1989 Vol. 7, No. 4
column
Display Method:
1989, 7(4): 3-13.
Abstract:
This paper studies the largest gas field-Weiyuan gas field in Sichuan ? basin . There are four gas-bearing layers in the gas pool, i.e. Triassic, Permian, Cambrian and Sinian. The main industry reservoir in the dolomite of the Siniansy stsyem. The oldest layer is about 700~800 x 106years. It is the largest and oldest gas field which has been found in China so far. It is significant for the study of early organic matter evolution, mineral and energy resources to study out the genesis ofgaspool, especially, to decide whether the source of Sinian gas pool may be relative to Precambrian layers.The characteristics of the gas constituent and the i so topic composition of C， H， S， Ar，He from this gas field are the following: 1. Compared with the other gas pools, Sinian gas pool gas high content of N2(9%), C02+H2S (5%), He (0.18) and Ar (0.05%)； 2.The value of 40Ar/36Ar in Sinian gas pool is very high, from 4400 to 9255, the average is 7000, showing high age-accumulating effect. The value of 3He/4He is low. only n x 10-8. This means that the He in the Wciyuan gas pool is mainly from the crustal matter; 3. He /Ar is from 5.39 to 6.14, the lowest value which has been found by us; 4. The values of N2/Ar and N2/He have better linear relativity; S.Triassic, Permian, Cambrian and Sinian gas pools can be classified with the isotopic composition of C, H, S， Ar, which shows the gas in these gas pools is from different gas sources; 6. The components of absorbed hydrocarbon from Sinian source rock are diiTcrent from other source rocks, and the value of C2/C3from the source rock can be well compared with that from gases.To sum up, we think that the Sinian gas pool is of autochthonous origin. It was formed by organic matter at the early stage of earth f s evolution. The CH4 and rare gas are not characteristics of mantle mater; but we cannot rule out a possibility that there may be some mantle matter being pux in this gas pool.
This paper studies the largest gas field-Weiyuan gas field in Sichuan ? basin . There are four gas-bearing layers in the gas pool, i.e. Triassic, Permian, Cambrian and Sinian. The main industry reservoir in the dolomite of the Siniansy stsyem. The oldest layer is about 700~800 x 106years. It is the largest and oldest gas field which has been found in China so far. It is significant for the study of early organic matter evolution, mineral and energy resources to study out the genesis ofgaspool, especially, to decide whether the source of Sinian gas pool may be relative to Precambrian layers.The characteristics of the gas constituent and the i so topic composition of C， H， S， Ar，He from this gas field are the following: 1. Compared with the other gas pools, Sinian gas pool gas high content of N2(9%), C02+H2S (5%), He (0.18) and Ar (0.05%)； 2.The value of 40Ar/36Ar in Sinian gas pool is very high, from 4400 to 9255, the average is 7000, showing high age-accumulating effect. The value of 3He/4He is low. only n x 10-8. This means that the He in the Wciyuan gas pool is mainly from the crustal matter; 3. He /Ar is from 5.39 to 6.14, the lowest value which has been found by us; 4. The values of N2/Ar and N2/He have better linear relativity; S.Triassic, Permian, Cambrian and Sinian gas pools can be classified with the isotopic composition of C, H, S， Ar, which shows the gas in these gas pools is from different gas sources; 6. The components of absorbed hydrocarbon from Sinian source rock are diiTcrent from other source rocks, and the value of C2/C3from the source rock can be well compared with that from gases.To sum up, we think that the Sinian gas pool is of autochthonous origin. It was formed by organic matter at the early stage of earth f s evolution. The CH4 and rare gas are not characteristics of mantle mater; but we cannot rule out a possibility that there may be some mantle matter being pux in this gas pool.
1989, 7(4): 69-76.
Abstract:
Tectonically the widely extensive East China Sea is considerably complex. It not only has a braod shelf, but also has a famous epi-Pacific system of trench-arc-trough. The sea is a new frontier with a significant hydrocarbon potential. Nevertheless, in the past, the stratigtaphy, the geological ccolution and tectonics of the East China Sea were less understood, they were merely conjuctured by the geological data of surrounding areas and islands.Until now, there is no relatively detailed palaeogeographic analysis.Recently, with the advance of petroleum exploration, the stratigraphic sequences of individual tectonic units can be established by a combination of the Seismic-stratigraphy, records of several wells, and the biostratigraphy of many neighboring islands.Thus a series of Cretaceous-Tertiary palaeogeograpohic maps (including Cretaceous, Paleocene, Eocene, Oligocene, Miocene and Pliocene) can be made, and the palaeogeographic changes of the East China Sea can be analysed. Based on the drililing data in raiwan and the southern part of the East China Sea， as well as Cretaceous outcrops with many fossil in the eastern Zhejiang province, the author proposes that Ihe area of Cretaceous transgression is extensive, and the Cretaceous strata most likely become a significant petroliferous formation in the East China Sea. Recently the extensive Paleocene is also proved by the data of exploration wells in Taiwan and offshore areas, as well as the interpretation of seismic-stratigraphy .The Eocene marine fades as a global extensive transgression naturally occupied a more extensive region.However, the Oligocene sedimentary area was reduced due to the influence of Puli movement, whereas the continental facies was increased.According to the series of maps composed by the author, during Paleogcne, the characteristic of the East China Sea is marine in the south part and land in the north part, i.e. the south of the latitude where Winzhou city located was a sea area with developed marine facies, whereas the north of it was dominated by continental facics.During Miocene, the shelf basin of the East China Sea had a trend of uplifting, thus a terrestrial deposit occupied most of the shelf.During Pliocene, an extensive transgression also occured in the East China sea, its north part reached the border between Huanghai and the East China Sea, and the west part approached the present coast.It is almost the same as the modern morphology of the East China Sea. According to the palaeogeographic evolution, therefore the diITerentiation bcl^vccn the south part and the north pari is quite obvious.During Cretaceous-Tertiary a terrestrial environment had persisted a relatively long time in the north part of the East China Sea, while the south part of the East China Sea and Taiwan had been a marine environment with the features o「 epicontinental sea basin-open shallowsea, until Miocene, relatively deep-water troughs under the extensional setting occured in the Okinawa trough.therefore the author consider, in terms of a palaeogeographic analysis, during Cretaceous-Terliary Ihe shelf of the shelf of lhe East China Sca is mainly a continenlal Craton basin.May be only since Miocene, a tectonic framework o「an i」Live continental margin has been formed at the eastern border of lhe East China Sea. In addilion, the author also briefly describe a model of PalaeoclimaUc evolution from a viewpoint of geological history.
Tectonically the widely extensive East China Sea is considerably complex. It not only has a braod shelf, but also has a famous epi-Pacific system of trench-arc-trough. The sea is a new frontier with a significant hydrocarbon potential. Nevertheless, in the past, the stratigtaphy, the geological ccolution and tectonics of the East China Sea were less understood, they were merely conjuctured by the geological data of surrounding areas and islands.Until now, there is no relatively detailed palaeogeographic analysis.Recently, with the advance of petroleum exploration, the stratigraphic sequences of individual tectonic units can be established by a combination of the Seismic-stratigraphy, records of several wells, and the biostratigraphy of many neighboring islands.Thus a series of Cretaceous-Tertiary palaeogeograpohic maps (including Cretaceous, Paleocene, Eocene, Oligocene, Miocene and Pliocene) can be made, and the palaeogeographic changes of the East China Sea can be analysed. Based on the drililing data in raiwan and the southern part of the East China Sea， as well as Cretaceous outcrops with many fossil in the eastern Zhejiang province, the author proposes that Ihe area of Cretaceous transgression is extensive, and the Cretaceous strata most likely become a significant petroliferous formation in the East China Sea. Recently the extensive Paleocene is also proved by the data of exploration wells in Taiwan and offshore areas, as well as the interpretation of seismic-stratigraphy .The Eocene marine fades as a global extensive transgression naturally occupied a more extensive region.However, the Oligocene sedimentary area was reduced due to the influence of Puli movement, whereas the continental facies was increased.According to the series of maps composed by the author, during Paleogcne, the characteristic of the East China Sea is marine in the south part and land in the north part, i.e. the south of the latitude where Winzhou city located was a sea area with developed marine facies, whereas the north of it was dominated by continental facics.During Miocene, the shelf basin of the East China Sea had a trend of uplifting, thus a terrestrial deposit occupied most of the shelf.During Pliocene, an extensive transgression also occured in the East China sea, its north part reached the border between Huanghai and the East China Sea, and the west part approached the present coast.It is almost the same as the modern morphology of the East China Sea. According to the palaeogeographic evolution, therefore the diITerentiation bcl^vccn the south part and the north pari is quite obvious.During Cretaceous-Tertiary a terrestrial environment had persisted a relatively long time in the north part of the East China Sea, while the south part of the East China Sea and Taiwan had been a marine environment with the features o「 epicontinental sea basin-open shallowsea, until Miocene, relatively deep-water troughs under the extensional setting occured in the Okinawa trough.therefore the author consider, in terms of a palaeogeographic analysis, during Cretaceous-Terliary Ihe shelf of the shelf of lhe East China Sca is mainly a continenlal Craton basin.May be only since Miocene, a tectonic framework o「an i」Live continental margin has been formed at the eastern border of lhe East China Sea. In addilion, the author also briefly describe a model of PalaeoclimaUc evolution from a viewpoint of geological history.
1989, 7(4): 85-96.
Abstract:
The Danchi Basin belongs to the secondary rift basin of Youjiang Rift Belt near the Jiangnan Oldland.The sedimentary fades can be divided into five fades area and thirteen facies belts, including dellaic, shoreline ， tidal Hat, lagoonal clastic shelf, carbonate-clastic shelf, Restricted platformal, open platforraal, bioherm, platform-marginal slope, platform-shelf and basinal sediments.The main characteristics of the sedimentary facies are listed in table 4.The gross tendency of sedimentation is that terrigenous elastics are deposited near the margin of the oldland, and carbonates and silicalites are deposited far from the oldland, and mixed deposites consisting of carbonates and elastics are favourable in the transitional area. During the Devonian to Permian, the clastic deposits decrease with the carbonates increasing. The formation of the basin, sedimentation and distribution of facies and sequences in the area are controlled by the activities of synsedimentary faultings.The main characteristics of which are as follows: 1) The facies belts extend in the trend of the faults. The rifting forms linear depressional belts, and strike-slipping causes local rises and depressions, and the facies zones are distributed in "S" or "counter-S" type. 2) The bioherms were distributed in linear along the margin of platforms which is controlled by the activities of synsedimentary faults. They are asymmetrical on the profiles, and the reef-front talus occurs usually on the side near the faults. 3) There are special sedimentary types. When the linear depressional zones caused by the activities of the faults strentch to the margin of the oldland,- they often are as some passageways along which a large quantity of terrigenous elastics is transported into the basin, so that the very thick turbidite fans are formed.The activities of the faults on the transitional belts betwwen the platform and basin can cause so steep slopes that the large- scale debris flow deposition, turbidite deposition, slump and collapse accumulations occurred in the belts. 4) There are some distinctive syndepositional deformative structures, for example, extensive syndepositional slump folds, pillow sedimentary bodis and convolute layers, one of whose main characteristics is that they are limited in some layers. 5) The isopach strike is closely relative to the extension of the synsedimentary faults. 6) The activities of synsedimentary faults usually cause the suddenly change of facies. The evolution of the activities of the synsedimentary faults are from startion with the rifting of the faults with NW- trend, through the NW trend extensional fracturing in coupling faults with NNE trend strike-sliping, and finally, finishing with the NW strike-ship faulting.On the profile, the evolution of the Danchi Basin is characterized in form of a semi-graben to graben type.
The Danchi Basin belongs to the secondary rift basin of Youjiang Rift Belt near the Jiangnan Oldland.The sedimentary fades can be divided into five fades area and thirteen facies belts, including dellaic, shoreline ， tidal Hat, lagoonal clastic shelf, carbonate-clastic shelf, Restricted platformal, open platforraal, bioherm, platform-marginal slope, platform-shelf and basinal sediments.The main characteristics of the sedimentary facies are listed in table 4.The gross tendency of sedimentation is that terrigenous elastics are deposited near the margin of the oldland, and carbonates and silicalites are deposited far from the oldland, and mixed deposites consisting of carbonates and elastics are favourable in the transitional area. During the Devonian to Permian, the clastic deposits decrease with the carbonates increasing. The formation of the basin, sedimentation and distribution of facies and sequences in the area are controlled by the activities of synsedimentary faultings.The main characteristics of which are as follows: 1) The facies belts extend in the trend of the faults. The rifting forms linear depressional belts, and strike-slipping causes local rises and depressions, and the facies zones are distributed in "S" or "counter-S" type. 2) The bioherms were distributed in linear along the margin of platforms which is controlled by the activities of synsedimentary faults. They are asymmetrical on the profiles, and the reef-front talus occurs usually on the side near the faults. 3) There are special sedimentary types. When the linear depressional zones caused by the activities of the faults strentch to the margin of the oldland,- they often are as some passageways along which a large quantity of terrigenous elastics is transported into the basin, so that the very thick turbidite fans are formed.The activities of the faults on the transitional belts betwwen the platform and basin can cause so steep slopes that the large- scale debris flow deposition, turbidite deposition, slump and collapse accumulations occurred in the belts. 4) There are some distinctive syndepositional deformative structures, for example, extensive syndepositional slump folds, pillow sedimentary bodis and convolute layers, one of whose main characteristics is that they are limited in some layers. 5) The isopach strike is closely relative to the extension of the synsedimentary faults. 6) The activities of synsedimentary faults usually cause the suddenly change of facies. The evolution of the activities of the synsedimentary faults are from startion with the rifting of the faults with NW- trend, through the NW trend extensional fracturing in coupling faults with NNE trend strike-sliping, and finally, finishing with the NW strike-ship faulting.On the profile, the evolution of the Danchi Basin is characterized in form of a semi-graben to graben type.
1989, 7(4): 105-111.
Abstract:
This paper deals with the information of sedimentary rocks ， primary sedimentary structures, stratigraphic sequence, grain size, fossils, heavy minerals, clay minerals, trace elements and well logging, which have been obtained from Upper Jurassic to Lower Cretaceous in Shibei district is analyzed by synthetical methods including the sedimentologic analysis, geochemical analysis, geophysical and mathematical statistics etc. Seven sedimentary facies types in this area have been identified.They are diluvium fan, fluvial facies, deltaic, shore and shallow lacustrine, deeper and deep-water lacustrine, subaqueous fan and deep-water turbidity fan facies.These formed in different and closely related sedimentary environments. Based on these data, it can be seen that due to the characteristics, especially in hydrodynamic condition of Shibei District, sorrow facies belt formed and facies change rapidly, even in series of facies belts lack of some one facies. Each of the facies has its own distinctive feature-all of these are evidently different from that of the same kind of sedimentary facies forming in giant basins and vast alluvial plain areas.The fluvial facies in studied area, with fans of braided stream and diluvial characteristics. Most of the deltaic facies in the area are "constructional delta* .Subaqueous fan are characterized by proximal, relatively coarser grains in shallow- water environment, and have characters both of alluvial and turbidity deposits. Deep-water environment and turbidity developed in intermittent all of which may be characteristics of facies of turbidity fanJn addition, the shapes of grain-size distribution curve of each facies are quite difTerent.lt can be summarized as eight types which can be used as one of the basis of identifying sedimentary facies types. The results show that Northeast trend Bainan Contemporaneous Faults No.2 & No.3 and Shibei Asymmetric Depression is controlled by these faults and the facies association may depend on which---during the active period diluvial and subaqueous fan developed in the steep bank zone of the depression whereas the fluvial (point bar) and deltaic facies association developed in the gentle slope belt; During the more active stage, subaqueous fan and trubidity fan, deep-water mudstone and shale facies are developed in a belt of steep bank whereas fluvial, deltaic, shore and shallow lacustrine facies may be developed in a gentle slope belt.On the other hand, deep lacustrine facies mainly developed in the central region of the lake.The succession of sedimentary facies has certain regularities. The facies association and succession are controlled strictly by many factors such as tectonism, paleoclimate, paleogeographic, condition of depositional medium. The author also studies the abundance of trace elements and characteristics of paired ratios, in which the different terrestrial environments being recognize.In the summary, the values of V/Ni, Sr/Ba, Rb/K ratio increasing synchronously, however, the values of Ni/Co, Fe/Mn, K /Na, Na/Ca, Sr/Ca, Mg/Ca ratio decreasing gradually with the evolution of facies from diluvial to fluvial, delta, shore and shallow lacustrine, deeper and deep lacustrine facies.These provide reference evidences for identifying sedimentary facies.
This paper deals with the information of sedimentary rocks ， primary sedimentary structures, stratigraphic sequence, grain size, fossils, heavy minerals, clay minerals, trace elements and well logging, which have been obtained from Upper Jurassic to Lower Cretaceous in Shibei district is analyzed by synthetical methods including the sedimentologic analysis, geochemical analysis, geophysical and mathematical statistics etc. Seven sedimentary facies types in this area have been identified.They are diluvium fan, fluvial facies, deltaic, shore and shallow lacustrine, deeper and deep-water lacustrine, subaqueous fan and deep-water turbidity fan facies.These formed in different and closely related sedimentary environments. Based on these data, it can be seen that due to the characteristics, especially in hydrodynamic condition of Shibei District, sorrow facies belt formed and facies change rapidly, even in series of facies belts lack of some one facies. Each of the facies has its own distinctive feature-all of these are evidently different from that of the same kind of sedimentary facies forming in giant basins and vast alluvial plain areas.The fluvial facies in studied area, with fans of braided stream and diluvial characteristics. Most of the deltaic facies in the area are "constructional delta* .Subaqueous fan are characterized by proximal, relatively coarser grains in shallow- water environment, and have characters both of alluvial and turbidity deposits. Deep-water environment and turbidity developed in intermittent all of which may be characteristics of facies of turbidity fanJn addition, the shapes of grain-size distribution curve of each facies are quite difTerent.lt can be summarized as eight types which can be used as one of the basis of identifying sedimentary facies types. The results show that Northeast trend Bainan Contemporaneous Faults No.2 & No.3 and Shibei Asymmetric Depression is controlled by these faults and the facies association may depend on which---during the active period diluvial and subaqueous fan developed in the steep bank zone of the depression whereas the fluvial (point bar) and deltaic facies association developed in the gentle slope belt; During the more active stage, subaqueous fan and trubidity fan, deep-water mudstone and shale facies are developed in a belt of steep bank whereas fluvial, deltaic, shore and shallow lacustrine facies may be developed in a gentle slope belt.On the other hand, deep lacustrine facies mainly developed in the central region of the lake.The succession of sedimentary facies has certain regularities. The facies association and succession are controlled strictly by many factors such as tectonism, paleoclimate, paleogeographic, condition of depositional medium. The author also studies the abundance of trace elements and characteristics of paired ratios, in which the different terrestrial environments being recognize.In the summary, the values of V/Ni, Sr/Ba, Rb/K ratio increasing synchronously, however, the values of Ni/Co, Fe/Mn, K /Na, Na/Ca, Sr/Ca, Mg/Ca ratio decreasing gradually with the evolution of facies from diluvial to fluvial, delta, shore and shallow lacustrine, deeper and deep lacustrine facies.These provide reference evidences for identifying sedimentary facies.
1989, 7(4): 121-131.
Abstract:
Shanraian coalfield, which is located in the western part of Henan Province, is one of the major coalfields in southern zone of the Late Palaeozoic coal-forming basin of North China.The coal-bearing strata consist of Taiyuan Formation of Late Carboniferous, Shanxi Formation of early Early Permian and Shihezi Group of Late Early Permian to early Late Permian. Coal II1, located in the lower part of Shanxi Formation, is the main minable coal bed in the study area.The deposits underlying coa II1bed are mainly formed on the shoreline and in the shallow sea. They can be divided, from bottom to top, into four menbers: bottom bauxitic mudstone member, lower clastic rock member, middle limestone member and upper clastic rock membes.The first three members are part of Taiyuan Formation, the last member belongs to top of Taiyuan Formation and lower part of Shanxi Formation.Chiefly descussed in this paper are the sedimentary fades, depositional environments and coal-forming characteristics of Upper Clastic Member and middle upper part of Shanxi Formation in the study area.The clastic rocks of upper member are mainly deposited on microtidal coast with extensive clastic tidal channels (medium to fine sandstone, fining upward sequence, sandbody shows branching from south to north (land diretion) in plan view and lenticular shape in trend section and lagoon-flats (grey silt, mudstone with abundant pyritc nodules, interbedcd bedding, lenticular and flaser bedding and biturbate structure) ， and barrier islands (medium to fine quartz sandstone, lower angle planar cross-bedding) in the study area. The middle-upper part of Shanxi Formation (which overlies the coal II1)is regarded as fluvial-dominated, tide-influenced delta system filling in a shallow bay.It is composed of extensive developed distributary channels (with abundant mica in bed plan, sandbody shows branching and thinning from north to south in plan view and lenticular shape in trend section* palaeocurrent is mainly single direction, some with reverse direction) ， interdistributary bay -tidal flats (interbedcd bedding, smalt ripple cross bedding, horizontal and incline biologic hole) and less developed subaquatic delta plain (distributary mouth bar, distal bar and pro delta) . On the whole, the deposits overlying coal II phow a regressive sequence from the deposits of subaqueous and lower delta plain (middle upper part of Shanxi Formation) towards those of upper delta plain (Shihezi Group). The thickness and quality of coal bed are affected directly by the precedent and contempora-neous depositional environments. Cloal bed (coal II1) fomed on banierlLagoonltidal flats of microtidal coast tends to be thick (0-14.10, mean 3.66m), laterally continuous and high in sulphur (2.5% 14.0%, mean 3.91%) . Conversely, delta plain coals are thin (0-3.22m,mean 0.52m), laterally discontinuous and low in sulphur (0.60%-0.73%, mean 0.66%). As far as a single coal bed, such as coal II1, is concerned, the thickness, laterally extent and quality of coal bed are mainly dependent Op sedimentary environments, where the tidal channels developed, the overlying coals tend to be thin (0-3m), low in sulphur (0-2.5%,but high in ash (higher than 40%). Where the lagoon-tidal flats developed, the overlying coals tend to be thick (thicker than 3m) , high in sulphur(higher than 2.5% ), but low in ash (10%-25%). The postdepositional environments of peat bed, such as delta distributary channels erode slightly the underlying peat deposits, fonning local thinning zone. The postedpositional tectonics is minor facters Influencing the thickness of coal scams.
Shanraian coalfield, which is located in the western part of Henan Province, is one of the major coalfields in southern zone of the Late Palaeozoic coal-forming basin of North China.The coal-bearing strata consist of Taiyuan Formation of Late Carboniferous, Shanxi Formation of early Early Permian and Shihezi Group of Late Early Permian to early Late Permian. Coal II1, located in the lower part of Shanxi Formation, is the main minable coal bed in the study area.The deposits underlying coa II1bed are mainly formed on the shoreline and in the shallow sea. They can be divided, from bottom to top, into four menbers: bottom bauxitic mudstone member, lower clastic rock member, middle limestone member and upper clastic rock membes.The first three members are part of Taiyuan Formation, the last member belongs to top of Taiyuan Formation and lower part of Shanxi Formation.Chiefly descussed in this paper are the sedimentary fades, depositional environments and coal-forming characteristics of Upper Clastic Member and middle upper part of Shanxi Formation in the study area.The clastic rocks of upper member are mainly deposited on microtidal coast with extensive clastic tidal channels (medium to fine sandstone, fining upward sequence, sandbody shows branching from south to north (land diretion) in plan view and lenticular shape in trend section and lagoon-flats (grey silt, mudstone with abundant pyritc nodules, interbedcd bedding, lenticular and flaser bedding and biturbate structure) ， and barrier islands (medium to fine quartz sandstone, lower angle planar cross-bedding) in the study area. The middle-upper part of Shanxi Formation (which overlies the coal II1)is regarded as fluvial-dominated, tide-influenced delta system filling in a shallow bay.It is composed of extensive developed distributary channels (with abundant mica in bed plan, sandbody shows branching and thinning from north to south in plan view and lenticular shape in trend section* palaeocurrent is mainly single direction, some with reverse direction) ， interdistributary bay -tidal flats (interbedcd bedding, smalt ripple cross bedding, horizontal and incline biologic hole) and less developed subaquatic delta plain (distributary mouth bar, distal bar and pro delta) . On the whole, the deposits overlying coal II phow a regressive sequence from the deposits of subaqueous and lower delta plain (middle upper part of Shanxi Formation) towards those of upper delta plain (Shihezi Group). The thickness and quality of coal bed are affected directly by the precedent and contempora-neous depositional environments. Cloal bed (coal II1) fomed on banierlLagoonltidal flats of microtidal coast tends to be thick (0-14.10, mean 3.66m), laterally continuous and high in sulphur (2.5% 14.0%, mean 3.91%) . Conversely, delta plain coals are thin (0-3.22m,mean 0.52m), laterally discontinuous and low in sulphur (0.60%-0.73%, mean 0.66%). As far as a single coal bed, such as coal II1, is concerned, the thickness, laterally extent and quality of coal bed are mainly dependent Op sedimentary environments, where the tidal channels developed, the overlying coals tend to be thin (0-3m), low in sulphur (0-2.5%,but high in ash (higher than 40%). Where the lagoon-tidal flats developed, the overlying coals tend to be thick (thicker than 3m) , high in sulphur(higher than 2.5% ), but low in ash (10%-25%). The postdepositional environments of peat bed, such as delta distributary channels erode slightly the underlying peat deposits, fonning local thinning zone. The postedpositional tectonics is minor facters Influencing the thickness of coal scams.
1989, 7(4): 141-148.
Abstract:
Dongpu basin is located in the North-Eastern Part of Henan Province and South-Western part of Shandong Province, with area of 5300km2. It started with intensive fault-subsiding activities at the end of the Mesozoic era. During Lower Tertiary, clastic rocks and evaporites with thickness of 7000m deposited in Shahejie group and Dongying group. There are four suits of evaporitc deposits in the Lower Tertiary Shahejie group of Dongpu basin. Three of thera occur in third member of the group. Three of them occur in third member of the group, the another occurs in first member of the broup. Evaporites localize generally near the centre of a sub-subsidence. Their total thickness onrmally is ca. 100-200ra, sometimes up to 400m. Evaporites of Dongpu basin are mainly halites, anhydrtes and rairabilite-glauberite rocks. Their raineralogical composition varies greatly iaterally and longitudinally. In addition to existence of minerals such as mirabilite-glauberite the mineralogical composition of the evaporites may display a certain significance to its origin. The bromine distribution in halites of Dongpu basin was studied. It has been discouvered that all samples have low values below 30 ppm, which are much lower than those of normally marine halites. The bromine contents in some samples of halites are approximate to or below IOppm， which indicates not only that the halites are second-cycled in origin but also that the secod-cycled halites are probably from non-marine or continental fresh water. At a certain geological tiem, sulfur isotope composition of marine evaporites and the correspondent sulfates of ancient oceans changes generally in a narrow range. δS34Valucs (‰) of the present marine evaporites and the oceanic sulfates are +20， more or less. There is no distinct difference in sulfur isotope composition of marine evaporites between the Tertiary and the present. However, it has been shown by determination of sulfur isotope composition of anhydrites from Dongpu basin, that their δS34 Valucs are from +33.1 to 37.5 and the sulfur is much enriched in S34 Corapared with the Tertiary marine type. So it is difficult to suggest that the anhydrites of Dongpu basin are typically marine in origin. Generally, only a difined amount of sulfates are contained within water body of a quite closed inland basin. Biological fractionation caused by reducing bacteria may change the original sulfer isotope composition greatly, finally the S34 is most enriched in sulfate deposites. The Dongpu basin would be such closed type of lake basins and the evaporites, enriched in S34， deposited in it correspondently. Similar to lake basins, e.g. Uintah basin Utah etc., consisting of the Green River Formation, probably the Dongpu basin experienced steps when the water body was chemically stratified. A strong fractionation of sulfur isotope occured and the chemically stratified structure in water body favoured accumulation of orgainc niattdr to produce a enormous potential of oils and gas in the basin.
Dongpu basin is located in the North-Eastern Part of Henan Province and South-Western part of Shandong Province, with area of 5300km2. It started with intensive fault-subsiding activities at the end of the Mesozoic era. During Lower Tertiary, clastic rocks and evaporites with thickness of 7000m deposited in Shahejie group and Dongying group. There are four suits of evaporitc deposits in the Lower Tertiary Shahejie group of Dongpu basin. Three of thera occur in third member of the group. Three of them occur in third member of the group, the another occurs in first member of the broup. Evaporites localize generally near the centre of a sub-subsidence. Their total thickness onrmally is ca. 100-200ra, sometimes up to 400m. Evaporites of Dongpu basin are mainly halites, anhydrtes and rairabilite-glauberite rocks. Their raineralogical composition varies greatly iaterally and longitudinally. In addition to existence of minerals such as mirabilite-glauberite the mineralogical composition of the evaporites may display a certain significance to its origin. The bromine distribution in halites of Dongpu basin was studied. It has been discouvered that all samples have low values below 30 ppm, which are much lower than those of normally marine halites. The bromine contents in some samples of halites are approximate to or below IOppm， which indicates not only that the halites are second-cycled in origin but also that the secod-cycled halites are probably from non-marine or continental fresh water. At a certain geological tiem, sulfur isotope composition of marine evaporites and the correspondent sulfates of ancient oceans changes generally in a narrow range. δS34Valucs (‰) of the present marine evaporites and the oceanic sulfates are +20， more or less. There is no distinct difference in sulfur isotope composition of marine evaporites between the Tertiary and the present. However, it has been shown by determination of sulfur isotope composition of anhydrites from Dongpu basin, that their δS34 Valucs are from +33.1 to 37.5 and the sulfur is much enriched in S34 Corapared with the Tertiary marine type. So it is difficult to suggest that the anhydrites of Dongpu basin are typically marine in origin. Generally, only a difined amount of sulfates are contained within water body of a quite closed inland basin. Biological fractionation caused by reducing bacteria may change the original sulfer isotope composition greatly, finally the S34 is most enriched in sulfate deposites. The Dongpu basin would be such closed type of lake basins and the evaporites, enriched in S34， deposited in it correspondently. Similar to lake basins, e.g. Uintah basin Utah etc., consisting of the Green River Formation, probably the Dongpu basin experienced steps when the water body was chemically stratified. A strong fractionation of sulfur isotope occured and the chemically stratified structure in water body favoured accumulation of orgainc niattdr to produce a enormous potential of oils and gas in the basin.
1989, 7(4): 57-67.
Abstract:
In the north of Guizhou the geological time of bauxites are early Permian, The some of them . (in the south of Zwenyi, Xifen and Kayang) are the type of accumulation in situ of crust of weathering their basements are clolomilite of Loshang 9 an group (∈2-3) .Others (in the Zwenyi, Ongan and Zhenan, Daoahen) are the type of head of crust of weathering, their bed rocks are shale, silt with limestone of Tongxiu formatis (O3) and Hanjiadion formation (S2) .There are phenonmena of transition between ore deposits and bed rocks. The metterils of the bauxites origin the weathering of rocks under it.The thickness of disintegration reduce gradutly from south to north.Its 700-1OOOm in the south of Zwenyi, Xifen and Kayanf, 400-500m in the Zwenyi and Ongan, more than 200m in the Zhenan and Daozhen. In the study area, the weathering and disintegrats were from Caledonian to thfe middle of Idercynian.During this time, the crust elerats slomly, up to the early of Permian, the sea mater inter intrusted the study area.In Interral time of weatherding and disintegration is about 1-1.22 hundred M.Y., the time of formed latcrite is about 0.48 hundred M.Y. In this area, the characteristic of the bauxites are follows: 1. There are no parallel bcding, structures, textures formed in the water, no Zooliths and its fragments.Thcse imply the bauxites formed-under the atmosphere conditions.2.If bed rocks are shale, silt and other clastic rocks, so have phenomena of transition, i.e., the stratc which have beding gradualy change to the strata which have no beding from lower to upper. The phenomena of head in situ is quite'clear. If the bed rocks is carbonate, the change of the thinkness of ore body is obvious, generaly it's from less than one meter to several tens meters, the ore body formed in the dolines.In this condition, the ore body is little, its length is only several hundred meters and the wide is about 100-300m.3. Sometimes, the swamp developed during the time of bauxite formed, hence, there arc the bands of a carbonolitc and poor coal in the bauxites.
In the north of Guizhou the geological time of bauxites are early Permian, The some of them . (in the south of Zwenyi, Xifen and Kayang) are the type of accumulation in situ of crust of weathering their basements are clolomilite of Loshang 9 an group (∈2-3) .Others (in the Zwenyi, Ongan and Zhenan, Daoahen) are the type of head of crust of weathering, their bed rocks are shale, silt with limestone of Tongxiu formatis (O3) and Hanjiadion formation (S2) .There are phenonmena of transition between ore deposits and bed rocks. The metterils of the bauxites origin the weathering of rocks under it.The thickness of disintegration reduce gradutly from south to north.Its 700-1OOOm in the south of Zwenyi, Xifen and Kayanf, 400-500m in the Zwenyi and Ongan, more than 200m in the Zhenan and Daozhen. In the study area, the weathering and disintegrats were from Caledonian to thfe middle of Idercynian.During this time, the crust elerats slomly, up to the early of Permian, the sea mater inter intrusted the study area.In Interral time of weatherding and disintegration is about 1-1.22 hundred M.Y., the time of formed latcrite is about 0.48 hundred M.Y. In this area, the characteristic of the bauxites are follows: 1. There are no parallel bcding, structures, textures formed in the water, no Zooliths and its fragments.Thcse imply the bauxites formed-under the atmosphere conditions.2.If bed rocks are shale, silt and other clastic rocks, so have phenomena of transition, i.e., the stratc which have beding gradualy change to the strata which have no beding from lower to upper. The phenomena of head in situ is quite'clear. If the bed rocks is carbonate, the change of the thinkness of ore body is obvious, generaly it's from less than one meter to several tens meters, the ore body formed in the dolines.In this condition, the ore body is little, its length is only several hundred meters and the wide is about 100-300m.3. Sometimes, the swamp developed during the time of bauxite formed, hence, there arc the bands of a carbonolitc and poor coal in the bauxites.
1989, 7(4): 77-84.
Abstract:
48 data sets on the major chemical compositions (Mn and Fe concentrations) and growth rates of manganese nodules from different sedimentary environments of the oceans have been collected and their fluxes of manganese and iron have been calculated. It has been shown that although the chemical compositions and growth rates of manganese nodules from different areas of the oceans are largely different ( Mn: 11.3-44.9% ； Fe: 0.724-20.5% ； growth rates； 0.8O-2OOmm/106yr) , there are small differences in Fe fluxes (10-102mg Fe/cm2 ? 106yr at most) but large one in Mn fluxes (in range of 10 to 104mg Mn/cm2 ? 106yr) ， reflecting that the diagenetic reactivity of manganese is much stronger than that of iron in marine environments. It has been demonstrated by statistical analyses the (I) the concentrations of manganese and iron of individual nodules are correlative positively for the nodules with the Mn /Fe ratios of ?1 but negatively for those with high Mn /Fe ratios becauce of different contribution of diagenetic manganese; (2) The relationships of Mn fluxes to Fe fluxes or Mn /Fe ratios of the manganese nodules are dependent on classification of sedimentary environments, but the changes of Mn fluxes and Mn /Fe ratios caused only by diagenetic processes are linearly correlative, independent on the classification of sedimentary environments. The following equation, derived from the correlation of Mn fluxes to Mn /Fe ratios of manganese modules, can be used to predict the growth rates from the Mn concentrations and Ma/Fe ratios of the nodules and reveal the importance of sedimentary environments to the chemical composition and growth rate of manganese nodules: S(mm/106yr) =[52.0(Mn/Fe-0.6O)125+ 10]/[Mn]
48 data sets on the major chemical compositions (Mn and Fe concentrations) and growth rates of manganese nodules from different sedimentary environments of the oceans have been collected and their fluxes of manganese and iron have been calculated. It has been shown that although the chemical compositions and growth rates of manganese nodules from different areas of the oceans are largely different ( Mn: 11.3-44.9% ； Fe: 0.724-20.5% ； growth rates； 0.8O-2OOmm/106yr) , there are small differences in Fe fluxes (10-102mg Fe/cm2 ? 106yr at most) but large one in Mn fluxes (in range of 10 to 104mg Mn/cm2 ? 106yr) ， reflecting that the diagenetic reactivity of manganese is much stronger than that of iron in marine environments. It has been demonstrated by statistical analyses the (I) the concentrations of manganese and iron of individual nodules are correlative positively for the nodules with the Mn /Fe ratios of ?1 but negatively for those with high Mn /Fe ratios becauce of different contribution of diagenetic manganese; (2) The relationships of Mn fluxes to Fe fluxes or Mn /Fe ratios of the manganese nodules are dependent on classification of sedimentary environments, but the changes of Mn fluxes and Mn /Fe ratios caused only by diagenetic processes are linearly correlative, independent on the classification of sedimentary environments. The following equation, derived from the correlation of Mn fluxes to Mn /Fe ratios of manganese modules, can be used to predict the growth rates from the Mn concentrations and Ma/Fe ratios of the nodules and reveal the importance of sedimentary environments to the chemical composition and growth rate of manganese nodules: S(mm/106yr) =[52.0(Mn/Fe-0.6O)125+ 10]/[Mn]
1989, 7(4): 97-104.
Abstract:
North China Platform is located, between the two latitude structural belts of Tianshan-Yinshan mountains and Kunlun-Qingling mountains with the total area of about one million square kilometres.The platform is a large polycyclic Cratonic coal-bearing basin which gradually evolved and formed on the base of stable crust during Late Paleozoic. The thickness of the sedimentary rocks deposited from the Middle and the Late Proterzoic to Ccnozoic in Narth China Platform is over ten thousnad metres.It is an important region for oil and gas exploration in the East part of China. The platform base was composed of Archaeozoic and Late Proterozoic. The Early Paleozoic sediments were carbonate rocks of shallow- sea platform facies.The Caledonian Movement made the platform uplift as a land in the Middle Ordovician and Late Ordovician and Early Carboniferous Systems were missing. The sediments from Late Carboniferous to Late Permian were a set of fluvial-lake - delta-shore sedimentary system of clastic rocks intercalated with carbonate rocks and coal beds .The total thickness is 320-1666m. During the Early period of Late Carboniferous the transgression ( the Jingyuan formation) of North China Platform came from the west of Qilian Sea, the sediments were only distributed in local areas if west margin of the platform, which could be contrasted with Namuyian of Europe in age, during the middle period of Late Carboniferous, the transgression (the Bengxi formation) was from west Qilian Sea and east ancient Yangzi, Sea， the paleogeographic units were dominated by sea gulf, lake front platform, tidle flat and coastal swamp, the age of them could be contrasted with Westphalina of Europe, during the Late Carboniferous (the Taiyuan formation) the transgression increased, the north part of the platform was dominated by delta sediments, the central and south parts of the platform' were dominated by coastal sediments, who's age could be contrasted to Stephanian of Europe.Dur-ing the early Permian (the Sanxi formation) ， the sea water began to regress towards east and west, the central part of the platform was wholly occupied by delta sediments.The three typics of peat bogs were almost distributed over the shole area, the age of which could be contrastrasted to European Autunian； during the late period of the Early Permian ( the Xiashinezi Formation) ， coastal sediments was ended, the delta deposits were only limited in the southern area of 36° northern latitude and the east part of 111° eastern longitude.Inland fresh water lake were formed in the west part of this area.The north and central parts of the platform were fluvial sedimentary areas, the age could be contrasted with Saxonian of Europe. The sedimentary envioronment and paleogeographic unit distribution in the late period of Early Permian were almost the same as compared to that of the lower Shihezi period, its age could be contrasted with early Zechstein of Europe; during the late period of Early Permian ( the Shiqianfeng Formation) ， the sedimentary facies was dominated by continental sedments, the delta sedments were basically vanished.The south of the platform was dominantly shallow-water lacustrine deposits, and the north and central parts were occupied by the fluvial and small type of lacustrine deposits: the age of them could be contrasted with late Zechstein of Europe. As stated above, the sediments from Late Paleozoic era in North China Platform were a set of marine-terrestrial transition facies. With the evolution of geologic history and the alteration of paleogeographic environment, the swamp deposits from older to new changed from north to south.
North China Platform is located, between the two latitude structural belts of Tianshan-Yinshan mountains and Kunlun-Qingling mountains with the total area of about one million square kilometres.The platform is a large polycyclic Cratonic coal-bearing basin which gradually evolved and formed on the base of stable crust during Late Paleozoic. The thickness of the sedimentary rocks deposited from the Middle and the Late Proterzoic to Ccnozoic in Narth China Platform is over ten thousnad metres.It is an important region for oil and gas exploration in the East part of China. The platform base was composed of Archaeozoic and Late Proterozoic. The Early Paleozoic sediments were carbonate rocks of shallow- sea platform facies.The Caledonian Movement made the platform uplift as a land in the Middle Ordovician and Late Ordovician and Early Carboniferous Systems were missing. The sediments from Late Carboniferous to Late Permian were a set of fluvial-lake - delta-shore sedimentary system of clastic rocks intercalated with carbonate rocks and coal beds .The total thickness is 320-1666m. During the Early period of Late Carboniferous the transgression ( the Jingyuan formation) of North China Platform came from the west of Qilian Sea, the sediments were only distributed in local areas if west margin of the platform, which could be contrasted with Namuyian of Europe in age, during the middle period of Late Carboniferous, the transgression (the Bengxi formation) was from west Qilian Sea and east ancient Yangzi, Sea， the paleogeographic units were dominated by sea gulf, lake front platform, tidle flat and coastal swamp, the age of them could be contrasted with Westphalina of Europe, during the Late Carboniferous (the Taiyuan formation) the transgression increased, the north part of the platform was dominated by delta sediments, the central and south parts of the platform' were dominated by coastal sediments, who's age could be contrasted to Stephanian of Europe.Dur-ing the early Permian (the Sanxi formation) ， the sea water began to regress towards east and west, the central part of the platform was wholly occupied by delta sediments.The three typics of peat bogs were almost distributed over the shole area, the age of which could be contrastrasted to European Autunian； during the late period of the Early Permian ( the Xiashinezi Formation) ， coastal sediments was ended, the delta deposits were only limited in the southern area of 36° northern latitude and the east part of 111° eastern longitude.Inland fresh water lake were formed in the west part of this area.The north and central parts of the platform were fluvial sedimentary areas, the age could be contrasted with Saxonian of Europe. The sedimentary envioronment and paleogeographic unit distribution in the late period of Early Permian were almost the same as compared to that of the lower Shihezi period, its age could be contrasted with early Zechstein of Europe; during the late period of Early Permian ( the Shiqianfeng Formation) ， the sedimentary facies was dominated by continental sedments, the delta sedments were basically vanished.The south of the platform was dominantly shallow-water lacustrine deposits, and the north and central parts were occupied by the fluvial and small type of lacustrine deposits: the age of them could be contrasted with late Zechstein of Europe. As stated above, the sediments from Late Paleozoic era in North China Platform were a set of marine-terrestrial transition facies. With the evolution of geologic history and the alteration of paleogeographic environment, the swamp deposits from older to new changed from north to south.
1989, 7(4): 113-119.
Abstract:
This article gives an account of an experiment which was carried out according to a theory of Sedimentary Phosphate Method (SPM) advanced by Nelson ( 1967) ， a theory which was closely related to the ratio of phosphate fractions in argillaceous sediments and to the water salinity. While applying Jackson" s (1957) system of phosphate fractionation determined in soil, the writers made some necessary improvements and simplification. Qualitative and quantitative appraisals of salinity and studies of sedimentary fades have been done on the modern deposits in regions of the South China Sea, the Yellow Sea, the Poyang Lake and the Hongze Lake as well as the deposits in different regions and in different periods ranging from the Quaternary of Tai Lake to the Early Tertiary of Tarimu Basin in Xinjiang and the Dongpu Depression in Henan Province. Experimental results revealed that the paleosalinity of the first member of the Early Tertiary Shahejie Formation at the Qongpu Depression in Henan and the Early Tertiary Tarimu Basin in Xinjiang was most similar to the salinity of the modem marine deposits, differing notably, however, from that of the freshwater of the Poyang Lake and Hongze Lake. This conclusion tallies with what has been synthetically analysed with respect to paleontology and the rock-forming depositional environments, thus testifying to the fact that the sedimentary phosphate method (SPM) as an indicator of paleosalinity may be regarded as something to be relied or depended upon. In this paper are also discussed the limitations of the method mentioned above as well as the points for attention while it is in use.
This article gives an account of an experiment which was carried out according to a theory of Sedimentary Phosphate Method (SPM) advanced by Nelson ( 1967) ， a theory which was closely related to the ratio of phosphate fractions in argillaceous sediments and to the water salinity. While applying Jackson" s (1957) system of phosphate fractionation determined in soil, the writers made some necessary improvements and simplification. Qualitative and quantitative appraisals of salinity and studies of sedimentary fades have been done on the modern deposits in regions of the South China Sea, the Yellow Sea, the Poyang Lake and the Hongze Lake as well as the deposits in different regions and in different periods ranging from the Quaternary of Tai Lake to the Early Tertiary of Tarimu Basin in Xinjiang and the Dongpu Depression in Henan Province. Experimental results revealed that the paleosalinity of the first member of the Early Tertiary Shahejie Formation at the Qongpu Depression in Henan and the Early Tertiary Tarimu Basin in Xinjiang was most similar to the salinity of the modem marine deposits, differing notably, however, from that of the freshwater of the Poyang Lake and Hongze Lake. This conclusion tallies with what has been synthetically analysed with respect to paleontology and the rock-forming depositional environments, thus testifying to the fact that the sedimentary phosphate method (SPM) as an indicator of paleosalinity may be regarded as something to be relied or depended upon. In this paper are also discussed the limitations of the method mentioned above as well as the points for attention while it is in use.
1989, 7(4): 133-140.
Abstract:
Diterpenoid biomarkers were evidently detected by GC and GC/MS analysis in the saturated hydrocarbon fractions of arboniferous and Permian humic coals in five coal mines in the western and Southern North China. Based on the characteristics of mass spectra, kovats indices as well as the comparison with literature ， their major conipcTnents were determined as five tetracyclic diterpanes with kaurane-typc skeletons, i.e., ent-beyerane, 16α(H) -and 16β(H) -phyllocladanes, 16α(H) -and 16β(H) -Kauraaes as well as atricyclic isopimarane, The discovery of a complete series of tetracyclic diterpanes in the Carboniferous and Permian coals in North China probably is the first case in the northern hemisphere. The differences of diterpenoid inner composition of humic coals trom different periods and positions in North China may reflect the variation of evolution and distribution of the palaeobotanic assemblages. The stereochemical configurations of phyllocladanes and kauranes could provide some information on the itiaturity of organic matter.
Diterpenoid biomarkers were evidently detected by GC and GC/MS analysis in the saturated hydrocarbon fractions of arboniferous and Permian humic coals in five coal mines in the western and Southern North China. Based on the characteristics of mass spectra, kovats indices as well as the comparison with literature ， their major conipcTnents were determined as five tetracyclic diterpanes with kaurane-typc skeletons, i.e., ent-beyerane, 16α(H) -and 16β(H) -phyllocladanes, 16α(H) -and 16β(H) -Kauraaes as well as atricyclic isopimarane, The discovery of a complete series of tetracyclic diterpanes in the Carboniferous and Permian coals in North China probably is the first case in the northern hemisphere. The differences of diterpenoid inner composition of humic coals trom different periods and positions in North China may reflect the variation of evolution and distribution of the palaeobotanic assemblages. The stereochemical configurations of phyllocladanes and kauranes could provide some information on the itiaturity of organic matter.
1989, 7(4): 149-156.
Abstract:
Occurring at the bottom of the He-No.2 member of the Hetaoyuan formation, the Anpeng nahcalite-bearing series is made up of rocks of four lithotypes.The first type is a fine to silty rock dominated by feldspar, with cements of aphanitic dolomite, and showing such sedimentary structures as current bedding, cross bedding and ripple mark.Next to the first, oil shale in fact represents a kind of organic rich microcrystalline dolomite propably compared with the oil shale formation of the Green River trona deposit, USA, consisting of aphanitic dolomite and laminated organic materials.The third type is provided by dolomite with a great amounts of the minerals of zeolite race and aggregate of shortite.Texturally, it locally has the form of intraclasl and, structurally, harizontal bedding, current bedding, drying cracks and washing marks only found in the contact with the overlying fine to silty rock. The finaltype is composed of principal bicarbonate and subnate wegscheiderite which scatter in the microcrystalline dolomite but highly concentrate to thiness of 15cm in Ihe core. The Anpeng nahcalite-bearing series is abundant in sedimentary structurces including ripple marks, washing prints, current bedding and drying cracks. The nahcalite-bearing silt in the Bi-No.69 barehole has individul ripple marks measured at wave lenth of 1.7cm, wave height of 0.28cm, wave trace index of 6.1 and symmetric index of 1.23.Taking the form of doubl-peak, some typical ripple marks are attributed to the reworking of the previous wave-formed ones.The attribution of the ripple marks reveals that the surfaces of the silt beds during deposition were direetly against the front of wave, a circumstance characteristic of fairly shallow basins.The then depth was less than 1.53m according to the auther ' s calculation using B,Diem ' s formula which is based on Airy wave theory and applicable to the estimation of paleodepth and some other paleowave parameters by wave-formed ripple mark.This further supports the shallowness of the basin where Ihe silt deposited. Washing structures develops a great deal at the uppermost part of the dolomhe whose lamellae seems to be cut cross by the overlying silt which is set down in those washing channels.Like the washing structures, current bedding is seen always in the dolomhe and sometimes in the whole nahcalite-bearing series, belonging to a small-sized bedding relative to running water. All the sedimentary structures appear so frequently the dolomite that a more strongly hydrodynamic regime is also believed to exist when the dolomite must be subjected to running water and wave action during deposition. Besides the above structural features, drying cracks are very of the found at intervals of teens to tens cm in the dolomite.They are in the form of irregular "V" or "U" and infilled with argillaceous and sandy miterials analogous IithoIogeally to those from the overlying silt.Its general but interval development in the dolomite allows that it emerged many times from the waters during formation and became carbonate mud flat.lt is from this almost wholly dried mud flat that what is now called as metasyngenetic dolomite generated by evaporative pumping. Some other evidences for the shallow deposition of the dolomite are given by its carrying a number of elliptical doloraatic gravels and stratified dolomatic cuttings. In a word, many aspects of sedimentary structures and their assemblages of the dolomite point to a shallow, even shallower and shallower to thoroughly dried, basin where the nahcalite-bearing series deposited. On the basis of paleobotanical and paleopolynological analyses combined with studies of sedimentary rhythms and structures, the period when the He-No.2 member took place is char acteristic of semi-arid to arid climate highly favorable for the evaporation of the basin. Lithological types, depositional rhythms, sedimentary structures and fades zonation, all exhibit that the Anpeng area was not deep at least during the deposition of the nahcalite-bearing series or the lower part of the member but shallow, thus leading to intersive evaporation. Such a sedimentary environment caused sedimentary structures, depositional rhythms, fades zonation etc. to become, ingeneral, good analogs to those of the Green River trona deposit which may be explained by so-called playas model. This model suggests facies distribution pattern from the margin of the basin to the centre, i.e., along the margin lime-cemented sandstone and conglomerate, in the middle cxtersively exposed, mainly doloraatic, carbonate mud flat, and at the centre bicarbonate owing to extreme shallowness and sometimes even dryup.
Occurring at the bottom of the He-No.2 member of the Hetaoyuan formation, the Anpeng nahcalite-bearing series is made up of rocks of four lithotypes.The first type is a fine to silty rock dominated by feldspar, with cements of aphanitic dolomite, and showing such sedimentary structures as current bedding, cross bedding and ripple mark.Next to the first, oil shale in fact represents a kind of organic rich microcrystalline dolomite propably compared with the oil shale formation of the Green River trona deposit, USA, consisting of aphanitic dolomite and laminated organic materials.The third type is provided by dolomite with a great amounts of the minerals of zeolite race and aggregate of shortite.Texturally, it locally has the form of intraclasl and, structurally, harizontal bedding, current bedding, drying cracks and washing marks only found in the contact with the overlying fine to silty rock. The finaltype is composed of principal bicarbonate and subnate wegscheiderite which scatter in the microcrystalline dolomite but highly concentrate to thiness of 15cm in Ihe core. The Anpeng nahcalite-bearing series is abundant in sedimentary structurces including ripple marks, washing prints, current bedding and drying cracks. The nahcalite-bearing silt in the Bi-No.69 barehole has individul ripple marks measured at wave lenth of 1.7cm, wave height of 0.28cm, wave trace index of 6.1 and symmetric index of 1.23.Taking the form of doubl-peak, some typical ripple marks are attributed to the reworking of the previous wave-formed ones.The attribution of the ripple marks reveals that the surfaces of the silt beds during deposition were direetly against the front of wave, a circumstance characteristic of fairly shallow basins.The then depth was less than 1.53m according to the auther ' s calculation using B,Diem ' s formula which is based on Airy wave theory and applicable to the estimation of paleodepth and some other paleowave parameters by wave-formed ripple mark.This further supports the shallowness of the basin where Ihe silt deposited. Washing structures develops a great deal at the uppermost part of the dolomhe whose lamellae seems to be cut cross by the overlying silt which is set down in those washing channels.Like the washing structures, current bedding is seen always in the dolomhe and sometimes in the whole nahcalite-bearing series, belonging to a small-sized bedding relative to running water. All the sedimentary structures appear so frequently the dolomite that a more strongly hydrodynamic regime is also believed to exist when the dolomite must be subjected to running water and wave action during deposition. Besides the above structural features, drying cracks are very of the found at intervals of teens to tens cm in the dolomite.They are in the form of irregular "V" or "U" and infilled with argillaceous and sandy miterials analogous IithoIogeally to those from the overlying silt.Its general but interval development in the dolomite allows that it emerged many times from the waters during formation and became carbonate mud flat.lt is from this almost wholly dried mud flat that what is now called as metasyngenetic dolomite generated by evaporative pumping. Some other evidences for the shallow deposition of the dolomite are given by its carrying a number of elliptical doloraatic gravels and stratified dolomatic cuttings. In a word, many aspects of sedimentary structures and their assemblages of the dolomite point to a shallow, even shallower and shallower to thoroughly dried, basin where the nahcalite-bearing series deposited. On the basis of paleobotanical and paleopolynological analyses combined with studies of sedimentary rhythms and structures, the period when the He-No.2 member took place is char acteristic of semi-arid to arid climate highly favorable for the evaporation of the basin. Lithological types, depositional rhythms, sedimentary structures and fades zonation, all exhibit that the Anpeng area was not deep at least during the deposition of the nahcalite-bearing series or the lower part of the member but shallow, thus leading to intersive evaporation. Such a sedimentary environment caused sedimentary structures, depositional rhythms, fades zonation etc. to become, ingeneral, good analogs to those of the Green River trona deposit which may be explained by so-called playas model. This model suggests facies distribution pattern from the margin of the basin to the centre, i.e., along the margin lime-cemented sandstone and conglomerate, in the middle cxtersively exposed, mainly doloraatic, carbonate mud flat, and at the centre bicarbonate owing to extreme shallowness and sometimes even dryup.
