2000 Vol. 18, No. 3
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Display Method:
2000, 18(3): 327-335.
Abstract:
Grain-size distribution of Chinese loess consistently shows bimode spectrum, which is composed of two distinct components. The main component is coarse grain size with, large kurtosis and narrow distribution range,makes up main part of loess material. This main component is likely produced in the season when winter monsoon dominate the paleoclimate of loess plateau, and therefore its grain size indicates East Asia winter monsoon strength. The other grain size component has a wide distribution range, lower kurtosis and fine average grain size. This fine component probably represents the general dust base level of atmosphere over loess plateau, which prevails in most of the season. In some extension, it is genetically connected to the Northern Hemisphere westerly. Grain size distribution function of Chinese loess can be expressed with a sum of two Weibull distribution functions that represent two components of loess grain size. By fitting measured grain-size data to proposed distribution function, all parameters of the function can be estimated. Meanwhile, distribution function as well as the ratio of the two components can also be obtained.
Grain-size distribution of Chinese loess consistently shows bimode spectrum, which is composed of two distinct components. The main component is coarse grain size with, large kurtosis and narrow distribution range,makes up main part of loess material. This main component is likely produced in the season when winter monsoon dominate the paleoclimate of loess plateau, and therefore its grain size indicates East Asia winter monsoon strength. The other grain size component has a wide distribution range, lower kurtosis and fine average grain size. This fine component probably represents the general dust base level of atmosphere over loess plateau, which prevails in most of the season. In some extension, it is genetically connected to the Northern Hemisphere westerly. Grain size distribution function of Chinese loess can be expressed with a sum of two Weibull distribution functions that represent two components of loess grain size. By fitting measured grain-size data to proposed distribution function, all parameters of the function can be estimated. Meanwhile, distribution function as well as the ratio of the two components can also be obtained.
2000, 18(3): 341-345.
Abstract:
As a main lodging of surface substances, lake sediments continuously and sensitively record information of regional climate and environment with annual to decadal resolution. The sediment core EH911208-3-5 with a length of 83cm was taken from deepwater location in Erhai Lake in 1991, using the sediment-water interface sampler specially designed by ourselves. The sediments were cut at intervals of 0.5～1.0cm and were measured for grain sizes by the Scanning Photo Sedimentograph “Analysette 20” made in Germany. Based on accurate dating by 137 Cs and 210 Pb ex, the author reconstructs the dry-humid transformation history of the regional climate according to the vertical profile of sediment particle sizes, which provides a new effective way for recovering the century-scale climatic changes. The following conclusions are drawn: (1) General environmental significance of sediment grain size should not be applied mechanically in reconstructing palaeoclimate. Only after concretely analyzing all the factors which affect sediment grain size, can credible conclusions be obtained during discussing different time-scales climate changes. (2) During long time-scale studies, lake level is the most important factor dominating sediment grain size. Sediments are finer during the humid period of high water level because coarse particles can not be transported to the lake's deepwater part. On the contrary, during short time-scale studies within a given climate period, rainfall change in the drainage basin becomes the key factor determining sediment grain size because the lake level is basically constant. When rainfall is heavy, runoff flow is strong enough to bring coarse terrestrial particles to the sampling location, resulting in larger grain sizes. (3) The 15th century was the driest in the region of Lake Erhai during the past 640 years. There exist two time-scales(100 and 200 years) climatic quasi-periodical changes. From the end of the last century, the regional climate has been becoming drier and drier as a whole. At present, it is at the end of the dry period, so the regional climate will become humid in near future.
As a main lodging of surface substances, lake sediments continuously and sensitively record information of regional climate and environment with annual to decadal resolution. The sediment core EH911208-3-5 with a length of 83cm was taken from deepwater location in Erhai Lake in 1991, using the sediment-water interface sampler specially designed by ourselves. The sediments were cut at intervals of 0.5～1.0cm and were measured for grain sizes by the Scanning Photo Sedimentograph “Analysette 20” made in Germany. Based on accurate dating by 137 Cs and 210 Pb ex, the author reconstructs the dry-humid transformation history of the regional climate according to the vertical profile of sediment particle sizes, which provides a new effective way for recovering the century-scale climatic changes. The following conclusions are drawn: (1) General environmental significance of sediment grain size should not be applied mechanically in reconstructing palaeoclimate. Only after concretely analyzing all the factors which affect sediment grain size, can credible conclusions be obtained during discussing different time-scales climate changes. (2) During long time-scale studies, lake level is the most important factor dominating sediment grain size. Sediments are finer during the humid period of high water level because coarse particles can not be transported to the lake's deepwater part. On the contrary, during short time-scale studies within a given climate period, rainfall change in the drainage basin becomes the key factor determining sediment grain size because the lake level is basically constant. When rainfall is heavy, runoff flow is strong enough to bring coarse terrestrial particles to the sampling location, resulting in larger grain sizes. (3) The 15th century was the driest in the region of Lake Erhai during the past 640 years. There exist two time-scales(100 and 200 years) climatic quasi-periodical changes. From the end of the last century, the regional climate has been becoming drier and drier as a whole. At present, it is at the end of the dry period, so the regional climate will become humid in near future.
Sedimentary Environment of the Lower CretaceousDuoba Formation of the Cuoqin Foreland Basin in Tibet
2000, 18(3): 349-354,368.
Abstract:
Cuoqin foreland basin is located in the north of Tibet, bettwen Gangdisi Arc and 13angong lake一Nu river frac- lure belt. It wnaly extents along east and west from Geji, Nima to Bange. Thousands of meters marine strata of the Mesozoic Tethys is developed in the basin. The Lower Cretaceous T3uoba Formation is a set of mixed sediments of carbonates and terrigenous elastics. In this paper,acmrding to a detailed study for several sedimentary sections,the author expounds sedimentary evolution of the Ihzoba Formation and its main controlling factors The lower part of Duoba Formation is made up of some non一isopach cycles which are composed of elastic rock, especially gray meth，一thin layer feldspathie litharenite.Each cycle represents a depositional phase that de- trital material of tidal一flat fades rapidly progradate and then retrogradate. These cycles can include tidal一flat channel,sand-flat and mud-flat sediments.There are always some carbonaceous fragments on sandstone layers. In the middle part of Duoba Formation, diffrent kind of medium一thin layer carbonate facies and elastic facies mm- pose a series of sedimentary cycles. Carbonate rock increases upward in these cycles. Each cycle is $0一130 meters, showing a transformation from the tip of tidal一flat deposition to carbonate platform deposition. The upper part of Duoha Formation is composed of three sedimentary cycles which is about 130一200 meters. From bottom to top, each cycle includes mudstone of low一energy subtidal facies,sandstone of tidal一flat end facies,mudstorie of suhti dal facies,carbonate rock of platform and its edge fades. Comparing with the middle part, carbonate rock distinctly increase and thicken, and thick layer nudist limestone or orbitolina limestone of shoal facies occurs too. As a whole,progradation of tidal一flat facies is primary in the early of depositional phase of the Duoba Forma- tion,and retrogradation of tidal一flat fades and extention of Carbonate platform is prominent in the late. This depo- sitional character shows not only in the whole Duoba Formation,but also in each Sedimentary cycle of the Duoba Formation.Synthesizing depositional character of the Duoba Formation, a depositional model can be reached. It is a mixed sediments model near shore for carbonates and terrigenous elastics, with plentiful supply of elastic and a gentle slope. From land to sea, there are two parts in the model: one by land is tidal-flat, and the other is carbonate plat- form,bettwen them develops mixed sediments of low-energy subtidai fades. From the south to the north,difference in depositional feature is obvious within narrow basset area of the Duo- ba Formation along east and west in Cucxtin basin. During deposition of the Duoba Formation, there are two car- bonate platforms about Guiya一Lunpola and Dongcuo, and Geji一Yanhu maybe is the third. Palaeotectonic system clearly controls distribution and depositional feature of the Lower Crezaceous including the Duoba Formation in Cuoqin basin. Bouned by.liangma一Geang lake fracture, the south near the Gangdisi Arc develops pyroclastic sediments with 2D00 meters thick near Cunqin, and its sedimentary environment is wedge-top and foredeep of foreland basin. This set of stratum is called Zhenong Formation(Kizl).On the contrary, the north develops mixed sediments of carbonates and terrigenous elastic. Its sedimentary environment is foredeep and fore- lift. This sediments forms the Duoba Formation. Clastic material mainly from Cangdisi Arc and wedge-top. Towards basin uplift near Bangong lake一Vu river fracture belt, carbonate rock in strata increases, and formation thickness reduces and gradully pinch一outs. These obviously show a sedimentary fracture of foreland which is con- troled by thrust belt.
Cuoqin foreland basin is located in the north of Tibet, bettwen Gangdisi Arc and 13angong lake一Nu river frac- lure belt. It wnaly extents along east and west from Geji, Nima to Bange. Thousands of meters marine strata of the Mesozoic Tethys is developed in the basin. The Lower Cretaceous T3uoba Formation is a set of mixed sediments of carbonates and terrigenous elastics. In this paper,acmrding to a detailed study for several sedimentary sections,the author expounds sedimentary evolution of the Ihzoba Formation and its main controlling factors The lower part of Duoba Formation is made up of some non一isopach cycles which are composed of elastic rock, especially gray meth，一thin layer feldspathie litharenite.Each cycle represents a depositional phase that de- trital material of tidal一flat fades rapidly progradate and then retrogradate. These cycles can include tidal一flat channel,sand-flat and mud-flat sediments.There are always some carbonaceous fragments on sandstone layers. In the middle part of Duoba Formation, diffrent kind of medium一thin layer carbonate facies and elastic facies mm- pose a series of sedimentary cycles. Carbonate rock increases upward in these cycles. Each cycle is $0一130 meters, showing a transformation from the tip of tidal一flat deposition to carbonate platform deposition. The upper part of Duoha Formation is composed of three sedimentary cycles which is about 130一200 meters. From bottom to top, each cycle includes mudstone of low一energy subtidal facies,sandstone of tidal一flat end facies,mudstorie of suhti dal facies,carbonate rock of platform and its edge fades. Comparing with the middle part, carbonate rock distinctly increase and thicken, and thick layer nudist limestone or orbitolina limestone of shoal facies occurs too. As a whole,progradation of tidal一flat facies is primary in the early of depositional phase of the Duoba Forma- tion,and retrogradation of tidal一flat fades and extention of Carbonate platform is prominent in the late. This depo- sitional character shows not only in the whole Duoba Formation,but also in each Sedimentary cycle of the Duoba Formation.Synthesizing depositional character of the Duoba Formation, a depositional model can be reached. It is a mixed sediments model near shore for carbonates and terrigenous elastics, with plentiful supply of elastic and a gentle slope. From land to sea, there are two parts in the model: one by land is tidal-flat, and the other is carbonate plat- form,bettwen them develops mixed sediments of low-energy subtidai fades. From the south to the north,difference in depositional feature is obvious within narrow basset area of the Duo- ba Formation along east and west in Cucxtin basin. During deposition of the Duoba Formation, there are two car- bonate platforms about Guiya一Lunpola and Dongcuo, and Geji一Yanhu maybe is the third. Palaeotectonic system clearly controls distribution and depositional feature of the Lower Crezaceous including the Duoba Formation in Cuoqin basin. Bouned by.liangma一Geang lake fracture, the south near the Gangdisi Arc develops pyroclastic sediments with 2D00 meters thick near Cunqin, and its sedimentary environment is wedge-top and foredeep of foreland basin. This set of stratum is called Zhenong Formation(Kizl).On the contrary, the north develops mixed sediments of carbonates and terrigenous elastic. Its sedimentary environment is foredeep and fore- lift. This sediments forms the Duoba Formation. Clastic material mainly from Cangdisi Arc and wedge-top. Towards basin uplift near Bangong lake一Vu river fracture belt, carbonate rock in strata increases, and formation thickness reduces and gradully pinch一outs. These obviously show a sedimentary fracture of foreland which is con- troled by thrust belt.
2000, 18(3): 362-368.
Abstract:
The high一frequency sea level changes in the North China epicontinental basin from the lzte Carboniferous to Early Permian are the main factozs controlling the basin一filling and coal accumulation. The mal一bearing succes- lion, therefore, has distinct cycles. The sea level changes in the North China epicontinental basin were composite sea level changes. The long一term。level changes are superposed访shorter一term cycles, the mid一term and shop，一term sea level changes. There were short一term reti,ogressive events in the process of long term transgres- live period, and multiple short periodic transgreSSive events superposed an the long一term transgressive period. Study shows that the base一level cycles in the North Ghina epicontinental basin may be substitute the relative sea level cycles, because the high一frequency sea level changes in the basin are the integrative results of the sea lev- e1 changes, the tectonin subsidence, the climate changes and the sediment supply. The later three factors, the tec- tonics, the climate and the sediment supply~relatively stable. The sea level changes, thus, become the domi- nant factor. Using the thought and methodology of high一resolution sequence stratigraphy, the authors investigate the characteristics of the high一resolution sequence stratigraphy of the coal measures in the Western Shandong, identi- fy and divide the mid一long term and mid一short term Ease一level cycles. Three long一term base一level changes lead to the formation of three third order sequences. The mid一term base一level cycles are approximately oorre- sponded to the systems tracts. Large一scale marine flooding events were caused by the mid一term base一level rise. Because of the hysteresis of the deposition, the thick一bedded limestanes were depceited in the period of maximum base一level rises, which occurred three times in the history of the epicontinental basin, representing the depositions of three times of maximum base一level rises. The outstanding feature of the paralic succession is the alternative oc- currences of the marine and terrestrial depositions, forming multiple cycles. That the marine layers directly super- posed on the malheds is another feature of the deposition in the epicontinental basin. Eighteen short一term base一 level cycles may be recognized in the epiwntinental succession of the Western Shandong. Most of cycles are asym- metric, seperated by episodic transgressive event surfaces, peatification event surfaces and large swpe of scouring surfaces. The short一term base一level cycles are of high frequency. The identification and come王ation of short一terrrt base一level cycles help to the division of high一resolution se- quence. The study of the epicontinental paralic base一level cycles in the Western 5handong indicates that the eigh- teen short一term Ease一level cycles arc corresponded to eighteen fifth一order sequences corresponding to the parasequences.The episodic transgressive events have great effect on the coal accumulation in the epicontinental basin; coal formation in the transgressive process is the outstanding feature of the coal formation in the Western shandong coalfields. The transgressive coalbeds in the long一term base一level cycles develop in the transgressive systems tracts, while the transgressive ooalbeds in the short一term base一level cycles occur in the high stand sys- terns tracts.
The high一frequency sea level changes in the North China epicontinental basin from the lzte Carboniferous to Early Permian are the main factozs controlling the basin一filling and coal accumulation. The mal一bearing succes- lion, therefore, has distinct cycles. The sea level changes in the North China epicontinental basin were composite sea level changes. The long一term。level changes are superposed访shorter一term cycles, the mid一term and shop，一term sea level changes. There were short一term reti,ogressive events in the process of long term transgres- live period, and multiple short periodic transgreSSive events superposed an the long一term transgressive period. Study shows that the base一level cycles in the North Ghina epicontinental basin may be substitute the relative sea level cycles, because the high一frequency sea level changes in the basin are the integrative results of the sea lev- e1 changes, the tectonin subsidence, the climate changes and the sediment supply. The later three factors, the tec- tonics, the climate and the sediment supply~relatively stable. The sea level changes, thus, become the domi- nant factor. Using the thought and methodology of high一resolution sequence stratigraphy, the authors investigate the characteristics of the high一resolution sequence stratigraphy of the coal measures in the Western Shandong, identi- fy and divide the mid一long term and mid一short term Ease一level cycles. Three long一term base一level changes lead to the formation of three third order sequences. The mid一term base一level cycles are approximately oorre- sponded to the systems tracts. Large一scale marine flooding events were caused by the mid一term base一level rise. Because of the hysteresis of the deposition, the thick一bedded limestanes were depceited in the period of maximum base一level rises, which occurred three times in the history of the epicontinental basin, representing the depositions of three times of maximum base一level rises. The outstanding feature of the paralic succession is the alternative oc- currences of the marine and terrestrial depositions, forming multiple cycles. That the marine layers directly super- posed on the malheds is another feature of the deposition in the epicontinental basin. Eighteen short一term base一 level cycles may be recognized in the epiwntinental succession of the Western Shandong. Most of cycles are asym- metric, seperated by episodic transgressive event surfaces, peatification event surfaces and large swpe of scouring surfaces. The short一term base一level cycles are of high frequency. The identification and come王ation of short一terrrt base一level cycles help to the division of high一resolution se- quence. The study of the epicontinental paralic base一level cycles in the Western 5handong indicates that the eigh- teen short一term Ease一level cycles arc corresponded to eighteen fifth一order sequences corresponding to the parasequences.The episodic transgressive events have great effect on the coal accumulation in the epicontinental basin; coal formation in the transgressive process is the outstanding feature of the coal formation in the Western shandong coalfields. The transgressive coalbeds in the long一term base一level cycles develop in the transgressive systems tracts, while the transgressive ooalbeds in the short一term base一level cycles occur in the high stand sys- terns tracts.
2000, 18(3): 376-383.
Abstract:
By identifying sequence boundary generated by base level cycle, the author have reloghizcd fled four sequences in upper part of middle Eocene series and upper Eocene series of Dongying depression. Every sequence has similar genesis and system tract trait. Lowstand system tract (LST) developed braided fluvial, incised channel一turbidity fans,fan deltas,abandoned deltas and subfan.Iacustrine expanding system tract (EST) developed lacustrine sys- tem, consisted of deep mudstone, oil shale, dolomite and shallow lacustrine, destroyed deltas and meandering streams. Lacustrine retreating system tract (R5T) developed shallow lacustrine, fluvial一delta system, and Ian delta system. Because sequence developed in different sites of the basin, the sequence shows three kinds of sequence style: A, deep lacustrine一delta environment sequence style distributing below structure break. fd, incised channel 一shallow lacustrine environment sequence style distributing upward structure break. C, fluvial - flooding plain se- quence environment style distributing beyond lacustrine. Based on comprehensive research, this paper has built up the genetic model of upper part of middle Eocene series and upper Eocene series in ilongying deprewsion.The model indicates that sequence generation was controlled by third cycle of base level as a function of tectonic movement and climate. Because water volume of lake is finite, tilting and faulting redistributes the lake water toward increased accommodation space area, base level fell to generate lowstand system tract characterized by incised channel and turbidity fart. In the inactive epoch faulting of, base level, affected by elirnate, rise rapidly to generate lacustrine expanding system tract characterized by lacustrine facies spreading. When the lake level recovering to the situation before faulting, Ease level arrived at summit and began to fall, because faulting made tolxg graphy steep, sedintenra- ry supplied enough, lacustrine retreating system tract characterigxd by delta was generated. Depositing fault Cannes near depression parts in front of the main lobe of delta distribute mainly lnwstand sands, which are the main accu- mulatinn canes of lowstand sand resen"oir and prospecting direction for exploring shelter reservoir.
By identifying sequence boundary generated by base level cycle, the author have reloghizcd fled four sequences in upper part of middle Eocene series and upper Eocene series of Dongying depression. Every sequence has similar genesis and system tract trait. Lowstand system tract (LST) developed braided fluvial, incised channel一turbidity fans,fan deltas,abandoned deltas and subfan.Iacustrine expanding system tract (EST) developed lacustrine sys- tem, consisted of deep mudstone, oil shale, dolomite and shallow lacustrine, destroyed deltas and meandering streams. Lacustrine retreating system tract (R5T) developed shallow lacustrine, fluvial一delta system, and Ian delta system. Because sequence developed in different sites of the basin, the sequence shows three kinds of sequence style: A, deep lacustrine一delta environment sequence style distributing below structure break. fd, incised channel 一shallow lacustrine environment sequence style distributing upward structure break. C, fluvial - flooding plain se- quence environment style distributing beyond lacustrine. Based on comprehensive research, this paper has built up the genetic model of upper part of middle Eocene series and upper Eocene series in ilongying deprewsion.The model indicates that sequence generation was controlled by third cycle of base level as a function of tectonic movement and climate. Because water volume of lake is finite, tilting and faulting redistributes the lake water toward increased accommodation space area, base level fell to generate lowstand system tract characterized by incised channel and turbidity fart. In the inactive epoch faulting of, base level, affected by elirnate, rise rapidly to generate lacustrine expanding system tract characterized by lacustrine facies spreading. When the lake level recovering to the situation before faulting, Ease level arrived at summit and began to fall, because faulting made tolxg graphy steep, sedintenra- ry supplied enough, lacustrine retreating system tract characterigxd by delta was generated. Depositing fault Cannes near depression parts in front of the main lobe of delta distribute mainly lnwstand sands, which are the main accu- mulatinn canes of lowstand sand resen"oir and prospecting direction for exploring shelter reservoir.
2000, 18(3): 389-394.
Abstract:
The devlopment history of ichnology and its current advances are briefly reviewed in this paper,and the measurement of ichnofabric indices is introduced.It is agreed that the ichnological suites and their variation could reflect changes in substrate consistency,physical environmental energy,sedimentation rate, bottom current,oxygen content,water chemistry and water depth, all these are consistent with both phases and magnitudes of the associated sea-level cycles.Based on the analysis above,it has been pointed out that the ichnofossils are sensitive to paleoenvironmental changes as a result of sea level dynamics,the potential of ichnology for the sequence stratigaphy could be indicated by at least the following five aspects:1.determination and analysis of cyclic sequences;2.recognition and interpreation of sequence stratigaphic boundaries;3.analysis of condensed section;4.facies succession analysis;5.definition of marine or lacustrine shore zones.
The devlopment history of ichnology and its current advances are briefly reviewed in this paper,and the measurement of ichnofabric indices is introduced.It is agreed that the ichnological suites and their variation could reflect changes in substrate consistency,physical environmental energy,sedimentation rate, bottom current,oxygen content,water chemistry and water depth, all these are consistent with both phases and magnitudes of the associated sea-level cycles.Based on the analysis above,it has been pointed out that the ichnofossils are sensitive to paleoenvironmental changes as a result of sea level dynamics,the potential of ichnology for the sequence stratigaphy could be indicated by at least the following five aspects:1.determination and analysis of cyclic sequences;2.recognition and interpreation of sequence stratigaphic boundaries;3.analysis of condensed section;4.facies succession analysis;5.definition of marine or lacustrine shore zones.
Internal－ Wave and Internal－ Tide Deposits of the Middle－ Upper Ordovician in the Center Tarim Basin
2000, 18(3): 400-407.
Abstract:
Deep一water traction currents of internal一wave and internal一ride origin are well developed on modern sea floor. They can not only produce sedimentary structures of cm一size but also build large一sca1e sediment waves of km一size. Moreover, mast of these sediment waves migrate upslope. In ancient stratigraphic record, small一scale sedimentation units of internal一wave and internal一tide origin have been recognized Gut large一scale sediment waves of internal一wave origin have not. Based on detailed studies, different kinds of internal一wave and internal 一tide deposits have been recognized in the clastic rocks of the middle一upper Ordovician in the Central Tarim Basin. Four basiC sedimentary micrpfacies and five identical successions of internal一wave and internal一tide de- posits have been recognized and summarized. These microfacies are (1)hi一directional cross一laminated very fine- grained sandstone microfacies, (2)unidirectional cross一bedded and bi一directional crass一laminated medium一to fine一grained sandstone microfacies, (3)alternating sandstone and mudstone microfacies, and (4)oolitic limestone andsand politic limestone microfacies. The vertical successions include (l)symmetrical graded succession consisting entirely of cross一laminated sandstone, (2)normal graded succession consisting of cross一laminated sandstone, (3) normal graded succession consisting of medium scale cross一bedding and bi一directional cross一laminations, (4) symmetrical graded一couplet succession, (5)mudstone一oolitic limestone一mudstone succession. More importantly, based on detailed studies of seismic profiles, the authors discovered large一scale sediment waves of upslope migra- tion developed in the continental slope facies of the middle一upper Ordovician. The characteristics of these sedi- meat waves are similar to those of the sediment waves well developed on modem seafloor. According to the theory of internal wave, the origin of these sediment waves can be explained satisfactorily.
Deep一water traction currents of internal一wave and internal一ride origin are well developed on modern sea floor. They can not only produce sedimentary structures of cm一size but also build large一sca1e sediment waves of km一size. Moreover, mast of these sediment waves migrate upslope. In ancient stratigraphic record, small一scale sedimentation units of internal一wave and internal一tide origin have been recognized Gut large一scale sediment waves of internal一wave origin have not. Based on detailed studies, different kinds of internal一wave and internal 一tide deposits have been recognized in the clastic rocks of the middle一upper Ordovician in the Central Tarim Basin. Four basiC sedimentary micrpfacies and five identical successions of internal一wave and internal一tide de- posits have been recognized and summarized. These microfacies are (1)hi一directional cross一laminated very fine- grained sandstone microfacies, (2)unidirectional cross一bedded and bi一directional crass一laminated medium一to fine一grained sandstone microfacies, (3)alternating sandstone and mudstone microfacies, and (4)oolitic limestone andsand politic limestone microfacies. The vertical successions include (l)symmetrical graded succession consisting entirely of cross一laminated sandstone, (2)normal graded succession consisting of cross一laminated sandstone, (3) normal graded succession consisting of medium scale cross一bedding and bi一directional cross一laminations, (4) symmetrical graded一couplet succession, (5)mudstone一oolitic limestone一mudstone succession. More importantly, based on detailed studies of seismic profiles, the authors discovered large一scale sediment waves of upslope migra- tion developed in the continental slope facies of the middle一upper Ordovician. The characteristics of these sedi- meat waves are similar to those of the sediment waves well developed on modem seafloor. According to the theory of internal wave, the origin of these sediment waves can be explained satisfactorily.
2000, 18(3): 414-418,423.
Abstract:
Longhupao Field Area is located in the Songliao Basin. The Gaotaizi Oil Bed belongs to the second and third sections of Lower Cretaceous Qingshanqkou Formation in Longhupao Field Area. The reservoir rocks mainly deposited in distributary month bar and front thin sand sheet of lacustrine delta. The current geotemperature is 65 to 90 ℃, and the geothermal gradient is 3.9 ℃/100 m for Gaotaizi Oil Layer in Longhupao Field Area. Most reservoir rocks are lithic arkosic siltstone. The framework grains consist of 80% to 90% of reservoir rocks by volume. The framework composition is 20%～37% quartz, 23%～41% feldspar, and 14%～35% lithic rock fragments. Most rock fragments are of sedimentary and volcanic rocks. Sometimes carbonate particles are present. The carbonate particles, which is mainly ostracodes skeletons, are present in minor to trace amount, making up usually less than 5% of reservoir rocks. All clasticg rains are less than 0.5 mm in diam are believed to have. Compaction, cementation, dissolution, change of clay minerals, and displacement modified the sediments. The rocks are buried in 1 537～2 402 m. Compaction produled influence on sediments to a medium ou high degree because of fine clastic grain, poor sorting, some content of matrix and plastic carbonate particles. As a result of compaction, grain contacts are dominantly of long and concavo-convex types, and reduction of original pores is obvious. Compaction caused loss of 61.32% to 78.59%. Calcite is the most abundant authigenic minerals. Authigenic clays are rarely present Authigenic quartz is common, but present in trace amount. Authigenic feldspar is much less than authigenic quartz. Most calcite, among which clastic grains float, occurs in poikilotopic cement. The δ 13 and δ 18 O values of calcite cement range from 1.358‰ to 7.165‰ and -21.428‰ to -11.662‰, and average 2.958‰ and -19.351‰ (PDB), respectively. The δ 13 C and δ 18 O values of calcite cement change irregularly with depth, suggesting that burial diagenesis only slightly effect on calcite cement. The low values and narrow range of δ 13 C suggest that calcite cement formed early before maturation of organic material. Feldspar and intermediate/basic volcanic rock fragments are dissolved in different degree, forming various types of pores. Dissolution of quartz is often present, but weak, and only small dissolution pits are present in rims of quartz grains. Dissolution of calcite is also weak, and occurs only in cement of ostracoda coelomata. Illite is main clay mineral, and chlorite is present only in minor amount. Kaolinite basically disappeared. Smectite mostly changed to illite or mixed-layered illite/smectite. Vitrinite reflectance (Ro) rages from 0.61% to 1.39%, suggesting that organic material has already matured. Ancient geotemperature is higher than current geotemperature. Diagenesis proceeded to middle late stage. Compaction and cementation are the principle processes contributing to reduction of porosity. Dissolution of feldspar and intermediate/basic volcanic rock fragments made porosity increase to some degree. Compaction and calcite cementation prevented growth of authigenic quartz and formation of secondary porosity zones. Partial preservation of original pores and development of feldspar dissolution are due to framework consisting of clastic grains and calcite cement of early precipitation.
Longhupao Field Area is located in the Songliao Basin. The Gaotaizi Oil Bed belongs to the second and third sections of Lower Cretaceous Qingshanqkou Formation in Longhupao Field Area. The reservoir rocks mainly deposited in distributary month bar and front thin sand sheet of lacustrine delta. The current geotemperature is 65 to 90 ℃, and the geothermal gradient is 3.9 ℃/100 m for Gaotaizi Oil Layer in Longhupao Field Area. Most reservoir rocks are lithic arkosic siltstone. The framework grains consist of 80% to 90% of reservoir rocks by volume. The framework composition is 20%～37% quartz, 23%～41% feldspar, and 14%～35% lithic rock fragments. Most rock fragments are of sedimentary and volcanic rocks. Sometimes carbonate particles are present. The carbonate particles, which is mainly ostracodes skeletons, are present in minor to trace amount, making up usually less than 5% of reservoir rocks. All clasticg rains are less than 0.5 mm in diam are believed to have. Compaction, cementation, dissolution, change of clay minerals, and displacement modified the sediments. The rocks are buried in 1 537～2 402 m. Compaction produled influence on sediments to a medium ou high degree because of fine clastic grain, poor sorting, some content of matrix and plastic carbonate particles. As a result of compaction, grain contacts are dominantly of long and concavo-convex types, and reduction of original pores is obvious. Compaction caused loss of 61.32% to 78.59%. Calcite is the most abundant authigenic minerals. Authigenic clays are rarely present Authigenic quartz is common, but present in trace amount. Authigenic feldspar is much less than authigenic quartz. Most calcite, among which clastic grains float, occurs in poikilotopic cement. The δ 13 and δ 18 O values of calcite cement range from 1.358‰ to 7.165‰ and -21.428‰ to -11.662‰, and average 2.958‰ and -19.351‰ (PDB), respectively. The δ 13 C and δ 18 O values of calcite cement change irregularly with depth, suggesting that burial diagenesis only slightly effect on calcite cement. The low values and narrow range of δ 13 C suggest that calcite cement formed early before maturation of organic material. Feldspar and intermediate/basic volcanic rock fragments are dissolved in different degree, forming various types of pores. Dissolution of quartz is often present, but weak, and only small dissolution pits are present in rims of quartz grains. Dissolution of calcite is also weak, and occurs only in cement of ostracoda coelomata. Illite is main clay mineral, and chlorite is present only in minor amount. Kaolinite basically disappeared. Smectite mostly changed to illite or mixed-layered illite/smectite. Vitrinite reflectance (Ro) rages from 0.61% to 1.39%, suggesting that organic material has already matured. Ancient geotemperature is higher than current geotemperature. Diagenesis proceeded to middle late stage. Compaction and cementation are the principle processes contributing to reduction of porosity. Dissolution of feldspar and intermediate/basic volcanic rock fragments made porosity increase to some degree. Compaction and calcite cementation prevented growth of authigenic quartz and formation of secondary porosity zones. Partial preservation of original pores and development of feldspar dissolution are due to framework consisting of clastic grains and calcite cement of early precipitation.
2000, 18(3): 424-430.
Abstract:
There is a suit of massive dolostones(as MD hereafter)which develop in the middle Majiagou Group of the Ordovician in the Ordos basin.It is mainly distributed in Majiagou Fm.Ⅳ,and it has several hundred metres at the zone of Dingbian County to Eteke Qi in the west part of Ordos basin, with maximum thickness 431 m in Dingtan Well 1.It becomes thinner and thinner from west to east,and is intercalated with limestones from the middle to eastern part of Ordos. The MD consist of coarse silt-sized to fine sand-sized dolomite crystals.The mottled texture is well developed in such dolostones,and the boundary of dolomitic spots is commonly stylolites.It shows that mottled dolomitization is obviously controlled by stylolites. The dolomites have uniform dar red colour under cathodoluminecence. The analytical data of 67 samples shows the ordering of dolomites averages 0.85,and the molar concentration of CaCO3 averages 50.65%;δ 13 C averages 0.6‰(PDB),δ18 O averages -7.4‰(PDB).The characteristics of cathodoluminecence and X-ray indicate approximate ideal dolomites are formed in stable diagenetic environment of slow conclear and crystalization.The homogeneous temperature of 21 primary inclusions in the host crystals is from 104℃ to 355℃(uncorrected by pressure),and the temperature of 104℃ is the lowest one.According to the earth temperature gradient of 3.98℃/100m in this area,the maximum burial depth of dolomitization is at least 2 600 m. Besides,the composition of inclusions has two parts-organic and inorganic and there is a certain of CH 4 both in gas phase and in liquid phase. All characteristics above prove that the huge thick dolostone body is formed in deep burial dolomitic environment.
There is a suit of massive dolostones(as MD hereafter)which develop in the middle Majiagou Group of the Ordovician in the Ordos basin.It is mainly distributed in Majiagou Fm.Ⅳ,and it has several hundred metres at the zone of Dingbian County to Eteke Qi in the west part of Ordos basin, with maximum thickness 431 m in Dingtan Well 1.It becomes thinner and thinner from west to east,and is intercalated with limestones from the middle to eastern part of Ordos. The MD consist of coarse silt-sized to fine sand-sized dolomite crystals.The mottled texture is well developed in such dolostones,and the boundary of dolomitic spots is commonly stylolites.It shows that mottled dolomitization is obviously controlled by stylolites. The dolomites have uniform dar red colour under cathodoluminecence. The analytical data of 67 samples shows the ordering of dolomites averages 0.85,and the molar concentration of CaCO3 averages 50.65%;δ 13 C averages 0.6‰(PDB),δ18 O averages -7.4‰(PDB).The characteristics of cathodoluminecence and X-ray indicate approximate ideal dolomites are formed in stable diagenetic environment of slow conclear and crystalization.The homogeneous temperature of 21 primary inclusions in the host crystals is from 104℃ to 355℃(uncorrected by pressure),and the temperature of 104℃ is the lowest one.According to the earth temperature gradient of 3.98℃/100m in this area,the maximum burial depth of dolomitization is at least 2 600 m. Besides,the composition of inclusions has two parts-organic and inorganic and there is a certain of CH 4 both in gas phase and in liquid phase. All characteristics above prove that the huge thick dolostone body is formed in deep burial dolomitic environment.
The Kinematics Characters of The Thrust- foldBelts Western Front Regions in Southern Tianshan, China
2000, 18(3): 439-444.
Abstract:
The Southern Tianshan thrust-fold systems are thin skin thrust structural belts formed after Miocene and Pliocene. Thrusting resulted in Palaozoic-Cenozoic clastic and carbonate rocks deforming in basin and margins regions. The kinematics characters of thrust front regions (Northern Bainkuluti and Kashi) were discussedThe Southern Tianshan thrust-fold systems were divided into six structural belts on plane and two tectonic layers in section. The blind thrust structural deltas were formed in thrust belts front.Thrusting made for Miocene strata deformation, uplift and denudation. There were two detachment surfaces. Thrusting on detachment surfaces gradually spreaded toward foreland and formed fault-related folds. That embranchment faults formed during structure activity made thrust belts more complication.The author indicated that thrust propagating of the Southern Tianshan thrust-fold systems were inverted sequence. The results were different from sequence of thrust-fold belts in Western Kunlun Mountain. It implicated that the Southern Tianshan thrust-fold systems were provided with unique kinematics characters. Using method of the balanced section, the structural crossing section was made and restored on the based of geology and geophysical data. Sequentially these were got that shorting percentage of the Southern Tianshan thrust-fold systems was 30%、that shorting amount was 50km and that shorting velocity was 9-10mm/a.
The Southern Tianshan thrust-fold systems are thin skin thrust structural belts formed after Miocene and Pliocene. Thrusting resulted in Palaozoic-Cenozoic clastic and carbonate rocks deforming in basin and margins regions. The kinematics characters of thrust front regions (Northern Bainkuluti and Kashi) were discussedThe Southern Tianshan thrust-fold systems were divided into six structural belts on plane and two tectonic layers in section. The blind thrust structural deltas were formed in thrust belts front.Thrusting made for Miocene strata deformation, uplift and denudation. There were two detachment surfaces. Thrusting on detachment surfaces gradually spreaded toward foreland and formed fault-related folds. That embranchment faults formed during structure activity made thrust belts more complication.The author indicated that thrust propagating of the Southern Tianshan thrust-fold systems were inverted sequence. The results were different from sequence of thrust-fold belts in Western Kunlun Mountain. It implicated that the Southern Tianshan thrust-fold systems were provided with unique kinematics characters. Using method of the balanced section, the structural crossing section was made and restored on the based of geology and geophysical data. Sequentially these were got that shorting percentage of the Southern Tianshan thrust-fold systems was 30%、that shorting amount was 50km and that shorting velocity was 9-10mm/a.
2000, 18(3): 449-452.
Abstract:
According to publications, the δ13 C value of the dolostones mainly ranges from -5‰ to +5‰ in a geological history except the Precambrian and Tertiary. However, we obtained some data of the dolostones which are more enriched in 13 C than +5‰ when we researched the dolostones in the Upper Permian Lucaogou Formation. The δ 13 C value of the dolostones varies in the range from +7.3‰ to +17.9‰ with an average of +11.7‰(7) and that of the dolomites from +7.9‰ to +16.1‰, averag +11.6‰(5). Based on the data of regional geology, petrology, mineralogy of the Upper Lucaogou Formation, the carbon isotopic characteristics of CO 2 from modern sedimentary sections in oceans and lakes and the simulation of bacterial process and carbonate minerals in ancient sedimentary sections we analyzed the distribution characteristics of the dolostones and considered that except higher buried rate of the global Permian living things and higher salinity of the researched area the anomally 13 C-enriched dolosdones are mainly due to the formation of 13C-depleted CH 4 and 13 C-enriched CO 2ed till now, but as one of possible sources of natural gas attention should be paid to it.
According to publications, the δ13 C value of the dolostones mainly ranges from -5‰ to +5‰ in a geological history except the Precambrian and Tertiary. However, we obtained some data of the dolostones which are more enriched in 13 C than +5‰ when we researched the dolostones in the Upper Permian Lucaogou Formation. The δ 13 C value of the dolostones varies in the range from +7.3‰ to +17.9‰ with an average of +11.7‰(7) and that of the dolomites from +7.9‰ to +16.1‰, averag +11.6‰(5). Based on the data of regional geology, petrology, mineralogy of the Upper Lucaogou Formation, the carbon isotopic characteristics of CO 2 from modern sedimentary sections in oceans and lakes and the simulation of bacterial process and carbonate minerals in ancient sedimentary sections we analyzed the distribution characteristics of the dolostones and considered that except higher buried rate of the global Permian living things and higher salinity of the researched area the anomally 13 C-enriched dolosdones are mainly due to the formation of 13C-depleted CH 4 and 13 C-enriched CO 2ed till now, but as one of possible sources of natural gas attention should be paid to it.
2000, 18(3): 460-464.
Abstract:
The Analysis Method Based on Ash-Composition is a new method in coal-accumulating environment analysis and reconstruction. Principles of the method are that all ash composition comes from the minerals and clasts in coal seams, so it is possible to reversely infer the sorts, contents and grading law of the minerals and clasts of coal seam from the sorts, contents and grading law of ash composition,in advance to judge the coal forming environment. Main points are as follows: (1) According to the end-member SiO2-Al2O3, analyze the sort, content and its grading law of clay minerals and land-source clasts in coal seams,in advance to judge the main direction of trasportion. (2) According to the end-member CaO-MgO, analyze the sort and content of calcium-magnesium mineral in coal, in advance to judge the distance between coal-accumulating environment and the marine. (3) According to the end-member Fe 2O 3-SO 3, analyze the sort and content of iron mineral (esp. pyrite), in advance to judge the oxidation-reduction condition of coal-accumulating environment. This method was applied in studying accumulating environment of coal seam No.10# in Taiyuan Group, Hedong Coal Basin, and achieved satisfactory result,which proved that the analysis method based on ash-composition is a valuable way in reconstructing coal forming environment.
The Analysis Method Based on Ash-Composition is a new method in coal-accumulating environment analysis and reconstruction. Principles of the method are that all ash composition comes from the minerals and clasts in coal seams, so it is possible to reversely infer the sorts, contents and grading law of the minerals and clasts of coal seam from the sorts, contents and grading law of ash composition,in advance to judge the coal forming environment. Main points are as follows: (1) According to the end-member SiO2-Al2O3, analyze the sort, content and its grading law of clay minerals and land-source clasts in coal seams,in advance to judge the main direction of trasportion. (2) According to the end-member CaO-MgO, analyze the sort and content of calcium-magnesium mineral in coal, in advance to judge the distance between coal-accumulating environment and the marine. (3) According to the end-member Fe 2O 3-SO 3, analyze the sort and content of iron mineral (esp. pyrite), in advance to judge the oxidation-reduction condition of coal-accumulating environment. This method was applied in studying accumulating environment of coal seam No.10# in Taiyuan Group, Hedong Coal Basin, and achieved satisfactory result,which proved that the analysis method based on ash-composition is a valuable way in reconstructing coal forming environment.
2000, 18(3): 469-474.
Abstract:
Forty seven species of fossil spores and pollen referred to 25 genera extracted from the crude oil samples collected from the reservoirs within the Upper Oligocene Zhuhai Formation in the Pearl River Mouth Basin of the North Continental Shelf of South China Sea were recorded in this paper. Based on the investigations of the spores and pollen in crude oil and their stratigraphical distribution, the Eogene petroleum source rocks of the petroliferous basin were determined. In accordance with the paleoecological characteristics of the original plants producing the spores and pollen, the sedimentary environment of the Eogene petroleum source rocks was discussed. The results of the study indicate that the black and dark grey clayrocks of the Middle Eocene Wenchang Formation and the Upper Eocene to Middle Oligocene Enping Formation should be the petroleum source rocks of the Pearl River Mouth Basin; and the petroleum source rocks might have originated and evolved in the subtropic lacustrine sedimentary environment under warm and wet climatic conditions.
Forty seven species of fossil spores and pollen referred to 25 genera extracted from the crude oil samples collected from the reservoirs within the Upper Oligocene Zhuhai Formation in the Pearl River Mouth Basin of the North Continental Shelf of South China Sea were recorded in this paper. Based on the investigations of the spores and pollen in crude oil and their stratigraphical distribution, the Eogene petroleum source rocks of the petroliferous basin were determined. In accordance with the paleoecological characteristics of the original plants producing the spores and pollen, the sedimentary environment of the Eogene petroleum source rocks was discussed. The results of the study indicate that the black and dark grey clayrocks of the Middle Eocene Wenchang Formation and the Upper Eocene to Middle Oligocene Enping Formation should be the petroleum source rocks of the Pearl River Mouth Basin; and the petroleum source rocks might have originated and evolved in the subtropic lacustrine sedimentary environment under warm and wet climatic conditions.
2000, 18(3): 480-483.
Abstract:
Thermal maturity is a necessary parameter in assessing source rocks and evolution of oils and gases in sedimentary basins. It is shown from the investigations of over the past twenty years that the maturity parameters of methylated dibenzothiophenes are expected to be the efficient molecular maturity indices of marine carbonate source rocks and their oils or gases at high and overmature stages. It has been an unsolved problem up to now to create relationship between methylated dibenzothiophene maturity parameters and Ro values of carbonate source rocks (converted from solid bitumen reflectance-Rb, or marine vitrinite reflectance-R M o) at high and overmature stages. The creation of the above relationship will provide a more reliable new method for calculation of oils and gases Ro values, as well as for oil-source or gas-source correlation of Lower Palaeozoic and Middle-Upper Proterozoic carbonate source rocks. Therefore, it has broader and brighter application prospects in guiding future oils and gases exploration of marine strata in chima.
Thermal maturity is a necessary parameter in assessing source rocks and evolution of oils and gases in sedimentary basins. It is shown from the investigations of over the past twenty years that the maturity parameters of methylated dibenzothiophenes are expected to be the efficient molecular maturity indices of marine carbonate source rocks and their oils or gases at high and overmature stages. It has been an unsolved problem up to now to create relationship between methylated dibenzothiophene maturity parameters and Ro values of carbonate source rocks (converted from solid bitumen reflectance-Rb, or marine vitrinite reflectance-R M o) at high and overmature stages. The creation of the above relationship will provide a more reliable new method for calculation of oils and gases Ro values, as well as for oil-source or gas-source correlation of Lower Palaeozoic and Middle-Upper Proterozoic carbonate source rocks. Therefore, it has broader and brighter application prospects in guiding future oils and gases exploration of marine strata in chima.
2000, 18(3): 336-340.
Abstract:
On the basis of environmental magnetism study on soils formed on Quaternary sediments in Yangtze River valley,the soil magnetic enhancement and its mechanism were discussed.Results showed that soils formed on Quaternary sediments exhibited a distinct ferrimagnetic profile with the magnetic susceptibility enhancement of soil horizons with respect to that of parent materials. It is suggested that formation of pedogenic ferrimagnetic minerals resulted in enhancement of magnetic susceptibility in soils.In addition,the pedogenic ferrimagnetic minerals are mostly superparamagnetic(SP) and stable single domain(SSD)grains.It is found that highly significant relationships between the magnetic susceptibility( χ ) values of the samples and frequency dependent susceptibility ( χ fd ) and between χ values of samples and anhysteretic susceptibility( χ ARM ).It is suggested that χ can be considered an indicator for the environmental fluctuation recorded in soils. Results also suggested that χ fd value of 5% can be regarded as an indicator to reflect the formation of pedogenic SP and SSD ferrimagnetic minerals in the continuous pedogenic development of soils.Thus,magnetic susceptibility can be used to study the Quaternary environmental changes.
On the basis of environmental magnetism study on soils formed on Quaternary sediments in Yangtze River valley,the soil magnetic enhancement and its mechanism were discussed.Results showed that soils formed on Quaternary sediments exhibited a distinct ferrimagnetic profile with the magnetic susceptibility enhancement of soil horizons with respect to that of parent materials. It is suggested that formation of pedogenic ferrimagnetic minerals resulted in enhancement of magnetic susceptibility in soils.In addition,the pedogenic ferrimagnetic minerals are mostly superparamagnetic(SP) and stable single domain(SSD)grains.It is found that highly significant relationships between the magnetic susceptibility( χ ) values of the samples and frequency dependent susceptibility ( χ fd ) and between χ values of samples and anhysteretic susceptibility( χ ARM ).It is suggested that χ can be considered an indicator for the environmental fluctuation recorded in soils. Results also suggested that χ fd value of 5% can be regarded as an indicator to reflect the formation of pedogenic SP and SSD ferrimagnetic minerals in the continuous pedogenic development of soils.Thus,magnetic susceptibility can be used to study the Quaternary environmental changes.
2000, 18(3): 346-348.
Abstract:
Erhai lake,the second largest lake in the Yunnan Plateau in Southwest China,is located in Dali Prefecture with 25°35'to 25°58'Nin Latitude 100°05'to 100°07'Ein logitude Erhai Lake is a typical rift lake in the Dali Basin developed along the YuaJiang Hoonghe great fault and has been in existence since Later Pliocene.In November 1996(winter),the lake water quality was still in a poor condition,with a low concentration of dissolved oxygen.The lowest Do value was 1.7 mg/L.Results of comprehensive assesment indicate that water quality at most of the sections was grade III,with some of them reaching grade IV.The sudden deterioration of water quality in Lake Erhai has clearly indicated that the lake's water quality is at a critical state.In order to prevent occurrence of more eutrophication in the future,study of nutrient and pollutant emissions from sediment to the lake by environment sedimentology methods would be necessary.By Studying relationship between nutrient and particle size distribution for the Erhai lake's superficial seddiments,the results show that clay mineral is generally positively correlated with total phosphorus,Fe P and O P. The multiple regression results suggest that there are apparently positive correlation among TN,TON(total organic nitrogen),T HN 3,A'% and deris minerals.The TP content is mainly comprised of inorganic posphorus and positively correlated with sediments with higher content of clay minerals and smaller particle size mainly deposited in the lake center in the northern part of Erhai lake.
Erhai lake,the second largest lake in the Yunnan Plateau in Southwest China,is located in Dali Prefecture with 25°35'to 25°58'Nin Latitude 100°05'to 100°07'Ein logitude Erhai Lake is a typical rift lake in the Dali Basin developed along the YuaJiang Hoonghe great fault and has been in existence since Later Pliocene.In November 1996(winter),the lake water quality was still in a poor condition,with a low concentration of dissolved oxygen.The lowest Do value was 1.7 mg/L.Results of comprehensive assesment indicate that water quality at most of the sections was grade III,with some of them reaching grade IV.The sudden deterioration of water quality in Lake Erhai has clearly indicated that the lake's water quality is at a critical state.In order to prevent occurrence of more eutrophication in the future,study of nutrient and pollutant emissions from sediment to the lake by environment sedimentology methods would be necessary.By Studying relationship between nutrient and particle size distribution for the Erhai lake's superficial seddiments,the results show that clay mineral is generally positively correlated with total phosphorus,Fe P and O P. The multiple regression results suggest that there are apparently positive correlation among TN,TON(total organic nitrogen),T HN 3,A'% and deris minerals.The TP content is mainly comprised of inorganic posphorus and positively correlated with sediments with higher content of clay minerals and smaller particle size mainly deposited in the lake center in the northern part of Erhai lake.
2000, 18(3): 355-361.
Abstract:
The Hoh Xil basin, which is the largest Tertiary sedimentary basin in the hinterland of the Tibet plateau, is bounded on the north margin by the Kunlun Mountains and the South Kunlun suture zone, and on the south margin by the Tanggula Mountains and the Kangbataqing fault. The basin contains a Tertiary sediment pile of approximately 5.4 km thick of fluvial mudstone, sandstone, and conglomerate and 0.4 km thick of limestone, which was reported to have a closed relationship with the continental collision and early uplift of the Tibet plateau. From lower to upper, the Tertiary sediments include the Early Eocene to Early Oligocene Fenghuoshan Group, the Early Oligocene Yaxicuo Group, and the Early Miocene Wudaoliang Group. Here we clarify the facies analysis of the Yaxicuo Group, which was magnetostratigraphically dated as 32.0-30.0 Ma, and discuss its paleoclimatic significance. The Yaxicuo Group is 670.0 m thick and consists mainly of violet alternating sandstone and mudstone with intercalated gray layered and tubercular gypsolith. The standard section GG2 of the Yaxicuo Group is situated in the southern part of the Wudaoliang area of the Hoh Xil basin. The Yaxicuo Group consists mainly of lacustrine facies, but contains fluvial facies in the lower-middle part. The lacustrine facies includes shore, shallow lake, and salt lake subfacies. They are characterized by coarsening and thickening upward of sandstone and siltstone. The fluvial facies consists of point bars, natural levees, and flood plains and is characterized by sandstone and conglomerate that fine and thin upward. Paleocurrent directions were measured from sedimentary structures of, for examples, lamination, planar cross-bedding, parallel bedding, and climbing-ripple cross-lamination. They indicate that the depocenter of the Hoh Xil basin was migrated eastward and northward during the period of 32.0-30.0 Ma. The very thin stratified and nodulated types of gypsolith started to suddenly abundantly develop in the lower of the Yaxicuo Group at about 32.0 Ma ago. However, only a few layers of very thin stratified of gypsolith was formed in the lower part of the Fenghuoshan Group, whereas the other parts of sediments belong to fluvial and lacustrine environment with normal salinity. Therefore, the development of the gypsolith at least reflects the drying event in the earliest Oligocene, which was recorded in the northern Tibetan plateau. The paleoclimatic event could be correlated well to the global cooling and drying events of the earliest Oligocene.
The Hoh Xil basin, which is the largest Tertiary sedimentary basin in the hinterland of the Tibet plateau, is bounded on the north margin by the Kunlun Mountains and the South Kunlun suture zone, and on the south margin by the Tanggula Mountains and the Kangbataqing fault. The basin contains a Tertiary sediment pile of approximately 5.4 km thick of fluvial mudstone, sandstone, and conglomerate and 0.4 km thick of limestone, which was reported to have a closed relationship with the continental collision and early uplift of the Tibet plateau. From lower to upper, the Tertiary sediments include the Early Eocene to Early Oligocene Fenghuoshan Group, the Early Oligocene Yaxicuo Group, and the Early Miocene Wudaoliang Group. Here we clarify the facies analysis of the Yaxicuo Group, which was magnetostratigraphically dated as 32.0-30.0 Ma, and discuss its paleoclimatic significance. The Yaxicuo Group is 670.0 m thick and consists mainly of violet alternating sandstone and mudstone with intercalated gray layered and tubercular gypsolith. The standard section GG2 of the Yaxicuo Group is situated in the southern part of the Wudaoliang area of the Hoh Xil basin. The Yaxicuo Group consists mainly of lacustrine facies, but contains fluvial facies in the lower-middle part. The lacustrine facies includes shore, shallow lake, and salt lake subfacies. They are characterized by coarsening and thickening upward of sandstone and siltstone. The fluvial facies consists of point bars, natural levees, and flood plains and is characterized by sandstone and conglomerate that fine and thin upward. Paleocurrent directions were measured from sedimentary structures of, for examples, lamination, planar cross-bedding, parallel bedding, and climbing-ripple cross-lamination. They indicate that the depocenter of the Hoh Xil basin was migrated eastward and northward during the period of 32.0-30.0 Ma. The very thin stratified and nodulated types of gypsolith started to suddenly abundantly develop in the lower of the Yaxicuo Group at about 32.0 Ma ago. However, only a few layers of very thin stratified of gypsolith was formed in the lower part of the Fenghuoshan Group, whereas the other parts of sediments belong to fluvial and lacustrine environment with normal salinity. Therefore, the development of the gypsolith at least reflects the drying event in the earliest Oligocene, which was recorded in the northern Tibetan plateau. The paleoclimatic event could be correlated well to the global cooling and drying events of the earliest Oligocene.
2000, 18(3): 369-375.
Abstract:
The sedimentary dynamic analysis of sequence structure and stacking pattern of base-level cycle is one of the most important contents to integrate and apply the theory and technology of high-resolution sequence stratigraphy.In this paper,the author takes the stratigraphic and sedimentary process-response dynamic principles as a theoretical basis, middle term base-level cycle as a period and short term base-level cycle as a genetic stratigraphic unit to discuss the relationship between the sequence structure,the sequence stacking pattern,the ratio variation of accommodation space to sedimentary alimentation (A/S ),the rise or fall range of base-level and the sedimentary dynamic condition.It shows that the short term base-level cycles with different sequence structure and stacking pattern distribute regularly in the middle term base-level cycle, and suggests the standard section architecture of the middle term base-level cycle.It is very significance that the sedimentary dynamic analysis on the sequence structure and stacking pattern of short or middle term base-level cycle in terms of theory mentioned above is completely consistent with the application aspects of the high-resolution sequence stratigraphy of the Mesozoicor Cenozoic terrestrial stratigraphy in Sichuan Basin,Ordos Basin and Liaohe Basin and so on and proves that the theoretical systerm and the analytical technology of the high-resolution sequence stratigraphy and completely adapted to employ the sequence research of the Mesozoic or Cenozoic terrigenous oil-bearing basins developed widely in China.
The sedimentary dynamic analysis of sequence structure and stacking pattern of base-level cycle is one of the most important contents to integrate and apply the theory and technology of high-resolution sequence stratigraphy.In this paper,the author takes the stratigraphic and sedimentary process-response dynamic principles as a theoretical basis, middle term base-level cycle as a period and short term base-level cycle as a genetic stratigraphic unit to discuss the relationship between the sequence structure,the sequence stacking pattern,the ratio variation of accommodation space to sedimentary alimentation (A/S ),the rise or fall range of base-level and the sedimentary dynamic condition.It shows that the short term base-level cycles with different sequence structure and stacking pattern distribute regularly in the middle term base-level cycle, and suggests the standard section architecture of the middle term base-level cycle.It is very significance that the sedimentary dynamic analysis on the sequence structure and stacking pattern of short or middle term base-level cycle in terms of theory mentioned above is completely consistent with the application aspects of the high-resolution sequence stratigraphy of the Mesozoicor Cenozoic terrestrial stratigraphy in Sichuan Basin,Ordos Basin and Liaohe Basin and so on and proves that the theoretical systerm and the analytical technology of the high-resolution sequence stratigraphy and completely adapted to employ the sequence research of the Mesozoic or Cenozoic terrigenous oil-bearing basins developed widely in China.
2000, 18(3): 384-388,394.
Abstract:
Dongpu depression is located in the southwest of Bohai Bay basin. The area is about 5300 square kilometers. The south is wide and the north is narrow. Lanliao fault controls its development and evolvement. On the basis of sequence stratigraphic theory, the author analyzed of the geologic, seimic, geochemical, paleobiological, drilling and logging data. There are two sequences (Sequence I and Sequence II) and eight systems tracts(one sequence includes LST, TST, HST and FSST) has been identified in Shahejie and Dongying formation. They are all have clear characteristics in seimic, geologic, core and logging dada. In continental basin, the influence of the three factors of tectonization, weather and sediments on sequence is different from that in marine basin, the weather is more important than that in marine sequence. After the synthetical analysis of sedimentary facies markers, the author has made the sedimentary lithofacies paleogeographic reconstruction of Shahejie formation of Eogene in Dongpu depression. In this paper the author also re-discussed the resource and the formation of salt-rock, which distributed widely and has a large thickness. The characteristics of chemical components, paleobiota, lithology and distribution of the salt-rock are different from the normal evaporite. It is not come from the evaporation of sea water. Combined the paleotectogenesis and the paleoclimate, the result of the study indicates that the salt-rock is originate from the hot bittern in deep earth and formed under a deep-water environment with a moist climate in Dongpu depression. The formed model is due to an event abruptly. Development of salt-rock is related to tectonization of Lanliao fault but not the climate. The salt-rock is located in TST or HST and developed with source rock. It is advantageous to source rock by preventing it from oxygen. It can also provide heat and pressure for source rock to change into oil or gas. The salt-rock is tighter than mudstone as seal-rock. Because of so many salt-rock formed with source rock and sand body, It is more propitious to form litho-reservoir which has a good matching relationship among source、reservoir and seal rock.
Dongpu depression is located in the southwest of Bohai Bay basin. The area is about 5300 square kilometers. The south is wide and the north is narrow. Lanliao fault controls its development and evolvement. On the basis of sequence stratigraphic theory, the author analyzed of the geologic, seimic, geochemical, paleobiological, drilling and logging data. There are two sequences (Sequence I and Sequence II) and eight systems tracts(one sequence includes LST, TST, HST and FSST) has been identified in Shahejie and Dongying formation. They are all have clear characteristics in seimic, geologic, core and logging dada. In continental basin, the influence of the three factors of tectonization, weather and sediments on sequence is different from that in marine basin, the weather is more important than that in marine sequence. After the synthetical analysis of sedimentary facies markers, the author has made the sedimentary lithofacies paleogeographic reconstruction of Shahejie formation of Eogene in Dongpu depression. In this paper the author also re-discussed the resource and the formation of salt-rock, which distributed widely and has a large thickness. The characteristics of chemical components, paleobiota, lithology and distribution of the salt-rock are different from the normal evaporite. It is not come from the evaporation of sea water. Combined the paleotectogenesis and the paleoclimate, the result of the study indicates that the salt-rock is originate from the hot bittern in deep earth and formed under a deep-water environment with a moist climate in Dongpu depression. The formed model is due to an event abruptly. Development of salt-rock is related to tectonization of Lanliao fault but not the climate. The salt-rock is located in TST or HST and developed with source rock. It is advantageous to source rock by preventing it from oxygen. It can also provide heat and pressure for source rock to change into oil or gas. The salt-rock is tighter than mudstone as seal-rock. Because of so many salt-rock formed with source rock and sand body, It is more propitious to form litho-reservoir which has a good matching relationship among source、reservoir and seal rock.
2000, 18(3): 395-399.
Abstract:
In the study of sedimentology,one of the most fundamental quantities that geoscientists seek to measure is the sedimentation rate,and it is crucial to a complete understanding of depositional process. The meteoritic dust is a kind of extraterestrial material with high abundance of iridium and cobalt.Most people think that the deposition quantity of meteoritic dust per year is almost constant on earth surface,and the average abundance of some characteristic elements such as Ir and Co in meteoritic dust are fixed,so there is a correlation between sedimentation rate and Ir (or Co) concentration.The abundance of Ir (or Co) in the sedimentary sample with low sedimentation rate is higher than in the sample with high sedimentation rate.According to this,the abundance of the element Ir or Co in sediment can be used to measure the deposition rate as a dating tool.Based on the previous work,the theory and method of using characteristic element from meteoritic dust ot calculate sediment rate have been suggested,and the formulae can be pariticularly expressed as follows: V s= V (Co)/｛ ρ ×[ A (Co)- w (Co)× A ”(Co)] ｝ where V s is the sedimentation rate of the sample which we want to calculate, V (Co) is the deposition rate of Co from meteoritic dust (6.48×10 -7 g/cm 2a), ρ is the density of the sample, A (Co) is the total abundance of Co in the sample, A ”(Co) is the abundance of Co in the source rock and w (Co) is contribution coefficient of Co from the terrigenious sources. Using this method,the sedimentation rates of the Eogene-Neogene section in Linqu County of Shandong Province has been measured as a case in this paper. Comparing with common methods,the method of using characteristic element from meteoritic dust to calculate sedimentation rate is more practical and accurate.
In the study of sedimentology,one of the most fundamental quantities that geoscientists seek to measure is the sedimentation rate,and it is crucial to a complete understanding of depositional process. The meteoritic dust is a kind of extraterestrial material with high abundance of iridium and cobalt.Most people think that the deposition quantity of meteoritic dust per year is almost constant on earth surface,and the average abundance of some characteristic elements such as Ir and Co in meteoritic dust are fixed,so there is a correlation between sedimentation rate and Ir (or Co) concentration.The abundance of Ir (or Co) in the sedimentary sample with low sedimentation rate is higher than in the sample with high sedimentation rate.According to this,the abundance of the element Ir or Co in sediment can be used to measure the deposition rate as a dating tool.Based on the previous work,the theory and method of using characteristic element from meteoritic dust ot calculate sediment rate have been suggested,and the formulae can be pariticularly expressed as follows: V s= V (Co)/｛ ρ ×[ A (Co)- w (Co)× A ”(Co)] ｝ where V s is the sedimentation rate of the sample which we want to calculate, V (Co) is the deposition rate of Co from meteoritic dust (6.48×10 -7 g/cm 2a), ρ is the density of the sample, A (Co) is the total abundance of Co in the sample, A ”(Co) is the abundance of Co in the source rock and w (Co) is contribution coefficient of Co from the terrigenious sources. Using this method,the sedimentation rates of the Eogene-Neogene section in Linqu County of Shandong Province has been measured as a case in this paper. Comparing with common methods,the method of using characteristic element from meteoritic dust to calculate sedimentation rate is more practical and accurate.
2000, 18(3): 408-413.
Abstract:
Ordovician carbonate rock formation is an important target for oil and gas exploration. In this paper, on the basis of regional structure backgrounds, Ordovician lithologic intervals are divided in Tazhong area and, structural-depositional model is built up. With the help of three dimension finite element simulation method, the favorable areas of carbonate fracture reservoirs are predicted. The purpose of this paper is to give a direction for carbonate oil and gas exploration in Tazhong area. Conclusions could be summed up as follows:(1) The lithologic characters of middle- upper Ordovician in the major part of Ordovician uplift in Tazhong are dramatically different from that of adjacent slope, especially from that of slope of south Manjiaer depression in the north of Tazhong number one fault. The lithology of Ordovician in the major part of Tazhong uplift is dominated by carbonate rocks, and the lithology of middle-upper Ordovician is mainly sandy mudstone in the slope of south Manjiaer in the north of Tazhong number one fault.(2) Sedimentation during Ordovician in Tazhong area is controlled by intracratonic depression and Cratonic margin aulacogen, which are with different properties of prototype basin. The uplift and sag in intracratonic depression have prominent control to the sedimentation of Ordovician. Middle-upper Ordovician deposition in the major part of Tazhong uplift is controlled by the large scale anticline in the intracratonic depression formedn early Caledonian (the end of early Ordovician). The restrained platform facies are developed in shallow water in such places where platform clinoform, platform margin, semi-restrained platform (include platform flat, lagoon) and Carbonate morphologic units are found. The northeast boundary of Tazhong area is sharp margin controlled by the early movement of normal fault of Tazhong number one fault. The sedimentation of south Manjiaer depression in north Tazhong is controlled by Kuluketage-Manjiaer aulacogen, the sediments are clastic rocks with slope and deep water basin facies. Middle-upper Ordovician deposition of Tanguzibasi area in south Tazhong is controlled by the syncline of intracratonic depression, the sediments consist of clastic and carbonate rocks with deeper open platform facies. Lower Ordovician in Tazhong area is platform facies controlled by the intracratonic depression, and the structure-sedimentation is no apparent difference between the major part of uplift and adjacent areas.(3) The first favorable fracture zones of Ordovician carbonate reservoirs being predicted in the major part of Tazhong uplift include the following areas:Tz161-Tz44 area, Tz24-Tz26-Tz27 area, Tz45 area, Tz3 area, Tz52 area, Tz403 area, Tz2 area, Tz22 area, the east part of Tz35 area, the west part of number one fault and so on. Correlation the results predicted with the observations of core fractures and well logging evaluating, the fitness is about over sixty-six percent. So it is proposed that three dimension finite element simulation method is very efficient in predicting carbonate fracture zone.
Ordovician carbonate rock formation is an important target for oil and gas exploration. In this paper, on the basis of regional structure backgrounds, Ordovician lithologic intervals are divided in Tazhong area and, structural-depositional model is built up. With the help of three dimension finite element simulation method, the favorable areas of carbonate fracture reservoirs are predicted. The purpose of this paper is to give a direction for carbonate oil and gas exploration in Tazhong area. Conclusions could be summed up as follows:(1) The lithologic characters of middle- upper Ordovician in the major part of Ordovician uplift in Tazhong are dramatically different from that of adjacent slope, especially from that of slope of south Manjiaer depression in the north of Tazhong number one fault. The lithology of Ordovician in the major part of Tazhong uplift is dominated by carbonate rocks, and the lithology of middle-upper Ordovician is mainly sandy mudstone in the slope of south Manjiaer in the north of Tazhong number one fault.(2) Sedimentation during Ordovician in Tazhong area is controlled by intracratonic depression and Cratonic margin aulacogen, which are with different properties of prototype basin. The uplift and sag in intracratonic depression have prominent control to the sedimentation of Ordovician. Middle-upper Ordovician deposition in the major part of Tazhong uplift is controlled by the large scale anticline in the intracratonic depression formedn early Caledonian (the end of early Ordovician). The restrained platform facies are developed in shallow water in such places where platform clinoform, platform margin, semi-restrained platform (include platform flat, lagoon) and Carbonate morphologic units are found. The northeast boundary of Tazhong area is sharp margin controlled by the early movement of normal fault of Tazhong number one fault. The sedimentation of south Manjiaer depression in north Tazhong is controlled by Kuluketage-Manjiaer aulacogen, the sediments are clastic rocks with slope and deep water basin facies. Middle-upper Ordovician deposition of Tanguzibasi area in south Tazhong is controlled by the syncline of intracratonic depression, the sediments consist of clastic and carbonate rocks with deeper open platform facies. Lower Ordovician in Tazhong area is platform facies controlled by the intracratonic depression, and the structure-sedimentation is no apparent difference between the major part of uplift and adjacent areas.(3) The first favorable fracture zones of Ordovician carbonate reservoirs being predicted in the major part of Tazhong uplift include the following areas:Tz161-Tz44 area, Tz24-Tz26-Tz27 area, Tz45 area, Tz3 area, Tz52 area, Tz403 area, Tz2 area, Tz22 area, the east part of Tz35 area, the west part of number one fault and so on. Correlation the results predicted with the observations of core fractures and well logging evaluating, the fitness is about over sixty-six percent. So it is proposed that three dimension finite element simulation method is very efficient in predicting carbonate fracture zone.
2000, 18(3): 419-423.
Abstract:
The term peritidal coined by Folk is a useful general name for the spectrum of nearshore and shoreline depositional environments and facies. Ancient peritidal carbonate lithofacies are characteristically organized stratigraphically into meter- to decameter-thick, shallowing-upward successions; their vertical stacking is a valuable record of the dynamics of carbonate platform development. There are currently three models used to explain how a shallowing-upward succession forms, 1) as a prograding wedge, 2) as a simultaneously aggrading sheet or, 3) as a mosaic of tidal flat islands. A prograding wedge is generated by the tidal flats prograding in two styles, simple offlap and staggered offlap. A simultaneously aggrading sheet accretes vertically to sea level and the whole platform becomes sequentially intertidal and then supratidal. Tidal flat islands nucleate and accrete by aggradation and progradation and shift in response to hydrographic forces.Much discussion exists currently as to what causes the rhythmic stacking into thick stratigraphic packages of ancient shallowing-upward successions. Two possible mechanisms are suggested,i,e., allocyclic and autocyclic mechanisms. The driving force behind the autocyclicity is the dynamics of sedimentation on the platform, while the allocyclicity emphasizes the factors of subsidence and eustacy that cause relative sea level change. However, the two mechanisms are not necessarily mutually exclusive.The Ordovician M5 section in central Ordos basin consists of a rhythmic repetition of several shallowing-upward peritidal carbonate successions deposited in epeiric sea. Based on the sedimentary structure and lithologic features of studied area, with the consideration of paleotectonics and paleogeography of the central basin, thirteen carbonate sedimentary-diagenetic microfacies are recognized that make up six sedimentary facies. The facies changes vertically and laterally. The paper presents the possible mechanism of the rhythmic package. Considering the geological settings of the studied area, Autocyclicity may interpret the formation of the repetition of peritidal carbonate shallowing-upward successions as the result of the peritidal prograding through simple offlap and staggered offlap.
The term peritidal coined by Folk is a useful general name for the spectrum of nearshore and shoreline depositional environments and facies. Ancient peritidal carbonate lithofacies are characteristically organized stratigraphically into meter- to decameter-thick, shallowing-upward successions; their vertical stacking is a valuable record of the dynamics of carbonate platform development. There are currently three models used to explain how a shallowing-upward succession forms, 1) as a prograding wedge, 2) as a simultaneously aggrading sheet or, 3) as a mosaic of tidal flat islands. A prograding wedge is generated by the tidal flats prograding in two styles, simple offlap and staggered offlap. A simultaneously aggrading sheet accretes vertically to sea level and the whole platform becomes sequentially intertidal and then supratidal. Tidal flat islands nucleate and accrete by aggradation and progradation and shift in response to hydrographic forces.Much discussion exists currently as to what causes the rhythmic stacking into thick stratigraphic packages of ancient shallowing-upward successions. Two possible mechanisms are suggested,i,e., allocyclic and autocyclic mechanisms. The driving force behind the autocyclicity is the dynamics of sedimentation on the platform, while the allocyclicity emphasizes the factors of subsidence and eustacy that cause relative sea level change. However, the two mechanisms are not necessarily mutually exclusive.The Ordovician M5 section in central Ordos basin consists of a rhythmic repetition of several shallowing-upward peritidal carbonate successions deposited in epeiric sea. Based on the sedimentary structure and lithologic features of studied area, with the consideration of paleotectonics and paleogeography of the central basin, thirteen carbonate sedimentary-diagenetic microfacies are recognized that make up six sedimentary facies. The facies changes vertically and laterally. The paper presents the possible mechanism of the rhythmic package. Considering the geological settings of the studied area, Autocyclicity may interpret the formation of the repetition of peritidal carbonate shallowing-upward successions as the result of the peritidal prograding through simple offlap and staggered offlap.
2000, 18(3): 431-438.
Abstract:
Siderite-silver-polymetallic deposits in Yindongzi and Daxigou,Shaanxi, Province, China, occur at the Middle Devonian hydrothermal sedimentary facies in the subbasin on the sea bed. There is a major economic orebody in Daxigou which is 2000 m long, from 10 m to more than 100 m thick, and there is the main economic orebody of silve-polymetals in Yingdongzi which is 1900 m long, from 1.0 m to 20.0 m thick. According to patterns of hydrothermal sedimentation,based on petrology,mineralogy, petrochemistry, geochemistry for the hydrothermal sedimentary facies,the hydrothermal sedimentary facies and their rocks can be classified into five subfacies, respectively,hydrothermal synsedimentary replacement-ebullitional subfacies,hydrothermal synsedimentary subfacies,hydrothermal synsedimentary-replacement subfacies,hot-brine vadose-replacement subfacies,and hydrothermal-mixing synsedimentary sub facies.First,the hydrothermal synsedimentary replacement-ebullitional subfacies consist of brecciated albite carbonate rock and ore-bearing brecciated albite siliceous rock.These brecciated rocks may have formed by the synsedimentary replacement and ebuilition of hydrothermal fluids along pouring passways (synfaults)in the subbasin on the sea bed,for hydrothermal fluids could explode and ebuilite along their passways covered by pre-existing hydrothermal sediments under the pressure of hydrothermal fluid overpassing total pressure of their overlying waterbody in the subbasin and their overlying sediments.Secondly,hydrothermal synsedimentary subfacies is made up of albite rock,sideritite, baritite. These rocks essentially stratiform with their elongation parallel to the bedding and with subfacies change and thinning-out. For examples,Bariteolites were formed by the Ba-richi sulfate hot-brine in a way of rapid chemical precipitation in the subbasin on the sea bed while sideriteolites were produced by Fe-rich carbonate hydrothermal fluid in the same way at the same subbasin.These rock layers are characterized by bedded,laminated,layer-massive structures which change regularly in the subbasin.Thirdly,the hydrothermal synsedimentary replacement subfacies include siliceous ferrodolomitite,ferrodolomite,dolomitic limeston and, siderite ferrodolomile.These hydrothermal rocks occur in the footwall rocks of the orebody or in the pinning-out layer of hydrothermal rocks.They might have been produced by the synsedimentation of the hydrothermal.At the same time, synmetasomatism between the hydrothermal fluids and soft sediments on the bed or the slope of the subbasin could take place because replacement structures are easily recognized in the field and lab study.Results of research on minerology,structures and textures of the rock and petrochemistry have suggested that SiO 2,Al 2O 3 and FeO from the hydrothermal in the subbasin has been extensively replaced in the underlying carbonate sediments on the sea bed. Fourthly,the hot-brine vadose-replacement subfacies is composed of scapolite biotite hornstone and scapolite slate. These rocks can be formed by K, Na and Cl-rich hot-brines during their diagenetic processes in the extensively geothermal environment but it is difficult for them to be formed by the processes related to magmatic activities during superimposed stage with the exception of the hornstone enclosing magmatic intrusions. Finally,the subfacies of mixing of different chemical components and physical-chemical states of the hydrothermal fluids,one of the most important subfacies,include sulfide rocks and albite chert with ore formation. These rock layers or ore layers are characterized by bedded,laminated,layer-massive, graded bedding and graded rhythmite.and chemical bedding, The most important characteristic exists in these rock layers or ore layers.The chemica lbedding is as follows: laminated albite layer→albite-sulfide layer→albite-carbonate mineral-sulfide layer→albite-barite laminated layer→lamineated barite layer→barite-albite-chert layer→ferrdolomite lamnated layer.
Siderite-silver-polymetallic deposits in Yindongzi and Daxigou,Shaanxi, Province, China, occur at the Middle Devonian hydrothermal sedimentary facies in the subbasin on the sea bed. There is a major economic orebody in Daxigou which is 2000 m long, from 10 m to more than 100 m thick, and there is the main economic orebody of silve-polymetals in Yingdongzi which is 1900 m long, from 1.0 m to 20.0 m thick. According to patterns of hydrothermal sedimentation,based on petrology,mineralogy, petrochemistry, geochemistry for the hydrothermal sedimentary facies,the hydrothermal sedimentary facies and their rocks can be classified into five subfacies, respectively,hydrothermal synsedimentary replacement-ebullitional subfacies,hydrothermal synsedimentary subfacies,hydrothermal synsedimentary-replacement subfacies,hot-brine vadose-replacement subfacies,and hydrothermal-mixing synsedimentary sub facies.First,the hydrothermal synsedimentary replacement-ebullitional subfacies consist of brecciated albite carbonate rock and ore-bearing brecciated albite siliceous rock.These brecciated rocks may have formed by the synsedimentary replacement and ebuilition of hydrothermal fluids along pouring passways (synfaults)in the subbasin on the sea bed,for hydrothermal fluids could explode and ebuilite along their passways covered by pre-existing hydrothermal sediments under the pressure of hydrothermal fluid overpassing total pressure of their overlying waterbody in the subbasin and their overlying sediments.Secondly,hydrothermal synsedimentary subfacies is made up of albite rock,sideritite, baritite. These rocks essentially stratiform with their elongation parallel to the bedding and with subfacies change and thinning-out. For examples,Bariteolites were formed by the Ba-richi sulfate hot-brine in a way of rapid chemical precipitation in the subbasin on the sea bed while sideriteolites were produced by Fe-rich carbonate hydrothermal fluid in the same way at the same subbasin.These rock layers are characterized by bedded,laminated,layer-massive structures which change regularly in the subbasin.Thirdly,the hydrothermal synsedimentary replacement subfacies include siliceous ferrodolomitite,ferrodolomite,dolomitic limeston and, siderite ferrodolomile.These hydrothermal rocks occur in the footwall rocks of the orebody or in the pinning-out layer of hydrothermal rocks.They might have been produced by the synsedimentation of the hydrothermal.At the same time, synmetasomatism between the hydrothermal fluids and soft sediments on the bed or the slope of the subbasin could take place because replacement structures are easily recognized in the field and lab study.Results of research on minerology,structures and textures of the rock and petrochemistry have suggested that SiO 2,Al 2O 3 and FeO from the hydrothermal in the subbasin has been extensively replaced in the underlying carbonate sediments on the sea bed. Fourthly,the hot-brine vadose-replacement subfacies is composed of scapolite biotite hornstone and scapolite slate. These rocks can be formed by K, Na and Cl-rich hot-brines during their diagenetic processes in the extensively geothermal environment but it is difficult for them to be formed by the processes related to magmatic activities during superimposed stage with the exception of the hornstone enclosing magmatic intrusions. Finally,the subfacies of mixing of different chemical components and physical-chemical states of the hydrothermal fluids,one of the most important subfacies,include sulfide rocks and albite chert with ore formation. These rock layers or ore layers are characterized by bedded,laminated,layer-massive, graded bedding and graded rhythmite.and chemical bedding, The most important characteristic exists in these rock layers or ore layers.The chemica lbedding is as follows: laminated albite layer→albite-sulfide layer→albite-carbonate mineral-sulfide layer→albite-barite laminated layer→lamineated barite layer→barite-albite-chert layer→ferrdolomite lamnated layer.
2000, 18(3): 445-448.
Abstract:
Undulation is one of the fundamental models of the geological effect,the undulation motion and variation in shape of earth crust is an geologic facts. In this paper,the undulation theory is applied to discuss the structure,deposit and paleogeography pattern of Paleozoic of Ordos Basin.The units of wave structure of Ordos and its neigbhouring areas are divided as:Yinshan wave trough,Yimeng wave crest,Central wave trough,Weibei wave crest,Qingling wave crest,Alashan wave crest,Helan wave trough,Central doming wave crest,Eastern wave trough and Kelan wave crest structure belt.The compound of Central wave trough and Eastern wave trough formed eastern salt depression.This area has also formed the big center of hydrocabon source that are the most important in under Paleozoic group of Ordos Basin.Central doming wave crest structure belt and Central wave trough structure belt were formed Dinbian compound areas,which make the central doming appear saddle in Dinbian.It also reasonably explains the phenomenon that Central doming is suspended in Dinbian area.
Undulation is one of the fundamental models of the geological effect,the undulation motion and variation in shape of earth crust is an geologic facts. In this paper,the undulation theory is applied to discuss the structure,deposit and paleogeography pattern of Paleozoic of Ordos Basin.The units of wave structure of Ordos and its neigbhouring areas are divided as:Yinshan wave trough,Yimeng wave crest,Central wave trough,Weibei wave crest,Qingling wave crest,Alashan wave crest,Helan wave trough,Central doming wave crest,Eastern wave trough and Kelan wave crest structure belt.The compound of Central wave trough and Eastern wave trough formed eastern salt depression.This area has also formed the big center of hydrocabon source that are the most important in under Paleozoic group of Ordos Basin.Central doming wave crest structure belt and Central wave trough structure belt were formed Dinbian compound areas,which make the central doming appear saddle in Dinbian.It also reasonably explains the phenomenon that Central doming is suspended in Dinbian area.
2000, 18(3): 453-459.
Abstract:
An INAA (Instrumental Neutron Activation Analysis)method is used to determine the contents of rare-earth elements of 13 coal samples in Huainan Mining Area, and the geochemistry of REE is discussed.Some conclusions are drawn as follows:The REE contents and REE distribution patterns vary significantly among different coal samples.The REE in coals is mainly continental origin,while seawater origin and plant origin are few.The REE in coals is concentrated in clay minerals,and the main occurrence is in kaolinite.The characteristics of REE have significance to indicate sedimentary environments.With the decreasing influence of seawater and the enhanced influenc of continental origin to swamps,the contents of REE in coal increase,and the REE distribution patterns change regularly.Eu anomaly is inherited by the source rock.The decrease of negative Eu anomaly is probably caused by the weakenss of continental origin and the enhancement of seawater's influence.In peat swamp environment,no effective influence is found to lose Ce by the invasion of seawater.
An INAA (Instrumental Neutron Activation Analysis)method is used to determine the contents of rare-earth elements of 13 coal samples in Huainan Mining Area, and the geochemistry of REE is discussed.Some conclusions are drawn as follows:The REE contents and REE distribution patterns vary significantly among different coal samples.The REE in coals is mainly continental origin,while seawater origin and plant origin are few.The REE in coals is concentrated in clay minerals,and the main occurrence is in kaolinite.The characteristics of REE have significance to indicate sedimentary environments.With the decreasing influence of seawater and the enhanced influenc of continental origin to swamps,the contents of REE in coal increase,and the REE distribution patterns change regularly.Eu anomaly is inherited by the source rock.The decrease of negative Eu anomaly is probably caused by the weakenss of continental origin and the enhancement of seawater's influence.In peat swamp environment,no effective influence is found to lose Ce by the invasion of seawater.
2000, 18(3): 465-468,479.
Abstract:
According to theory of low-velocity seepage and the true information of ultra-pressure caprock of the first section in Nenjiang group in Songliao Basin, the essence factor forming ultra-pressure in caprock is discussed in this paper, it is adsorption resistance of capillary for water in caprock. It has been confirmed that the sealing ability of the ultra-pressure of caprock is equal to twice as much as ultra-pressure value of fluid in the pore of caprock, the total sealing ability of ultra-pressure caprock is equal to the sum of displacement pressure and twice ultra-pressure value of caprock. The forming time of ultra-pressure caprock, effectiveness of ultra-pressure caporock for sealing hydrocarbon and evaluating method are researched, and take the regional caprock of the first section in Nenjiang group to the east of Daqing placantiline in Songliao Basin as example, the effectiveness that the ultra-pressure caprock seals the oil and gas coming from the source rock of Qingshankou group is studied, the significance of ultra-pressure caprock for to protect hydrocarbons is generally discussed.
According to theory of low-velocity seepage and the true information of ultra-pressure caprock of the first section in Nenjiang group in Songliao Basin, the essence factor forming ultra-pressure in caprock is discussed in this paper, it is adsorption resistance of capillary for water in caprock. It has been confirmed that the sealing ability of the ultra-pressure of caprock is equal to twice as much as ultra-pressure value of fluid in the pore of caprock, the total sealing ability of ultra-pressure caprock is equal to the sum of displacement pressure and twice ultra-pressure value of caprock. The forming time of ultra-pressure caprock, effectiveness of ultra-pressure caporock for sealing hydrocarbon and evaluating method are researched, and take the regional caprock of the first section in Nenjiang group to the east of Daqing placantiline in Songliao Basin as example, the effectiveness that the ultra-pressure caprock seals the oil and gas coming from the source rock of Qingshankou group is studied, the significance of ultra-pressure caprock for to protect hydrocarbons is generally discussed.
2000, 18(3): 475-479.
Abstract:
From the Silurian period, there have been three times of hydrocarbon generation and expulsion for the lower Paleozoic source rocks in Tarim basin, and the hydrocarbon generation ages of the lower Paleozoic and the trap formation ages of the Silurian together controlled the filling ages and evolution of the Silurian asphalt sandstones. After being formed in early of the Silurian, the Silurian asphalt sandstones underwent several sedimentary and tectonic events and three times of hydrocarbon filling and mixing, and these made the original distribution and occurrence of asphalt in the Silurian paleo-oil reservoirs complicated. The three times of hydrocarbon filling to the Silurian asphalt sandstones are as follows: the first time of filling took place in the late Caledonian, the second from the late Hercynian to Indosinian, and the third from the Yanshanian to Himalayan. Therefore, the mixture of asphalt, heavy oil, and normal oil and gas shows that the Silurian asphalt sandstones are the result of the three times of hydrocarbon filling.
From the Silurian period, there have been three times of hydrocarbon generation and expulsion for the lower Paleozoic source rocks in Tarim basin, and the hydrocarbon generation ages of the lower Paleozoic and the trap formation ages of the Silurian together controlled the filling ages and evolution of the Silurian asphalt sandstones. After being formed in early of the Silurian, the Silurian asphalt sandstones underwent several sedimentary and tectonic events and three times of hydrocarbon filling and mixing, and these made the original distribution and occurrence of asphalt in the Silurian paleo-oil reservoirs complicated. The three times of hydrocarbon filling to the Silurian asphalt sandstones are as follows: the first time of filling took place in the late Caledonian, the second from the late Hercynian to Indosinian, and the third from the Yanshanian to Himalayan. Therefore, the mixture of asphalt, heavy oil, and normal oil and gas shows that the Silurian asphalt sandstones are the result of the three times of hydrocarbon filling.
2000, 18(3): 484-488.
Abstract:
Genetic sequence stratigraphy on the basis of genetic stratigraphic sequence proposed by Galloway (1989) is a paradigm of Exxon's depositional sequence model. A genetic stratigraphic sequence is the sedimentary product of a depositional episode. The sequence consists of three important components: offlap components, onlap or transgressive components, and top and base bounding surfaces reflecting maximum marine flooding.\;The model of genetic stratigraphic sequence is firstly capplied to the northwest Gulf of Mexico Cenozoic basin, U.S.A. Galloway (1989) recognized nine genetic stratigraphic sequences for the Cenozoic strata of the basin. The extrabasinal fluvial systems and associated depocenters shift significantly from a genetic stratigraphic sequence to the following sequence. Within each genetic stratigraphic sequence, the paleogeography remains comparatively stable, but depositional styles and patterns between offlap components and onlap or transgressive components change as relative sea level changes.\;Galloway (1990) studied the relationship among Paleogene depositional episodes, genetic stratigraphic sequences, and sediment accumulation rates NW Gulf of Mexico basin. He found that the genetic stratigraphic sequences record episodes of high supply, punctuated by intervals of low supply and consequent transgressive flooding of the basin margin. Within sequences, depositional rates vary with position relative to the contemporaneous shelf margin, with depositional system, and between subbasins. Liu and Galloway (1997) studied Tertiary sediment supply to the North Sea basin. They concluded that all episodes of Tertiary sedimen supply correlate to source-terrain tectonic pulses. The history of changing source-area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on North Sea Cenozoic sequence development.\;The precepts of genetic sequence stratigraphy were developed from the study of marine basins, but they can be applied to nonmarine basins. The Qingshankou, Yaojia, and Nenjiang (QYN) formations in the Songliao basin can be used to illustrate the application of sequence analysis in a lacustrine setting (Xue and Galloway, 1993). They proposed that use of subaerial unconformity and transgressive surfaces allows further subdivision of the QYN sequence into a progradational systems tract, lowstand prograding complex, and retrogradational systems tract. Hamilton and Tadros (1994) chose the regional extensive coals as genetic stratigraphic sequence boundaries in coal-bearing strata in the Gunnedah basin, Australia. Regionally extensive coals can exhibit the essential attributes of sequence boundaries. Coals of regional extent require interruption in sediment supply at a basin-wide scale and can bound the sequences.\;High-resolution sequences are also studied in genetic sequence stratigraphy. One example is the sequence analysis of the middle Wilcox subgroup in the Texas coastal plain (Xue and Galloway, 1995). Two high-resolution gentic stratigraphic sequences of the middle Wilcox were delineated within the interval time span of 1.5-2.2 m.y. based on detailed corrlation of approximately 700 well logs. They discussed the issue of high-resolution stratigraphic correlation using well-log data and concluded that maximum flooding surfaces are easily recognizable because of good lateral continuity whereas unconformities are difficult to identify due to poor lateral continuity, especially in shelf environment. The ofher example is case study of the Eocene Yegua Formation in Texas Gulf Coast (Meckel and Galloway, 1996). The Eocene Yegua Formation is made up of six fourth-order sequences, which have average durations of 0.8 million years or less. The formation of these sequences is controlled by accommodation or by sediment supply. The significant change seen in fourth-order sequences is the shift in overall regime ratio and reorganization of depositional processes.\;Cyclicity of genetic stratigraphic sequences is another research topic.
Genetic sequence stratigraphy on the basis of genetic stratigraphic sequence proposed by Galloway (1989) is a paradigm of Exxon's depositional sequence model. A genetic stratigraphic sequence is the sedimentary product of a depositional episode. The sequence consists of three important components: offlap components, onlap or transgressive components, and top and base bounding surfaces reflecting maximum marine flooding.\;The model of genetic stratigraphic sequence is firstly capplied to the northwest Gulf of Mexico Cenozoic basin, U.S.A. Galloway (1989) recognized nine genetic stratigraphic sequences for the Cenozoic strata of the basin. The extrabasinal fluvial systems and associated depocenters shift significantly from a genetic stratigraphic sequence to the following sequence. Within each genetic stratigraphic sequence, the paleogeography remains comparatively stable, but depositional styles and patterns between offlap components and onlap or transgressive components change as relative sea level changes.\;Galloway (1990) studied the relationship among Paleogene depositional episodes, genetic stratigraphic sequences, and sediment accumulation rates NW Gulf of Mexico basin. He found that the genetic stratigraphic sequences record episodes of high supply, punctuated by intervals of low supply and consequent transgressive flooding of the basin margin. Within sequences, depositional rates vary with position relative to the contemporaneous shelf margin, with depositional system, and between subbasins. Liu and Galloway (1997) studied Tertiary sediment supply to the North Sea basin. They concluded that all episodes of Tertiary sedimen supply correlate to source-terrain tectonic pulses. The history of changing source-area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on North Sea Cenozoic sequence development.\;The precepts of genetic sequence stratigraphy were developed from the study of marine basins, but they can be applied to nonmarine basins. The Qingshankou, Yaojia, and Nenjiang (QYN) formations in the Songliao basin can be used to illustrate the application of sequence analysis in a lacustrine setting (Xue and Galloway, 1993). They proposed that use of subaerial unconformity and transgressive surfaces allows further subdivision of the QYN sequence into a progradational systems tract, lowstand prograding complex, and retrogradational systems tract. Hamilton and Tadros (1994) chose the regional extensive coals as genetic stratigraphic sequence boundaries in coal-bearing strata in the Gunnedah basin, Australia. Regionally extensive coals can exhibit the essential attributes of sequence boundaries. Coals of regional extent require interruption in sediment supply at a basin-wide scale and can bound the sequences.\;High-resolution sequences are also studied in genetic sequence stratigraphy. One example is the sequence analysis of the middle Wilcox subgroup in the Texas coastal plain (Xue and Galloway, 1995). Two high-resolution gentic stratigraphic sequences of the middle Wilcox were delineated within the interval time span of 1.5-2.2 m.y. based on detailed corrlation of approximately 700 well logs. They discussed the issue of high-resolution stratigraphic correlation using well-log data and concluded that maximum flooding surfaces are easily recognizable because of good lateral continuity whereas unconformities are difficult to identify due to poor lateral continuity, especially in shelf environment. The ofher example is case study of the Eocene Yegua Formation in Texas Gulf Coast (Meckel and Galloway, 1996). The Eocene Yegua Formation is made up of six fourth-order sequences, which have average durations of 0.8 million years or less. The formation of these sequences is controlled by accommodation or by sediment supply. The significant change seen in fourth-order sequences is the shift in overall regime ratio and reorganization of depositional processes.\;Cyclicity of genetic stratigraphic sequences is another research topic.
