1991 Vol. 9, No. 4
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Display Method:
1991, 9(4): 1-11.
Abstract:
Large lacustrine deltas are mainly formed in the shore area of fresh or low salinity lakes. They are usually interpreted as the type of Mississippi river-dominated deltas because of low wave energy and lacking of tidal effect. The development of a complete progradational sequence is used as an important criterion for the identification of such deltas in subsurface geological study, and the river mouth bars are considered as an essential genetic facies which marks the site of major accumulation of sand deposits and represents a favourable fades zone for hydroncarbon accumulation. Based on observation and analysis of modern and ancient lacustrine deltaic deposits, the authors suggest that the marine Mississippi delta can not be used as a universal model for lacustrine deltas. The majority of lacustrine deltas in the subaerial basins bearing oil and gas of China are formed in freshwater lakes. The bed load is translated into the lake far off the river mouth instead of constructing conspicuous river-mouth bars, because the density of river water ladden with sediments is usually greater than that of lake water and river can maintain a high speed after entering the lake. Even though any thin river-mouth bars are ever formed,they are likely to be eroded by latter river action which sometimes cuts deep into the basement of the lake. The skeletal sand bodies of lacustrine deltas are therefore composed mainly of river channel or distributary channel sands. The lacustrine deltas in the Oidos basm and other oil-bearing basins of China are subdivided into two basic types on the basis of their stratigraphic character, namely shallow-water platform delta with an incomplete progradational sequence and deep-water basin delta with a fairly complete and thick progradational sequence. The former is formed in the shallow shore area with a stable bassement. It progrades lakeward quickly and has a wide distribution with banded channel sand bodies. The latter is the product of delta prograding onto the deep basin filled with thick argillaceous deposits, and its extent of distribution is often limited due to destruction by slumping, occurring chiefly in podiform river-channel sand bodies thickened as the result of subsidence. The deltaic system in large lake basins passes in space from the shallow-water into the deep-water type and in time from the deep-water into the shallow-water type as the basin becomes increasingly filled.
Large lacustrine deltas are mainly formed in the shore area of fresh or low salinity lakes. They are usually interpreted as the type of Mississippi river-dominated deltas because of low wave energy and lacking of tidal effect. The development of a complete progradational sequence is used as an important criterion for the identification of such deltas in subsurface geological study, and the river mouth bars are considered as an essential genetic facies which marks the site of major accumulation of sand deposits and represents a favourable fades zone for hydroncarbon accumulation. Based on observation and analysis of modern and ancient lacustrine deltaic deposits, the authors suggest that the marine Mississippi delta can not be used as a universal model for lacustrine deltas. The majority of lacustrine deltas in the subaerial basins bearing oil and gas of China are formed in freshwater lakes. The bed load is translated into the lake far off the river mouth instead of constructing conspicuous river-mouth bars, because the density of river water ladden with sediments is usually greater than that of lake water and river can maintain a high speed after entering the lake. Even though any thin river-mouth bars are ever formed,they are likely to be eroded by latter river action which sometimes cuts deep into the basement of the lake. The skeletal sand bodies of lacustrine deltas are therefore composed mainly of river channel or distributary channel sands. The lacustrine deltas in the Oidos basm and other oil-bearing basins of China are subdivided into two basic types on the basis of their stratigraphic character, namely shallow-water platform delta with an incomplete progradational sequence and deep-water basin delta with a fairly complete and thick progradational sequence. The former is formed in the shallow shore area with a stable bassement. It progrades lakeward quickly and has a wide distribution with banded channel sand bodies. The latter is the product of delta prograding onto the deep basin filled with thick argillaceous deposits, and its extent of distribution is often limited due to destruction by slumping, occurring chiefly in podiform river-channel sand bodies thickened as the result of subsidence. The deltaic system in large lake basins passes in space from the shallow-water into the deep-water type and in time from the deep-water into the shallow-water type as the basin becomes increasingly filled.
1991, 9(4): 20-26.
Abstract:
Roofrock is the prerequisite for the accumulation of light hydrocarbon, and displacement pressure is one of the key parameters in roofrock evaluation. In the past, because of the time penetrating through clay rock was neglected, the calculated-pressure penetrating through clay rock was too large to accord with the true displacement pressure of rock. This paper deals with the relationship between pressure and time penetralting through clay rock. It shows that time penetrating through clay rock relates to that of pressure functionly. The method of getting rock displacement pressure is also studied mainly through experiments on clay rock and it is proved that the method is effective and practical. According to experimental results and practical data, the criterion for roofrock evaluation of natural gas is put forward. The evaluation table may give accordance to evaluate the prospect of a region.
Roofrock is the prerequisite for the accumulation of light hydrocarbon, and displacement pressure is one of the key parameters in roofrock evaluation. In the past, because of the time penetrating through clay rock was neglected, the calculated-pressure penetrating through clay rock was too large to accord with the true displacement pressure of rock. This paper deals with the relationship between pressure and time penetralting through clay rock. It shows that time penetrating through clay rock relates to that of pressure functionly. The method of getting rock displacement pressure is also studied mainly through experiments on clay rock and it is proved that the method is effective and practical. According to experimental results and practical data, the criterion for roofrock evaluation of natural gas is put forward. The evaluation table may give accordance to evaluate the prospect of a region.
1991, 9(4): 34-42.
Abstract:
Songliao Basin formed by rifting in craton interior during the Yanshan Movement of Late Jurassic. The deep stratigraphy of Songliao Basin includes the Upper Jurassic (J2-3) and the Lower Cretaceous formations (K1d K1q1-2). The succession consisting mainly of sandstone, shale and coal-bearing sequence and partially volcanics, volcaniclastic rocks were established during the rifting and the early depression stage. The clastic sequence displays terrestrial alluvial fan, fan delta, fluvial floodplane and lacustrine sedimentary facies. The sandstone reservoirs are mineralogically characterized by immature feldspathic litharenite and lithic arkose and have been altered by a series of diagenetic alteration. The secondary dissolution pores are frequently found as the dominant type of porosity including framework dissolution porosity, intergranular dissolution enhanced porosity and authigenetic laumontite dissolution porosity. This paper describes the dissolution mechanism and its control factors. The effect of organic acids on dissolution of aluminosilicate is closely taken into account since many information of organic-inorganic interaction and sandstone porosity enhancement have been demonstrated in recent years. 1. The generation mechanism of framework grain dissolution porosity and intergranular dissolution enhanced porosity. Two types of mechanism are suggested based on the distribution and association of these dissolution pores. One is related to the telogenetic percolating meteoric water in correspondence with the sedimentary hiatus during the end of K,d stage. As the result, porosity are largely by combinning the intergranular dissolution enhanced porosity and detrital grain dissolution porosity. The generation mechanism of framework grain dissolution porosity could be basically contributed to the maturation of type Ⅲ kerogen in the Jurassic coal-bearing sequence. Carbonic acid and short-chain aliphatic acid effectively provides H+ and Al-complexing agent to the pore solution. Thus this type of dissolution is obviously influenced by the organic matter content in the shale, type of kerogen and the shale to sand ratio. 2. Dissolution mechanism of authigenetic laumontite. Unstable laumontite could be easily dissolved under the condition of lower pH value, high maturation of organic material and the thermal degration of hydrocarbon during the progressive burial of sediments. It could be concluded that the generation of the secondary pores closely related to sedimentary hiatus(or unconformity) and maturation of organic matter. To understand the generation mechanism and control factors of dissolution porosity would allow us to make a regional evaluation of reservoirs.
Songliao Basin formed by rifting in craton interior during the Yanshan Movement of Late Jurassic. The deep stratigraphy of Songliao Basin includes the Upper Jurassic (J2-3) and the Lower Cretaceous formations (K1d K1q1-2). The succession consisting mainly of sandstone, shale and coal-bearing sequence and partially volcanics, volcaniclastic rocks were established during the rifting and the early depression stage. The clastic sequence displays terrestrial alluvial fan, fan delta, fluvial floodplane and lacustrine sedimentary facies. The sandstone reservoirs are mineralogically characterized by immature feldspathic litharenite and lithic arkose and have been altered by a series of diagenetic alteration. The secondary dissolution pores are frequently found as the dominant type of porosity including framework dissolution porosity, intergranular dissolution enhanced porosity and authigenetic laumontite dissolution porosity. This paper describes the dissolution mechanism and its control factors. The effect of organic acids on dissolution of aluminosilicate is closely taken into account since many information of organic-inorganic interaction and sandstone porosity enhancement have been demonstrated in recent years. 1. The generation mechanism of framework grain dissolution porosity and intergranular dissolution enhanced porosity. Two types of mechanism are suggested based on the distribution and association of these dissolution pores. One is related to the telogenetic percolating meteoric water in correspondence with the sedimentary hiatus during the end of K,d stage. As the result, porosity are largely by combinning the intergranular dissolution enhanced porosity and detrital grain dissolution porosity. The generation mechanism of framework grain dissolution porosity could be basically contributed to the maturation of type Ⅲ kerogen in the Jurassic coal-bearing sequence. Carbonic acid and short-chain aliphatic acid effectively provides H+ and Al-complexing agent to the pore solution. Thus this type of dissolution is obviously influenced by the organic matter content in the shale, type of kerogen and the shale to sand ratio. 2. Dissolution mechanism of authigenetic laumontite. Unstable laumontite could be easily dissolved under the condition of lower pH value, high maturation of organic material and the thermal degration of hydrocarbon during the progressive burial of sediments. It could be concluded that the generation of the secondary pores closely related to sedimentary hiatus(or unconformity) and maturation of organic matter. To understand the generation mechanism and control factors of dissolution porosity would allow us to make a regional evaluation of reservoirs.
1991, 9(4): 49-58.
Abstract:
In the present paper, the author's discussion focus on the following problems of the surface sediments of the Great Wall Bay and its coast in Antarctica: grain size, minerals, bulk elements, trace elements, REE. environmental factors, organic component, and the feature, zonation and grouping of microfossils. It is pointed out that the sediments of this region, have glacial梞arine action feature and obvious regional differences in grain composition, grain-size distribution, grain-size parameters as well as in grain size curves. The lithologic composition of gravels, the mineral composition of sediments and the content of bulk elements consist with those of basaltic volcanic and subvolcanic rocks of the Fildes Peninsula. The organic constituents in the sediments come mainly from terrestrial higher plant and marine organisms. Based on the grain-size distribution, mineral composition, geochemical indicators, and contents of microfossils in sediments, the study area is divided into three different sedimentary environments:(a)The littoral area of the Great Wall Bay is an erosion-oxidation environment with coarse and bad sorting sediments, lacks of microfossils. The mineral assemblage is simple, and pyrite which indicates reducing environment has been wholery oxidized. The geochemical indicators are characterized by high Fe--- . low Fe++. Oc . N. P, and lack of biosilica. (b)In the area of the Great Wall Bay and South Ardley Bay. sediments are fine to median sorted and contain a lot of diatoms but little foraminifera. Its mineral assemblage is complex, and the content of pyrite is higher. The geochemical indicators are characterized by high Si. Fe++. Oc , N, P. biosilica and low Fe+++, Mg and Ca. showing this area as being a low-energy reduction sedimentary environment. (c)The mouthes of the Great Wall Bay and South Ardley Bay have finer and median sorting sediments and more calcareous-siliceous microfossils. Mineral assemblage where is more complex with little or no pyrite. The geochemical indicators are characterized by high Fe+++and low Fe++. Oc , N. P and biosilica, showing this area as being a weak oxidation environment.
In the present paper, the author's discussion focus on the following problems of the surface sediments of the Great Wall Bay and its coast in Antarctica: grain size, minerals, bulk elements, trace elements, REE. environmental factors, organic component, and the feature, zonation and grouping of microfossils. It is pointed out that the sediments of this region, have glacial梞arine action feature and obvious regional differences in grain composition, grain-size distribution, grain-size parameters as well as in grain size curves. The lithologic composition of gravels, the mineral composition of sediments and the content of bulk elements consist with those of basaltic volcanic and subvolcanic rocks of the Fildes Peninsula. The organic constituents in the sediments come mainly from terrestrial higher plant and marine organisms. Based on the grain-size distribution, mineral composition, geochemical indicators, and contents of microfossils in sediments, the study area is divided into three different sedimentary environments:(a)The littoral area of the Great Wall Bay is an erosion-oxidation environment with coarse and bad sorting sediments, lacks of microfossils. The mineral assemblage is simple, and pyrite which indicates reducing environment has been wholery oxidized. The geochemical indicators are characterized by high Fe--- . low Fe++. Oc . N. P, and lack of biosilica. (b)In the area of the Great Wall Bay and South Ardley Bay. sediments are fine to median sorted and contain a lot of diatoms but little foraminifera. Its mineral assemblage is complex, and the content of pyrite is higher. The geochemical indicators are characterized by high Si. Fe++. Oc , N, P. biosilica and low Fe+++, Mg and Ca. showing this area as being a low-energy reduction sedimentary environment. (c)The mouthes of the Great Wall Bay and South Ardley Bay have finer and median sorting sediments and more calcareous-siliceous microfossils. Mineral assemblage where is more complex with little or no pyrite. The geochemical indicators are characterized by high Fe+++and low Fe++. Oc , N. P and biosilica, showing this area as being a weak oxidation environment.
1991, 9(4): 69-77.
Abstract:
The present paper mainly studies the diagenesis and its influence on reservoir property of lithic sandstone which is little studied in China. Reservoir rock of well Lu-1 is terrigenous lithic sandstone including a lot of pyroclastic rock fragments. Porosity and permeability of reservoir reduce swiftly with the increase of burial depth, but there is an abnormal increase of porosity at the depth of 3750-4300m. There are four main pore * types of sandstone: primary intergranular pores, inner grains dissoluted pores and micropores. Diagenesis and Sedimentary facies are the two main factors affecting reservoir property of well Lu- 1, but the influence of the latter is not very obvious. The diagenetic influence on reservoir property of sandstone is signifcant and has its particularity to this kind of low mature lithic sandstone of well Lu-1. Compaction and hydration, especially hydration, are the two most important factors which let to the swiftly reduce of porosity, cementation is another important factor of making porosity and permeability worse. Cements of sandstone are calcite, quartz, authigenic clay, zeolite and a little terrigenous matter. Selective dissolution of calcite cement is the main reason which made the porosity and permeability of partial section better. The influence of calcite replacement on porosity and permeability is not valuable. The formation of seceondary dissolution pore is related to CO2 which formed by evolution of organic matter. CO2 can be formed during the whole maturation process especially in stage "A". Generally, the developing belt of secondary pore is in the early period of "A",however, calcite cement in this period hasn't any trace of dissolution in well Lu-1, on the contrary, a lot of elastics are replaced by calcite. Selective dissolution of calcite hasn't take place until late period of "A" and early period of "B". The reason is that; during early period of "A", under alkalline diagenetic environment formed by hydration, the action of CO2 is favourable to the precipitation of calcite, and made replacement developed, but in late period of "A" and early period of "B". hydration nearly disappeared and the neutralization of CO2 changed pores into weak acidity (there is a little CO2 in this period), selective dissolution of calcite cement can be taken place then the belt of secondary pore was formed.
The present paper mainly studies the diagenesis and its influence on reservoir property of lithic sandstone which is little studied in China. Reservoir rock of well Lu-1 is terrigenous lithic sandstone including a lot of pyroclastic rock fragments. Porosity and permeability of reservoir reduce swiftly with the increase of burial depth, but there is an abnormal increase of porosity at the depth of 3750-4300m. There are four main pore * types of sandstone: primary intergranular pores, inner grains dissoluted pores and micropores. Diagenesis and Sedimentary facies are the two main factors affecting reservoir property of well Lu- 1, but the influence of the latter is not very obvious. The diagenetic influence on reservoir property of sandstone is signifcant and has its particularity to this kind of low mature lithic sandstone of well Lu-1. Compaction and hydration, especially hydration, are the two most important factors which let to the swiftly reduce of porosity, cementation is another important factor of making porosity and permeability worse. Cements of sandstone are calcite, quartz, authigenic clay, zeolite and a little terrigenous matter. Selective dissolution of calcite cement is the main reason which made the porosity and permeability of partial section better. The influence of calcite replacement on porosity and permeability is not valuable. The formation of seceondary dissolution pore is related to CO2 which formed by evolution of organic matter. CO2 can be formed during the whole maturation process especially in stage "A". Generally, the developing belt of secondary pore is in the early period of "A",however, calcite cement in this period hasn't any trace of dissolution in well Lu-1, on the contrary, a lot of elastics are replaced by calcite. Selective dissolution of calcite hasn't take place until late period of "A" and early period of "B". The reason is that; during early period of "A", under alkalline diagenetic environment formed by hydration, the action of CO2 is favourable to the precipitation of calcite, and made replacement developed, but in late period of "A" and early period of "B". hydration nearly disappeared and the neutralization of CO2 changed pores into weak acidity (there is a little CO2 in this period), selective dissolution of calcite cement can be taken place then the belt of secondary pore was formed.
1991, 9(4): 87-95.
Abstract:
On the basis of physicochemical conditions of bauxite forming obtained by geologic analysis, in this paper the dissolving tests of (1) dissolution of A12O3 and SiO2 of kaoline in the solutions with different pH under oxidizing condition, (2) dissolution of A12O3, SiO2 and Fe2O3 of laterite under the above conditions, (3) dissolution of A12O3, SiO2 and Fe2O3 of laterite in CO2-H2O systems with different Eh and pH, (4)dissolu-tion of A12O3, SiO2 and Fe2O3 of laterite in the solutions of different organic acids with different concentration and (5) tentative test of removal of iron from hard clay by means of microorganisms are carried out. Elemental interdifferentiations in the forming process of bauxite and consistency of expremental research with geologic research are discussed. The results show that the interdifferentiation of Fe2O3 with A12O3 is not easy under oxidizing condition. Interdifferentiation of SiO2 with A12O3 is easier in the oxidizing and neutral to weak acid conditions. In reducing conditions, dissolution and transportation of SiO2 and Fe2O3, preservation and concentration of A12O3 are favourable when the system is neutral to weak acid. It is possible that bacteria, organisms, organic acids play important roles in the interdifferentiation of SiO2 and Fe2O3 with A12O3.
On the basis of physicochemical conditions of bauxite forming obtained by geologic analysis, in this paper the dissolving tests of (1) dissolution of A12O3 and SiO2 of kaoline in the solutions with different pH under oxidizing condition, (2) dissolution of A12O3, SiO2 and Fe2O3 of laterite under the above conditions, (3) dissolution of A12O3, SiO2 and Fe2O3 of laterite in CO2-H2O systems with different Eh and pH, (4)dissolu-tion of A12O3, SiO2 and Fe2O3 of laterite in the solutions of different organic acids with different concentration and (5) tentative test of removal of iron from hard clay by means of microorganisms are carried out. Elemental interdifferentiations in the forming process of bauxite and consistency of expremental research with geologic research are discussed. The results show that the interdifferentiation of Fe2O3 with A12O3 is not easy under oxidizing condition. Interdifferentiation of SiO2 with A12O3 is easier in the oxidizing and neutral to weak acid conditions. In reducing conditions, dissolution and transportation of SiO2 and Fe2O3, preservation and concentration of A12O3 are favourable when the system is neutral to weak acid. It is possible that bacteria, organisms, organic acids play important roles in the interdifferentiation of SiO2 and Fe2O3 with A12O3.
1991, 9(4): 105-109.
Abstract:
Based on the paleomagnetic results obtained from Upper Paleozoic Erathem along the southwestern margin of the Tarim Block, this paper paleomagnetically discusses some fundamenlal geologic problems related to the area researched. The following conclusions were drawn from this study: 1) Artashi Area rapidly drifted northwards from Devonian to Carboniferous and researched mid-latitudinal area from a low-latitudinal area resulting an increase of about 16 in paleolatitude. 2) Duwa Area essentially remained relatively stable from Carboniferous to Permian and did not experience any horizontal motion evidently. 3) The Carboniferous System in Duwa Area is younger than that in Artashi Area. 4) There existed an open sea about 800km wide lying between Artashi Area and Duwa Area during carboniferous. 5) Duwa Area started moving northwards again in Permian Period. Tiekelike Uplift Zone began bending as an arc and got strengthened continuously in subsequent tectonic movements. This study further demonstrates paleomagntically that until late Permian the Tarim Block and the North China Block were still two independent tectonic units which were separated far away from each ather.
Based on the paleomagnetic results obtained from Upper Paleozoic Erathem along the southwestern margin of the Tarim Block, this paper paleomagnetically discusses some fundamenlal geologic problems related to the area researched. The following conclusions were drawn from this study: 1) Artashi Area rapidly drifted northwards from Devonian to Carboniferous and researched mid-latitudinal area from a low-latitudinal area resulting an increase of about 16 in paleolatitude. 2) Duwa Area essentially remained relatively stable from Carboniferous to Permian and did not experience any horizontal motion evidently. 3) The Carboniferous System in Duwa Area is younger than that in Artashi Area. 4) There existed an open sea about 800km wide lying between Artashi Area and Duwa Area during carboniferous. 5) Duwa Area started moving northwards again in Permian Period. Tiekelike Uplift Zone began bending as an arc and got strengthened continuously in subsequent tectonic movements. This study further demonstrates paleomagntically that until late Permian the Tarim Block and the North China Block were still two independent tectonic units which were separated far away from each ather.
1991, 9(4): 120-127.
Abstract:
The bioturbate limestone at the upper member of Hezhou Formation of Lower Carboniferous in north-ern Chao County w'as caused by Tlralassinoides sp. which produced at the semiconsolidated, but not fullylithified discontinuity surfaces. It could be attributed to Glossifungites ichnofacies which was formed in theintertidal flat environment. The features of carbonate microfacies and chemical components of the fills in the burrow systems differfrom that of the host rock. The fotmter is finely crystaline limestone mainly with crinoidal debris and containshigher clay minerals and dolomite than that of the latter. The latter is biomicrite bearing foraminifer,fusulina, molluscan and crinoidal debris. These differences imply that they were not formed in the same timeand environment. The fills were piped in the burrow systems in the next transgression after the halt of deposi-tron. The occurrence of Glossifungites ichnofacies at the uppetirtost surface of Hezhou Formation could pro-vide a new important stratigraphic information for interpreting the lacking of Laohudong Formation be-tween Huanglong Formation of Upper Carboniferous and Hezhou Formation of Lower Carboniferous herewhich prevails in southern Chao County.
The bioturbate limestone at the upper member of Hezhou Formation of Lower Carboniferous in north-ern Chao County w'as caused by Tlralassinoides sp. which produced at the semiconsolidated, but not fullylithified discontinuity surfaces. It could be attributed to Glossifungites ichnofacies which was formed in theintertidal flat environment. The features of carbonate microfacies and chemical components of the fills in the burrow systems differfrom that of the host rock. The fotmter is finely crystaline limestone mainly with crinoidal debris and containshigher clay minerals and dolomite than that of the latter. The latter is biomicrite bearing foraminifer,fusulina, molluscan and crinoidal debris. These differences imply that they were not formed in the same timeand environment. The fills were piped in the burrow systems in the next transgression after the halt of deposi-tron. The occurrence of Glossifungites ichnofacies at the uppetirtost surface of Hezhou Formation could pro-vide a new important stratigraphic information for interpreting the lacking of Laohudong Formation be-tween Huanglong Formation of Upper Carboniferous and Hezhou Formation of Lower Carboniferous herewhich prevails in southern Chao County.
1991, 9(4): 136-142.
Abstract:
The features of bipmarker assemblage in the saturate and aromatic fractions of source rocks from Member 2 of Funing formation, Lower Tertiary, Jinhu, Subei Basin have been systematically studied, and the obvious differences in biomarker components are indicated which would clearly show the changes of sedimentary environments during their deposition. Based on n-alkane distribution and biomarker assemblage, source rocks from Member 2 of Funing Formation may be devided into two types: One is characteristic of even carbon predominance in n-alkane distribution with a very sttong phytane preference. The content ofβ-carotane preserved and formed under reducing conditions is high, gammacerane usually indicating a hypersaline environment is enriched, and dehydroxytocopherol, rellection the paleaosalinity of sedimentary basin has been identified in the aromatic fraction sf the same source rocks, all of them show that these source rocks may be reffered to a strong reduced, brackish deposit, implying a salinized period during the lake lifetime. Another is of odd carbon predominance in n-alkane distribution, its phytane preference relatively less. the abundances of β-carotane and gammacerane is much lower, and dehydroxytopcopherol is not detected. Therefore, it is characterised by normal lacustrine deposits and formed during a freshening period.
The features of bipmarker assemblage in the saturate and aromatic fractions of source rocks from Member 2 of Funing formation, Lower Tertiary, Jinhu, Subei Basin have been systematically studied, and the obvious differences in biomarker components are indicated which would clearly show the changes of sedimentary environments during their deposition. Based on n-alkane distribution and biomarker assemblage, source rocks from Member 2 of Funing Formation may be devided into two types: One is characteristic of even carbon predominance in n-alkane distribution with a very sttong phytane preference. The content ofβ-carotane preserved and formed under reducing conditions is high, gammacerane usually indicating a hypersaline environment is enriched, and dehydroxytocopherol, rellection the paleaosalinity of sedimentary basin has been identified in the aromatic fraction sf the same source rocks, all of them show that these source rocks may be reffered to a strong reduced, brackish deposit, implying a salinized period during the lake lifetime. Another is of odd carbon predominance in n-alkane distribution, its phytane preference relatively less. the abundances of β-carotane and gammacerane is much lower, and dehydroxytopcopherol is not detected. Therefore, it is characterised by normal lacustrine deposits and formed during a freshening period.
1991, 9(4): 12-19.
Abstract:
According to the stratigraphic position, depositional facies relationships and mode of formation, the late-Quaternary barrier-lagoon depositional systems along the coast of China can be classified into four types: 1 transgressive; 2 regressive; 3 stable; and 4 locally transgressive. On vertical section, the transgressive barrier-lagoon system occurs in the lower part of the sediment layers between the continental shelf and the boundary of maximum transgression; the regressive type occurs in the upper part of the Holocenc strata between the boundary of maximum post-glacier transgression and the present coastal line; the stable type occurs in the narrow zone near the maximum transgressive limit, which constitute ideal distribution model of various barrier-lagoon system. The coast of China cuts across the tectonic uplift and the subsidence belts. More than 90 percent of the total riverine sediments discharge into the subsidence belt forming broad coastal plain and thick depositional layers, which provides favorable conditions for the developing and preservation of ideal distribution model of barrier-lagoon systems. In the uplift belt, due to the poor sediment supply, stable and local transgressive types tend to be developed. The optimistic site for the development of barrier-lagoon system lies in the transitional area between the uplift belt and subsidence belt.
According to the stratigraphic position, depositional facies relationships and mode of formation, the late-Quaternary barrier-lagoon depositional systems along the coast of China can be classified into four types: 1 transgressive; 2 regressive; 3 stable; and 4 locally transgressive. On vertical section, the transgressive barrier-lagoon system occurs in the lower part of the sediment layers between the continental shelf and the boundary of maximum transgression; the regressive type occurs in the upper part of the Holocenc strata between the boundary of maximum post-glacier transgression and the present coastal line; the stable type occurs in the narrow zone near the maximum transgressive limit, which constitute ideal distribution model of various barrier-lagoon system. The coast of China cuts across the tectonic uplift and the subsidence belts. More than 90 percent of the total riverine sediments discharge into the subsidence belt forming broad coastal plain and thick depositional layers, which provides favorable conditions for the developing and preservation of ideal distribution model of barrier-lagoon systems. In the uplift belt, due to the poor sediment supply, stable and local transgressive types tend to be developed. The optimistic site for the development of barrier-lagoon system lies in the transitional area between the uplift belt and subsidence belt.
1991, 9(4): 27-33.
Abstract:
Porosity within micritized ooids may exceed 15 percent with permeabilities up to about 1 millidarcy. The most porous and permeable micritized ooids all exhibit a characteristic texture: they consist of euhedral calcite rhombs 1 to 5 microns in longest dimension. Massive Cotton Valley gas wells interpreted to produce from this type of microporosity may initially yield as much as 300,000 cubic feet of gas per day or more. Intraooid porosity may constitute a significant reservoir for gas, but not for oil. Micritized ooids from 14 samples ranging in age from Ordovician .to Jurassic exhibit a common fabric and may have been altered by a common process. Micritization of these ooids may have occurred during mineralogical stabilization from aragonite to calcite. The micritized texture of the ooids described in this paper is not a product of leaching, for this type of micritized ooid is common in strata unaffected by leaching. Micritization of ooids may be of great significance to the development of gas fields in grainy rocks which have not been dolomitized or leached. Micritized ooids may also be important in many oil reservoirs with binodal pore sizes.
Porosity within micritized ooids may exceed 15 percent with permeabilities up to about 1 millidarcy. The most porous and permeable micritized ooids all exhibit a characteristic texture: they consist of euhedral calcite rhombs 1 to 5 microns in longest dimension. Massive Cotton Valley gas wells interpreted to produce from this type of microporosity may initially yield as much as 300,000 cubic feet of gas per day or more. Intraooid porosity may constitute a significant reservoir for gas, but not for oil. Micritized ooids from 14 samples ranging in age from Ordovician .to Jurassic exhibit a common fabric and may have been altered by a common process. Micritization of these ooids may have occurred during mineralogical stabilization from aragonite to calcite. The micritized texture of the ooids described in this paper is not a product of leaching, for this type of micritized ooid is common in strata unaffected by leaching. Micritization of ooids may be of great significance to the development of gas fields in grainy rocks which have not been dolomitized or leached. Micritized ooids may also be important in many oil reservoirs with binodal pore sizes.
1991, 9(4): 43-48.
Abstract:
The fill sediments deposited on the lake margin slope during the Oligocene-Miocene, front Aerjin shan, western Chaidamu basin, were composed of the alluvial-lacustrine and fandelta-lacustrine sedimentary systems.The deposition of the two kinds of sedimentary system were controlled by the lake-level changes episodically. There are two types of sedimentary sequences. The sequence at high lake-level stand consist of fandelta- lacustrine system in which there are some important deposition microfacies such as fandeita plain ( lakeshore channel, subwater distributary channel and interchannel) , front fandelta (overflow deposits and front sheet sediments) and fandelta-front.The sequence at low lakelevel stand come from alluvial fanlacustrine system.Under the condition of basically balance between basin subsidience and sediments accumulation rate, replacement of the sedimantary systems was dependent on the lake條evel fluctuationes. Sedimentary processes of the fan delta and its fades distributary influenced by lake-level changes is different from ones of the fault depression basin margins. Relationship between alluvial fan and lacustrine at low lake-level stand is also distinguish from the normal facies model in addition to gravity flow deposits that originate from flood water channel.
The fill sediments deposited on the lake margin slope during the Oligocene-Miocene, front Aerjin shan, western Chaidamu basin, were composed of the alluvial-lacustrine and fandelta-lacustrine sedimentary systems.The deposition of the two kinds of sedimentary system were controlled by the lake-level changes episodically. There are two types of sedimentary sequences. The sequence at high lake-level stand consist of fandelta- lacustrine system in which there are some important deposition microfacies such as fandeita plain ( lakeshore channel, subwater distributary channel and interchannel) , front fandelta (overflow deposits and front sheet sediments) and fandelta-front.The sequence at low lakelevel stand come from alluvial fanlacustrine system.Under the condition of basically balance between basin subsidience and sediments accumulation rate, replacement of the sedimantary systems was dependent on the lake條evel fluctuationes. Sedimentary processes of the fan delta and its fades distributary influenced by lake-level changes is different from ones of the fault depression basin margins. Relationship between alluvial fan and lacustrine at low lake-level stand is also distinguish from the normal facies model in addition to gravity flow deposits that originate from flood water channel.
1991, 9(4): 59-68.
Abstract:
It is a hard problem to determine the plan extension of sedimentary microfacies in cases of lacking the coring wells in oil fields. This paper discussed the method of the digit judgment using. GR log data, and mapped the plan extension of the sedimentary microfacies in Wenliu area, Dongpu Depression GR has sensitive response to the petrography of clastic rock.The GR's amplitude is affected by the intermediate value of mud content, so it is available to determine the ratio of sand to mud in strata, and the composing features of GR amplitude is a symble of sedimentary rhythm on sections. The digit judgment and analysis using GR logging data involves the following steps: 1) Chose one or more core wells, analyse their sedimentary microfacies by means of petrography, sedimentary structures, grain size and so on; 2) Evaluate the judgment criterion corresponding to microfacies and establish the GR model of them; 3) Judge the types of the microfacies using GR data in no-core wells, determine and map the plan extension of sedimentary mirofacies in study area. 2) and 3) can be finished in IBM-PC XT. The plan extension of sedimentary micrlfacies of the 3+4 and 5+6 intervals in upper Sha-4 member are provided. Through the analysis of the petrography, sedimentary structure, the featuer of grainsize and the trace fossils the core of well-109, the following microfacies can be outlined: overflow, channal point bar, midfan slump turbidity, midfan shallow water turbidity and externalfan fine turbidity. The GR standard model is established and criterion values of the facies are mapped. The maps (Fig.5 and Fig.6 ) showed: 1) 3+4 intervals in upper Sha-4 member, from north to south, vary from midfan slump turbidity, midfan shallow water turbidity to externalfan fine turbidity; 2) 5+6 intervals in lower Sha-4 member are subjected to the ephemeral facies complex in which the channal . poit bar deposit distributes along the line joining well-109, well-64, well-22, and overflow deposite cover others.
It is a hard problem to determine the plan extension of sedimentary microfacies in cases of lacking the coring wells in oil fields. This paper discussed the method of the digit judgment using. GR log data, and mapped the plan extension of the sedimentary microfacies in Wenliu area, Dongpu Depression GR has sensitive response to the petrography of clastic rock.The GR's amplitude is affected by the intermediate value of mud content, so it is available to determine the ratio of sand to mud in strata, and the composing features of GR amplitude is a symble of sedimentary rhythm on sections. The digit judgment and analysis using GR logging data involves the following steps: 1) Chose one or more core wells, analyse their sedimentary microfacies by means of petrography, sedimentary structures, grain size and so on; 2) Evaluate the judgment criterion corresponding to microfacies and establish the GR model of them; 3) Judge the types of the microfacies using GR data in no-core wells, determine and map the plan extension of sedimentary mirofacies in study area. 2) and 3) can be finished in IBM-PC XT. The plan extension of sedimentary micrlfacies of the 3+4 and 5+6 intervals in upper Sha-4 member are provided. Through the analysis of the petrography, sedimentary structure, the featuer of grainsize and the trace fossils the core of well-109, the following microfacies can be outlined: overflow, channal point bar, midfan slump turbidity, midfan shallow water turbidity and externalfan fine turbidity. The GR standard model is established and criterion values of the facies are mapped. The maps (Fig.5 and Fig.6 ) showed: 1) 3+4 intervals in upper Sha-4 member, from north to south, vary from midfan slump turbidity, midfan shallow water turbidity to externalfan fine turbidity; 2) 5+6 intervals in lower Sha-4 member are subjected to the ephemeral facies complex in which the channal . poit bar deposit distributes along the line joining well-109, well-64, well-22, and overflow deposite cover others.
1991, 9(4): 78-86.
Abstract:
In endogenic deposits, Fe, Co, and Ni are closely paragenetic at the valences of two. But in the process of they will deposit or migrate separately according to different pH and Eh conditions of the water-medium. And. in a certain pH and Eh condition, the relative amount of depositiion of these three elements are quite different. Thus, the paleo-pH value and the paleo-Eh value of the water-medium during sedimentation could be indicated by Fe, Co, and Ni contents in the sediment. From eastern Yunnan Province to western Guizhou Province in southwestern China, the sedimentaary environments of the Late Permian Coal-bearing Formation change gradually from a continental environment to a marine one. Therefore, these are right sites for the study of sedimentary geochemistry of coal-bearing formation. And, coal seams formed in these different sedimentary environments are the important targets for the study of this topic. Six representative coal seams of the coal-bearing formation were sampled separately from roof down to floor. Each division sample was analyzed for Fe. Co. and Ni with an atomic absorption spectrometer. Then. 1520 ratios of 10 kinds (Fe/Co/Ni. Fe/(Co+Ni), Fe/Co, Fe / Ni, Co / Ni, InFe/ InCo / InNi, InFe / (InCo+lnNi), InFe / InCo, InFe / InNi, and InCo / InNi) were computed. The results showed that the ratio of Fe. Co, and Ni contents in a coal seam, especially the ratios after taking the natural logarithm, might serve as the paleo-pH indicator of the coal-forming swamp. Among these ratios, InFe / (InCo+lnNi) is the best. A series of studies, inferences, and calculations arrived at three empirical formulae which are recommended for calculating the paleo-pH value of the water-medium of continental facies, transitional facies, and marine facies, respectively. According to formula (1). the pH values of Minnie's Lake site and Chesser Prairie site, the two major peatforming environments in Okefenokee Swamp, Georgia. USA, were calculated, which are 4.47 and 3.68, respectively. This is basically coincident with the description that "the freshwater peat (Okefenokee Swamp) is at the pH 4" by Casagrande et al. (1977). And it is then proved from one aspect that the above mentioned empirical formulae are close to practically useful. Finally, since there is a certain relationship between Eh adn pH: Eh = E -0.059pH. such as in an open-system (Po2 = 1 atmospheric pressure) of 25@@ . the oxygen in water solution has the Eh= 1.229-0.059pH, the paleo-Eh value of the coal-forming swamp may then similarly be determined by the Fe, Co, and Ni contents in the coal seam. And the paleo-Eh value of oxygen in a coal-forming swamp could be calculated according to other formula.
In endogenic deposits, Fe, Co, and Ni are closely paragenetic at the valences of two. But in the process of they will deposit or migrate separately according to different pH and Eh conditions of the water-medium. And. in a certain pH and Eh condition, the relative amount of depositiion of these three elements are quite different. Thus, the paleo-pH value and the paleo-Eh value of the water-medium during sedimentation could be indicated by Fe, Co, and Ni contents in the sediment. From eastern Yunnan Province to western Guizhou Province in southwestern China, the sedimentaary environments of the Late Permian Coal-bearing Formation change gradually from a continental environment to a marine one. Therefore, these are right sites for the study of sedimentary geochemistry of coal-bearing formation. And, coal seams formed in these different sedimentary environments are the important targets for the study of this topic. Six representative coal seams of the coal-bearing formation were sampled separately from roof down to floor. Each division sample was analyzed for Fe. Co. and Ni with an atomic absorption spectrometer. Then. 1520 ratios of 10 kinds (Fe/Co/Ni. Fe/(Co+Ni), Fe/Co, Fe / Ni, Co / Ni, InFe/ InCo / InNi, InFe / (InCo+lnNi), InFe / InCo, InFe / InNi, and InCo / InNi) were computed. The results showed that the ratio of Fe. Co, and Ni contents in a coal seam, especially the ratios after taking the natural logarithm, might serve as the paleo-pH indicator of the coal-forming swamp. Among these ratios, InFe / (InCo+lnNi) is the best. A series of studies, inferences, and calculations arrived at three empirical formulae which are recommended for calculating the paleo-pH value of the water-medium of continental facies, transitional facies, and marine facies, respectively. According to formula (1). the pH values of Minnie's Lake site and Chesser Prairie site, the two major peatforming environments in Okefenokee Swamp, Georgia. USA, were calculated, which are 4.47 and 3.68, respectively. This is basically coincident with the description that "the freshwater peat (Okefenokee Swamp) is at the pH 4" by Casagrande et al. (1977). And it is then proved from one aspect that the above mentioned empirical formulae are close to practically useful. Finally, since there is a certain relationship between Eh adn pH: Eh = E -0.059pH. such as in an open-system (Po2 = 1 atmospheric pressure) of 25@@ . the oxygen in water solution has the Eh= 1.229-0.059pH, the paleo-Eh value of the coal-forming swamp may then similarly be determined by the Fe, Co, and Ni contents in the coal seam. And the paleo-Eh value of oxygen in a coal-forming swamp could be calculated according to other formula.
1991, 9(4): 96-104.
Abstract:
Ceshui Formation is an important coal-bearing stratum of Carboniferous in Hunan province. It mainly consists of fine quartz sandstones, quartz siltstones, mudstones, some quartz pebble conglomerates and carbonate rocks with coal beds. It can be divided into two parts, the lower contains 1-7 layers of coals, and the no coal beds in the upper . The coals No.3 and No.5 are the main mining beds and the others are local minable or unminable ones. The synthetical study of petrology, palaeontology, trace fossils, geochemistry show that this formation is deposited in the barrier bar-tidal flat-lagoon depositional systems. The subenvironments are freshening lagoon, brackish lagoon, transgressive barrier bar, regressive barrier bar, tidal channel, intertidal flat, swamps, littoral and shelf. The sedimentary environments are related closely to the coal beds. Three types of swamps exist in Ceshui Formation; The first is located in the slope of back barrier bar, the seams are thiner and discontinous, the content of sulfur ranges from 3.5% to 5%; The second is formed by lagoon fill, the coals vary greatly in thickness, from zero to more than 10 m, generally 0.5m to 3m, the content of sulfur is 1.3% to 9.7%, this type of coal beds split or want out in short distance, and their bottom is silty mudstone with large amount of siderite noddles; The last type of swamp exists in the intertidal flat with complicated structure, its variation in thickness is slight, from 1.5m to 2.5m, the content of sulfur ranges from 1% to 5.3%, generally 1% to 3%. The local coal beds often washed away by tidal channels. The thickness of coal has a close relation to the tidal channels, the thick coal beds located at the thiner channel sandstones or close to the dendritic channel sandstones.
Ceshui Formation is an important coal-bearing stratum of Carboniferous in Hunan province. It mainly consists of fine quartz sandstones, quartz siltstones, mudstones, some quartz pebble conglomerates and carbonate rocks with coal beds. It can be divided into two parts, the lower contains 1-7 layers of coals, and the no coal beds in the upper . The coals No.3 and No.5 are the main mining beds and the others are local minable or unminable ones. The synthetical study of petrology, palaeontology, trace fossils, geochemistry show that this formation is deposited in the barrier bar-tidal flat-lagoon depositional systems. The subenvironments are freshening lagoon, brackish lagoon, transgressive barrier bar, regressive barrier bar, tidal channel, intertidal flat, swamps, littoral and shelf. The sedimentary environments are related closely to the coal beds. Three types of swamps exist in Ceshui Formation; The first is located in the slope of back barrier bar, the seams are thiner and discontinous, the content of sulfur ranges from 3.5% to 5%; The second is formed by lagoon fill, the coals vary greatly in thickness, from zero to more than 10 m, generally 0.5m to 3m, the content of sulfur is 1.3% to 9.7%, this type of coal beds split or want out in short distance, and their bottom is silty mudstone with large amount of siderite noddles; The last type of swamp exists in the intertidal flat with complicated structure, its variation in thickness is slight, from 1.5m to 2.5m, the content of sulfur ranges from 1% to 5.3%, generally 1% to 3%. The local coal beds often washed away by tidal channels. The thickness of coal has a close relation to the tidal channels, the thick coal beds located at the thiner channel sandstones or close to the dendritic channel sandstones.
1991, 9(4): 110-119.
Abstract:
The data from several hundreds measured samples of Palaeozoic-Mesozoic sedimentary rocks shows that the magnetic susceptibility of samples of the dark rock systems is higher than that of the lightcolor rock systems and redbeds in Ordos Basin. For example, the dark limestones of the lower Ordovician, the coal-bearing formation of the upper Carboniferous as well as the dark-grey sandstones of the upper Triassic and the susceptibility of samples and the applying of the directions of magnetic linears in original susceptibility fabrics, the directions of the palaeocurrents and the confluences regions are showed in the Late Triassic Period when the main oil source beds were deposited. By the parameter (Km) of patternal changes of the anisotropic susceptibility ellipsoids, the relatively strength of the tectonic stress (horizontal tectonic press) is discussed in basinal scale. According to the theory of the influence of tectonic stress on the forming of oil and gas, it'suggests that the eastern Ordos has a good condition of preserving the Palaeozonic oil and gas because the region had undergone weaker tectonic stress from the Late Palaeozoic to the Late Triassic Period; while lower Jurassic is 1-2 number grade higher than that of other rock systems. Even within dark rock systems the susceptibilities of samples from the organic rich rocks is higher than those of organic poor ones, and within lightcolor rock systems the data from oil-bearing rocks is also higher than those from other rocks. These phenomena imply that there may exist some relation between the high susceptibilities and organic matter. The results of thermal demage show that most of ramanence of the rock samples is removed prior to 450℃, which indicates that the magnetic minerals in rocks might be mainly the type of Fe+2 . By measuring and analysing of the anisotropic magnetic the western Ordos might have unfavourable condition because the region had undergone stronger tectonic stress in the end of the Triassic, which made the Palaeozoic oil and gas region matured early but not easy to be preserved. Since the Jurassic Period, stronger tectonic stress led to the maturation of oil and gas source rock (Palaeozoic-Mesozoic) of eastern Ordos and made the preservative ability better.
The data from several hundreds measured samples of Palaeozoic-Mesozoic sedimentary rocks shows that the magnetic susceptibility of samples of the dark rock systems is higher than that of the lightcolor rock systems and redbeds in Ordos Basin. For example, the dark limestones of the lower Ordovician, the coal-bearing formation of the upper Carboniferous as well as the dark-grey sandstones of the upper Triassic and the susceptibility of samples and the applying of the directions of magnetic linears in original susceptibility fabrics, the directions of the palaeocurrents and the confluences regions are showed in the Late Triassic Period when the main oil source beds were deposited. By the parameter (Km) of patternal changes of the anisotropic susceptibility ellipsoids, the relatively strength of the tectonic stress (horizontal tectonic press) is discussed in basinal scale. According to the theory of the influence of tectonic stress on the forming of oil and gas, it'suggests that the eastern Ordos has a good condition of preserving the Palaeozonic oil and gas because the region had undergone weaker tectonic stress from the Late Palaeozoic to the Late Triassic Period; while lower Jurassic is 1-2 number grade higher than that of other rock systems. Even within dark rock systems the susceptibilities of samples from the organic rich rocks is higher than those of organic poor ones, and within lightcolor rock systems the data from oil-bearing rocks is also higher than those from other rocks. These phenomena imply that there may exist some relation between the high susceptibilities and organic matter. The results of thermal demage show that most of ramanence of the rock samples is removed prior to 450℃, which indicates that the magnetic minerals in rocks might be mainly the type of Fe+2 . By measuring and analysing of the anisotropic magnetic the western Ordos might have unfavourable condition because the region had undergone stronger tectonic stress in the end of the Triassic, which made the Palaeozoic oil and gas region matured early but not easy to be preserved. Since the Jurassic Period, stronger tectonic stress led to the maturation of oil and gas source rock (Palaeozoic-Mesozoic) of eastern Ordos and made the preservative ability better.
1991, 9(4): 128-135.
Abstract:
This paper chiefly deals with the composition, occurrence and sedimentary environments of the three unusually differential ichnocoenoses that are distinguished from the trace fossils well preserved in the Upper Permian, Lower Triassic and Upper Cretaceous fluvial deposits in Emei area. The three ichnocoenoses are recognized: (1)Scoyenia-Rhizoliths ichnocoenosis which occurs in the Shawan Formation (P2), mainly consists of Scoyenia, Planolites, Muensteria, Psammichnites, Skolithos, of. Stipsellus and Rhizoliths (mostly horizontal root casts, diagonal root casts, and partly vertical root casts) and so on, associated with the flood plain deposit that was made up of grey-yellow or green fine-grain sandstones, violet-red siltstones and mudstones as well as less intercalated carbonaceous shales contained plant fossils and thin-bedded coal, it might be explained to be formed in a hot, humid, fluvial environment. (2)Trichichnus ichnocoenosis generated in the second and the third members of the Feixianguan Formation (T2), is an Oppor tunistic ichnotaxa of high abundance and low diversity, i. e. highly concentrated trace fossil of Trichichnus occurs in red thin-bedded fine-grained sandstone, siltstone and muddy siltstone of the flood plain deposits comprising very little other trace fossils of Planolites, Gordia , Skolithos and so forth, which may serve to represent a frequently hot-dry and unstable river environment on the alluvial plain near the sea shore. (3)Scoyenia-Rusophycus ichnocoenosis from Jiaguan Formation (K2), is composed of extraordinarily di-versed and well preserved trace fossils including two different assemblages: Scoyenia-Steinichnus-Rusophycus and Skolithos-Arenicolites. The former contains Fodinichnia, Pascichnia or trails, Repichnia, Cubichnia and some small-patterned Domichnia, of which common ichnogenera are Scoyenia, Cystichnium (ichnogen. nov.), cf. Oniscoidichnus, Monomorphichnus, Pelecypodichnus, Rusophycus and so on, which formed in the flood plain deposits; The latter occurs generally in the channel bar or near shore deposits of the river fades and comprises only Skolithos, Arenicolites as well as other vertical burrows. Most of the trace fossils of this ichnocoenosis are associated with a lot of mudcracks, raindrop imprints, and asymmetrical current ripples on bedding surface of the red fine-grained sandstone, siltstone and mudstone, it is therefore interpreted to be originated in a regularly desiccated fluviatile environment (including extremely shallow lacustrine condition on the flood plain).
This paper chiefly deals with the composition, occurrence and sedimentary environments of the three unusually differential ichnocoenoses that are distinguished from the trace fossils well preserved in the Upper Permian, Lower Triassic and Upper Cretaceous fluvial deposits in Emei area. The three ichnocoenoses are recognized: (1)Scoyenia-Rhizoliths ichnocoenosis which occurs in the Shawan Formation (P2), mainly consists of Scoyenia, Planolites, Muensteria, Psammichnites, Skolithos, of. Stipsellus and Rhizoliths (mostly horizontal root casts, diagonal root casts, and partly vertical root casts) and so on, associated with the flood plain deposit that was made up of grey-yellow or green fine-grain sandstones, violet-red siltstones and mudstones as well as less intercalated carbonaceous shales contained plant fossils and thin-bedded coal, it might be explained to be formed in a hot, humid, fluvial environment. (2)Trichichnus ichnocoenosis generated in the second and the third members of the Feixianguan Formation (T2), is an Oppor tunistic ichnotaxa of high abundance and low diversity, i. e. highly concentrated trace fossil of Trichichnus occurs in red thin-bedded fine-grained sandstone, siltstone and muddy siltstone of the flood plain deposits comprising very little other trace fossils of Planolites, Gordia , Skolithos and so forth, which may serve to represent a frequently hot-dry and unstable river environment on the alluvial plain near the sea shore. (3)Scoyenia-Rusophycus ichnocoenosis from Jiaguan Formation (K2), is composed of extraordinarily di-versed and well preserved trace fossils including two different assemblages: Scoyenia-Steinichnus-Rusophycus and Skolithos-Arenicolites. The former contains Fodinichnia, Pascichnia or trails, Repichnia, Cubichnia and some small-patterned Domichnia, of which common ichnogenera are Scoyenia, Cystichnium (ichnogen. nov.), cf. Oniscoidichnus, Monomorphichnus, Pelecypodichnus, Rusophycus and so on, which formed in the flood plain deposits; The latter occurs generally in the channel bar or near shore deposits of the river fades and comprises only Skolithos, Arenicolites as well as other vertical burrows. Most of the trace fossils of this ichnocoenosis are associated with a lot of mudcracks, raindrop imprints, and asymmetrical current ripples on bedding surface of the red fine-grained sandstone, siltstone and mudstone, it is therefore interpreted to be originated in a regularly desiccated fluviatile environment (including extremely shallow lacustrine condition on the flood plain).
1991, 9(4): 143-150.
Abstract:
Based on the shallow shaft sections made for mining placer gold , general characteristics , heavy minerals and palaeo- sedimentary environments of Late Pleistocene in Guanmadian , eastern Liaoning are disscussed in this paper. Late Pleistocene strata can be divided into three sections in Guanmadian according to the lithological characteristis: sand-gravel bed in the lower, gravel-bearing loess in the middle and clayey soil in the upper section.The assemblage of heavy minerals shows that there are two kinds of sand-graval sediments: one is short transported and deposited in situ , aother is long distance transported allochthonous deposit and loess of which are both autochthonous and allochthonous.The palaeoclimate can also be revealed by heavy minerals that it was a little drier and cooler than the present when the bottom of the section was deposited, and then , it turned warmer, finally it became very draught and cold (i.e. the loess sediment) and turned into periglacial climate. Heavy minerals , mean dip vector and mean grain size of gravels indicat that during Late Pleistocene, Guanmadian area was a part of p^laeochannel which flown from Xidian to Xiaohekou, while deposits are mainly slope wash facies, river facies and flood plain facies , and loess sdeiments were form by both wind and water flow. Placer gold of Guanmadian area mainly distribute in the bottom of Late Pleistocene, the components of which is very complicated and belongs to eluvial and slope washed material. Alluvial placer distribute mainly along with the palaeochannel as bands and the contents of gold is very stable .There is little placer in the upper of Late Pleistocene.
Based on the shallow shaft sections made for mining placer gold , general characteristics , heavy minerals and palaeo- sedimentary environments of Late Pleistocene in Guanmadian , eastern Liaoning are disscussed in this paper. Late Pleistocene strata can be divided into three sections in Guanmadian according to the lithological characteristis: sand-gravel bed in the lower, gravel-bearing loess in the middle and clayey soil in the upper section.The assemblage of heavy minerals shows that there are two kinds of sand-graval sediments: one is short transported and deposited in situ , aother is long distance transported allochthonous deposit and loess of which are both autochthonous and allochthonous.The palaeoclimate can also be revealed by heavy minerals that it was a little drier and cooler than the present when the bottom of the section was deposited, and then , it turned warmer, finally it became very draught and cold (i.e. the loess sediment) and turned into periglacial climate. Heavy minerals , mean dip vector and mean grain size of gravels indicat that during Late Pleistocene, Guanmadian area was a part of p^laeochannel which flown from Xidian to Xiaohekou, while deposits are mainly slope wash facies, river facies and flood plain facies , and loess sdeiments were form by both wind and water flow. Placer gold of Guanmadian area mainly distribute in the bottom of Late Pleistocene, the components of which is very complicated and belongs to eluvial and slope washed material. Alluvial placer distribute mainly along with the palaeochannel as bands and the contents of gold is very stable .There is little placer in the upper of Late Pleistocene.
