1985 Vol. 3, No. 4
column
Display Method:
1985, 3(4): 1-12.
Abstract:
Based on the simulating experiments on the formation mechanism of banded iron-silica formation in the solution from weathering-leaching basalts, the authors have come to the conclusion that Archaean seawater was an acid solution evolving from strong acid to weak acid, in which a series of sedimentary rocks and ores bodies were formed. For example, banded iron-silica formations found in the ancient shields of the world, according to the simulating experiments ( 1 ) ,had been formed at the strong acid-acid stage of seawater in early geological history. The authors pointed out that primary seawater was a strong acid solution formed by condensation of volcanic gases, with pH of about 0.3. Volcanic degassing reduced the pH value of the seawater and afterwards in the stage of inactivity, pH would be raised as hypergene weathering-leathing went on. Volcanic degassing is in contradiction with hypergene weathering-leathing and it is just the couple of contradictions controlling the pH of the seawater and its evolution. When volcanic degassing was intensive in early geologic history, the pH of seawater was quite acid, but later, when the crust became more stable, and hypergene weathering-leaching gradually occupied a dominant position, the pH of the seawater rose and at last becam e alkaline. The velocity, at which strong acid seawater was neutralized, was also disscused. The authors pointed out that Archaean strong acid seawater was pH-stable"buffer", even in the intermitent period of volcanic activity, it is most likely to take millions and tens of millions years for its neutralization. The long-term acid condition and slow neutralization process were much favourable for the enrichment of ore-forming elements in the seawater and their chemical differentiation and forming sedimentary ores. The characteristics of hypergene weathering-leaching in Archaean were also disscused. The authors suggested that there had been weathering-leaching conditions of alternative strong acid meteoric water polluted by volcanic gases or rain saturated with CO2 gas. During the first period formed acid ore-bearing seawater and during the second differentiating and precipitating ore-bearing seawater was neutralized by weathering. So the Archaean weathering-leaching conditions were disadvantageous factors for the formation of the ore deposit of -weathering crust, but supplied sedimentary deposits with more ore-forming materials. In the discussion on the problem of minerogenesis in seawater controlled by pH the authors lined up the chemical analyses of sequent products precipitated in the weathering-leaching basalt solutions, in which pH gradually rose from strong acid by adding NaOH. As the simulating experiments showed when pH varied below 1.25, there had precipiteted in the solution only amorphous sillica; when the pH of the solution ranged among 1.25-6.0,thered hadropped the banded iron-sillica formation following the temperatures fluctuating periodically from room temperature to 100℃; when the pH of the solution reached 3.5-4.2 from strong acid, there had precipiteted sediments containing much hydroxides of aluminium; According to the author's calculation the partial pressure of CO2 in the atmosphere reached about 10-20 atm 2600 million years ago. The equilibrium pH with the atmospheric CO2 at which carbonates were formed is about 4,5; when the pH of the solution exceeded 5,5, there would precipetate iron silicates instead of amorphous silica. The comparison between these lower limits of pH in which corresponding compounds were precipitated and the earliest minerogenetic ages of corresponding ores shows a general course of pH-evolution of Archaean seawaten The pH was 0.3 about 4000 million years ago when primary seawater had been formed; 3800 million years ago, when the banded iron-silica formations had appeared the seawater' s pH exceeded 1.25 about 3200 million years ago old schists covering some old shields contained appreciable hydroxide of aluminium and corundolite. That means the pH of seawater at that time had reached over 3.5.
Based on the simulating experiments on the formation mechanism of banded iron-silica formation in the solution from weathering-leaching basalts, the authors have come to the conclusion that Archaean seawater was an acid solution evolving from strong acid to weak acid, in which a series of sedimentary rocks and ores bodies were formed. For example, banded iron-silica formations found in the ancient shields of the world, according to the simulating experiments ( 1 ) ,had been formed at the strong acid-acid stage of seawater in early geological history. The authors pointed out that primary seawater was a strong acid solution formed by condensation of volcanic gases, with pH of about 0.3. Volcanic degassing reduced the pH value of the seawater and afterwards in the stage of inactivity, pH would be raised as hypergene weathering-leathing went on. Volcanic degassing is in contradiction with hypergene weathering-leathing and it is just the couple of contradictions controlling the pH of the seawater and its evolution. When volcanic degassing was intensive in early geologic history, the pH of seawater was quite acid, but later, when the crust became more stable, and hypergene weathering-leaching gradually occupied a dominant position, the pH of the seawater rose and at last becam e alkaline. The velocity, at which strong acid seawater was neutralized, was also disscused. The authors pointed out that Archaean strong acid seawater was pH-stable"buffer", even in the intermitent period of volcanic activity, it is most likely to take millions and tens of millions years for its neutralization. The long-term acid condition and slow neutralization process were much favourable for the enrichment of ore-forming elements in the seawater and their chemical differentiation and forming sedimentary ores. The characteristics of hypergene weathering-leaching in Archaean were also disscused. The authors suggested that there had been weathering-leaching conditions of alternative strong acid meteoric water polluted by volcanic gases or rain saturated with CO2 gas. During the first period formed acid ore-bearing seawater and during the second differentiating and precipitating ore-bearing seawater was neutralized by weathering. So the Archaean weathering-leaching conditions were disadvantageous factors for the formation of the ore deposit of -weathering crust, but supplied sedimentary deposits with more ore-forming materials. In the discussion on the problem of minerogenesis in seawater controlled by pH the authors lined up the chemical analyses of sequent products precipitated in the weathering-leaching basalt solutions, in which pH gradually rose from strong acid by adding NaOH. As the simulating experiments showed when pH varied below 1.25, there had precipiteted in the solution only amorphous sillica; when the pH of the solution ranged among 1.25-6.0,thered hadropped the banded iron-sillica formation following the temperatures fluctuating periodically from room temperature to 100℃; when the pH of the solution reached 3.5-4.2 from strong acid, there had precipiteted sediments containing much hydroxides of aluminium; According to the author's calculation the partial pressure of CO2 in the atmosphere reached about 10-20 atm 2600 million years ago. The equilibrium pH with the atmospheric CO2 at which carbonates were formed is about 4,5; when the pH of the solution exceeded 5,5, there would precipetate iron silicates instead of amorphous silica. The comparison between these lower limits of pH in which corresponding compounds were precipitated and the earliest minerogenetic ages of corresponding ores shows a general course of pH-evolution of Archaean seawaten The pH was 0.3 about 4000 million years ago when primary seawater had been formed; 3800 million years ago, when the banded iron-silica formations had appeared the seawater' s pH exceeded 1.25 about 3200 million years ago old schists covering some old shields contained appreciable hydroxide of aluminium and corundolite. That means the pH of seawater at that time had reached over 3.5.
1985, 3(4): 31-44.
Abstract:
Pb-210 atmospheric flux of 2.06dpm/cm2·year has been determined by means ofmeasuring the soil sample from the area near the East China Sea continental shelf.The result agrees with the value prodicted from the model. After the Pb-210 activities in the sediments have been determined from more thantwenty columns in the estuary of the Changj:iang River and its adjacent shelf, it isfound that both virtical and horizontal distibutions of Pb-210 follow certain laws. The virtical distribution of Pb-210 in the estuary of the Changjiang River andits adjacent shelf can be divided into two typc;s and sis forms. The normal type coast-sts of three-region,two region and one regin forms, and the abnormal type consistsof parallel, upside-down and disorder forms.The normal virtical distribution of Pb-210 reflects the enviromental condition of steady-sate deposits and from the gradi-eat of Pb-210 profile, the sedimentary accumulation can be calculated.The abnormalvertical distribution of Pb-210 ref lects the enviromental condition of unsteady-state de-posits, some sudden events,such as resuspension, reworking and sliding, may takeplace in this area. The horizontal distribution of Pb-210 in the estuary of the Changjiang Riverand its adjacent shelf is quite different.Pb-210 activities of the surface layer in theinner-shelf mud deposit era almost two times smaller than those of the offshore muddeposit and relict sand area.The sedimentary accumulation is the main controllingfactor to the Pb-210 distribution·There is a negative relationship between the se-dimentarp accumulation and horizontal distribution of Pb-210, and a positive rela-tioaship between the sedimentary accumulation and virtical depth of Pb-210 in sedi-meats as well as the total Pb-210 radioactive quantity. The total Pb-210 radioactive quantity in the inner-shelf mud deposit area is ashigh as 160dpm/cm2, much higher than the predicted value of.60dpm/cm2, while thevalue of the offshore mud deposit and relict sand area is 30dpm/cm2 approximately,much less than the predicted one. The Pb-210 deposit flux in the inner-shelf muddeposit area is four times greater than the predicted one, whereas in the offshoremud deposit and relict sand.area is oaly 60%of the value predicted, From the factsdescribed above, it can be sees obviously that the Pb-210 has been intensely focusedin the inner-shelf mud deposit area, but is the offshore mud二deposit and_relict sandarea, the Pb-210 has been largely dispersed. Based upon these geochemistry charac-teristics of Pb-210, it can be predicted that most of the lead pollutants carried bythe Changjiang River are scavenged in the inner-shelf mud deposit area, only asmall part of them is darried into offshore and open sea.
Pb-210 atmospheric flux of 2.06dpm/cm2·year has been determined by means ofmeasuring the soil sample from the area near the East China Sea continental shelf.The result agrees with the value prodicted from the model. After the Pb-210 activities in the sediments have been determined from more thantwenty columns in the estuary of the Changj:iang River and its adjacent shelf, it isfound that both virtical and horizontal distibutions of Pb-210 follow certain laws. The virtical distribution of Pb-210 in the estuary of the Changjiang River andits adjacent shelf can be divided into two typc;s and sis forms. The normal type coast-sts of three-region,two region and one regin forms, and the abnormal type consistsof parallel, upside-down and disorder forms.The normal virtical distribution of Pb-210 reflects the enviromental condition of steady-sate deposits and from the gradi-eat of Pb-210 profile, the sedimentary accumulation can be calculated.The abnormalvertical distribution of Pb-210 ref lects the enviromental condition of unsteady-state de-posits, some sudden events,such as resuspension, reworking and sliding, may takeplace in this area. The horizontal distribution of Pb-210 in the estuary of the Changjiang Riverand its adjacent shelf is quite different.Pb-210 activities of the surface layer in theinner-shelf mud deposit era almost two times smaller than those of the offshore muddeposit and relict sand area.The sedimentary accumulation is the main controllingfactor to the Pb-210 distribution·There is a negative relationship between the se-dimentarp accumulation and horizontal distribution of Pb-210, and a positive rela-tioaship between the sedimentary accumulation and virtical depth of Pb-210 in sedi-meats as well as the total Pb-210 radioactive quantity. The total Pb-210 radioactive quantity in the inner-shelf mud deposit area is ashigh as 160dpm/cm2, much higher than the predicted value of.60dpm/cm2, while thevalue of the offshore mud deposit and relict sand area is 30dpm/cm2 approximately,much less than the predicted one. The Pb-210 deposit flux in the inner-shelf muddeposit area is four times greater than the predicted one, whereas in the offshoremud deposit and relict sand.area is oaly 60%of the value predicted, From the factsdescribed above, it can be sees obviously that the Pb-210 has been intensely focusedin the inner-shelf mud deposit area, but is the offshore mud二deposit and_relict sandarea, the Pb-210 has been largely dispersed. Based upon these geochemistry charac-teristics of Pb-210, it can be predicted that most of the lead pollutants carried bythe Changjiang River are scavenged in the inner-shelf mud deposit area, only asmall part of them is darried into offshore and open sea.
1985, 3(4): 55-62.
Abstract:
Ancient resedimented carbonates along platform-foreslope are considered as a deep-water type of carbonates, including gravity flows, gravity slide ( slump ) deposits, and talus wedges ( aprons ) . A series of deposits belonging to this kind of carbonates found from the intraplatform basin developed in Middle Devonian Qiziqiao Formation,north of Daoxing and east of Ningyuan, Hunan.They are around or adjacent to the restricted platform ( RC ) or open platform ( P ) (Fig.1 ) .The following four kinds of allochthonous carbonate sediments basically belonging to foreslope can be recongnized:( 1 )the slump psephitic limestone of fore-platform(Platel-l); (2)the allochthonous calcarenite Plate 1-2,3 ,Fig. 2 ); ( 3 ) the allochthonous calcisiltite ( Plate 2 -2 , 3 ); and ( 4 ) the talus limestone of reef-scarp (Plat 2-1 , Fig. 3 ) . These types of sedimentary rocks represent a transitional series which can be respectively regarded by the author as the product of gravity slide, secondary grain flows, foreset bed of turbidity flows (Fig. 2, below ) and talus reef-scarp aprons. Several different types of deposits, such as gravity slide and gravity flow, can be found on the same vertically geological section. The debris slides may synchronously bring about extensive debris flows, secon-dary grain flows and turbidity flows.According to their occurrence, petrological cha- racters, single bed thickness, inversely graded bedding,and massive non-graded unit, etc., it seems that the calcarenites of the study area may be compared with the modern secondary grain flows at the base of Bahama Escarpment 400m below reported by H.T.Mullins, and to have a similar sequence to allochthnous turbidity limestone ( Eder, 1970) .However, compared with mass calcarenites newly interpreted by I.M. Hurst,et al. ( 1983 ) ,the most likely mechanism for deposition of the calcarenites is the transition from high-density turbidity flows to liquefied flows.The gravity flows were quite developed from the last Middle to early Upper Devonian in South China. In addition to gravity flows and gravity slides of that age,synsedimentary faults at sea floor, a series of crinkled bedding of contemporaneous deformation, as well as submarine fans in northern Guangdong Province next to this area, and submarine erupted basalts in Guangxi Province are all the best evidences for the powerfully submarine tectonic movements. The gravitation on foreslope. especially the associated paleoearthquake, is probably the major factor of the mass movement of sediments at the sea-floor.
Ancient resedimented carbonates along platform-foreslope are considered as a deep-water type of carbonates, including gravity flows, gravity slide ( slump ) deposits, and talus wedges ( aprons ) . A series of deposits belonging to this kind of carbonates found from the intraplatform basin developed in Middle Devonian Qiziqiao Formation,north of Daoxing and east of Ningyuan, Hunan.They are around or adjacent to the restricted platform ( RC ) or open platform ( P ) (Fig.1 ) .The following four kinds of allochthonous carbonate sediments basically belonging to foreslope can be recongnized:( 1 )the slump psephitic limestone of fore-platform(Platel-l); (2)the allochthonous calcarenite Plate 1-2,3 ,Fig. 2 ); ( 3 ) the allochthonous calcisiltite ( Plate 2 -2 , 3 ); and ( 4 ) the talus limestone of reef-scarp (Plat 2-1 , Fig. 3 ) . These types of sedimentary rocks represent a transitional series which can be respectively regarded by the author as the product of gravity slide, secondary grain flows, foreset bed of turbidity flows (Fig. 2, below ) and talus reef-scarp aprons. Several different types of deposits, such as gravity slide and gravity flow, can be found on the same vertically geological section. The debris slides may synchronously bring about extensive debris flows, secon-dary grain flows and turbidity flows.According to their occurrence, petrological cha- racters, single bed thickness, inversely graded bedding,and massive non-graded unit, etc., it seems that the calcarenites of the study area may be compared with the modern secondary grain flows at the base of Bahama Escarpment 400m below reported by H.T.Mullins, and to have a similar sequence to allochthnous turbidity limestone ( Eder, 1970) .However, compared with mass calcarenites newly interpreted by I.M. Hurst,et al. ( 1983 ) ,the most likely mechanism for deposition of the calcarenites is the transition from high-density turbidity flows to liquefied flows.The gravity flows were quite developed from the last Middle to early Upper Devonian in South China. In addition to gravity flows and gravity slides of that age,synsedimentary faults at sea floor, a series of crinkled bedding of contemporaneous deformation, as well as submarine fans in northern Guangdong Province next to this area, and submarine erupted basalts in Guangxi Province are all the best evidences for the powerfully submarine tectonic movements. The gravitation on foreslope. especially the associated paleoearthquake, is probably the major factor of the mass movement of sediments at the sea-floor.
1985, 3(4): 73-82.
Abstract:
The Upper Devonian in Guilin district consists of a series of carbonate strata of marine facies. Obviously, they are of the same period and different facies. They can be divided into two lithofacies. One is dolomitic limestone facies, its lower part being Guilin Formation ( D3g ) and its upper part Rongxian Formation ( D3r ). The other is siliceous lenticular (nodular ) limestone facies, its lower part being Liujiang Formation ( D31 ), its upper part Sanli Formation ( D3s ). Guilin Formation can be compared with Liujiang Formation while Rongxian Formation corresponds to Sanli Formation. The author suggests that Guilin Formation be formed in a semi-restricted lagoon environment of a carbonate platform ( semi-restricted lagoon facies ) , Rongxian Formation in a tidal flat environment ( tidal flat facies), whereas Liujiang Formation was formed in a deep-water basin enviroment (deep-water basin facies ) of a carbonate platform, Sanli Formation in a semi-deep-water basin environment ( semi- deep-water basin facies ) of a carbonate platform. Lithologically, the semi-restricted lagoon facies is dark in colour, medium in stratification. It comprises such rocks as dendritic stromatopora limestone, dark micrite limestone, laminar limestone and micrite clastic limestone. They are all strongly dolomitized. The laminar structure is the main sedimentary structure. Biologically, they are characteristics of euryhalinous organisms, including marine algae, dendro-spheroidal stromatopora, mono-coral, brachiopoda and ostracoda, specially rich in Amphipora,which represents the static reduction environment with low-energy subtide, sometimes with the intervention of the intermittent oscillation. Tidal flat facies consists of laminar algae limestone, micrite limestone, clastic and sparry limestone, oolitic-algae limestone and gravel-clastic limestone. It's light in colour, pure in quality and thick in layers. As a result of the evaporation of tidal flat, they are prominent in dolomitization. The algae laminae structure, bird's eye structure , laminae structure, suture-line structure are all developed, so are the sedimentary rhythms, which become light upwards. It's rich in algae, but rare in biofossil, representing intertidal and subtidal shallow water oxidation environments. Deep-water basin facies is the dark grey thin silicalite with argillaceous, organic matters and pyrite. It's full of horizontal laminae and lack of benthonic organism,but rich in tenticulites, a kind of plankton. The depth of water may be below the"calcite compensation depth", indicating the socalled"Hungry Basin", whose sedimentary speed is slower than that of settlement. Semi-deep-water basin facies is composed mainly of carbonate podzol and argillaceous sediments, including chert micrite limestone, lenticular limestone, argillo-banded limestone and micrite limestone, sometimes with carbonate clastic sediments and calc-clastic turbidite. Lenticular structure, argillo-banded structure, laminae structure, grainorder bedding and Bouma sequences are their common structures. The sediments lie under the wave base and near the oxidation interface. It's lack of benthonic organism, and it is characterized as a static deep-water reduction environment. All of the above sedimentary facies have been controlled by Caledonian basement faults. The wide continental sea is composed of horst and graben fault basins. The former is carbonate platform, and the latter is the deep water basin. It's steep from the platform to the basin, and obviously different in the lithologic character. Its thickness abruptly becomes thin so that the facies changes sharply and the changing width is narrow. The abruptly-changed facies, to which the author has paid great attention, is often covered by Quaternary or disrupted by faults. Moreover, the carbonate sediment longitudinally shows obvious successions and stages.
The Upper Devonian in Guilin district consists of a series of carbonate strata of marine facies. Obviously, they are of the same period and different facies. They can be divided into two lithofacies. One is dolomitic limestone facies, its lower part being Guilin Formation ( D3g ) and its upper part Rongxian Formation ( D3r ). The other is siliceous lenticular (nodular ) limestone facies, its lower part being Liujiang Formation ( D31 ), its upper part Sanli Formation ( D3s ). Guilin Formation can be compared with Liujiang Formation while Rongxian Formation corresponds to Sanli Formation. The author suggests that Guilin Formation be formed in a semi-restricted lagoon environment of a carbonate platform ( semi-restricted lagoon facies ) , Rongxian Formation in a tidal flat environment ( tidal flat facies), whereas Liujiang Formation was formed in a deep-water basin enviroment (deep-water basin facies ) of a carbonate platform, Sanli Formation in a semi-deep-water basin environment ( semi- deep-water basin facies ) of a carbonate platform. Lithologically, the semi-restricted lagoon facies is dark in colour, medium in stratification. It comprises such rocks as dendritic stromatopora limestone, dark micrite limestone, laminar limestone and micrite clastic limestone. They are all strongly dolomitized. The laminar structure is the main sedimentary structure. Biologically, they are characteristics of euryhalinous organisms, including marine algae, dendro-spheroidal stromatopora, mono-coral, brachiopoda and ostracoda, specially rich in Amphipora,which represents the static reduction environment with low-energy subtide, sometimes with the intervention of the intermittent oscillation. Tidal flat facies consists of laminar algae limestone, micrite limestone, clastic and sparry limestone, oolitic-algae limestone and gravel-clastic limestone. It's light in colour, pure in quality and thick in layers. As a result of the evaporation of tidal flat, they are prominent in dolomitization. The algae laminae structure, bird's eye structure , laminae structure, suture-line structure are all developed, so are the sedimentary rhythms, which become light upwards. It's rich in algae, but rare in biofossil, representing intertidal and subtidal shallow water oxidation environments. Deep-water basin facies is the dark grey thin silicalite with argillaceous, organic matters and pyrite. It's full of horizontal laminae and lack of benthonic organism,but rich in tenticulites, a kind of plankton. The depth of water may be below the"calcite compensation depth", indicating the socalled"Hungry Basin", whose sedimentary speed is slower than that of settlement. Semi-deep-water basin facies is composed mainly of carbonate podzol and argillaceous sediments, including chert micrite limestone, lenticular limestone, argillo-banded limestone and micrite limestone, sometimes with carbonate clastic sediments and calc-clastic turbidite. Lenticular structure, argillo-banded structure, laminae structure, grainorder bedding and Bouma sequences are their common structures. The sediments lie under the wave base and near the oxidation interface. It's lack of benthonic organism, and it is characterized as a static deep-water reduction environment. All of the above sedimentary facies have been controlled by Caledonian basement faults. The wide continental sea is composed of horst and graben fault basins. The former is carbonate platform, and the latter is the deep water basin. It's steep from the platform to the basin, and obviously different in the lithologic character. Its thickness abruptly becomes thin so that the facies changes sharply and the changing width is narrow. The abruptly-changed facies, to which the author has paid great attention, is often covered by Quaternary or disrupted by faults. Moreover, the carbonate sediment longitudinally shows obvious successions and stages.
1985, 3(4): 95-108.
Abstract:
The marine turbidite deposit rock of Middle Triassic is widely distributed in Napanjiang River of the Yunnan-Guizhou-Guangxi boundary and the Youjiang River region of western Guangxi. It is abundant, dark-gray coloured, medium-or-thin-bed, cyclotheric and clastic graywacke, its thickness is 3,000-5,000m and its distribution area is about 80,000km2. The distribution of marine and terrestrial interdi-gitational bearing-coal deposit in Upper Triassic is limited at the edge zone of the platform. There was turbidite deposit in the early Carnic stage.In the study of the turbidite within the area, the external platform area of turbidite basins and adjacent oldland are recognizied as main material source areas. So the turbidite in Middle Triassic of the Nanpanjiang River and Youjiang River is supposed as multi-material source and multi-centre deposits. This paper suggests that the tectonic background of turbidite genesis be related to the rise of the new Hunan-Guangxi-Guangdong structural system of Middle Triassic in eastern Guangxi which is the synorogenic deposit of this system.The source of turbidite deposit comes from growing structural system instead of adjacent old land. So the turbidite within the area is related to geosyncline. The Yunnan-Guizhou-Guangxi sea area in Early Triassic is a part of the sea basin of Southern China. It is a platform area from Kaiyuan-Qiubei, Yunnan to the northwest part of Zhenfeng-Anshun-Guiyang, Guizhou; the Nanpanjiang River-Youjiang River area in the southwest part is a structural unit of subsidence. The Early Triassic deposit in this area consists of greyblack, thin-plate marls with rich-contained Ammonoidea, mud shales with silicious, thin intercalated layers and volcanic debris rocks, its bed thickness is 100-200m, showing the deposit feature of hungry basin. Volcanic debris comes from volcanic island arcs in East and Southeast Guangxi. In Early Middle Triassic, after large scale eruption of volcanos and intrusion of magma, Southwest Hunan, East and Southeast Guangxi and West Guangdong areas rose and became extending toward north and connecting with the Jiangnan old land so as to form a new Hunan-Guangxi-Guangdong structural system. On the west side of this system,the Nanpanjiang River and Youjiang River area subsided relatively,and deposited turbidite with the thickness of several thousands meters. Main mineral elements of turbidite consist of quartz (56%), feldspar ( 3.6% ) , debris ( 14% ), chlorite and hydromica clay matrix ( 19.8% ). The chemical constituent of turbidite consists of SiO2 ( 71.22% ) , Na2O ( 1.48% ) , K2O ( 1.05% ) and Fe2O3/FeO< 1 , in accordance with the chemical constituent of graywacke in the other parts of the -world. In the research of recongnizing source area of turbidite, according to plenty of developed trench model structure, it is measured that the direction of water current is 260°-320°, dominantly 300°, which shows the turbidite flow running from east to west.In Qiubei,Guangnan of Yunnan and Xilin,of Northwest Guangxi,i.e. the west of the turbidite basin, the proportion between mudstone and sandstone is 1 : 1, and it changes gradually into 1 : 2 eastward to Doaglan, Guangxi, which reflects that the location of the source area is in the east side and the farther it is from the material-area, the less sandstone deposits are. The chemical constituent of turbidite and the kinds of heavy minerals all indicate that turbidite deposits come from the matrix area of granite. The constitutional type of debris shows a strong movement of magma intrusion and a high relief in the source area. In the platform of external turbidite basin and the edge zone of Maguan Oldland, the Middle Triassic series consists of limestone and dolomite coexisting with turbidite deposits of the Nanpanjiang River and Youjiang River area. In the turbidite deposits of this area, there is neither any massive sands tone of middle-fan, thick bed pebble sandstone, nor conglomerate deposits of the innerfan. So it is not suitable to predict turbidite deposits of the Nanpanjiang River a
The marine turbidite deposit rock of Middle Triassic is widely distributed in Napanjiang River of the Yunnan-Guizhou-Guangxi boundary and the Youjiang River region of western Guangxi. It is abundant, dark-gray coloured, medium-or-thin-bed, cyclotheric and clastic graywacke, its thickness is 3,000-5,000m and its distribution area is about 80,000km2. The distribution of marine and terrestrial interdi-gitational bearing-coal deposit in Upper Triassic is limited at the edge zone of the platform. There was turbidite deposit in the early Carnic stage.In the study of the turbidite within the area, the external platform area of turbidite basins and adjacent oldland are recognizied as main material source areas. So the turbidite in Middle Triassic of the Nanpanjiang River and Youjiang River is supposed as multi-material source and multi-centre deposits. This paper suggests that the tectonic background of turbidite genesis be related to the rise of the new Hunan-Guangxi-Guangdong structural system of Middle Triassic in eastern Guangxi which is the synorogenic deposit of this system.The source of turbidite deposit comes from growing structural system instead of adjacent old land. So the turbidite within the area is related to geosyncline. The Yunnan-Guizhou-Guangxi sea area in Early Triassic is a part of the sea basin of Southern China. It is a platform area from Kaiyuan-Qiubei, Yunnan to the northwest part of Zhenfeng-Anshun-Guiyang, Guizhou; the Nanpanjiang River-Youjiang River area in the southwest part is a structural unit of subsidence. The Early Triassic deposit in this area consists of greyblack, thin-plate marls with rich-contained Ammonoidea, mud shales with silicious, thin intercalated layers and volcanic debris rocks, its bed thickness is 100-200m, showing the deposit feature of hungry basin. Volcanic debris comes from volcanic island arcs in East and Southeast Guangxi. In Early Middle Triassic, after large scale eruption of volcanos and intrusion of magma, Southwest Hunan, East and Southeast Guangxi and West Guangdong areas rose and became extending toward north and connecting with the Jiangnan old land so as to form a new Hunan-Guangxi-Guangdong structural system. On the west side of this system,the Nanpanjiang River and Youjiang River area subsided relatively,and deposited turbidite with the thickness of several thousands meters. Main mineral elements of turbidite consist of quartz (56%), feldspar ( 3.6% ) , debris ( 14% ), chlorite and hydromica clay matrix ( 19.8% ). The chemical constituent of turbidite consists of SiO2 ( 71.22% ) , Na2O ( 1.48% ) , K2O ( 1.05% ) and Fe2O3/FeO< 1 , in accordance with the chemical constituent of graywacke in the other parts of the -world. In the research of recongnizing source area of turbidite, according to plenty of developed trench model structure, it is measured that the direction of water current is 260°-320°, dominantly 300°, which shows the turbidite flow running from east to west.In Qiubei,Guangnan of Yunnan and Xilin,of Northwest Guangxi,i.e. the west of the turbidite basin, the proportion between mudstone and sandstone is 1 : 1, and it changes gradually into 1 : 2 eastward to Doaglan, Guangxi, which reflects that the location of the source area is in the east side and the farther it is from the material-area, the less sandstone deposits are. The chemical constituent of turbidite and the kinds of heavy minerals all indicate that turbidite deposits come from the matrix area of granite. The constitutional type of debris shows a strong movement of magma intrusion and a high relief in the source area. In the platform of external turbidite basin and the edge zone of Maguan Oldland, the Middle Triassic series consists of limestone and dolomite coexisting with turbidite deposits of the Nanpanjiang River and Youjiang River area. In the turbidite deposits of this area, there is neither any massive sands tone of middle-fan, thick bed pebble sandstone, nor conglomerate deposits of the innerfan. So it is not suitable to predict turbidite deposits of the Nanpanjiang River a
1985, 3(4): 121-130.
Abstract:
The northern part of South China Sea lies in the sea area between 16°00'-23°00' N and 108°00'-120°00'E,covering an area about 400,000km2.There are wildely distributed the Tertiary deposits of which the thickness is over 10,000m.The area with sedimentary rocks over 1,000m thick covers more than 300,000km2, in which five sedimentary basins have been established: Beibu Bay Basin, Yinggehai Basin, Southeastern Qiong Basin,the Pearl River Mouth Basin and Southwestern Taiwan Basin. The main source and reservoir rocks containing very good oil and gas are of Tertiary age. The rocks of Tertiary age underwent three stages of development, each formed a specific sedimentary system of its own: 1. The system of fluvio-lacustrine deposits in rift depressions from Paleocene to early Oligocene. The system of Paleocene f luvio-lacustrine deposits was of infilling rift depressions, and the Eocene f luvio-lacustrine deposites lay down with the deepening of the water body in the process of expansion of depressions. In early Oligocene the fault depressions became larger and f luvio-lacustrine deposites became more extensive, but the water body got shallow. 2. The system of semi-closed sea deposits from Late Oligocene to Early Miocene. 3. The system of deltaic-open sea deposits from Middle Miocene to Pliocene. Under the control of these three sedimentary systems, there occur in northern South China Sea three suits of source rocks, three suits of reservoir rocks and three groups of independent oil pools containing source, reservoir and cap rocks. The three suits of source rocks are: ( 1 ) the Eocene Liushagang Formation in the Beibu Bay basin, which is regarded as the best source rock so far discovered in the area, and which is quite probably the principal regional source rock region in the northern South China Sea; ( 2 ) the Oligocene Zhuhai Formation in the Pearl River Mouth basin; and ( 3 ) the lower Miocene series in the Pearl River Mouth basin. The three suits of reservoir rocks are: ( 1 ) the fluvio-lacustrine sandstone bodies in the Liushagang Formation) ( 2 ) the f luvio-lacustrine sand bodies and shallow sea sandstone bodies in the Zhuhai Formation and Lingshui Formation; and ( 3 ) the Neogene deltaic, littoral and shallow-sea sand bodies and bioherms, with the sandstone reservoirs of Middle Miocene as the best in physical properties. The three groups of independent oil pools containing source, reservoir and cap rocks are ( 1 ) the oil pools in the Eocene formation being in the lower partj ( 2 ) the oil pools at the bottom of Oligocene-Lower Miocene being in the middle part; ( 3 ) the oil pools in the Miocene formation in the upper part. The first two are more important. In the Beibu Bay basin, Eocene pools of the lower part predomina-te; in the Southeastern Qiong basin, independent oil pools are mostly in the Oligocene-Lower Miocene series of the middle part and in the Eocene series of the lower part; while in the Yinggehai basin, such pools may mostly occur in Miocene and Oligocene-Lower Miocene series. And, in the Pearl River Mouth basin, all the three groups of independent oil pools are likely to occur. It is essential to make out the geological formations of this part of the sea through stratigraphic correlation and deep-going study of the lithofacies and paleogeo-graphic features of the various formations, and to pay particular attention to finding out favourable source rocks in the different Paleogene rift depressions as the objectives of our exploration. This is a key to the rasie of success ratio in search of oil and gas fields of commercial value.
The northern part of South China Sea lies in the sea area between 16°00'-23°00' N and 108°00'-120°00'E,covering an area about 400,000km2.There are wildely distributed the Tertiary deposits of which the thickness is over 10,000m.The area with sedimentary rocks over 1,000m thick covers more than 300,000km2, in which five sedimentary basins have been established: Beibu Bay Basin, Yinggehai Basin, Southeastern Qiong Basin,the Pearl River Mouth Basin and Southwestern Taiwan Basin. The main source and reservoir rocks containing very good oil and gas are of Tertiary age. The rocks of Tertiary age underwent three stages of development, each formed a specific sedimentary system of its own: 1. The system of fluvio-lacustrine deposits in rift depressions from Paleocene to early Oligocene. The system of Paleocene f luvio-lacustrine deposits was of infilling rift depressions, and the Eocene f luvio-lacustrine deposites lay down with the deepening of the water body in the process of expansion of depressions. In early Oligocene the fault depressions became larger and f luvio-lacustrine deposites became more extensive, but the water body got shallow. 2. The system of semi-closed sea deposits from Late Oligocene to Early Miocene. 3. The system of deltaic-open sea deposits from Middle Miocene to Pliocene. Under the control of these three sedimentary systems, there occur in northern South China Sea three suits of source rocks, three suits of reservoir rocks and three groups of independent oil pools containing source, reservoir and cap rocks. The three suits of source rocks are: ( 1 ) the Eocene Liushagang Formation in the Beibu Bay basin, which is regarded as the best source rock so far discovered in the area, and which is quite probably the principal regional source rock region in the northern South China Sea; ( 2 ) the Oligocene Zhuhai Formation in the Pearl River Mouth basin; and ( 3 ) the lower Miocene series in the Pearl River Mouth basin. The three suits of reservoir rocks are: ( 1 ) the fluvio-lacustrine sandstone bodies in the Liushagang Formation) ( 2 ) the f luvio-lacustrine sand bodies and shallow sea sandstone bodies in the Zhuhai Formation and Lingshui Formation; and ( 3 ) the Neogene deltaic, littoral and shallow-sea sand bodies and bioherms, with the sandstone reservoirs of Middle Miocene as the best in physical properties. The three groups of independent oil pools containing source, reservoir and cap rocks are ( 1 ) the oil pools in the Eocene formation being in the lower partj ( 2 ) the oil pools at the bottom of Oligocene-Lower Miocene being in the middle part; ( 3 ) the oil pools in the Miocene formation in the upper part. The first two are more important. In the Beibu Bay basin, Eocene pools of the lower part predomina-te; in the Southeastern Qiong basin, independent oil pools are mostly in the Oligocene-Lower Miocene series of the middle part and in the Eocene series of the lower part; while in the Yinggehai basin, such pools may mostly occur in Miocene and Oligocene-Lower Miocene series. And, in the Pearl River Mouth basin, all the three groups of independent oil pools are likely to occur. It is essential to make out the geological formations of this part of the sea through stratigraphic correlation and deep-going study of the lithofacies and paleogeo-graphic features of the various formations, and to pay particular attention to finding out favourable source rocks in the different Paleogene rift depressions as the objectives of our exploration. This is a key to the rasie of success ratio in search of oil and gas fields of commercial value.
1985, 3(4): 141-153.
Abstract:
It is clear that different clay minerals are usually of different grain size. In order to study their interrelationship, six grades of grain size were seperated in this paper ( i. e. 0.5μ, 1μ, 2μ, 4 μ, 8μ, and 20μ) , their mineral composition and geochemical characteristics were examined. Minerals from treated samples were identified and quantitatively calculated by means of X-ray diffraction and electronic microscope. Meanwhile, atomic-absorption spectrum was applied to certain elements contained in various grades of grain size in quantitative analyses.Based on the above data,it is recognized that clay minerals, are mainly composed of illite and secondly chloride, kaolinite,montmorillonite, etc.. Minor hydrated kaolinite minerals can also be seen under electronic microscope.Based on the comprehensive analyses, the conclusions on the correlation between sediment grain-Sige,minera Iconstuction and chemical composition have been drawn as follows: 1 With the increase of sediment grain-size, the clay mineral content decreases and the clastic mineral increases. The clay mineral dominates the sediments with a grain-size0.5μ; quartz is low in content; feldspar and calcite are hardly seen. On the other hand, in sediments with a grain-size of20μ clay mineral decreases in contenti quartz and feldspar increase in amount and clastic minerals, such as calcite, dolomite and mica can also be found. 2 Montmorillonite content decreases with the increase of sediment grain-size, so does the kaolinite content. This relationship becomes apparent while the grain size of sediments increases up to 8μ.However, chloride content is contrary to the kaolinite content as the grain size of sediments increases. No clear correlation can be observed between illite and its grain size. 3 The contents of K, Fe, Co, Ni, Zn and Cu decrease while these of elements, such as Ca, Na, increase as the grain size of sediments increases. 4 The properties of regional distribution of clay-mineral content are modified mainly by the salinity of water media as well as grain size. From the estuary to- wards seashore, montmorillonite and chloride increase in content while the kaolinite content decreases. 5 Elements in sediments, such as Fe, Mn, Ni, Co, Cu and Zn, occur mainly in a state of absorption while Na, Ca exist right in the crystal lattice of minerals.
It is clear that different clay minerals are usually of different grain size. In order to study their interrelationship, six grades of grain size were seperated in this paper ( i. e. 0.5μ, 1μ, 2μ, 4 μ, 8μ, and 20μ) , their mineral composition and geochemical characteristics were examined. Minerals from treated samples were identified and quantitatively calculated by means of X-ray diffraction and electronic microscope. Meanwhile, atomic-absorption spectrum was applied to certain elements contained in various grades of grain size in quantitative analyses.Based on the above data,it is recognized that clay minerals, are mainly composed of illite and secondly chloride, kaolinite,montmorillonite, etc.. Minor hydrated kaolinite minerals can also be seen under electronic microscope.Based on the comprehensive analyses, the conclusions on the correlation between sediment grain-Sige,minera Iconstuction and chemical composition have been drawn as follows: 1 With the increase of sediment grain-size, the clay mineral content decreases and the clastic mineral increases. The clay mineral dominates the sediments with a grain-size0.5μ; quartz is low in content; feldspar and calcite are hardly seen. On the other hand, in sediments with a grain-size of20μ clay mineral decreases in contenti quartz and feldspar increase in amount and clastic minerals, such as calcite, dolomite and mica can also be found. 2 Montmorillonite content decreases with the increase of sediment grain-size, so does the kaolinite content. This relationship becomes apparent while the grain size of sediments increases up to 8μ.However, chloride content is contrary to the kaolinite content as the grain size of sediments increases. No clear correlation can be observed between illite and its grain size. 3 The contents of K, Fe, Co, Ni, Zn and Cu decrease while these of elements, such as Ca, Na, increase as the grain size of sediments increases. 4 The properties of regional distribution of clay-mineral content are modified mainly by the salinity of water media as well as grain size. From the estuary to- wards seashore, montmorillonite and chloride increase in content while the kaolinite content decreases. 5 Elements in sediments, such as Fe, Mn, Ni, Co, Cu and Zn, occur mainly in a state of absorption while Na, Ca exist right in the crystal lattice of minerals.
1985, 3(4): 17-30.
Abstract:
This paper mainly deals with how to determine paleosalinity by means of δ13C. In addition, the determination of paleotemperature is also dealt with by the use of δ12O. By a thorough analysis of the systematic data,the author has reached the following conclusions; ( 1 ) Both δ18O and δ13C values relate to the salinity of medium and the chang shows a trend that the higher the salinity, the higher the δ values. Therefore, it is feasible to distinguish marine limestone from freshwater limestone of Jurassic period of more young ages by the formula of Keith and Weber ; Z = 2.048 (δ13CpBD + 50) + 0498 (δ18OpBD + 50 ) .This paper gives an example of analysing the beachrocks in Hainan Island, South China.It shows the relationship between isotopes and salinity. ( 2 ) The δ18O and δ13C values of the tediments ( rocks ) older than Jurassic have been greatly changed because of the displacement of the isotope elements during the long geological time, so that the paleosalinity determined by theδ13C and δ18O values of ancient rocks would not be reliable. Through the study of this aspect the author suggests that in the process of dia-genesis,the exchange of carbon isotope between rock and medium is much weaker than that of oxygen isotope. Since the Cambrian period the δ13C value has not notably changed,hence, it is feasible to determine paleosalinity by using the δ13C values. (3 ) The exchange between O18 and O18 after sedimentation is strong and the δ18O value changes with the geological ages, that is , the δ18O value increases from old to new rocks, so that the δ18O value of ancient marine limestone would approximately be equal to that of freshwater limestone. Therefore, the δ18O values in an- cient rock can not be used on determining paleosalinity. ( 4 ) As the δ18O value increases with geological ages from old to new, so that it could not be used to determine paleosalinity.Since the δ18O value of ancient fa-cies rocks relates to the diagenetic environment so it can, no doubt, reflect the strength of diagenesis
This paper mainly deals with how to determine paleosalinity by means of δ13C. In addition, the determination of paleotemperature is also dealt with by the use of δ12O. By a thorough analysis of the systematic data,the author has reached the following conclusions; ( 1 ) Both δ18O and δ13C values relate to the salinity of medium and the chang shows a trend that the higher the salinity, the higher the δ values. Therefore, it is feasible to distinguish marine limestone from freshwater limestone of Jurassic period of more young ages by the formula of Keith and Weber ; Z = 2.048 (δ13CpBD + 50) + 0498 (δ18OpBD + 50 ) .This paper gives an example of analysing the beachrocks in Hainan Island, South China.It shows the relationship between isotopes and salinity. ( 2 ) The δ18O and δ13C values of the tediments ( rocks ) older than Jurassic have been greatly changed because of the displacement of the isotope elements during the long geological time, so that the paleosalinity determined by theδ13C and δ18O values of ancient rocks would not be reliable. Through the study of this aspect the author suggests that in the process of dia-genesis,the exchange of carbon isotope between rock and medium is much weaker than that of oxygen isotope. Since the Cambrian period the δ13C value has not notably changed,hence, it is feasible to determine paleosalinity by using the δ13C values. (3 ) The exchange between O18 and O18 after sedimentation is strong and the δ18O value changes with the geological ages, that is , the δ18O value increases from old to new rocks, so that the δ18O value of ancient marine limestone would approximately be equal to that of freshwater limestone. Therefore, the δ18O values in an- cient rock can not be used on determining paleosalinity. ( 4 ) As the δ18O value increases with geological ages from old to new, so that it could not be used to determine paleosalinity.Since the δ18O value of ancient fa-cies rocks relates to the diagenetic environment so it can, no doubt, reflect the strength of diagenesis
1985, 3(4): 45-54.
Abstract:
The samples of the Holocene beachrock in Hainan Island studied in this paper were taken in Shuiweiling Sanya Bay, Xizhou Island,Xiaodonghai, Dongmao Island, Ximao Island, Tianyahaijiao County, Yinggehai. Ledong County and Yuye, Wench-ang County. This paper mainly deals with the relationship between the cementation and diagenetic environment of beachrock. The cements of the Holocene beachrock in Hainan Island are mainly aragonite, high-Mg calcite and low-Mg calcite. The aragonite mainly appears fibrous to aci-cular,sometimes micrite: the high-calcite appears micrite and pelletoid:and the low-Mg calcite appears isoaxial granular. They make up of various cementation fabrics respectively, such as.(1)fibrous to acicular circumgranular fabric,(2)micrite cement fabric, (3)pelletoid fabric, (4)micrite packing fabric, (5)fibrous pendant fabric(a-ragonite),(6)isoaxial granular fabric, (7)fibrous (or bladed) pendant fabric(low-Mg calcite). (8)isoaxial granular meniscus fibric, and(9)isoaxial granular pendant fabric. All the fabrics are closely related to the diagenetic environment, they can be used as the symbols of marine environment ( both phreatic and vadose zones ) and fresh-water environment ( both phreatic and vadose zones). The recent beachrock which is still in the marine environment or is inf luencedmainly by marine environment is of the cementation fabrics(1)to(5).In the naturally vertical sections of beachrock the cementation fabrics have a zonation: the micrite and fib- rous-acicular circumgranular fabrics distributed in the lower part of the sections, and the fibrous-acicular pendant fabric ( aragonite ) distributed in the upper part of the sections. They represent marine phreatic ( the lower part of intertidal zone ) and marine vadose ( the upper part of intertidal zone)diagenetic environments respectively. Because the cementation fabrics (1) to (4) are similar to those of shallow sub-tidal zone ( both are in the marine phreatic environment ) , the cementaion fabric(5) -the fibrous pendant fabric(aragonite)is the characteristic symbol of recongnizing beachrocks. The Middle-Late Holocene beachrock which is now in the meteoric fresh-water environment is of cementation fabrics (6) to (9), among which the cenmentation fabrics (8) to (9) are only distributed in the freshwater vadose environment,and the cementation fabrics (6) to (7) are distributed both in fresh-water phreatic and vadose environment. The authors think that the cementation fabric (7)-fibrous ( or bladed ) pendant fabric ( low-Mg calcite is not the product which was precipitated in the fresh-water vadose environment, but is the residual fabric of aragonite neomor-phism under the influence of atmosphere fresh-water,and the primary aragonite was the fibrous pendant cement fabric precipitated in the marine vadose environment.The presence of the cement fabric in the Middle to Late Holocene beachrock indicates that it used to have the diagenetic history of marine vadose environment. The organism plays an important role in the formation of micrite cement. The features of the micrite cement and pelletoid cement under microscope dealt with in this paper provide some evidences for the organism origin of the micrite cement.
The samples of the Holocene beachrock in Hainan Island studied in this paper were taken in Shuiweiling Sanya Bay, Xizhou Island,Xiaodonghai, Dongmao Island, Ximao Island, Tianyahaijiao County, Yinggehai. Ledong County and Yuye, Wench-ang County. This paper mainly deals with the relationship between the cementation and diagenetic environment of beachrock. The cements of the Holocene beachrock in Hainan Island are mainly aragonite, high-Mg calcite and low-Mg calcite. The aragonite mainly appears fibrous to aci-cular,sometimes micrite: the high-calcite appears micrite and pelletoid:and the low-Mg calcite appears isoaxial granular. They make up of various cementation fabrics respectively, such as.(1)fibrous to acicular circumgranular fabric,(2)micrite cement fabric, (3)pelletoid fabric, (4)micrite packing fabric, (5)fibrous pendant fabric(a-ragonite),(6)isoaxial granular fabric, (7)fibrous (or bladed) pendant fabric(low-Mg calcite). (8)isoaxial granular meniscus fibric, and(9)isoaxial granular pendant fabric. All the fabrics are closely related to the diagenetic environment, they can be used as the symbols of marine environment ( both phreatic and vadose zones ) and fresh-water environment ( both phreatic and vadose zones). The recent beachrock which is still in the marine environment or is inf luencedmainly by marine environment is of the cementation fabrics(1)to(5).In the naturally vertical sections of beachrock the cementation fabrics have a zonation: the micrite and fib- rous-acicular circumgranular fabrics distributed in the lower part of the sections, and the fibrous-acicular pendant fabric ( aragonite ) distributed in the upper part of the sections. They represent marine phreatic ( the lower part of intertidal zone ) and marine vadose ( the upper part of intertidal zone)diagenetic environments respectively. Because the cementation fabrics (1) to (4) are similar to those of shallow sub-tidal zone ( both are in the marine phreatic environment ) , the cementaion fabric(5) -the fibrous pendant fabric(aragonite)is the characteristic symbol of recongnizing beachrocks. The Middle-Late Holocene beachrock which is now in the meteoric fresh-water environment is of cementation fabrics (6) to (9), among which the cenmentation fabrics (8) to (9) are only distributed in the freshwater vadose environment,and the cementation fabrics (6) to (7) are distributed both in fresh-water phreatic and vadose environment. The authors think that the cementation fabric (7)-fibrous ( or bladed ) pendant fabric ( low-Mg calcite is not the product which was precipitated in the fresh-water vadose environment, but is the residual fabric of aragonite neomor-phism under the influence of atmosphere fresh-water,and the primary aragonite was the fibrous pendant cement fabric precipitated in the marine vadose environment.The presence of the cement fabric in the Middle to Late Holocene beachrock indicates that it used to have the diagenetic history of marine vadose environment. The organism plays an important role in the formation of micrite cement. The features of the micrite cement and pelletoid cement under microscope dealt with in this paper provide some evidences for the organism origin of the micrite cement.
1985, 3(4): 63-72.
Abstract:
The Middle-Late Devonian of northern Guangdong is mainly composed of sedimentary rocks of marine carbonate facies.The belt of carbonate facies of tidal flat is the most developed sedimentary facies in this region, it is mainly distributed in the sedimentary rocks in late Middle Devonian and early Late Devonian rocks of Le-chang and Renhua Counties.The belt includes laminated dolomite facies, allochem limestone facies, stromatolithic micrite facies, biocalcarenite facies, biolithite facies, coral reef facies and intraclastic limestone facies, etc.The belt of the partial barrier sea basin facies is found in Late Devonian deposits from Lechang and Renhua Counties to Shaoguan city. It is mainly composed of carbonaceous muddy biolithite facies, sulfide micrite facies and biomechanically disturbed micrite facies. The belt of open sea basin facies, which is a suit of rhythmite that consists of alternation of oncolite limestone facies,micrite facies with siliceous nodules and styliolinida micrite facies, occurs in the western region of Yaoshan anticlinorium in Middle-Late Devonian and in the area from Lechang to Shaoguan in Late Devonian. The belt of slope facies, being a suit of carbonate slumping sedimentary conglomerate, is distributed along the western margin of Yaoshan anticlinorium and the northern margin from Wudianmeihua anticlinorium to Yunkai oldland in early Late Devonian. The belt of trench facies is distributed in the area of Yingde County in Middle-Late Devonian. It is a formation of micrite containing some of tentaculitida, styliolinida and radiolaria with a bed of abyssal mudstone. Separated by the Yaoshan barrier islands and Xueshan barrier islands, the region from Lechang to Shaoguan has been developed into a barrier sea basin.To the western part of Yaoshan barrier islands is the Meihua open sea basin and between Xueshan barrier islands and Yunkai oldland is the Yingde trench.It is worth noticing that the E-W trend of Yingde trench lies exactly on the dividing lines between two tectonic systems of Pre-Devonian in northern Guangdong, which are mutual perpendicular-one being NNW, and the other NEE. So it can be inferred that the Yingde trench was developed on the basis of tectonic rift strap formed in Caledonian movement. The distribution of many pyrites and polymetal ore deposits along either side of Yingde trench shows that the rift strap may be an important zone of mineralization.
The Middle-Late Devonian of northern Guangdong is mainly composed of sedimentary rocks of marine carbonate facies.The belt of carbonate facies of tidal flat is the most developed sedimentary facies in this region, it is mainly distributed in the sedimentary rocks in late Middle Devonian and early Late Devonian rocks of Le-chang and Renhua Counties.The belt includes laminated dolomite facies, allochem limestone facies, stromatolithic micrite facies, biocalcarenite facies, biolithite facies, coral reef facies and intraclastic limestone facies, etc.The belt of the partial barrier sea basin facies is found in Late Devonian deposits from Lechang and Renhua Counties to Shaoguan city. It is mainly composed of carbonaceous muddy biolithite facies, sulfide micrite facies and biomechanically disturbed micrite facies. The belt of open sea basin facies, which is a suit of rhythmite that consists of alternation of oncolite limestone facies,micrite facies with siliceous nodules and styliolinida micrite facies, occurs in the western region of Yaoshan anticlinorium in Middle-Late Devonian and in the area from Lechang to Shaoguan in Late Devonian. The belt of slope facies, being a suit of carbonate slumping sedimentary conglomerate, is distributed along the western margin of Yaoshan anticlinorium and the northern margin from Wudianmeihua anticlinorium to Yunkai oldland in early Late Devonian. The belt of trench facies is distributed in the area of Yingde County in Middle-Late Devonian. It is a formation of micrite containing some of tentaculitida, styliolinida and radiolaria with a bed of abyssal mudstone. Separated by the Yaoshan barrier islands and Xueshan barrier islands, the region from Lechang to Shaoguan has been developed into a barrier sea basin.To the western part of Yaoshan barrier islands is the Meihua open sea basin and between Xueshan barrier islands and Yunkai oldland is the Yingde trench.It is worth noticing that the E-W trend of Yingde trench lies exactly on the dividing lines between two tectonic systems of Pre-Devonian in northern Guangdong, which are mutual perpendicular-one being NNW, and the other NEE. So it can be inferred that the Yingde trench was developed on the basis of tectonic rift strap formed in Caledonian movement. The distribution of many pyrites and polymetal ore deposits along either side of Yingde trench shows that the rift strap may be an important zone of mineralization.
1985, 3(4): 83-94.
Abstract:
The Dalinghe oil bed of Liaohe Basin is in the lower part of the Shahejie-3 Formation of the Oligocene.It is distributed in the western depression of Liaohe Basin, and consists of conglomerates, pebbled sandstones, sandstones and deep-water mudstones. Coarse tailed graded bedding, normal graded bedding as well as various sole marks are well developed while traction structures are rare. Besides the typical turbidites, non-typical turbidites facies occur more frequently,such as chaotic coarse conglomerate facies, conglomerate sandstone facies with coarse tailed graded be-d ding, inverse-normal grading pebbled sandstone facies, massive sandstone facies and sandstone facies with diagonal bedding. Each facies has its special types of lithesome and sedimentary structures. The oil layer in the Baling River belongs to gravity current channel-flood turbidity of lacustrine fan system.Lacustrine fans developed in deep water area. The gravity current channel was a canal of leading the flood turbidity current into the lake basin, it began at the shore, passed through the shallow water area, and conjoined with lacustrine fans in deep water area. The lacustrine fans can be subdivided into inner-fan,mid-fan and outer-fan sub-facies. The main channel with levees was developed in the inner-fan. High-density turbidites were mainly in the channels and developed into coarse conglomerate facies with chaotic structure,while the levees located at both sides of the channel were classic turbidites mainly resulted from the lower-density turbidity current sediments. The mid-fan subfacies was lobe-shaped. The braided channels without levee were developed on the lobe near the upper-fan, and they gradually vanished along the current flowing direction and were changed into the channelless area. The braided channels were mainly the well developed coarse-tail grading pebbled sandstone facies resulted from high-density turbidity current sediments.The channelless area was characterized by the classic proximal turbidites.The topography of the lower fan area is flat, and the deposits were mainly the distal classic turbidites resulted from the lower-density turbidity current. The gravity current channel-lacustrine fan system is probably a kind of important turbidites in the faulted lake basin. Many kinds of stratum-lithological traps can be developed in the lacustrine fan, especially in the mid-fan area. Source, reservoir and cap rock complexes are well present in the lacustrine fans, so they are the important fields for petroleum exploration.
The Dalinghe oil bed of Liaohe Basin is in the lower part of the Shahejie-3 Formation of the Oligocene.It is distributed in the western depression of Liaohe Basin, and consists of conglomerates, pebbled sandstones, sandstones and deep-water mudstones. Coarse tailed graded bedding, normal graded bedding as well as various sole marks are well developed while traction structures are rare. Besides the typical turbidites, non-typical turbidites facies occur more frequently,such as chaotic coarse conglomerate facies, conglomerate sandstone facies with coarse tailed graded be-d ding, inverse-normal grading pebbled sandstone facies, massive sandstone facies and sandstone facies with diagonal bedding. Each facies has its special types of lithesome and sedimentary structures. The oil layer in the Baling River belongs to gravity current channel-flood turbidity of lacustrine fan system.Lacustrine fans developed in deep water area. The gravity current channel was a canal of leading the flood turbidity current into the lake basin, it began at the shore, passed through the shallow water area, and conjoined with lacustrine fans in deep water area. The lacustrine fans can be subdivided into inner-fan,mid-fan and outer-fan sub-facies. The main channel with levees was developed in the inner-fan. High-density turbidites were mainly in the channels and developed into coarse conglomerate facies with chaotic structure,while the levees located at both sides of the channel were classic turbidites mainly resulted from the lower-density turbidity current sediments. The mid-fan subfacies was lobe-shaped. The braided channels without levee were developed on the lobe near the upper-fan, and they gradually vanished along the current flowing direction and were changed into the channelless area. The braided channels were mainly the well developed coarse-tail grading pebbled sandstone facies resulted from high-density turbidity current sediments.The channelless area was characterized by the classic proximal turbidites.The topography of the lower fan area is flat, and the deposits were mainly the distal classic turbidites resulted from the lower-density turbidity current. The gravity current channel-lacustrine fan system is probably a kind of important turbidites in the faulted lake basin. Many kinds of stratum-lithological traps can be developed in the lacustrine fan, especially in the mid-fan area. Source, reservoir and cap rock complexes are well present in the lacustrine fans, so they are the important fields for petroleum exploration.
1985, 3(4): 109-120.
Abstract:
In china, hydrogen sulphide contents of natural gas are obviously controlled by reservoir lithology. H2S contents of natural gas in clastic rocks are very low even down to zero. The highest H2S contents of natural gas in those rocks are 0.68%, which can be found in Upper Triassic Xiangxi sandstones in Sichuan Basin.Carbonate reservoirs commonly contain H2S, sometimes with high contents. Natural gas containing H2S more than 1 % is all in carbonate rocks ( Fig. 1 ) in China, which consist of Sinian system ( Dengying Formation ) , Ordovician system ( Nanjinguan Formation ) , Permian system ( Maokou and Changxing Formations ) , Triassic system ( Feixianguan, Jialingjiang and Leikoupo Formations ) and lower Tertiary system ( Kongdian and Shahejie Formations ) in succession of strata. The highest H2S contents of natural gas in carbonate reservoirs are about 92%, which are accumulated in Kongdian Formation of lower Tertiary. H2S reservoirs of natural gas higher than 1 % cover a quarter of the total non-associated gas reserves in China. At present, it is one of the main sources for sulphur-producing. According to the H2S contents of natural gas, and their characteristics of strati-graphic suite, with reference to the original phase in gas pools or in natural gas, and the demands of desulphurization process after gas development, gas pools containing H2S can be classified as follows: 1. H2S gas pools: H2S contents in natural gas are over 70%, which are distributed in sulfate-carbonate sequence, for example, H2S contents in Zhaolanzhuang gas pools are about 92%. Underground H2S is in liquid phase. 2. High H2S gas pools: H2S contents in natural gas are about 2-70%, which are also accumlated in stratigraphic suite of sulfate-carbonate, such a gas pools of Changxing, Jialingjiang and Leikoupo Formations in Sichuan Basin. Underground H2S is not in liquid phase. 3. Low H2S gas pools: H2S contents in natural gas are about 0.5-2 %, most of them are less than 1.5%,which developed in carbonate sequence,such as the Weiyuan gas pool in Sichuan Basin. 4. poor H2S gas pools: H2S contents are only a little, about 0-0.5%, most of them are less than 0.05%, which developed in carbonate sequence as well as clastic sequence. 5. Gas pools without H2S or non H2S gas pools, which mainly developed in clastic strata as well as carbonate reservoirs. Maximum H2S contents of natural gas for individual stratum are listed in Table 3 . Based on the characteristics of stratigraphic suites containing H2S gas, reservoir behaviours and geochemical characteristics of gas generation, the genesis of H2S can be classified into four types. 1. Nonbiogenic reduction type Under reducing environment with high temperature, hydrocarbon or organic matters are able to convert sulfates into H2S gas, So H2S gas pools and high H2S gas pools are commonly formed in these conditions. 2. Biogenic reduction type Hydrocarbon contained in sulfate stratum was converted into H2S by decomposition of sulfate bacterial reduction. 3. Thermal cracking type Oil and sapropel types of kerogen in carbonate sequence underwent thermal cracking during the stage of over heating. After the thermal cracking, only a small amount of H2S gas could be formed, because the source of sulphur in carbonates is not so abundant as that in sulfatec-arbonate sequence, thus, all these gas pools belong to low H2S gas pool. 4. Secondary type H2S-generating was not in relation to reservoirs, it migrated from other strata into clastic reservoirs in various ways, so all gas pools are poor H2S gas pools.
In china, hydrogen sulphide contents of natural gas are obviously controlled by reservoir lithology. H2S contents of natural gas in clastic rocks are very low even down to zero. The highest H2S contents of natural gas in those rocks are 0.68%, which can be found in Upper Triassic Xiangxi sandstones in Sichuan Basin.Carbonate reservoirs commonly contain H2S, sometimes with high contents. Natural gas containing H2S more than 1 % is all in carbonate rocks ( Fig. 1 ) in China, which consist of Sinian system ( Dengying Formation ) , Ordovician system ( Nanjinguan Formation ) , Permian system ( Maokou and Changxing Formations ) , Triassic system ( Feixianguan, Jialingjiang and Leikoupo Formations ) and lower Tertiary system ( Kongdian and Shahejie Formations ) in succession of strata. The highest H2S contents of natural gas in carbonate reservoirs are about 92%, which are accumulated in Kongdian Formation of lower Tertiary. H2S reservoirs of natural gas higher than 1 % cover a quarter of the total non-associated gas reserves in China. At present, it is one of the main sources for sulphur-producing. According to the H2S contents of natural gas, and their characteristics of strati-graphic suite, with reference to the original phase in gas pools or in natural gas, and the demands of desulphurization process after gas development, gas pools containing H2S can be classified as follows: 1. H2S gas pools: H2S contents in natural gas are over 70%, which are distributed in sulfate-carbonate sequence, for example, H2S contents in Zhaolanzhuang gas pools are about 92%. Underground H2S is in liquid phase. 2. High H2S gas pools: H2S contents in natural gas are about 2-70%, which are also accumlated in stratigraphic suite of sulfate-carbonate, such a gas pools of Changxing, Jialingjiang and Leikoupo Formations in Sichuan Basin. Underground H2S is not in liquid phase. 3. Low H2S gas pools: H2S contents in natural gas are about 0.5-2 %, most of them are less than 1.5%,which developed in carbonate sequence,such as the Weiyuan gas pool in Sichuan Basin. 4. poor H2S gas pools: H2S contents are only a little, about 0-0.5%, most of them are less than 0.05%, which developed in carbonate sequence as well as clastic sequence. 5. Gas pools without H2S or non H2S gas pools, which mainly developed in clastic strata as well as carbonate reservoirs. Maximum H2S contents of natural gas for individual stratum are listed in Table 3 . Based on the characteristics of stratigraphic suites containing H2S gas, reservoir behaviours and geochemical characteristics of gas generation, the genesis of H2S can be classified into four types. 1. Nonbiogenic reduction type Under reducing environment with high temperature, hydrocarbon or organic matters are able to convert sulfates into H2S gas, So H2S gas pools and high H2S gas pools are commonly formed in these conditions. 2. Biogenic reduction type Hydrocarbon contained in sulfate stratum was converted into H2S by decomposition of sulfate bacterial reduction. 3. Thermal cracking type Oil and sapropel types of kerogen in carbonate sequence underwent thermal cracking during the stage of over heating. After the thermal cracking, only a small amount of H2S gas could be formed, because the source of sulphur in carbonates is not so abundant as that in sulfatec-arbonate sequence, thus, all these gas pools belong to low H2S gas pool. 4. Secondary type H2S-generating was not in relation to reservoirs, it migrated from other strata into clastic reservoirs in various ways, so all gas pools are poor H2S gas pools.
1985, 3(4): 131-140.
Abstract:
Clay minerals in ancient deposits are regarded as sensitive indicators for the changes in sendimentary environment, which makes it possible to trace back to the origin of materials, paleoclimatic conditions and environmental characteristics of sedimentary basins. The samples studied in this paper were detrmined by means of X-ray diffraction, differential thermal analysis,infrared absorbed spectral analysis, electron microscope and chemical analysis. These analyses show that the clay fractions in Late Cretaceous consist of smectite, illite, chlorite with a minor amount of quartz, feldspar, analcite and carbonate among which the illite is the most abundant and common clay mineral in the basin, and it is mostly detrital in origin, with some characters inherited form the mother rock according to TEM studies. The Qing Shankou and Nenjiang Formations contain hexagonal authigenic illite, which was formed by the fixation of potassium and the expulsion of inter-layer water on smectite layers through diagenetic alternation, reflecting a condition of alkaline water medium rich in K+. The smectite appears abundant throughout the formations except the Qing Shankou Formation which chiefly originated form volcanic source rocks and was formed under an alkaline medium condition with a hot and arid climate. The chlorite includes detrital and authigenic forms. The content of the former might indicate the distance of the sediments from the erosion areas, while that of the authigenic can be interpreted as a result of halmyrolytic alternation, reflecting effects of the sea water. The analcite is also related to volcanic materials which were transformed into analcites under a condition of water medium with increasing salinity and alkalinity through diagenetic alternation.Therefore,the presence of analcite indicates an environment marked by the increasing salinity and alkalinity. The terrigenous feldspar is one of the important non-clay minerals in the basin, and its well-preserved tabular crystals indicating an arid paleoclimatic condition. The"suitable B content" of the clay minerals relates directly to paleosalinity, possibly indicating the salinity of water medium. The clay assemblages and stratigraphic variations can be summarized as follows: The Quantou Formation is composed of illite, chlorite, smectite and non-clay minerals such as feldspar and quartz. The"suitable B content"is 140 ppm, reflecting a condition of fresh water and alkaline water medium with hot to arid climates and representing sediments close to erosion areas. In the Qing Shankou Formation, the clay fractions are rich in illite with small quantity of authigenic chlorite, illite and analcite, but no smectite and feldspar, the"suitable B content"is 240 ppm.These sedimentary components had ever been subjected to transgression, indicating a brackish and alkaline water medium. The Yaojia Formation contains illite and smectite with rich feldspar, but no chlorite, the"suitable B content"is 100 ppm, suggesting drier climate than before and a fresh water medium condition. Nenjiang Formation is characterized by the abundant smectite associated with illite, chlorite and feldspar. The "suitable B content" is 285 ppm, reflecting a brackish water medium. The well-crystallized smectite in Members D1 and D3 indicates a stable and deepened water body. The feldspar decreases from Member D3 upwards, and the siderite appears. The basin was uplifted under a moist climate. Based on the preliminary study, the author is inclined to suggest that the Late Cretaceous Song-Liao basin should be a hemipelagic one rather than an inland lake as traditionally recognized, and that its strata were mainly formed under the enviro-ment with an arid paloeoclimate and a freshbrackish alkaline water medium.Both the Qing Shankou and Nenjiang Formations had been subjected to transgression. These results are somewhat useful in the genetic research on oil-bearing strata.
Clay minerals in ancient deposits are regarded as sensitive indicators for the changes in sendimentary environment, which makes it possible to trace back to the origin of materials, paleoclimatic conditions and environmental characteristics of sedimentary basins. The samples studied in this paper were detrmined by means of X-ray diffraction, differential thermal analysis,infrared absorbed spectral analysis, electron microscope and chemical analysis. These analyses show that the clay fractions in Late Cretaceous consist of smectite, illite, chlorite with a minor amount of quartz, feldspar, analcite and carbonate among which the illite is the most abundant and common clay mineral in the basin, and it is mostly detrital in origin, with some characters inherited form the mother rock according to TEM studies. The Qing Shankou and Nenjiang Formations contain hexagonal authigenic illite, which was formed by the fixation of potassium and the expulsion of inter-layer water on smectite layers through diagenetic alternation, reflecting a condition of alkaline water medium rich in K+. The smectite appears abundant throughout the formations except the Qing Shankou Formation which chiefly originated form volcanic source rocks and was formed under an alkaline medium condition with a hot and arid climate. The chlorite includes detrital and authigenic forms. The content of the former might indicate the distance of the sediments from the erosion areas, while that of the authigenic can be interpreted as a result of halmyrolytic alternation, reflecting effects of the sea water. The analcite is also related to volcanic materials which were transformed into analcites under a condition of water medium with increasing salinity and alkalinity through diagenetic alternation.Therefore,the presence of analcite indicates an environment marked by the increasing salinity and alkalinity. The terrigenous feldspar is one of the important non-clay minerals in the basin, and its well-preserved tabular crystals indicating an arid paleoclimatic condition. The"suitable B content" of the clay minerals relates directly to paleosalinity, possibly indicating the salinity of water medium. The clay assemblages and stratigraphic variations can be summarized as follows: The Quantou Formation is composed of illite, chlorite, smectite and non-clay minerals such as feldspar and quartz. The"suitable B content"is 140 ppm, reflecting a condition of fresh water and alkaline water medium with hot to arid climates and representing sediments close to erosion areas. In the Qing Shankou Formation, the clay fractions are rich in illite with small quantity of authigenic chlorite, illite and analcite, but no smectite and feldspar, the"suitable B content"is 240 ppm.These sedimentary components had ever been subjected to transgression, indicating a brackish and alkaline water medium. The Yaojia Formation contains illite and smectite with rich feldspar, but no chlorite, the"suitable B content"is 100 ppm, suggesting drier climate than before and a fresh water medium condition. Nenjiang Formation is characterized by the abundant smectite associated with illite, chlorite and feldspar. The "suitable B content" is 285 ppm, reflecting a brackish water medium. The well-crystallized smectite in Members D1 and D3 indicates a stable and deepened water body. The feldspar decreases from Member D3 upwards, and the siderite appears. The basin was uplifted under a moist climate. Based on the preliminary study, the author is inclined to suggest that the Late Cretaceous Song-Liao basin should be a hemipelagic one rather than an inland lake as traditionally recognized, and that its strata were mainly formed under the enviro-ment with an arid paloeoclimate and a freshbrackish alkaline water medium.Both the Qing Shankou and Nenjiang Formations had been subjected to transgression. These results are somewhat useful in the genetic research on oil-bearing strata.
