain size distribution characters and to make it more exactly and more comprehensively.
To draw a computer plotted cumulative curve by an interPolation function, it is essential to Possess the characters of monotonicity and smoothness. Based on a method to construct a sort of monotone and smooth interpolation function, the computer drawing of the cumulative curve of the tgrain size data has been realized with the monotonicity and the first or more than first order of smoothness of the cumulative curve. By the derivative function of the interpolation function, the homologous frequency curve has been plotted in the computer as well with its smoothness corresponding to that of the cumulative curve. Because the grain siza distribution (in phi scale ) of sediments follows the normal distribution and Rosin's distribution, while as an approximating function, the cubic spline interpolation function can satisfy (with some restriction) the monotonicity of the probability distribution functions of these two sorts of distribution in an interval, in which there is more than 90% of the area under the probability density curve, so in the method introduced in this paper, the cubic spline function is taken to be the interpolation function in the main part of the data interval [a,b]. In those subintervals in which there exist points of s' (x)0,two classes of the elementary functions are assigned to be the interpolation functions with the character of monotonicity and at least first order of smoothness at all knots. By this interpolation function.besides plotting the monotone and smooth cumulative curve and corresponding frequency curve,grain size parameters of moment and graphic measures can be calculated through the interpolation and percentiles computation. From the information revealed by the frequency curve, such as number of the peaks, location of each Peak, the Peak values, correlation among the peaks, and so on, the further studies could be taken out on the characteristics of the dynamics, environment,source and transportation of the sediment. The method has provided a basis for developing a software of the grain size analysis data processing to treat the data effectively and with high quality.And it is of benefit to remedy the defect of other means in exptessing grain size distribution characters and to make it more exactly and more comprehensively.
1995, 13(3): 23-31.
Abstract:
The authors established a new method for the quantitative study of the depositional and erosional processes of sedimentary basins by the analysis method of wave process in basin evolution combining with the case study of the Huanghua Depression directed by Prof. Vladimir Shpilman. Prof. Zhang Yiwei and Prof. Vladimir Shpilman pointed out in 1982-1983 that the interference of a series of identical cyclic processes may result in a non-cyclic process, i. e., the observed spacious cyclic process called as sedimentary cycle or rhythm is the interference result of a number of wave processes with a cerium cycle and amplitude. Astronomy has proven that the cycle of solar system's revolution around the Galaxy is 200Ma, and geoscience shows that 60-70Ma, 30Ma are the important cycles to the earth evolution, mantle' s convection and organic evolution. These cycles control the evolution of a sedimentary basin, and there are still other cycles, such as 10, 7, 5, 3, 1, 0.65Ma which affect the evolution of the basin. During the revolution and rotation of the earth, the obliquity of the ecliptic and precession change regularly with cycles of 10×104, 4×104, 2×104 years. This is the famous Milankovitch theory which supports to study the high frequency wave processes and to predict the distribution of source rocks, reservoirs and cover beds.If Function F(t) that can describe the depositional and erosional processes of a basin has been obtained by the Study of strata data, including outcrop, drilling and well logging, the primarythickness of the observed strata is F(t), here t. and t refer to the starting and ending times of basin evolution, respectively, whereas the erosed thickness of a hiatus is, F (t), here t1 and t2 refer to the stuning and ending times of the hiatus, respectively.In order to complete the studies mentioned above, the following steps are prerequisite, (1)the selection of areas for study, (2)the statistics of raw data for every area, (3)the trasformation from lithology thichness section to Lithology- time section, (4) restoring the primary thickness and calculating the depeitonal rate, (5)drawing the curve of depositional rate, (6)establishing the wave equation. The reliability of raw data is the key to success. The restoration of primary thickness and calculation of depeitional rate require the study of subsidence history and the determination of strata age. And the use of sliding window is the effective means to separate cyclic waves. The analysis and calculation have proven that the erosion quantity of O2 in the Huanghua area of the Huabei platform is 220m, whether or not there is a depositional process in the Triassic in the Huabei platform is still an arguement. It is made out by us that there is a 15.5m of the Triassic deposit and erosional quantity of the platform in the Cretaceous is 128m. Another obvious advantage of this method is that it can tell you whether or not there is a depositional process during the period of hiatus, for example, three small scale dePOsitional processes from O3 to C1 may be seen from Fig. 3.
The authors established a new method for the quantitative study of the depositional and erosional processes of sedimentary basins by the analysis method of wave process in basin evolution combining with the case study of the Huanghua Depression directed by Prof. Vladimir Shpilman. Prof. Zhang Yiwei and Prof. Vladimir Shpilman pointed out in 1982-1983 that the interference of a series of identical cyclic processes may result in a non-cyclic process, i. e., the observed spacious cyclic process called as sedimentary cycle or rhythm is the interference result of a number of wave processes with a cerium cycle and amplitude. Astronomy has proven that the cycle of solar system's revolution around the Galaxy is 200Ma, and geoscience shows that 60-70Ma, 30Ma are the important cycles to the earth evolution, mantle' s convection and organic evolution. These cycles control the evolution of a sedimentary basin, and there are still other cycles, such as 10, 7, 5, 3, 1, 0.65Ma which affect the evolution of the basin. During the revolution and rotation of the earth, the obliquity of the ecliptic and precession change regularly with cycles of 10×104, 4×104, 2×104 years. This is the famous Milankovitch theory which supports to study the high frequency wave processes and to predict the distribution of source rocks, reservoirs and cover beds.If Function F(t) that can describe the depositional and erosional processes of a basin has been obtained by the Study of strata data, including outcrop, drilling and well logging, the primarythickness of the observed strata is F(t), here t. and t refer to the starting and ending times of basin evolution, respectively, whereas the erosed thickness of a hiatus is, F (t), here t1 and t2 refer to the stuning and ending times of the hiatus, respectively.In order to complete the studies mentioned above, the following steps are prerequisite, (1)the selection of areas for study, (2)the statistics of raw data for every area, (3)the trasformation from lithology thichness section to Lithology- time section, (4) restoring the primary thickness and calculating the depeitonal rate, (5)drawing the curve of depositional rate, (6)establishing the wave equation. The reliability of raw data is the key to success. The restoration of primary thickness and calculation of depeitional rate require the study of subsidence history and the determination of strata age. And the use of sliding window is the effective means to separate cyclic waves. The analysis and calculation have proven that the erosion quantity of O2 in the Huanghua area of the Huabei platform is 220m, whether or not there is a depositional process in the Triassic in the Huabei platform is still an arguement. It is made out by us that there is a 15.5m of the Triassic deposit and erosional quantity of the platform in the Cretaceous is 128m. Another obvious advantage of this method is that it can tell you whether or not there is a depositional process during the period of hiatus, for example, three small scale dePOsitional processes from O3 to C1 may be seen from Fig. 3.
1995, 13(3): 39-45.
Abstract:
From the study of Nd isotope geochemistry for low grade metamorphic rocks, covering strata sedimentary rochs and associated volcanic rocks occured in the distribution area of Proterozoic Shangxi Group (traditionally called the Jiangnan old land) and surroundings in the southeastern margin of Yangtze Block, it is shown that the Nd isotopic model ages of the Sinian to Permian sedimentary rocks in the north side and south side of Jiangnan Deep Fault (or called Su-Zhe-Wan Palaeozoic Aulacogrn), as well as low-grade metamorphic rocks of Shangxi Group are 1.9-2.IGa, 1.2-1.3Ga and 1.7Ga, respectivelly. Therefore, the provenances of the Sinian to Palaeozoic sedimentary rocks on hath sides of the Jiangnan hop Fault were different and the idea that the Jiangnan hop Fault was harrier for edment transportation is proved by Nd isotopic geochemical evidence.There is a distribution area of the Palaeozoic strata between the Shangxi Group area and Jiangshan-Shaoxing Fault adjacent to Cathaysia Block. The Nd model ages of 2 samples for the Sinian to Silurian sedimentary rocks are 1. 8- 1. 7Ga, but the Nd model age of the basement rocks in cathaysia Block is older, for example, the model age of 2.1-2.5Ga for Chencai Group. It is indicated that the sediment supplment for the area to the south of the Shangxi Group distribution area mainly comes from the low metamorphic rock of Shangxi Group, and the basement rocks in Cathaysia Block are not an important contributors. So that the provenance of sedimentary rocks over the area between Jiangnan Deep Fault and Jiangshao Fault is the distribution area of Shangxi Group and named "Shanxi Provenance". The sediment provenance for the north side of Jiangnan Deep Fault is a particular block in the north and named "Yangtze provenance".The Nd model ages of the Sinian eedimentary rocks in the Shangxi Group distribution area and its northern margin are 1.2-1.3Ga, lower than that of Shangxi Group. The andesitic volcanic rock of Puling Formation in the northern margin of the Shangxi Group area and its xenoliths also give lower Nd model age of 1.3-1.4Ga. The intermediate and acidic volcanic rocks of Jingtan Formation in the southern margin of Shangxi Group area give Nd model ages of 1.6-2.2 Ga.From the variation of Nd model age in space and time, it is deduced that there were an orogenic movement in late Proterozoic Era there and the effect of mantle materials on sediment supplement at that time.
From the study of Nd isotope geochemistry for low grade metamorphic rocks, covering strata sedimentary rochs and associated volcanic rocks occured in the distribution area of Proterozoic Shangxi Group (traditionally called the Jiangnan old land) and surroundings in the southeastern margin of Yangtze Block, it is shown that the Nd isotopic model ages of the Sinian to Permian sedimentary rocks in the north side and south side of Jiangnan Deep Fault (or called Su-Zhe-Wan Palaeozoic Aulacogrn), as well as low-grade metamorphic rocks of Shangxi Group are 1.9-2.IGa, 1.2-1.3Ga and 1.7Ga, respectivelly. Therefore, the provenances of the Sinian to Palaeozoic sedimentary rocks on hath sides of the Jiangnan hop Fault were different and the idea that the Jiangnan hop Fault was harrier for edment transportation is proved by Nd isotopic geochemical evidence.There is a distribution area of the Palaeozoic strata between the Shangxi Group area and Jiangshan-Shaoxing Fault adjacent to Cathaysia Block. The Nd model ages of 2 samples for the Sinian to Silurian sedimentary rocks are 1. 8- 1. 7Ga, but the Nd model age of the basement rocks in cathaysia Block is older, for example, the model age of 2.1-2.5Ga for Chencai Group. It is indicated that the sediment supplment for the area to the south of the Shangxi Group distribution area mainly comes from the low metamorphic rock of Shangxi Group, and the basement rocks in Cathaysia Block are not an important contributors. So that the provenance of sedimentary rocks over the area between Jiangnan Deep Fault and Jiangshao Fault is the distribution area of Shangxi Group and named "Shanxi Provenance". The sediment provenance for the north side of Jiangnan Deep Fault is a particular block in the north and named "Yangtze provenance".The Nd model ages of the Sinian eedimentary rocks in the Shangxi Group distribution area and its northern margin are 1.2-1.3Ga, lower than that of Shangxi Group. The andesitic volcanic rock of Puling Formation in the northern margin of the Shangxi Group area and its xenoliths also give lower Nd model age of 1.3-1.4Ga. The intermediate and acidic volcanic rocks of Jingtan Formation in the southern margin of Shangxi Group area give Nd model ages of 1.6-2.2 Ga.From the variation of Nd model age in space and time, it is deduced that there were an orogenic movement in late Proterozoic Era there and the effect of mantle materials on sediment supplement at that time.
1995, 13(3): 54-65.
Abstract:
Southern Guizhou region, a relative stable platform adjoined to an intrashelf trough (or basin) southward, was flooded by the rapid sea level rising in South China in the late Early Devonian (Middle Emsian).Terrigenous depositional systems (i. e. fluvial, barrier-lagoon systems) were developed in the late Early Devonian, and hybrid terrigenous/carbonate (rimmed platform or ramp) depositional systems with grand mixed cycles (or sequences) in the Middle Devonian. Spatial configurations(or distribution ) of depositional systems are formed in different sedimentary conditions (i. e. eustusy, tectonism,source supplies), they consist of (1) barrier-lagoon-fluvial complex systems, reflecting an early basin fill stage with abundant source supplies at a relative low sea level, (2) mixed carbonate ramp-siliciclastic barrier-lagoon complex systems formed after rapid sea level rising, (3) mixed rimmed carbonate platform-siliciclastic delta (or tidal) complex systems developed often in late sea level lowstands with a relative rapid subsidence rate at platform margin, and (4) mixed carbonate ramp-siliciclastic delta systems established after rapid sea level rising as (2). In southern Guizhou, the NW-SE extensional faulting zone determines the range of two absolutely different dePOSitional patterns of platform and intraplatform (or intrashelf) trough (or basin), and establishes the peleogeographic framework of sedimentary evolution.Six third-order depositional sequences including two terrigenous siliciclastic sequences in the late Early Devonian and four mixed cabonate-siliciclastic sequences in the Middle Devonian were recognized based on the sedimentary studies. The formation of the sequences is controlled largely by sea level changes.The terrigenous depeitional systems develop in the early basin-fill stage with abundant source supplies. The shoreline and fluvial besinward Ptogradation characterizes the lowstand of sea level. Withdrawal of the sea level below the depostiional break initially leads to the shelf exposure, fluvial incision, and formation of lowstand fans and wedges (progradational shoreline or delta deposits).The rapid sea level rising causes the shoreline to recede landwards swiftly and the semi-pelagic black shale to blanket the trailing edge of the shelf. During the highstand of sea level, the shoreline deposits that aggradationally stack in the early stage gradually change into the progradational coastal or deltaic plain deposits subsequently as the sea level begins to fall.In mixed carbonate-siliciclastic depositional systems, the sedimentary response to changes in relative sea level indicates that basinward transporting of elastics predominates the lowstand of sea level. The elastic materials are conveyed through the incised valley to the intrashelf trough (or basin), forming the lowstand fan and lowstand wedge. Sometimes, organic reefs are developed during the late lowstand (V, VI), and terminated by the rapid sea level rising. The rapid sea level rising leads the shoreline to retrograde quickly and causes intrashelf trough deposits (black shale,nodular limotone etc.) to onlap updip the depositional break. Continual sea level rising above the shelf (or platform) increases the accommodation space, which allows the resumption of carbonate production, hence, the carbonate deposits dominate over the early highstands. However, the siliciclastic systems on the proximal shelf begin to rejuvenate and to prograde basinwards during the late highstands when the accommodation space reduces.
Southern Guizhou region, a relative stable platform adjoined to an intrashelf trough (or basin) southward, was flooded by the rapid sea level rising in South China in the late Early Devonian (Middle Emsian).Terrigenous depositional systems (i. e. fluvial, barrier-lagoon systems) were developed in the late Early Devonian, and hybrid terrigenous/carbonate (rimmed platform or ramp) depositional systems with grand mixed cycles (or sequences) in the Middle Devonian. Spatial configurations(or distribution ) of depositional systems are formed in different sedimentary conditions (i. e. eustusy, tectonism,source supplies), they consist of (1) barrier-lagoon-fluvial complex systems, reflecting an early basin fill stage with abundant source supplies at a relative low sea level, (2) mixed carbonate ramp-siliciclastic barrier-lagoon complex systems formed after rapid sea level rising, (3) mixed rimmed carbonate platform-siliciclastic delta (or tidal) complex systems developed often in late sea level lowstands with a relative rapid subsidence rate at platform margin, and (4) mixed carbonate ramp-siliciclastic delta systems established after rapid sea level rising as (2). In southern Guizhou, the NW-SE extensional faulting zone determines the range of two absolutely different dePOSitional patterns of platform and intraplatform (or intrashelf) trough (or basin), and establishes the peleogeographic framework of sedimentary evolution.Six third-order depositional sequences including two terrigenous siliciclastic sequences in the late Early Devonian and four mixed cabonate-siliciclastic sequences in the Middle Devonian were recognized based on the sedimentary studies. The formation of the sequences is controlled largely by sea level changes.The terrigenous depeitional systems develop in the early basin-fill stage with abundant source supplies. The shoreline and fluvial besinward Ptogradation characterizes the lowstand of sea level. Withdrawal of the sea level below the depostiional break initially leads to the shelf exposure, fluvial incision, and formation of lowstand fans and wedges (progradational shoreline or delta deposits).The rapid sea level rising causes the shoreline to recede landwards swiftly and the semi-pelagic black shale to blanket the trailing edge of the shelf. During the highstand of sea level, the shoreline deposits that aggradationally stack in the early stage gradually change into the progradational coastal or deltaic plain deposits subsequently as the sea level begins to fall.In mixed carbonate-siliciclastic depositional systems, the sedimentary response to changes in relative sea level indicates that basinward transporting of elastics predominates the lowstand of sea level. The elastic materials are conveyed through the incised valley to the intrashelf trough (or basin), forming the lowstand fan and lowstand wedge. Sometimes, organic reefs are developed during the late lowstand (V, VI), and terminated by the rapid sea level rising. The rapid sea level rising leads the shoreline to retrograde quickly and causes intrashelf trough deposits (black shale,nodular limotone etc.) to onlap updip the depositional break. Continual sea level rising above the shelf (or platform) increases the accommodation space, which allows the resumption of carbonate production, hence, the carbonate deposits dominate over the early highstands. However, the siliciclastic systems on the proximal shelf begin to rejuvenate and to prograde basinwards during the late highstands when the accommodation space reduces.
1995, 13(3): 89-97.
Abstract:
The sedimentary environment in Baoshan, western Yunnan was a shallow-sea carbonate platform in the Early Carboniferous, in which carbonate grains were generally micritized. The micritized grains are mainly colds, crinoides and brachiopoda, as well as a little calcirude and oncoid. The micritization was resulted by the puncture of bacteria and algae, and generally developed towards the center. However, some micritization was only in the central hole and joint of crinoide stalks. The micritization in a single grain shows periodicity. According to the shape and degree of micritization, it can be devided into 4 stages with 6 types. preP8ring stage-puncture of bacteria and algae, occurring stage-micritic pit. micritic net and radiation lines, developing stagemicritic envelope and maturating sarge-casting mould of micrtization. After puncture, the ways of micritization were not only biochemical precipituion (i. e. filling), but also biomechanical fragmentation and biochemical erosion(i. e. soilization occuring on the ocean bottom).The micritized grains of the Lower in Baoshan, Western Yunnan Chrboniferous occured mainly in shoal, secondly in platform, A few grains which belong to allochthonous deposits can also be found from platform-basin. Generally types of micritized grains are abundant and widely developed. The micritized rocks are mainly spar-oolite limestone and spar-allochemical limestone. Abundance of mieritized grains, especially micritic envelopes and casting mould can be considered as marks of shoal; The micritized grains gradually decrease from the central of the shoal; The degree of micritized depth shows an inverse ratio to the velocity of dePOsition: The homogeneity of micritization shows a direct ratio to the seawater turbulence, which is the rolling time of the grains. The complexity of the combination types of micritization was related to storm sedimentation.Corrosion holes and negative colds are the mark of an exposure environment, i. e. leaching mark of fresh water. The grain micritization would speed up the mechanical fragmentation by seawater and the buried diagenesis by compaction to fine carbonate grains and to produce intraclast and micrite. Concentric colds could be transformed into radiant ooids and pseudooids by micritization.
The sedimentary environment in Baoshan, western Yunnan was a shallow-sea carbonate platform in the Early Carboniferous, in which carbonate grains were generally micritized. The micritized grains are mainly colds, crinoides and brachiopoda, as well as a little calcirude and oncoid. The micritization was resulted by the puncture of bacteria and algae, and generally developed towards the center. However, some micritization was only in the central hole and joint of crinoide stalks. The micritization in a single grain shows periodicity. According to the shape and degree of micritization, it can be devided into 4 stages with 6 types. preP8ring stage-puncture of bacteria and algae, occurring stage-micritic pit. micritic net and radiation lines, developing stagemicritic envelope and maturating sarge-casting mould of micrtization. After puncture, the ways of micritization were not only biochemical precipituion (i. e. filling), but also biomechanical fragmentation and biochemical erosion(i. e. soilization occuring on the ocean bottom).The micritized grains of the Lower in Baoshan, Western Yunnan Chrboniferous occured mainly in shoal, secondly in platform, A few grains which belong to allochthonous deposits can also be found from platform-basin. Generally types of micritized grains are abundant and widely developed. The micritized rocks are mainly spar-oolite limestone and spar-allochemical limestone. Abundance of mieritized grains, especially micritic envelopes and casting mould can be considered as marks of shoal; The micritized grains gradually decrease from the central of the shoal; The degree of micritized depth shows an inverse ratio to the velocity of dePOsition: The homogeneity of micritization shows a direct ratio to the seawater turbulence, which is the rolling time of the grains. The complexity of the combination types of micritization was related to storm sedimentation.Corrosion holes and negative colds are the mark of an exposure environment, i. e. leaching mark of fresh water. The grain micritization would speed up the mechanical fragmentation by seawater and the buried diagenesis by compaction to fine carbonate grains and to produce intraclast and micrite. Concentric colds could be transformed into radiant ooids and pseudooids by micritization.
1995, 13(3): 107-116.
Abstract:
The transmission Electron Microscopy examination of ultrathin sections of a series of Carboniferous Taiyuan Formation and Permian Shanxi Formation vitrinites collected from 18 mining areas of the eastern port of North China, has revealed that vitrinites of Taiyuan Formation are rich in submicroliptinite, which is dominahtly derived from bacteria and algae. There is significant difference in the amount of submicroliptinites in vitrinite between Taiyuan Formation and Shanxi Formation. The amounts of submicroliptinite are related to chemical properties and behaviors in technical processes of vitrinite. The reasons of differences in vitrinite properties between Taiyuan Formation and Shanxi Formation have been explained in the level of maceral, submaceral and submicromaceral. The reasons of anomalous coal properties of Taiyuan Formation and reductivity of humic coal have been analysed and discussed. The results suggest that abundant algae and bacteria contribution, in the forms of liptinite, submicroliptinite and molecular level lipoid materials incorpotated in huminite/vitrinite, may be one of the important reasons for anomalous coal properties of Taiyuan Formation.
The transmission Electron Microscopy examination of ultrathin sections of a series of Carboniferous Taiyuan Formation and Permian Shanxi Formation vitrinites collected from 18 mining areas of the eastern port of North China, has revealed that vitrinites of Taiyuan Formation are rich in submicroliptinite, which is dominahtly derived from bacteria and algae. There is significant difference in the amount of submicroliptinites in vitrinite between Taiyuan Formation and Shanxi Formation. The amounts of submicroliptinite are related to chemical properties and behaviors in technical processes of vitrinite. The reasons of differences in vitrinite properties between Taiyuan Formation and Shanxi Formation have been explained in the level of maceral, submaceral and submicromaceral. The reasons of anomalous coal properties of Taiyuan Formation and reductivity of humic coal have been analysed and discussed. The results suggest that abundant algae and bacteria contribution, in the forms of liptinite, submicroliptinite and molecular level lipoid materials incorpotated in huminite/vitrinite, may be one of the important reasons for anomalous coal properties of Taiyuan Formation.
1995, 13(3): 126-131.
Abstract:
The14C and 230Th data of the sedimentS from the cores CK826 of the Dabusun region and from the cores CK2022 of the Bieletan region have been accumulated in the study of chronology since 1976.From 1989, we made a systematic determination of14C and230Th on the samples of cores 88-01 and 89-04, and obtained more detailed data in the Study of evolution of Qarhan Playa.Cores 88-01 and 89-04 is located in the north shore of Dabusun Lake. The depths of both cores are 47m and 45m, respectively. The sediments are similiar not only in depositional characteristics,but also in salt-forming ages. A ages vs. depth chart is given in this paper, and a linear equation is obtained from the chart.It can be seen from the chart that there is a good correlation between the ages and the depths.From the linear equation, rough salt-forming ages of the four salt layers in the Dabusun region are obtained. The ages of the bottom layer S1, S2, S3, S4are 50000, 36000, 30000, 18000a. B. P.,respectively. In addition, the surface salt crust of Qarhan Playa was formed in about 8000- 9000a.B. P.. In order to make the explanation more clear, the core section chart and age data of cores 88-01 and 88-04 are made together with those of the four cores described in the reference (3). The result indicates that the salt-forming age in the Dabusun region is about 50000 a. B. P., which is largely different.from those of cores CK2o22,CK6and CK1308, and they reveal the salt-forming age of the Bieletan region. The salt-forming age of the Dabusun region is about 2000 years older than that of the Bieletan region.
The14C and 230Th data of the sedimentS from the cores CK826 of the Dabusun region and from the cores CK2022 of the Bieletan region have been accumulated in the study of chronology since 1976.From 1989, we made a systematic determination of14C and230Th on the samples of cores 88-01 and 89-04, and obtained more detailed data in the Study of evolution of Qarhan Playa.Cores 88-01 and 89-04 is located in the north shore of Dabusun Lake. The depths of both cores are 47m and 45m, respectively. The sediments are similiar not only in depositional characteristics,but also in salt-forming ages. A ages vs. depth chart is given in this paper, and a linear equation is obtained from the chart.It can be seen from the chart that there is a good correlation between the ages and the depths.From the linear equation, rough salt-forming ages of the four salt layers in the Dabusun region are obtained. The ages of the bottom layer S1, S2, S3, S4are 50000, 36000, 30000, 18000a. B. P.,respectively. In addition, the surface salt crust of Qarhan Playa was formed in about 8000- 9000a.B. P.. In order to make the explanation more clear, the core section chart and age data of cores 88-01 and 88-04 are made together with those of the four cores described in the reference (3). The result indicates that the salt-forming age in the Dabusun region is about 50000 a. B. P., which is largely different.from those of cores CK2o22,CK6and CK1308, and they reveal the salt-forming age of the Bieletan region. The salt-forming age of the Dabusun region is about 2000 years older than that of the Bieletan region.
1995, 13(3): 137-146.
Abstract:
This article gives a definition of the mutual dilution mixture:if a sedimentary rock is formed by mixing of two end-members; the concentrations of element m in the end-members A and B are Ma and Mb, respectively, and M２aMb≥0;the concentrations of element P in the end-members A and B are Pa and Pb, respectively;then the concentration relationship between elements M and p in a sedimentary rock series formed by mixing of the end-members A and B is defined as the mutual dilution mixture.The element abuneances(x and y)in a rock with petrogenesis of mixture obey the law of the fractional linear function:where a,b, c and d are abundance relationship constants which are only related to the abundances (x1,y1;x2,y2) of two known rocks (1 and 2)in the rock series and equal to the mirror ∑transformation (or mixture transformation)of them:Based on the type of the element abundance relatioship of two known rocks with petrogenesis of binary mixture and by listing the column matrix of abundances and rearranging the column matrix by a certain model, the abundance relationship constants could be calculated conveniently. If the ratio of conements b and c is negative,then the element abundance relationship between y and x is a mutual diluhon mixture.Based on the element abundances of the two end-members in a sedimentary rock series, themutual dilution mixture (MDM) can be devided into three types:Pure MDM, half pure MDM and impure MDM.For a sedimentary rock series, provided the element concentrations of any two rocks with different compositions are known, the element abundances of the end-members of the sedimentary rock can be surely estimated, in turn the compositions of materials in the end-members can be figured out.Applying the theory and method discussed here, the data of the sandstone-claystone series in the northern Sichuan, obtained from neutron activation analysis, were dealt with. The resultsindicate that the concentration relationshipe between CaO and Al2O3 and between Na2O and K2O belong to the mutual dilution mixture. The components of the end-members in the sandstone claystone series of the northerm Sichuan are estimated based on the equation of the mixture (mirror ∑) transformation:1)one end-member is the complex of pure carbonate,siliceous materials and organic carbon the other is pute clay component. 2)the potassium-bearing materials in pure clay component are mainly the hydro-muscovite with minor alkalifeldspar and clay minerals;the mean composition of odium-bearing components is similar to that of the andesine.
This article gives a definition of the mutual dilution mixture:if a sedimentary rock is formed by mixing of two end-members; the concentrations of element m in the end-members A and B are Ma and Mb, respectively, and M２aMb≥0;the concentrations of element P in the end-members A and B are Pa and Pb, respectively;then the concentration relationship between elements M and p in a sedimentary rock series formed by mixing of the end-members A and B is defined as the mutual dilution mixture.The element abuneances(x and y)in a rock with petrogenesis of mixture obey the law of the fractional linear function:where a,b, c and d are abundance relationship constants which are only related to the abundances (x1,y1;x2,y2) of two known rocks (1 and 2)in the rock series and equal to the mirror ∑transformation (or mixture transformation)of them:Based on the type of the element abundance relatioship of two known rocks with petrogenesis of binary mixture and by listing the column matrix of abundances and rearranging the column matrix by a certain model, the abundance relationship constants could be calculated conveniently. If the ratio of conements b and c is negative,then the element abundance relationship between y and x is a mutual diluhon mixture.Based on the element abundances of the two end-members in a sedimentary rock series, themutual dilution mixture (MDM) can be devided into three types:Pure MDM, half pure MDM and impure MDM.For a sedimentary rock series, provided the element concentrations of any two rocks with different compositions are known, the element abundances of the end-members of the sedimentary rock can be surely estimated, in turn the compositions of materials in the end-members can be figured out.Applying the theory and method discussed here, the data of the sandstone-claystone series in the northern Sichuan, obtained from neutron activation analysis, were dealt with. The resultsindicate that the concentration relationshipe between CaO and Al2O3 and between Na2O and K2O belong to the mutual dilution mixture. The components of the end-members in the sandstone claystone series of the northerm Sichuan are estimated based on the equation of the mixture (mirror ∑) transformation:1)one end-member is the complex of pure carbonate,siliceous materials and organic carbon the other is pute clay component. 2)the potassium-bearing materials in pure clay component are mainly the hydro-muscovite with minor alkalifeldspar and clay minerals;the mean composition of odium-bearing components is similar to that of the andesine.
