2014 Vol. 32, No. 2
Display Method:
2014, 32(2): 189-197.
Abstract:
The rise of quantitative geology promotes the rapid development of earth science, while the study on the quantitative relation between gravel roundness and transport distance has not made obvious progress at home and abroad for a long time. The study on rounding laws and influencing factors of gravels has very important significance to the research of sedimentary environment, provenance analysis and paleogeography recovery in geological history. Four rivers were investigated in this study including Yongding River, Duijiuyu River, Luanhe River and Dashi River. Luanhe River and Dashi River are in Hebei province. Yongding River and Duijiuyu River that are in Beijing are studied in detail. The four rivers all lie on the east of North China platform around the Bohai bay. They have the similar geological backgrounds, climate conditions, and flood seasons. And their parent rocks are all magmatic rocks. All those factors cause the similar change law of roundness. Field investigation is the base of this study. Field investigation starts from the mountain-pass of each river where river flows out of the mountain. Investigation points were set from the mountain-pass to the downstream in each river. And 100 samples were taken at each point, described and statistically analyzed in detail. Based on the above study, the relation between roundness and transport distance is established, and influencing factors of gravel roundness are defined. Roundness class is defined by visual observation, according to the roundness classification standard and the figure of roundness shapes and classes from Powers. The roundness of gravel is divided into sharply angular, angular, subangular, subrounded, rounded, and well rounded. To minish the subjective errors from person, five people are needed to classify the roundness of every sample. When four or five people have the same result, then the result is eligible. This method can avoid the subjective errors, and make the results authentic and credible. Roundness of magmatic gravel becomes better with the increase of transport distance. It varies fast at the early stage of transport, then slower, and stable at the final. The particle size decreases gradually with the increase of the transport distance. In the upstream the flow is of high capability of transportation and can carry coarse grain because of the high flow velocity. To the downstream the flow is of low capability of transportation and can only carry fine grain because of the low flow velocity. Roundness mode is the highest proportion roundness class in each investigation point. It is a very useful parameter in the study of mixed accumulated gravels that are of different roundnesses. In this study the quantitative relation of roundness and transport distance is established based on the study of Yongding River, Duijiuyu River, Luanhe River and Dashi River. Magmatic gravels usually need to be carried 3~6 km from angular to subangular. They need to be carried 12~21 km from subangular to subrounded, and most of rounded gravels need to be carried at least 22~31 km. The roundness of gravel has a quantitative relation with the transport distance, which is universally applicable in the same geological background. The rounding law and the quantitative relation are significant in the source direction analysis and transport distance prediction. The change law of gravel roundness in the vertical profile can be used to analyze the evolution history of river and the size of basin. Gravel roundness is affected by transport distance, original composition, particle size and breaking. Magmatic gravels come from the mechanical disruption of source rock. The gravels are mainly sharply angular or angular without being rounded when they first form. They are subject to abrasion in the whole process of transport. Angular and subangular gravels are fast rounded to subrounded or rounded in the early stage of transport because of poor abrasion resistance, while it is very difficult from rounded to well rounded. The component of source rock affects the hardness and the abrasive resistance of gravel. The rounding rate of gravel with different original component is greatly different. The abrasion resistance of magmatic rocks is much higher than limestone, and is much lower than quartz. Based on the study of the four rivers, we find that the magmatic gravels are fast rounded within 30 km in the early stage of transport. The slope of the middle roundness curve is medium. The rounding of quartzose gravel is very slow. It has no great change after being carried for 250 km in Colorado River. The rounding of limestone gravel is the fastest. They are fast rounded after being carried 10 km in South Dakota. And the slop of the middle roundness curve of limestone gravel is the highest. So the rounding speed of magmatic gravel is faster than quartz and is slower than limestone. When the gravels have the same original composition and transport distance, coarse gravel is rounded faster than fine-grained gravel. The breaking lower roundness, and makes the roundness of a few gravels inconsistent with the distance of transport. Gravels are subject to mechanical breaking in the process of transport. The collision between the gravels is the main reason causing the breaking. And the gravels which are of high brittleness or have dissolved fractures are easy to break in the process of transport.
The rise of quantitative geology promotes the rapid development of earth science, while the study on the quantitative relation between gravel roundness and transport distance has not made obvious progress at home and abroad for a long time. The study on rounding laws and influencing factors of gravels has very important significance to the research of sedimentary environment, provenance analysis and paleogeography recovery in geological history. Four rivers were investigated in this study including Yongding River, Duijiuyu River, Luanhe River and Dashi River. Luanhe River and Dashi River are in Hebei province. Yongding River and Duijiuyu River that are in Beijing are studied in detail. The four rivers all lie on the east of North China platform around the Bohai bay. They have the similar geological backgrounds, climate conditions, and flood seasons. And their parent rocks are all magmatic rocks. All those factors cause the similar change law of roundness. Field investigation is the base of this study. Field investigation starts from the mountain-pass of each river where river flows out of the mountain. Investigation points were set from the mountain-pass to the downstream in each river. And 100 samples were taken at each point, described and statistically analyzed in detail. Based on the above study, the relation between roundness and transport distance is established, and influencing factors of gravel roundness are defined. Roundness class is defined by visual observation, according to the roundness classification standard and the figure of roundness shapes and classes from Powers. The roundness of gravel is divided into sharply angular, angular, subangular, subrounded, rounded, and well rounded. To minish the subjective errors from person, five people are needed to classify the roundness of every sample. When four or five people have the same result, then the result is eligible. This method can avoid the subjective errors, and make the results authentic and credible. Roundness of magmatic gravel becomes better with the increase of transport distance. It varies fast at the early stage of transport, then slower, and stable at the final. The particle size decreases gradually with the increase of the transport distance. In the upstream the flow is of high capability of transportation and can carry coarse grain because of the high flow velocity. To the downstream the flow is of low capability of transportation and can only carry fine grain because of the low flow velocity. Roundness mode is the highest proportion roundness class in each investigation point. It is a very useful parameter in the study of mixed accumulated gravels that are of different roundnesses. In this study the quantitative relation of roundness and transport distance is established based on the study of Yongding River, Duijiuyu River, Luanhe River and Dashi River. Magmatic gravels usually need to be carried 3~6 km from angular to subangular. They need to be carried 12~21 km from subangular to subrounded, and most of rounded gravels need to be carried at least 22~31 km. The roundness of gravel has a quantitative relation with the transport distance, which is universally applicable in the same geological background. The rounding law and the quantitative relation are significant in the source direction analysis and transport distance prediction. The change law of gravel roundness in the vertical profile can be used to analyze the evolution history of river and the size of basin. Gravel roundness is affected by transport distance, original composition, particle size and breaking. Magmatic gravels come from the mechanical disruption of source rock. The gravels are mainly sharply angular or angular without being rounded when they first form. They are subject to abrasion in the whole process of transport. Angular and subangular gravels are fast rounded to subrounded or rounded in the early stage of transport because of poor abrasion resistance, while it is very difficult from rounded to well rounded. The component of source rock affects the hardness and the abrasive resistance of gravel. The rounding rate of gravel with different original component is greatly different. The abrasion resistance of magmatic rocks is much higher than limestone, and is much lower than quartz. Based on the study of the four rivers, we find that the magmatic gravels are fast rounded within 30 km in the early stage of transport. The slope of the middle roundness curve is medium. The rounding of quartzose gravel is very slow. It has no great change after being carried for 250 km in Colorado River. The rounding of limestone gravel is the fastest. They are fast rounded after being carried 10 km in South Dakota. And the slop of the middle roundness curve of limestone gravel is the highest. So the rounding speed of magmatic gravel is faster than quartz and is slower than limestone. When the gravels have the same original composition and transport distance, coarse gravel is rounded faster than fine-grained gravel. The breaking lower roundness, and makes the roundness of a few gravels inconsistent with the distance of transport. Gravels are subject to mechanical breaking in the process of transport. The collision between the gravels is the main reason causing the breaking. And the gravels which are of high brittleness or have dissolved fractures are easy to break in the process of transport.
2014, 32(2): 205-217.
Abstract:
Yingtaogou Formation in the Helan Mountain area, located in the western margin of Ordos basin, consists of a set of terrigenous detrital rocks, with carbonate slump gravity flow deposits. The Early Paleozoic tectonic setting of Ordos basin is still in debate due to the lack of reliable material source data. In this paper, the petrologic and geochemical characteristics have been researched systematically. The characteristics of debris composition of sandstone show that Yingtaogou Formation comes from recycling orogeny area. The geochemical signatures of major and trace elements of sandstone from Yingtaogou Formation indicate its double provenance supply feature. More specifically, comparison study on REE distribution patterns shows clastic rocks from Yingtaogou Formation derive from Alashan and/or North Qilian orogenic belt. The geochemical signatures of major and trace elements and REEs, in Combination with the discrimination diagrams for tectonic settings have mirrored that the study area when Yingtaogou Formation deposited was surrounded by the active and passive continental margin, which means it is affected by both Helan aulacogen and North Qilian Early Paleozoic orogenic belt. REE patterns between Yingtaogou Formation and its adjacent areas display the former is in accordance with Alashan paleolandmass to the northwest and granite from North Qilian Early Paleozoic orogenic belt, and the REE distribution pattern show they are rich in LREE and lack of HREE and exhibit slightly Eu anomalies and marked negative Tm anomalies. After comprehensive consideration of the middle Ordovician palaeocurrents in the western Ordos and detrital zircon age features, this paper suggests that the provenance of Yingtaogou Formation was mainly the North Qilian orogenic belt and the Alashan paleolandmass as a minor one.
Yingtaogou Formation in the Helan Mountain area, located in the western margin of Ordos basin, consists of a set of terrigenous detrital rocks, with carbonate slump gravity flow deposits. The Early Paleozoic tectonic setting of Ordos basin is still in debate due to the lack of reliable material source data. In this paper, the petrologic and geochemical characteristics have been researched systematically. The characteristics of debris composition of sandstone show that Yingtaogou Formation comes from recycling orogeny area. The geochemical signatures of major and trace elements of sandstone from Yingtaogou Formation indicate its double provenance supply feature. More specifically, comparison study on REE distribution patterns shows clastic rocks from Yingtaogou Formation derive from Alashan and/or North Qilian orogenic belt. The geochemical signatures of major and trace elements and REEs, in Combination with the discrimination diagrams for tectonic settings have mirrored that the study area when Yingtaogou Formation deposited was surrounded by the active and passive continental margin, which means it is affected by both Helan aulacogen and North Qilian Early Paleozoic orogenic belt. REE patterns between Yingtaogou Formation and its adjacent areas display the former is in accordance with Alashan paleolandmass to the northwest and granite from North Qilian Early Paleozoic orogenic belt, and the REE distribution pattern show they are rich in LREE and lack of HREE and exhibit slightly Eu anomalies and marked negative Tm anomalies. After comprehensive consideration of the middle Ordovician palaeocurrents in the western Ordos and detrital zircon age features, this paper suggests that the provenance of Yingtaogou Formation was mainly the North Qilian orogenic belt and the Alashan paleolandmass as a minor one.
2014, 32(2): 228-237.
Abstract:
Hainan located in adjacent areas of northeastern Yinggehai Basin, it is one of important sources of sediment to basin filling. In this paper, we analyzed the content, assemblages and index of heavy minerals in sediments which come form the mouth of the seven rivers in western Hainan. The study revealed that heavy minerals content, roundness, assemblages and index are obviously different from the north to south, reflecting the transport distance and parent rocks also different. The northern Zhubijiang mainly for near distance source, including a provenance of acid rocks with some metamorphic and basic-ultrabasic rocks, the dominated heavy minerals are ilmenite, tourmaline, zircon, epidote and tremolite; The northern Changhuajiang river is mainly for the long distance transportation of acid to basic rocks, the dominated heavy minerals are ilmenite, magnetite and zircon; The central Beilihe and Tongtianhe rivers are mainly from near distance source, the acid, basic and metamorphic rocks without long distance transporting, and the dominated heavy minerals are ilmenite, tourmaline, zircon, garnet and tremolite; The central Ganenhe mainly for stable-very stable minerals, they are zircon, ilmenite, titanite, tourmaline and limonite; The southern Wanglouhe and Ningyuanhe are from near transporting parent rocks, including a provenance of acid, basic and metamorphic rocks, the heavy minerals mainly for ilmenite, magnetite, limonite and epidote. Different characteristics of heavy minerals in different rivers are closely related to its source, the areas of transport and the rock types. By studying the different assemblages system of heavy minerals in different rivers, it can help to carry out source-sink comparison and analysis of Yinggehai Basin, to establish the identification signs of different detrital source area of oil and gas reservoir, and has an important geological significance for provenance identification of natural gas in different reservoir.
Hainan located in adjacent areas of northeastern Yinggehai Basin, it is one of important sources of sediment to basin filling. In this paper, we analyzed the content, assemblages and index of heavy minerals in sediments which come form the mouth of the seven rivers in western Hainan. The study revealed that heavy minerals content, roundness, assemblages and index are obviously different from the north to south, reflecting the transport distance and parent rocks also different. The northern Zhubijiang mainly for near distance source, including a provenance of acid rocks with some metamorphic and basic-ultrabasic rocks, the dominated heavy minerals are ilmenite, tourmaline, zircon, epidote and tremolite; The northern Changhuajiang river is mainly for the long distance transportation of acid to basic rocks, the dominated heavy minerals are ilmenite, magnetite and zircon; The central Beilihe and Tongtianhe rivers are mainly from near distance source, the acid, basic and metamorphic rocks without long distance transporting, and the dominated heavy minerals are ilmenite, tourmaline, zircon, garnet and tremolite; The central Ganenhe mainly for stable-very stable minerals, they are zircon, ilmenite, titanite, tourmaline and limonite; The southern Wanglouhe and Ningyuanhe are from near transporting parent rocks, including a provenance of acid, basic and metamorphic rocks, the heavy minerals mainly for ilmenite, magnetite, limonite and epidote. Different characteristics of heavy minerals in different rivers are closely related to its source, the areas of transport and the rock types. By studying the different assemblages system of heavy minerals in different rivers, it can help to carry out source-sink comparison and analysis of Yinggehai Basin, to establish the identification signs of different detrital source area of oil and gas reservoir, and has an important geological significance for provenance identification of natural gas in different reservoir.
2014, 32(2): 244-252.
Abstract:
Using data of measured and observed outcrop successions, drilling information and predecessors' research achievements, lithofacies palaeogeography and the origin of dolomites of Middle Cambrian in the Middle-upper Yangtze plate were studied. lithofacies paleographic map was plotted based on comprehensive study on outcrops, wells and a series of contour maps, such as thickness of Middle Cambrian, thickness percentage of micritic dolomites, thickness of gypsum rocks and so on. In Middle Cambrian of Middle-upper Yangtze plate, from ancient land to deep sea basin（northwest to southeast）developed shallow fine-grained clastic continental shelf, restricted carbonate platform, slope and deep-sea basin. As the ancient land was low and gentle in Middle Cambrian, the sediments were fine-grained, such as sand, silt and mud. Restricted carbonate platform could be divided into different secondary paleogeography units, such as tidal flats, lagoons, particle beaches and so on. The slope in the east of the study area was gentle and the sediments were mainly micrite carbonate sediments and mud, and sediments in deep sea basin were black chert and mud. Sediments in restricted carbonate platform were gypsum and microcrystalline carbonate sediments. Origin of dolomites, sequences in plane and vertical successions were controlled by paleogeography. Layers of gypsum were Interbedded with dolomites, and little particle beach developed in interior platform, while lagoon, tidal flat, restricted subtidal zone developed. At the margin of Middle-Upper Yangtze platform, more particle beaches developed and layers of gypsum decreased. According to crystal sizes of dolomites, micritic dolomites were separated from sugar shaped dolomites (fine-grained dolomites, medium dolomites and coarse-grained dolomites). Micritic dolomites were formed in penecomtemporaneous diagenetic stage in tidal flat environments, with mechanism of evaporative pumping. High salinity fluid with abundant magnesium that dolomitization needed came from concentrated seawater in lagoon and normal salinity water of open platform. Sugar shaped dolomites were formed with the mechanism of seepage reflection, the high salinity fluid of which came from redundant fluid of evaporative pumping and lagoon. Seepage reflection went on slowly and coarse-grained dolomites were formed. In addition, mechanisms of dolomitization combined in three-dimensional space, and vertical sequence changed regularly. From top to bottom, micritic dolomites with no gypsum crystals, micritic dolomites with gypsum crystals, sugar shaped dolomites formed successively, which was affected by paleogeographic changes.
Using data of measured and observed outcrop successions, drilling information and predecessors' research achievements, lithofacies palaeogeography and the origin of dolomites of Middle Cambrian in the Middle-upper Yangtze plate were studied. lithofacies paleographic map was plotted based on comprehensive study on outcrops, wells and a series of contour maps, such as thickness of Middle Cambrian, thickness percentage of micritic dolomites, thickness of gypsum rocks and so on. In Middle Cambrian of Middle-upper Yangtze plate, from ancient land to deep sea basin（northwest to southeast）developed shallow fine-grained clastic continental shelf, restricted carbonate platform, slope and deep-sea basin. As the ancient land was low and gentle in Middle Cambrian, the sediments were fine-grained, such as sand, silt and mud. Restricted carbonate platform could be divided into different secondary paleogeography units, such as tidal flats, lagoons, particle beaches and so on. The slope in the east of the study area was gentle and the sediments were mainly micrite carbonate sediments and mud, and sediments in deep sea basin were black chert and mud. Sediments in restricted carbonate platform were gypsum and microcrystalline carbonate sediments. Origin of dolomites, sequences in plane and vertical successions were controlled by paleogeography. Layers of gypsum were Interbedded with dolomites, and little particle beach developed in interior platform, while lagoon, tidal flat, restricted subtidal zone developed. At the margin of Middle-Upper Yangtze platform, more particle beaches developed and layers of gypsum decreased. According to crystal sizes of dolomites, micritic dolomites were separated from sugar shaped dolomites (fine-grained dolomites, medium dolomites and coarse-grained dolomites). Micritic dolomites were formed in penecomtemporaneous diagenetic stage in tidal flat environments, with mechanism of evaporative pumping. High salinity fluid with abundant magnesium that dolomitization needed came from concentrated seawater in lagoon and normal salinity water of open platform. Sugar shaped dolomites were formed with the mechanism of seepage reflection, the high salinity fluid of which came from redundant fluid of evaporative pumping and lagoon. Seepage reflection went on slowly and coarse-grained dolomites were formed. In addition, mechanisms of dolomitization combined in three-dimensional space, and vertical sequence changed regularly. From top to bottom, micritic dolomites with no gypsum crystals, micritic dolomites with gypsum crystals, sugar shaped dolomites formed successively, which was affected by paleogeographic changes.
2014, 32(2): 260-269.
Abstract:
Bohai Basin is characterized by stable tectonics with steady and slow subsidence, which formed in low-relief and low gradient during the Neogene. The paleoclimate data confirmed that the Bohai area was humid subtropical to warm temperate climate and widely developed shallow-water delta and shallow lake sedimentation system in Middle Neogene (sedimentary period of the Lower Member of Minghuazhen Formation). Changes of palaeogeomorphology, palaeoclimate and ancient water depth controlled shallow water deltaic distributary systems’ front sandbodiesis’ architectures, distribution and evolution. Application of the principle of sequence stratigraphy, the lower member of Minghuazhen Formation in Huanghekou sag will be divided into one three order sequence and three system tracts which is LST, TST and HST. On the basic, recognized three kinds of sand body architectures include the stacked channel type, isolated channel type, sheeted channel type. According to core, logging, seismic, means of modern sediments and tank simulation experiment, we established depositional model of Huanghekou sag fluvial-dominated delta in the lower member of Minghuazhen Formation.
Bohai Basin is characterized by stable tectonics with steady and slow subsidence, which formed in low-relief and low gradient during the Neogene. The paleoclimate data confirmed that the Bohai area was humid subtropical to warm temperate climate and widely developed shallow-water delta and shallow lake sedimentation system in Middle Neogene (sedimentary period of the Lower Member of Minghuazhen Formation). Changes of palaeogeomorphology, palaeoclimate and ancient water depth controlled shallow water deltaic distributary systems’ front sandbodiesis’ architectures, distribution and evolution. Application of the principle of sequence stratigraphy, the lower member of Minghuazhen Formation in Huanghekou sag will be divided into one three order sequence and three system tracts which is LST, TST and HST. On the basic, recognized three kinds of sand body architectures include the stacked channel type, isolated channel type, sheeted channel type. According to core, logging, seismic, means of modern sediments and tank simulation experiment, we established depositional model of Huanghekou sag fluvial-dominated delta in the lower member of Minghuazhen Formation.
2014, 32(2): 278-289.
Abstract:
The field experiment gained continuous temperature, salinity, current velocity, turbidity data synchronously in several layers through the tripod platform. The tripod performed stability during the field experiment, and it can be applied in high resolution measurement of sediment dynamics and transport in shallow sea. The results showed that there was residual current which towards land in bottom boundary layer and gradually decreased during observation periods, which was caused by asymmetric of flood and ebb flow, strong wind and density circulation also affected the residual current strength. Bottom shear stress was greater than threshold shear stress in most time of observation periods, so sediment can be transported and even resuspended significantly. The response of suspended sediment concentration to dynamics was different in flood and ebb, spring and neap tide, changes of hydrodynamic, length of acceleration and deceleration periods of tidal current, the available erosion sediment, settlement of sediment of above water were the reasons of changes of suspended sediment concentration; asymmetric sediment transportation of flood and ebb tide lead to suspended sediment net transport to inside of estuary in bottom boundary layer.
The field experiment gained continuous temperature, salinity, current velocity, turbidity data synchronously in several layers through the tripod platform. The tripod performed stability during the field experiment, and it can be applied in high resolution measurement of sediment dynamics and transport in shallow sea. The results showed that there was residual current which towards land in bottom boundary layer and gradually decreased during observation periods, which was caused by asymmetric of flood and ebb flow, strong wind and density circulation also affected the residual current strength. Bottom shear stress was greater than threshold shear stress in most time of observation periods, so sediment can be transported and even resuspended significantly. The response of suspended sediment concentration to dynamics was different in flood and ebb, spring and neap tide, changes of hydrodynamic, length of acceleration and deceleration periods of tidal current, the available erosion sediment, settlement of sediment of above water were the reasons of changes of suspended sediment concentration; asymmetric sediment transportation of flood and ebb tide lead to suspended sediment net transport to inside of estuary in bottom boundary layer.
2014, 32(2): 296-305.
Abstract:
In this paper, based on 58 surface sediment samples collected in the mud deposited zone along the southern distal Yangtze subaqueous delta recently, the grain size of the surface sediment was analyzed and the sub-bottom stratigraphic structure was also measured. Results show that the clayey silt is the main type of the sediment in the study area. These sediments are characterized by high water content (46%), high porosity, high compressibility and low shear strength which are potentially vulnerable to coast erosion. The upper part of the seismic profiles shows horizontal neritic strata. Underlying bedrocks are discovered in the area of reefs and the southern profiles. Sparse shallow gas is found in the eastern part of Profile I, with top imbedded depth about 12 m. The thickness of the Holocene sediment is 4~23 m and the sedimentation rate is estimated about 0.57~3.29 m/ka. Considering low sedimentation rate of the study area, recent accelerated human activity in the river basin, leading to decreased sediment discharge from Changjiang River, will cause a potential threat to the seabed stability of the Zhejiang coast.
In this paper, based on 58 surface sediment samples collected in the mud deposited zone along the southern distal Yangtze subaqueous delta recently, the grain size of the surface sediment was analyzed and the sub-bottom stratigraphic structure was also measured. Results show that the clayey silt is the main type of the sediment in the study area. These sediments are characterized by high water content (46%), high porosity, high compressibility and low shear strength which are potentially vulnerable to coast erosion. The upper part of the seismic profiles shows horizontal neritic strata. Underlying bedrocks are discovered in the area of reefs and the southern profiles. Sparse shallow gas is found in the eastern part of Profile I, with top imbedded depth about 12 m. The thickness of the Holocene sediment is 4~23 m and the sedimentation rate is estimated about 0.57~3.29 m/ka. Considering low sedimentation rate of the study area, recent accelerated human activity in the river basin, leading to decreased sediment discharge from Changjiang River, will cause a potential threat to the seabed stability of the Zhejiang coast.
2014, 32(2): 314-324.
Abstract:
Grain size analysis and parameter calculation have been carried out based on 70 surface sediments collected from the coastal waters of Shantou City, and characteristics of frequency distribution have been researched. The results show that the surface sediments of the area are made up of 9 kinds of sediment types, the main types are clayey silt, sandy silt and sand-silt-clay. The content of gravel, sand, silt, and clay in the surface sediments is 1.4%, 29.2%, 51.0 %, and 18.4 %, respectively. The mean grain size of sediments in this area is 0.12~7.30 and the average is 5.53 . The coefficient of sorting is 0.50~2.94 and the average is 1.82. Skewness is -0.65~0.30 and the average is -0.02. Kurtosis is 0.63~2.67 and the average is 1.11. The modern sedimentary environment in coastal waters of Shantou can be classified into 4 types by system cluster analysis and factor analysis. Spline interpolation method was employed to the data of grain size parameters over the study area. Then, the sediment transport trends were simulated by using GSTA (Grain Size Trend Analysis) model. The grain size trends analysis shows that: In Shantou harbor that the water depth ＜10 m, sediments from the runoff and sea were converged to the estuaries and offshore; Sediments in Shantou harbor that the water depth ＞10 m are transported towards the northeast along the coast. In Zhelin Bay, the sediments’migration trends are from coasts/islands to bay. This pattern is highly consistent with the provenance of sediments and the local hydrodynamics, which could be applied to the decision-making in port and waterway engineering.
Grain size analysis and parameter calculation have been carried out based on 70 surface sediments collected from the coastal waters of Shantou City, and characteristics of frequency distribution have been researched. The results show that the surface sediments of the area are made up of 9 kinds of sediment types, the main types are clayey silt, sandy silt and sand-silt-clay. The content of gravel, sand, silt, and clay in the surface sediments is 1.4%, 29.2%, 51.0 %, and 18.4 %, respectively. The mean grain size of sediments in this area is 0.12~7.30 and the average is 5.53 . The coefficient of sorting is 0.50~2.94 and the average is 1.82. Skewness is -0.65~0.30 and the average is -0.02. Kurtosis is 0.63~2.67 and the average is 1.11. The modern sedimentary environment in coastal waters of Shantou can be classified into 4 types by system cluster analysis and factor analysis. Spline interpolation method was employed to the data of grain size parameters over the study area. Then, the sediment transport trends were simulated by using GSTA (Grain Size Trend Analysis) model. The grain size trends analysis shows that: In Shantou harbor that the water depth ＜10 m, sediments from the runoff and sea were converged to the estuaries and offshore; Sediments in Shantou harbor that the water depth ＞10 m are transported towards the northeast along the coast. In Zhelin Bay, the sediments’migration trends are from coasts/islands to bay. This pattern is highly consistent with the provenance of sediments and the local hydrodynamics, which could be applied to the decision-making in port and waterway engineering.
2014, 32(2): 325-333.
Abstract:
Based on integrated investigation of outcrops, well logs and cores, the sequence stratigraphy framework of northern Tarim Basin was set up, and the sequence architecture of Triassic in outcrop of Kuche depression and Northern Uplift of Tarim Basin was studied. In each sequence, coarse grained lithosomic bodies such as alluvial fan, braided river and braided river delta are dominant in the lowstand systems tracts (LST), and the upper parts of the sequences are composed of fine grained lacustrine mudstone which are called lacustrine transgressive-highstand systems tracts (T-HST). Every single sequence is coarse in lower part and fine in the upper part. The special sequence architecture is mainly associated to episodic compressive movement of Tarim Basin in Triassic. At the beginning of the compression, the accommodation increases slowly, for the short distance from provenance to basin and sufficient sediment supply, the LSTs are mainly coarse sediments. The water became deeper with the intensified compressive force, then the fine-grained transgressive systems tracts (TST) are deposited. When the basin base was broken, lake water dropped down quickly, with little mudstone deposited as highstand systems tracts (HST). Finally, a sequence evolution model of Triassic in the northern Tarim Basin was proposed. In tectonic compression period, some coarse-grained lithosomic bodies such as fan delta, braided river delta were deposited; when the compressive force persisted and discharged in a short time, fine-grained lacustrine sediments deposited which were defined as T-HST as the upper parts of sequences. For the special dual feature of the sequences, the coarse-grained lower LSTs are suitable for reservoir, and the upper fine-grained T-HSTs could be the source or seal of the reservoir, so it is indicated that, besides the tectonic reservoir, the lithologic reservoir and lithologic-tectonic reservoir in the LSTs of each sequence are major exploration targets of Triassic in northern Tarim Basin.
Based on integrated investigation of outcrops, well logs and cores, the sequence stratigraphy framework of northern Tarim Basin was set up, and the sequence architecture of Triassic in outcrop of Kuche depression and Northern Uplift of Tarim Basin was studied. In each sequence, coarse grained lithosomic bodies such as alluvial fan, braided river and braided river delta are dominant in the lowstand systems tracts (LST), and the upper parts of the sequences are composed of fine grained lacustrine mudstone which are called lacustrine transgressive-highstand systems tracts (T-HST). Every single sequence is coarse in lower part and fine in the upper part. The special sequence architecture is mainly associated to episodic compressive movement of Tarim Basin in Triassic. At the beginning of the compression, the accommodation increases slowly, for the short distance from provenance to basin and sufficient sediment supply, the LSTs are mainly coarse sediments. The water became deeper with the intensified compressive force, then the fine-grained transgressive systems tracts (TST) are deposited. When the basin base was broken, lake water dropped down quickly, with little mudstone deposited as highstand systems tracts (HST). Finally, a sequence evolution model of Triassic in the northern Tarim Basin was proposed. In tectonic compression period, some coarse-grained lithosomic bodies such as fan delta, braided river delta were deposited; when the compressive force persisted and discharged in a short time, fine-grained lacustrine sediments deposited which were defined as T-HST as the upper parts of sequences. For the special dual feature of the sequences, the coarse-grained lower LSTs are suitable for reservoir, and the upper fine-grained T-HSTs could be the source or seal of the reservoir, so it is indicated that, besides the tectonic reservoir, the lithologic reservoir and lithologic-tectonic reservoir in the LSTs of each sequence are major exploration targets of Triassic in northern Tarim Basin.
2014, 32(2): 344-353.
Abstract:
Based on lithology combination, logging curves stacking pattern and seismic reflection characteristics, this article divides Dongying delta into eight cycles, parasequence set 8 to parasequence set 1(PS8~PS1). Between two cycles mudstone wedge deposits for small scale lake-flooding. According to core observation and logging analysis of sedimentary facies, it indicates that delta-gravity flow-lacustrine depositional system develops in the study area. Delta distributary channel, mouth bar and sheet sands deposits in southeast, and slide congeries, slump turbidite, distal turbidite associated with delta front slump deposits in northwest. From PS8 to PS1,the active delta migrates from south to north. When wave force and river energy are well matched and alternating motion, the sheet sands and mouth bars deposit, forming large thickness of delta progradation wedge. Under the effect of lake level change, tectonic subsidence rate and sediment supply rate, in early regressive system tract PS7~PS4, the gravity flow sand bodies are rich in oil, and the sheet sands and mouth bars, depositing near the parasequence set boundary are also well oil-bearing, because of close to mudstone wedge and swamp deposition which are lateral sealing and local cap rock.
Based on lithology combination, logging curves stacking pattern and seismic reflection characteristics, this article divides Dongying delta into eight cycles, parasequence set 8 to parasequence set 1(PS8~PS1). Between two cycles mudstone wedge deposits for small scale lake-flooding. According to core observation and logging analysis of sedimentary facies, it indicates that delta-gravity flow-lacustrine depositional system develops in the study area. Delta distributary channel, mouth bar and sheet sands deposits in southeast, and slide congeries, slump turbidite, distal turbidite associated with delta front slump deposits in northwest. From PS8 to PS1,the active delta migrates from south to north. When wave force and river energy are well matched and alternating motion, the sheet sands and mouth bars deposit, forming large thickness of delta progradation wedge. Under the effect of lake level change, tectonic subsidence rate and sediment supply rate, in early regressive system tract PS7~PS4, the gravity flow sand bodies are rich in oil, and the sheet sands and mouth bars, depositing near the parasequence set boundary are also well oil-bearing, because of close to mudstone wedge and swamp deposition which are lateral sealing and local cap rock.
2014, 32(2): 365-375.
Abstract:
The quantitative calculation of sandstone porosity evolution based on casting section data is one of important techniques for diagenetic change and reservoir simulations. Because of the problems in parameters determination and calculation process, the results are not accurate in many cases. For this reason, based on the analysis of previous computation process and their errors, the original porosity determination method is decided, and COPL, CEPL and CRPI (corrosional porosity increase) calculation formula are deducted. To the determination of original porosity, Beard and Weyl’s wet packing experiment is more accurate than the method of assigning a constant value for all the samples according to the sedimentary facies or the Scherer’s equation based on the relationship between original porosity and coefficient of sorting. Under the consideration of rock bulk volume’s reduction in the compacting process, COPL, CEPL and CRPI calculation formula are deducted, and the errors in situation that the bulk volume’s reduction is neglected is analysed, and the errors’ extent is calculated. Instead of the method contrasting the intergranular porosity and ΦHe without calculation of CRPI, the approach considering all diagenesis sorts and rock bulk volume’s reduction in the compacting process is established in calculation result accuracy check-out. The application of the above-mentioned calculation methods of sandstone porosity evolution in Chang8 reservoir of Huanjiang area, Ordos Basin, is satisfying with 1.1% absolute error and 15.3% relative error of porosity.
The quantitative calculation of sandstone porosity evolution based on casting section data is one of important techniques for diagenetic change and reservoir simulations. Because of the problems in parameters determination and calculation process, the results are not accurate in many cases. For this reason, based on the analysis of previous computation process and their errors, the original porosity determination method is decided, and COPL, CEPL and CRPI (corrosional porosity increase) calculation formula are deducted. To the determination of original porosity, Beard and Weyl’s wet packing experiment is more accurate than the method of assigning a constant value for all the samples according to the sedimentary facies or the Scherer’s equation based on the relationship between original porosity and coefficient of sorting. Under the consideration of rock bulk volume’s reduction in the compacting process, COPL, CEPL and CRPI calculation formula are deducted, and the errors in situation that the bulk volume’s reduction is neglected is analysed, and the errors’ extent is calculated. Instead of the method contrasting the intergranular porosity and ΦHe without calculation of CRPI, the approach considering all diagenesis sorts and rock bulk volume’s reduction in the compacting process is established in calculation result accuracy check-out. The application of the above-mentioned calculation methods of sandstone porosity evolution in Chang8 reservoir of Huanjiang area, Ordos Basin, is satisfying with 1.1% absolute error and 15.3% relative error of porosity.
2014, 32(2): 385-394.
Abstract:
The Lucaogou Formation, the main hydrocarbon source rocks in Jimus sag, is characterized by various lithology, which are mainly transitional types. Aiming at obtainning the difference in hydrocarbon generation potential characteristics of various sorts of mudstone, shale in this formation is divided into four types based on the logging lithology, which are pure shale, sandy mudstone, lime mudstone and dolomitic mudstone. And an evaluation about hydrocarbon generation potential characteristics of the four types of mudstone is made respectively from the organic geochemistry perspective. The results show that the abundance of organic material of pure shale is higher than other three types of mudstones, like lime mudstone, dolomitic mudstone, and sandy mudstone. Considering the type of organic matter in shale, pure mudstone is the best of them, followed by lime mudstone and dolomitic mudstone, and sandy mudstone is the worst, and combining what has been discussed above and the analysis of HI, it is concluded that pure mudstone shows the greatest hydrocarbon generation potential, followed by lime mudstone and dolomitic mudstone and sandy mudstone.
The Lucaogou Formation, the main hydrocarbon source rocks in Jimus sag, is characterized by various lithology, which are mainly transitional types. Aiming at obtainning the difference in hydrocarbon generation potential characteristics of various sorts of mudstone, shale in this formation is divided into four types based on the logging lithology, which are pure shale, sandy mudstone, lime mudstone and dolomitic mudstone. And an evaluation about hydrocarbon generation potential characteristics of the four types of mudstone is made respectively from the organic geochemistry perspective. The results show that the abundance of organic material of pure shale is higher than other three types of mudstones, like lime mudstone, dolomitic mudstone, and sandy mudstone. Considering the type of organic matter in shale, pure mudstone is the best of them, followed by lime mudstone and dolomitic mudstone, and sandy mudstone is the worst, and combining what has been discussed above and the analysis of HI, it is concluded that pure mudstone shows the greatest hydrocarbon generation potential, followed by lime mudstone and dolomitic mudstone and sandy mudstone.
2014, 32(2): 198-204.
Abstract:
According to calculative cycle thickness by the natural gamma logging curve, using Fischer plots to identify the high-frequency sedimentary cycle Superposition type, trying to proclaim the relation between GR logs reflective fluctuation of clay content and climate cycle. Choosing well SN109 natural gamma logging curve which possess clearly top and bottom and continuous layers in Dongling area of Songliao Basin as experimental data. Using the extreme point method, 1 166 high-frequency depositional cycles can be identified. The thickness of these cycles change form 0.125 m to 2.75 m, the average is 0.62 m. According to Fischer plots, the estimation of the average period of high-frequency depositional cycles is 17.2 ka, the average period of medium-frequency depositional cycles is between 86.1~103.3 ka, the average period of low-frequency depositional cycles is between 305~416 ka, corresponding with 19~24 ka of the precession of equinox, 85~140 ka of the short eccentricity, and 350~400 ka of the long eccentricity of Milankovitch cycles, respectively. It is suggested that the production of lacustrine depositional cycles of Quantou Formation was controlled by the Milankovitch cycles.
According to calculative cycle thickness by the natural gamma logging curve, using Fischer plots to identify the high-frequency sedimentary cycle Superposition type, trying to proclaim the relation between GR logs reflective fluctuation of clay content and climate cycle. Choosing well SN109 natural gamma logging curve which possess clearly top and bottom and continuous layers in Dongling area of Songliao Basin as experimental data. Using the extreme point method, 1 166 high-frequency depositional cycles can be identified. The thickness of these cycles change form 0.125 m to 2.75 m, the average is 0.62 m. According to Fischer plots, the estimation of the average period of high-frequency depositional cycles is 17.2 ka, the average period of medium-frequency depositional cycles is between 86.1~103.3 ka, the average period of low-frequency depositional cycles is between 305~416 ka, corresponding with 19~24 ka of the precession of equinox, 85~140 ka of the short eccentricity, and 350~400 ka of the long eccentricity of Milankovitch cycles, respectively. It is suggested that the production of lacustrine depositional cycles of Quantou Formation was controlled by the Milankovitch cycles.
2014, 32(2): 218-227.
Abstract:
On the basis of integrated analysis of core, well logging, seismic and grain size probability curves data, sedimentary characteristics of sublacustrine fan in Liu-1 Formation of Weixinan sag is comprehensively studied. Sublacustrine fan is characterized by the Bouma sequence implying typical turbidite, it is classified into two types of powerful hydrodynamic sedimentation and weak hydrodynamic sedimentation. For depositional texture, sublacustrine fan features grain distribution character of typical turbidite deposit in terms of grain size probability curves and C—M map, moreover, it contains large numbers of turbidite deposit structures. Sublacustrine fan is resulted from the condition of cliffy paleolandform and abundant sedimentary supply, and formed at the location of deep water lacustrine area of fault slope-break zone or syndepositional structural slope-break zone. The sublacustrine fan formed from deep lacustrine, trap condition is excellent, a near source rock, hydrocarbon source is abundant, easily forming hydrocarbon reservoirs, already obtained commercial oil-gas flow in numbers of drilled well, and have great exploration foreground.
On the basis of integrated analysis of core, well logging, seismic and grain size probability curves data, sedimentary characteristics of sublacustrine fan in Liu-1 Formation of Weixinan sag is comprehensively studied. Sublacustrine fan is characterized by the Bouma sequence implying typical turbidite, it is classified into two types of powerful hydrodynamic sedimentation and weak hydrodynamic sedimentation. For depositional texture, sublacustrine fan features grain distribution character of typical turbidite deposit in terms of grain size probability curves and C—M map, moreover, it contains large numbers of turbidite deposit structures. Sublacustrine fan is resulted from the condition of cliffy paleolandform and abundant sedimentary supply, and formed at the location of deep water lacustrine area of fault slope-break zone or syndepositional structural slope-break zone. The sublacustrine fan formed from deep lacustrine, trap condition is excellent, a near source rock, hydrocarbon source is abundant, easily forming hydrocarbon reservoirs, already obtained commercial oil-gas flow in numbers of drilled well, and have great exploration foreground.
2014, 32(2): 238-243.
Abstract:
Combined the results of the physical simulation experiment with the seismic and core information, a new understanding about the tectonic position, paleogeographic position of salt sediment and the genetic mechanism were proposed in Dongpu Depression. The research suggested that the sedimentation of salt was earlier in shallow parts such as the edge of the lake basin sag and the central uplift belt, the salt layer were thick, the particle size of salt rock was small while the size was large and with a thin or absent layer near the center of the lake basin; a single salt layer with large thickness and small particle size may be deposited, while near the center of the lake basin, there are enough time for the mineral to crystallize, salt rock with large particle was deposited,and the thickness of a single salt layer can be very flexible, or can even be absent. The paleogeographic position of salt rock sediment were obviously impacted by paleosalinity. The salt layer at the bottom of the lake has already formed in certain depth in most areas of the saline lake basin, and has a certain thickness when lakes become shallower, that ensures the reducing environment of the lower part of the shale, and the basic original structure was kept after the salt sediment, the upper can again accept shale deposition; The salt rock can still deposit after the lake receded in the leakage zone at the edge of the lake basin, there salt layer is thinnest, small particle size, symbol of redox environment were commonly in sight in the lower strata.
Combined the results of the physical simulation experiment with the seismic and core information, a new understanding about the tectonic position, paleogeographic position of salt sediment and the genetic mechanism were proposed in Dongpu Depression. The research suggested that the sedimentation of salt was earlier in shallow parts such as the edge of the lake basin sag and the central uplift belt, the salt layer were thick, the particle size of salt rock was small while the size was large and with a thin or absent layer near the center of the lake basin; a single salt layer with large thickness and small particle size may be deposited, while near the center of the lake basin, there are enough time for the mineral to crystallize, salt rock with large particle was deposited,and the thickness of a single salt layer can be very flexible, or can even be absent. The paleogeographic position of salt rock sediment were obviously impacted by paleosalinity. The salt layer at the bottom of the lake has already formed in certain depth in most areas of the saline lake basin, and has a certain thickness when lakes become shallower, that ensures the reducing environment of the lower part of the shale, and the basic original structure was kept after the salt sediment, the upper can again accept shale deposition; The salt rock can still deposit after the lake receded in the leakage zone at the edge of the lake basin, there salt layer is thinnest, small particle size, symbol of redox environment were commonly in sight in the lower strata.
2014, 32(2): 253-259.
Abstract:
There are several kilometers thick dolomites in Cambrian of Tarim basin. Saddle dolomite could be found in the strata, which record fluid evolution during diagenesis. The basic geology, internal structure and geochemical characteristics of saddle dolomite viod-filling were analyzed by electron microprober to reveal the relation between fluid and tectonic evolution in dolomite diagenesis in the study. Three main types of saddle dolomite were indentified in the study area: dedolomitzation zone saddle dolomite, Fe-rich zone saddle dolomite and Fe-rich and Mn-rich saddle dolomite. There are some differences in three types of dolomite. The dedolomitzation zone saddle dolomite often is milky white, irregular lumps, more uniform internal, and dedolomitization zonal edge. The dolomite void-filling has low Fe-Mn content. The δ18O values of dolomite void-filling are -12.2‰ to -10.1‰. The uniform temperature of inclusions are in the 87℃~140℃, The value of 87Sr/86Sr are 0.708 979 to 0.709 038. The Fe-rich zone saddle dolomite often are blue-gray, jagged output in dolomite cracks or dissolved pores, its internal structure is very complex, it can be divided into three parts: core, zone and outer edge. The core of crystal are dark, enriched white calcite inclusions spreading like star point, the edge of crystal was zonal because of the different iron content. The inner ring with rich calcite inclusions is comprised by alternating dark and light colored stripes, the outer ring does not basically have calcite inclusions, but most of dolomite has only one dark layer of light-colored pinstripe. The dolomite viod-filling has high Fe content. The δ18O values of dolomite viod-filling are -9‰~-5‰(VPDB), The uniform temperature of inclusions are 100℃~150℃, The value of 87Sr/86Sr are 0.708 824~0.709 391. The Mn-rich saddle dolomite is mostly meat-red, jagged output fractures in dolomite or dissolved pores. The internal structure of the dolomite void-filling is very complex, and the development of multi-stage and multi-type stripes, showing a "roses" shape. It can be simply divided into two parts: the inner zone and the outer zone. The inner zone with a small amount of calcite inclusions is lighter colors and blurred boundaries. The stripes are thin and numerous. The outer zone is the lighter color ring, stripes is little and thick. There is often only contain a thick bright stripes. The bright-dark boundary is obvious. Many different between inner and outer ring are caused by iron and manganese content. The dolomite void-filing have the highest value content of Fe and Mn. The measuring points of the outer ring in the crystal with a bright stripe on the Fe content are up to 124 172 μg/g. The Fe content are from 19 950 to 38 057 μg/g in most of the points, while the inner ring with the Fe content 6 907~25 091 μg/g and Mn content of the highest values up to 5 056 μg/g. Three types of dolomite formed in different environment, the nature of the formation fluid was also significant differences. Dedolomitzation zone saddle dolomite may be related to the inter-layer fluid, Fe-rich zone saddle dolomite and Fe-rich and Mn-rich saddle dolomite may have been impacted by fault-related fluid, and the formation fluid of Fe- rich and Mn-rich saddle dolomite may come from more deep than the former.
There are several kilometers thick dolomites in Cambrian of Tarim basin. Saddle dolomite could be found in the strata, which record fluid evolution during diagenesis. The basic geology, internal structure and geochemical characteristics of saddle dolomite viod-filling were analyzed by electron microprober to reveal the relation between fluid and tectonic evolution in dolomite diagenesis in the study. Three main types of saddle dolomite were indentified in the study area: dedolomitzation zone saddle dolomite, Fe-rich zone saddle dolomite and Fe-rich and Mn-rich saddle dolomite. There are some differences in three types of dolomite. The dedolomitzation zone saddle dolomite often is milky white, irregular lumps, more uniform internal, and dedolomitization zonal edge. The dolomite void-filling has low Fe-Mn content. The δ18O values of dolomite void-filling are -12.2‰ to -10.1‰. The uniform temperature of inclusions are in the 87℃~140℃, The value of 87Sr/86Sr are 0.708 979 to 0.709 038. The Fe-rich zone saddle dolomite often are blue-gray, jagged output in dolomite cracks or dissolved pores, its internal structure is very complex, it can be divided into three parts: core, zone and outer edge. The core of crystal are dark, enriched white calcite inclusions spreading like star point, the edge of crystal was zonal because of the different iron content. The inner ring with rich calcite inclusions is comprised by alternating dark and light colored stripes, the outer ring does not basically have calcite inclusions, but most of dolomite has only one dark layer of light-colored pinstripe. The dolomite viod-filling has high Fe content. The δ18O values of dolomite viod-filling are -9‰~-5‰(VPDB), The uniform temperature of inclusions are 100℃~150℃, The value of 87Sr/86Sr are 0.708 824~0.709 391. The Mn-rich saddle dolomite is mostly meat-red, jagged output fractures in dolomite or dissolved pores. The internal structure of the dolomite void-filling is very complex, and the development of multi-stage and multi-type stripes, showing a "roses" shape. It can be simply divided into two parts: the inner zone and the outer zone. The inner zone with a small amount of calcite inclusions is lighter colors and blurred boundaries. The stripes are thin and numerous. The outer zone is the lighter color ring, stripes is little and thick. There is often only contain a thick bright stripes. The bright-dark boundary is obvious. Many different between inner and outer ring are caused by iron and manganese content. The dolomite void-filing have the highest value content of Fe and Mn. The measuring points of the outer ring in the crystal with a bright stripe on the Fe content are up to 124 172 μg/g. The Fe content are from 19 950 to 38 057 μg/g in most of the points, while the inner ring with the Fe content 6 907~25 091 μg/g and Mn content of the highest values up to 5 056 μg/g. Three types of dolomite formed in different environment, the nature of the formation fluid was also significant differences. Dedolomitzation zone saddle dolomite may be related to the inter-layer fluid, Fe-rich zone saddle dolomite and Fe-rich and Mn-rich saddle dolomite may have been impacted by fault-related fluid, and the formation fluid of Fe- rich and Mn-rich saddle dolomite may come from more deep than the former.
2014, 32(2): 270-277.
Abstract:
Through the satellite images analysis of modern delta sedimentary , we could obtain the planar distributions as well as the quantitative rules of the subaqueous distributary channels and river mouth bars, which enrichs and perfects the reservoir geological repository. By combining the modern sedimentary satellite images of Wax Lake Delta and taking Poyang Lake Delta as a research object, this article qualitatively and quantitatively analyses the plane distribution features and relations of subaqueous distributary channels and mouth bars in typical lobate fluvial-dominated delta front has been described.Research results show that the bifurcation angle of subaqueous distributary channel is nearly 50 °, of which the width is narrower towards lake basin (0.72 times reduction in width), the quantity is more and the shape presents like divergent leaf. The single river mouth bar present triangular shape and narrow mid-channel-bar-like, of which the triangle shaped one is developed at the lower part of the delta front, while the narrow mid-channel-bar-like one is located in the upper part, and there is a fair good linear relationship for the length and width of mouth bar. These results could effectively guide the research on fine microfacies distribution of similar underground reservoir.
Through the satellite images analysis of modern delta sedimentary , we could obtain the planar distributions as well as the quantitative rules of the subaqueous distributary channels and river mouth bars, which enrichs and perfects the reservoir geological repository. By combining the modern sedimentary satellite images of Wax Lake Delta and taking Poyang Lake Delta as a research object, this article qualitatively and quantitatively analyses the plane distribution features and relations of subaqueous distributary channels and mouth bars in typical lobate fluvial-dominated delta front has been described.Research results show that the bifurcation angle of subaqueous distributary channel is nearly 50 °, of which the width is narrower towards lake basin (0.72 times reduction in width), the quantity is more and the shape presents like divergent leaf. The single river mouth bar present triangular shape and narrow mid-channel-bar-like, of which the triangle shaped one is developed at the lower part of the delta front, while the narrow mid-channel-bar-like one is located in the upper part, and there is a fair good linear relationship for the length and width of mouth bar. These results could effectively guide the research on fine microfacies distribution of similar underground reservoir.
2014, 32(2): 290-295.
Abstract:
The Yangtze River is one of the major rivers in the world. Originating from the Tibetan Plateau, the river flows eastward across the three major topographic levels. Its drainage covers more than one- fifth of the continental area of China before finally entering the East China Sea. The huge Yangtze drainage basin is more than 6300 km in length and has a catchment area of 1.8×106km2. It is located between 24°27′~35°44′ N and 90°33′~122°19′ E. The Yangtze drainage basin spans the regional structure of China with three-grade relief and can be divided into three parts, the upper, middle and lower reaches. Although study of the evolution of the Yangtze River has a long history of more than 100 years, it is still controversial. Previous studies proposed that the Yangtze River can be dated back to the Cretaceous or the early Tertiary, the early Quaternary or the late Pleistocene. The source to sink process of the modern river sediments played a fundamental role in the research of the evolution of the Yangtze River. Sediments of the modern Yangtze River were mostly derived from the upper Yangtze drainage basin. Therefore, the erosion process of sediments from the upper Yangtze River played an important role in the erosion process of sediments from the whole river drainage system. The Sr-Nd isotopes have been proved to be rarely influenced by weathering, sediment transport and deposition process, especially the Nd isotope. We have reported the geochemical and Neodymium isotopic compositions of the late Cenozoic sediments in the Jianghan Basin to decipher information on the changing provenance and provide more constraints on the evolution of the Yangtze River. In this study, the fine-grained samples were collected from the main stream and tributaries (the Jinshajiang River, the Minjiang River and the Jialingjiang River) of the upper Yangtze River for Sr-Nd isotopic measurements. The results revealed that samples collected from the Jinshajiang River and the Minjiang River show high εNd(0) values. Although the source rocks in the Yangtze drainage basin are complicated including Archean metamorphic rocks, Paleozoic carbonate and sedimentary rocks, Mesozoic-Cenozoic igneous and clastic rocks, and Quaternary detrital sediments. It indicates that the influence of the large Emeishan Basalt Province is widely distributed in the upper Yangtze River valley in the Yunnan and Sichuan provinces. During the humid and warm climate, it undergoes rapid chemical weathering and the higher εNd(0) values could dominate the Nd isotopic compositions of the Yangtze River sediments. Samples from the Jianglingjiang River sediments show much lower εNd(0) values, indicating that the average Nd isotopic values of the source rocks in the Jialingjiang valley is much lower. Compared with Nd, the Sr isotopic values show a wider range, indicating that the Sr isotopic sediments of sediments are affected by much more complicated factors. In order to better understand how the modern Yangtze River generated sediments, we also collected the SrNd isotopic values reported by other researchers. The results have revealed that sediments from the main stream can be divided into two parts. One part of the sediments is characterized by high εNd (0) values and low 87Sr/86Sr values. The other part of the sediments is characterized by low εNd(0) values and high 87Sr/86Sr values. However, we find that both of these sediments were located in the same area with the samples collected from the Jinshajiang River (No matter from this study or previous studies). It indicates that these sediments were mainly derived from source rocks distributed in the Jinshajiang valley. The influence of the sediments from the Jialingjiang River could be excluded. However, this was not consistent with the information provided by the Changjiang (the Yangtze River) Sediment Bulletin that the Jialingjiang River is an important sediment supplier to the mainstream.
The Yangtze River is one of the major rivers in the world. Originating from the Tibetan Plateau, the river flows eastward across the three major topographic levels. Its drainage covers more than one- fifth of the continental area of China before finally entering the East China Sea. The huge Yangtze drainage basin is more than 6300 km in length and has a catchment area of 1.8×106km2. It is located between 24°27′~35°44′ N and 90°33′~122°19′ E. The Yangtze drainage basin spans the regional structure of China with three-grade relief and can be divided into three parts, the upper, middle and lower reaches. Although study of the evolution of the Yangtze River has a long history of more than 100 years, it is still controversial. Previous studies proposed that the Yangtze River can be dated back to the Cretaceous or the early Tertiary, the early Quaternary or the late Pleistocene. The source to sink process of the modern river sediments played a fundamental role in the research of the evolution of the Yangtze River. Sediments of the modern Yangtze River were mostly derived from the upper Yangtze drainage basin. Therefore, the erosion process of sediments from the upper Yangtze River played an important role in the erosion process of sediments from the whole river drainage system. The Sr-Nd isotopes have been proved to be rarely influenced by weathering, sediment transport and deposition process, especially the Nd isotope. We have reported the geochemical and Neodymium isotopic compositions of the late Cenozoic sediments in the Jianghan Basin to decipher information on the changing provenance and provide more constraints on the evolution of the Yangtze River. In this study, the fine-grained samples were collected from the main stream and tributaries (the Jinshajiang River, the Minjiang River and the Jialingjiang River) of the upper Yangtze River for Sr-Nd isotopic measurements. The results revealed that samples collected from the Jinshajiang River and the Minjiang River show high εNd(0) values. Although the source rocks in the Yangtze drainage basin are complicated including Archean metamorphic rocks, Paleozoic carbonate and sedimentary rocks, Mesozoic-Cenozoic igneous and clastic rocks, and Quaternary detrital sediments. It indicates that the influence of the large Emeishan Basalt Province is widely distributed in the upper Yangtze River valley in the Yunnan and Sichuan provinces. During the humid and warm climate, it undergoes rapid chemical weathering and the higher εNd(0) values could dominate the Nd isotopic compositions of the Yangtze River sediments. Samples from the Jianglingjiang River sediments show much lower εNd(0) values, indicating that the average Nd isotopic values of the source rocks in the Jialingjiang valley is much lower. Compared with Nd, the Sr isotopic values show a wider range, indicating that the Sr isotopic sediments of sediments are affected by much more complicated factors. In order to better understand how the modern Yangtze River generated sediments, we also collected the SrNd isotopic values reported by other researchers. The results have revealed that sediments from the main stream can be divided into two parts. One part of the sediments is characterized by high εNd (0) values and low 87Sr/86Sr values. The other part of the sediments is characterized by low εNd(0) values and high 87Sr/86Sr values. However, we find that both of these sediments were located in the same area with the samples collected from the Jinshajiang River (No matter from this study or previous studies). It indicates that these sediments were mainly derived from source rocks distributed in the Jinshajiang valley. The influence of the sediments from the Jialingjiang River could be excluded. However, this was not consistent with the information provided by the Changjiang (the Yangtze River) Sediment Bulletin that the Jialingjiang River is an important sediment supplier to the mainstream.
2014, 32(2): 306-313.
Abstract:
Paleohydrological investigations were carried out in the upper reach of the Hanjiang River, which is the source of the “South-to-North Water Diversion Project”. During the fieldwork, typical palaeoflood slackwater deposit (SWD) was identified in the Holocene eolian loess-soil profile on the river banks in the Shangjiahe reach in Yunxian county of Hubei province. Sediment and OSL dating samples were taken from the profile. Laboratory analysis of the grain-size distribution and the magnetic susceptibility show that the SWD was deposited from floodwater during an extraordinary palaeoflood event. The peak flood discharge was estimated to be 63 720 m3/s, which is much larger than the recorded floods. OSL dating on quartz grains separated from the samples was carried out by using the single aliquot regenerative-dose (SAR) protocol. The measured ages of the samples are between 940±140 and 3 190±100 a. The extraordinary palaeoflood event recorded by the SWD is therefore dated to between 900 a B.P. and 1000 a B.P., corresponding to the Northern Song/Liao Dynasty. This is a period with abnormal changes of climate and increased monsoonal variability. Both the serious droughts and extraordinary floods occurred during this period. This result is of great significance in understanding the river’s hydrological response to global climatic change.
Paleohydrological investigations were carried out in the upper reach of the Hanjiang River, which is the source of the “South-to-North Water Diversion Project”. During the fieldwork, typical palaeoflood slackwater deposit (SWD) was identified in the Holocene eolian loess-soil profile on the river banks in the Shangjiahe reach in Yunxian county of Hubei province. Sediment and OSL dating samples were taken from the profile. Laboratory analysis of the grain-size distribution and the magnetic susceptibility show that the SWD was deposited from floodwater during an extraordinary palaeoflood event. The peak flood discharge was estimated to be 63 720 m3/s, which is much larger than the recorded floods. OSL dating on quartz grains separated from the samples was carried out by using the single aliquot regenerative-dose (SAR) protocol. The measured ages of the samples are between 940±140 and 3 190±100 a. The extraordinary palaeoflood event recorded by the SWD is therefore dated to between 900 a B.P. and 1000 a B.P., corresponding to the Northern Song/Liao Dynasty. This is a period with abnormal changes of climate and increased monsoonal variability. Both the serious droughts and extraordinary floods occurred during this period. This result is of great significance in understanding the river’s hydrological response to global climatic change.
2014, 32(2): 334-342.
Abstract:
Hailaer Basin, featured by frequent structural movement, simple depositional cycle, multi-and near-sources, coarse clastic, narrow-sedimentary facies and more fans, is Mesozoic Early Cretaceous fault depressed lacustrine basin developed on the Hercynian geosyncline folded base in northeast China. After its formation, Hailaer Basin had gone through three tectonic phases, including rift initiation, rift extension and post-rift episodes, and each phase has its own depositional system. Based on the theory of sequence stratigraphy and used all data such as seismic, well log, core analysis and palaeophyte, this paper focuses on sandbodies distribution in a sequence stratigraphic framework in Lower Cretaceous of Beier depression. Studies show that there are three second-order sequence correspond to three tectonic phases, including rift initiation sequence SQⅠ(Tongbomiao group K1t), rift extension sequence SQⅡ(Nantun group K1n) as well as post- rift sequence SQⅢ(Damoguaihe group K1d), and six third-order sequence including SQA(Tongbomiao Group K1t), SQB(Nanyi member K1n1), SQC(Nan’er member K1n2), SQD(Dayi member K1d1), SQE(Daer member K1d2) and SQF(Yimin Group K1y) as well as fourteen systems tracts. In the third-order sequence stratigraphic framework, the spatial distributions and sedimentary assemblages of depositional system are varying significantly in different depositional stage. In the depositional period of sequence SQA(formed in the rift initiation episode), which developed the coarse clastic sedimentary assemblage as alluvial fan and subaqueous fan. During the depositing period of sequence SQB～SQC (formed in the rift extension episode), which developed the sedimentary assemblage as subaqueous fan, turbidite fan, fan delta and semi-deep. While during the depositing period of sequence SQD ~SQF(formed in post-rift episode), which developed the sedimentary assemblage as delta, shore-shallow lacustrine and semi-deep, as well as fluvial and paludal facies. Lowstand system tracts sandbodies were mostly distributed in rift extension sequence SQⅡwith favorable reservoir conditions. Meanwhile, the above thick claystone in transgressive and highstand system tracts act as cap rocks at the same time. So they can firm favorable reservoir-seal assemblage and lithologic-stratigraphic traps. Studies also show that lowstand system tracts sandbodies are mainly distributed in the depositing period of sequence SQA～SQC, while few in SQD～SQF. The main types of sandbodies are braided river channel, subaqueous fan, turbidite fan, fan delta and so on, which are featured by muti-layers with thick single layers. Controlled by multi sources, lowstand system tracts sandbodies had superposed and jointed in most of the depression.The sandbodies controlling factors are very complicate in these kinds of basins. From the aspects of analyzing the function of structure controlling depositional system, synsedimentary structures often play an important part in sandbodies deposition and its distribution. Especially, lowstand system tracts sandbodies, of which spatial distribution are mainly influenced by episodic tectonic movements and the types of structural slope break zone formed by many different level and types of faults, is the most important reservoirs for lithologic traps. The formation and distribution of lowstand system tracts sandbodies is mainly controlled by the types of structural slope break zone vertically. Three types of structural slope break zone developed on the basin margin, resulting in three types of depositional systems. Nearshore subaqueous fan system resulted from faulted scarp type break in-slope; slope fans system developed on faulted terrace type break in-slope; fan-deltas and sub-lake fan system developed on steep slope type break in-slope. While in plane, sandbodies, featured by thin thickness, small range of extension, a rapid horizontal variation and along fault strike in bands or apron shape, are controlled by the style of faulted slope-break zone. Especially, the shape and scale of sandbodies is controlled by fault-accommodation zones. Four basic types fault-accommodation zones including fault-bend, fault-connect, fault-valley and fault-intersect, and six complex types fault-accommodation zones including fault-bend and fault-intersect, fault-bend and fault-connect, fault-bend and fault-valley, fault-connect and fault-intersect, fault-connect and fault-valley, and fault-intersect and fault-valley are concluded by genesis. As a result, different kinds of sandbodies tend to be superposed and jointed in middle sag, which are the material basis of lithologic-stratigraphic traps-forming. In system tracts sequence stratigraphy framework, controlled by fault-accommodation zones and their combinations, sandbodies have various scales and shapes and show striped distribution along fault strike in Beier depression. During the depositing period of lowstand system tracts of sequence SQB, sedimentary facies of this area is shore-shallow lacustrine to semi-deep lake sediments. The lowstand system tracts of Nanyi member mainly develop fan delta, subaqueous fan and turbidite fan. Especially, in southwestern Beixi sub-depression, fault-intersect type mostly developed in steep slope for fault terrace, while fault-bend and fault-connect types in gentle slope for many consequent faults. For small deposition area and shallow water, this area has many kinds of lowstand system tracts sandbodies, which are controlled by fault-accommodation zones and show striped distribution along the long axis direction of Beier depression.
Hailaer Basin, featured by frequent structural movement, simple depositional cycle, multi-and near-sources, coarse clastic, narrow-sedimentary facies and more fans, is Mesozoic Early Cretaceous fault depressed lacustrine basin developed on the Hercynian geosyncline folded base in northeast China. After its formation, Hailaer Basin had gone through three tectonic phases, including rift initiation, rift extension and post-rift episodes, and each phase has its own depositional system. Based on the theory of sequence stratigraphy and used all data such as seismic, well log, core analysis and palaeophyte, this paper focuses on sandbodies distribution in a sequence stratigraphic framework in Lower Cretaceous of Beier depression. Studies show that there are three second-order sequence correspond to three tectonic phases, including rift initiation sequence SQⅠ(Tongbomiao group K1t), rift extension sequence SQⅡ(Nantun group K1n) as well as post- rift sequence SQⅢ(Damoguaihe group K1d), and six third-order sequence including SQA(Tongbomiao Group K1t), SQB(Nanyi member K1n1), SQC(Nan’er member K1n2), SQD(Dayi member K1d1), SQE(Daer member K1d2) and SQF(Yimin Group K1y) as well as fourteen systems tracts. In the third-order sequence stratigraphic framework, the spatial distributions and sedimentary assemblages of depositional system are varying significantly in different depositional stage. In the depositional period of sequence SQA(formed in the rift initiation episode), which developed the coarse clastic sedimentary assemblage as alluvial fan and subaqueous fan. During the depositing period of sequence SQB～SQC (formed in the rift extension episode), which developed the sedimentary assemblage as subaqueous fan, turbidite fan, fan delta and semi-deep. While during the depositing period of sequence SQD ~SQF(formed in post-rift episode), which developed the sedimentary assemblage as delta, shore-shallow lacustrine and semi-deep, as well as fluvial and paludal facies. Lowstand system tracts sandbodies were mostly distributed in rift extension sequence SQⅡwith favorable reservoir conditions. Meanwhile, the above thick claystone in transgressive and highstand system tracts act as cap rocks at the same time. So they can firm favorable reservoir-seal assemblage and lithologic-stratigraphic traps. Studies also show that lowstand system tracts sandbodies are mainly distributed in the depositing period of sequence SQA～SQC, while few in SQD～SQF. The main types of sandbodies are braided river channel, subaqueous fan, turbidite fan, fan delta and so on, which are featured by muti-layers with thick single layers. Controlled by multi sources, lowstand system tracts sandbodies had superposed and jointed in most of the depression.The sandbodies controlling factors are very complicate in these kinds of basins. From the aspects of analyzing the function of structure controlling depositional system, synsedimentary structures often play an important part in sandbodies deposition and its distribution. Especially, lowstand system tracts sandbodies, of which spatial distribution are mainly influenced by episodic tectonic movements and the types of structural slope break zone formed by many different level and types of faults, is the most important reservoirs for lithologic traps. The formation and distribution of lowstand system tracts sandbodies is mainly controlled by the types of structural slope break zone vertically. Three types of structural slope break zone developed on the basin margin, resulting in three types of depositional systems. Nearshore subaqueous fan system resulted from faulted scarp type break in-slope; slope fans system developed on faulted terrace type break in-slope; fan-deltas and sub-lake fan system developed on steep slope type break in-slope. While in plane, sandbodies, featured by thin thickness, small range of extension, a rapid horizontal variation and along fault strike in bands or apron shape, are controlled by the style of faulted slope-break zone. Especially, the shape and scale of sandbodies is controlled by fault-accommodation zones. Four basic types fault-accommodation zones including fault-bend, fault-connect, fault-valley and fault-intersect, and six complex types fault-accommodation zones including fault-bend and fault-intersect, fault-bend and fault-connect, fault-bend and fault-valley, fault-connect and fault-intersect, fault-connect and fault-valley, and fault-intersect and fault-valley are concluded by genesis. As a result, different kinds of sandbodies tend to be superposed and jointed in middle sag, which are the material basis of lithologic-stratigraphic traps-forming. In system tracts sequence stratigraphy framework, controlled by fault-accommodation zones and their combinations, sandbodies have various scales and shapes and show striped distribution along fault strike in Beier depression. During the depositing period of lowstand system tracts of sequence SQB, sedimentary facies of this area is shore-shallow lacustrine to semi-deep lake sediments. The lowstand system tracts of Nanyi member mainly develop fan delta, subaqueous fan and turbidite fan. Especially, in southwestern Beixi sub-depression, fault-intersect type mostly developed in steep slope for fault terrace, while fault-bend and fault-connect types in gentle slope for many consequent faults. For small deposition area and shallow water, this area has many kinds of lowstand system tracts sandbodies, which are controlled by fault-accommodation zones and show striped distribution along the long axis direction of Beier depression.
2014, 32(2): 354-364.
Abstract:
The reef-bank complex of Lianglitag Formation in Tazhong area hosts abundant oil and gas resources. By integrating scientists' achievement and our comprehensive research on drilling, logging, core and thin section analysis, the categories and characteristics of grain-beach subfacies in Tazhong No.I slope-break zone of Upper Ordovician Lianglitag Formation have been studied systematically. Tazhong No.I slope-break zone is a large rimed carbonate platform margin reef-bank complex sedimentary system, which is composed of four subfacies, including reef mound, carbonate mud mound, grain shoal and interbank sea. Characterized by diversity, multicycle and large thickness, the marginal-platform grain shoals of Lianglitag Formation in Tazhong area are divided into four types, including intraclast bank,bioclastic bank, oncolite bank and oolitic bank, among which psammitic bank and biological psammitic-psephitic bank are two main types of intraclast bank. It is considered that there are some differences on the category and scale of grain bank in the inner zone and outer zone of carbonate platform margin. The outer zone is mainly composed of high-to-moderate energy grain banks, while the inner zone primarily consists of low-to-moderate energy grain banks. The vertical and horizontal distribution of grain shoals are not isolated, and usually associated with reefs, forming the stacked modes vertically, interdigitated horizontally reef-flat complex. One of the Special canonical features of oil-gas distribution of Upper Ordovician Lianglitag Formation in Tazhong area is that isolated grain shoal or reef usually cannot form high-quality reservoir, while the reservoir property of grain bank or reef associated with each other is better, and usually hold large amount of hydrocarbons. In the perpendicular direction, it is considered that the superposed characteristics of the carbonate platform margin reef-bank complex of Upper Ordovician Lianglitag Formation in Tazhong No.I slope-break zone display in the form of multiple cyclic assemblages of grain shoals, reefs and lime mud mounds.Individual reef-bank complex or mud-mound-bank complex develops with grain bank at the bottom, carbonate reef mound or(and) lime mud mound overriding it in its upper part, which is overlapped by the next cyclic grain bank. In the vertical direction, reef mound subface consists of four microfacies, including reef base, reef core, reef flat-reef top and reef cover, on the lateral, reef mound subfacies is composed of four microfacies, including reef core, reef flank, reef front and reef behind. The assemblage of grain shoal and reef subface presents multicyclic characteristics, and the same grain bank can exist simultaneously as the microfacies component part of two different reef mounds located in the vertical orientation of each other, not only can be the reef base of the upper reef knoll, but also can be the reef cover of the lower reef mound. In addition, grain bank can also be one of the parts of reef mound subfacies in the form of reef flat-reef top, reef flank, reef front and reef behind microfacies. Because of the interreef depositional setting of margin-platform reef is composed of high-to-moderate energy grain bank, low-to-moderate energy grain bank and interbank sea sedimentary subfacies, grain bank can occur in interreef subfacies as well. The combination regularity of grain bank and carbonate mud mound has a similar feature to that of grain bank and reef mound. The results show that biological psammitic-psephitic bank and reef mound often exist simultaneously in the form of assemblage in the upper part of the 1st Member and the 2nd Member of the Lianglitag Formation; The oncolite bank and oolitic bank present a property of thin thickness compared with other grain banks, which range from a few meters across to several decametres,and often appear in combination with lime mud mound; The bioclastic bank (mainly crinoidal or echinoderm bank) usually occurs at reef flank or other terrains which are relatively lower, with high reservoir quality and its thickness ranging from a few meters to over twenty metres or so. The distribution characteristics of grain bank in the vertical and horizontal direction is chiefly controlled by two factors, one is the alternation of hydrodynamic condition caused by the fluctuation of relative sea level, the other is the diversity of secondary palaeogeomorphology of the carbonate platform margin. The marginal-platform grain-beach subfacies presents zonal distribution feature along Tazhong No.I slope-break zone, with its width narrows down from west to east. In the depositional setting of psammitic banks, the other grain shoals spread among them in stripped, blocky or punctuate modalities. In the matter of the categories and distribution regularities of grain beach in Tazhong No.I slope-break zone of Upper Ordovician Lianglitag Formation, different well blocks demonstrate dissimilar particularities. In the depositional setting of psammitic banks, wellblock Tazhong 45 and wellblock Zhonggu 2 are mainly composed of bioclastic banks, with biological psammitic-psephitic banks and oncolite banks distribute among them infrequently, and oolitic banks occur at Well Tazhong 86; Biological psammitic-psephitic banks develop well in wellblock Tazhong 82, oncolite banks exist in the neighbourhood of Well Tazhong 826 and Well Tazhong 82, and oolitic banks appear at Well Tazhong 822; Biological psammitic-psephitic bank and bioclastic bank are two cardinal types of grain shoals in wellblock Tazhong 62, and oncolite banks can be discovered at Well Tazhong 84; In wellblock Tazhong 24-26, biological psammitic-psephitic bank and bioclastic bank are two fundamental categories with oncolite banks scattered among them.
The reef-bank complex of Lianglitag Formation in Tazhong area hosts abundant oil and gas resources. By integrating scientists' achievement and our comprehensive research on drilling, logging, core and thin section analysis, the categories and characteristics of grain-beach subfacies in Tazhong No.I slope-break zone of Upper Ordovician Lianglitag Formation have been studied systematically. Tazhong No.I slope-break zone is a large rimed carbonate platform margin reef-bank complex sedimentary system, which is composed of four subfacies, including reef mound, carbonate mud mound, grain shoal and interbank sea. Characterized by diversity, multicycle and large thickness, the marginal-platform grain shoals of Lianglitag Formation in Tazhong area are divided into four types, including intraclast bank,bioclastic bank, oncolite bank and oolitic bank, among which psammitic bank and biological psammitic-psephitic bank are two main types of intraclast bank. It is considered that there are some differences on the category and scale of grain bank in the inner zone and outer zone of carbonate platform margin. The outer zone is mainly composed of high-to-moderate energy grain banks, while the inner zone primarily consists of low-to-moderate energy grain banks. The vertical and horizontal distribution of grain shoals are not isolated, and usually associated with reefs, forming the stacked modes vertically, interdigitated horizontally reef-flat complex. One of the Special canonical features of oil-gas distribution of Upper Ordovician Lianglitag Formation in Tazhong area is that isolated grain shoal or reef usually cannot form high-quality reservoir, while the reservoir property of grain bank or reef associated with each other is better, and usually hold large amount of hydrocarbons. In the perpendicular direction, it is considered that the superposed characteristics of the carbonate platform margin reef-bank complex of Upper Ordovician Lianglitag Formation in Tazhong No.I slope-break zone display in the form of multiple cyclic assemblages of grain shoals, reefs and lime mud mounds.Individual reef-bank complex or mud-mound-bank complex develops with grain bank at the bottom, carbonate reef mound or(and) lime mud mound overriding it in its upper part, which is overlapped by the next cyclic grain bank. In the vertical direction, reef mound subface consists of four microfacies, including reef base, reef core, reef flat-reef top and reef cover, on the lateral, reef mound subfacies is composed of four microfacies, including reef core, reef flank, reef front and reef behind. The assemblage of grain shoal and reef subface presents multicyclic characteristics, and the same grain bank can exist simultaneously as the microfacies component part of two different reef mounds located in the vertical orientation of each other, not only can be the reef base of the upper reef knoll, but also can be the reef cover of the lower reef mound. In addition, grain bank can also be one of the parts of reef mound subfacies in the form of reef flat-reef top, reef flank, reef front and reef behind microfacies. Because of the interreef depositional setting of margin-platform reef is composed of high-to-moderate energy grain bank, low-to-moderate energy grain bank and interbank sea sedimentary subfacies, grain bank can occur in interreef subfacies as well. The combination regularity of grain bank and carbonate mud mound has a similar feature to that of grain bank and reef mound. The results show that biological psammitic-psephitic bank and reef mound often exist simultaneously in the form of assemblage in the upper part of the 1st Member and the 2nd Member of the Lianglitag Formation; The oncolite bank and oolitic bank present a property of thin thickness compared with other grain banks, which range from a few meters across to several decametres,and often appear in combination with lime mud mound; The bioclastic bank (mainly crinoidal or echinoderm bank) usually occurs at reef flank or other terrains which are relatively lower, with high reservoir quality and its thickness ranging from a few meters to over twenty metres or so. The distribution characteristics of grain bank in the vertical and horizontal direction is chiefly controlled by two factors, one is the alternation of hydrodynamic condition caused by the fluctuation of relative sea level, the other is the diversity of secondary palaeogeomorphology of the carbonate platform margin. The marginal-platform grain-beach subfacies presents zonal distribution feature along Tazhong No.I slope-break zone, with its width narrows down from west to east. In the depositional setting of psammitic banks, the other grain shoals spread among them in stripped, blocky or punctuate modalities. In the matter of the categories and distribution regularities of grain beach in Tazhong No.I slope-break zone of Upper Ordovician Lianglitag Formation, different well blocks demonstrate dissimilar particularities. In the depositional setting of psammitic banks, wellblock Tazhong 45 and wellblock Zhonggu 2 are mainly composed of bioclastic banks, with biological psammitic-psephitic banks and oncolite banks distribute among them infrequently, and oolitic banks occur at Well Tazhong 86; Biological psammitic-psephitic banks develop well in wellblock Tazhong 82, oncolite banks exist in the neighbourhood of Well Tazhong 826 and Well Tazhong 82, and oolitic banks appear at Well Tazhong 822; Biological psammitic-psephitic bank and bioclastic bank are two cardinal types of grain shoals in wellblock Tazhong 62, and oncolite banks can be discovered at Well Tazhong 84; In wellblock Tazhong 24-26, biological psammitic-psephitic bank and bioclastic bank are two fundamental categories with oncolite banks scattered among them.
2014, 32(2): 376-384.
Abstract:
Industrial petroleum was discovered from Palaeozoic deep horizons in the Nanpu depression, Bohai Bay Basin, which is different from the overlying Tertiary oils from view of physical and chemical properties. Conventional geochemical methods were used to delineate the oils combined with geological analysis. There are two types of the deep buried hill oils were discovered, one is high waxy oil in the Ordovician and another is condensate oils in the Cambrian. It was observed by GC, GC-MS that, the buried hill oils contain high contents of alkyl alkanes while low concentrations of biomarkers such as steranes and hopanes. The distinguishing characteristics of the oils are high to super-high concentrations of diasteranes, diahopane, 18α(H) -22, 27, 29-trinorhopane and (Ts) and C29Ts detected in the oils with obvious thermal cracking of homohopanes, suggesting high thermal maturity of the oils. Oil-oil and oil-source rock correlations show that the oils have close genetic affinity with the Es2+3 source rocks. Hydrocarbons can be charged into the burial hill from the Es2+3 rocks directly overlying on the buried hill and/or contacted with the buried hill reservoir through faults displacement, characterized by short migration distance. Meanwhile, hydrocarbons derived from source rocks can also migrate through deeply cutting faults and Palaeozoic weathered crust into the buried hill reservoir with relatively long migration distance. It was suggested that both the kerogen type (Ⅱ2-Ⅲ) of the source rocks and gas invasion in geological history should be responsible for the formation of the high waxy oils. The former is liable to generate waxy hydrocarbons, and the latter can be inferred from the fact that the n-alkanes with carbon number less than C19 in the oils were commonly depleted and the relative concentration of naphthalenes are a little less than that of the phenanthrenes. These phenomena are obviously abnormal compared with that of the shallow oils overlying. This study is helpful for unraveling hydrocarbons accumulation mechanisms and deep petroleum resources evaluation in the area.
Industrial petroleum was discovered from Palaeozoic deep horizons in the Nanpu depression, Bohai Bay Basin, which is different from the overlying Tertiary oils from view of physical and chemical properties. Conventional geochemical methods were used to delineate the oils combined with geological analysis. There are two types of the deep buried hill oils were discovered, one is high waxy oil in the Ordovician and another is condensate oils in the Cambrian. It was observed by GC, GC-MS that, the buried hill oils contain high contents of alkyl alkanes while low concentrations of biomarkers such as steranes and hopanes. The distinguishing characteristics of the oils are high to super-high concentrations of diasteranes, diahopane, 18α(H) -22, 27, 29-trinorhopane and (Ts) and C29Ts detected in the oils with obvious thermal cracking of homohopanes, suggesting high thermal maturity of the oils. Oil-oil and oil-source rock correlations show that the oils have close genetic affinity with the Es2+3 source rocks. Hydrocarbons can be charged into the burial hill from the Es2+3 rocks directly overlying on the buried hill and/or contacted with the buried hill reservoir through faults displacement, characterized by short migration distance. Meanwhile, hydrocarbons derived from source rocks can also migrate through deeply cutting faults and Palaeozoic weathered crust into the buried hill reservoir with relatively long migration distance. It was suggested that both the kerogen type (Ⅱ2-Ⅲ) of the source rocks and gas invasion in geological history should be responsible for the formation of the high waxy oils. The former is liable to generate waxy hydrocarbons, and the latter can be inferred from the fact that the n-alkanes with carbon number less than C19 in the oils were commonly depleted and the relative concentration of naphthalenes are a little less than that of the phenanthrenes. These phenomena are obviously abnormal compared with that of the shallow oils overlying. This study is helpful for unraveling hydrocarbons accumulation mechanisms and deep petroleum resources evaluation in the area.
2014, 32(2): 391-398.
Abstract:
As an ipmortance component of crude oil and source rocks, aromatic biomarkers have been analysed for source, depositional envirment and maturity. Particularly, it’s more difficult biodegradation than the saturated hydrocarbon, so aromatic biomarkers perhaps will be widely used for the study of biodegradation oil. The biodegradation oil exsits widely in the Qiangtang Basin, Tibet plateau. In order to effectively carry out the oil source correlation analysis, aromatic fractions of six oils from Longeni area of Qiangtang Basin were analyzed using GC-MS techique. Fifteen aromatic series of hydrocarbon detected such as naphthalene, phenanthrene, terfluorene( more than One hundred and seventy aromatic hydrocarbon compounds) were used to analyze the origin and maturity of the oil. Oils are characterized by a high abundance of phenanthrene and low of naphthalene, in the meantime, a certain amount of components regarded as the marker of terrestrial high plant were detected, such as cadalene, pimanthrene, retene and so on, which indicate the oil have derived from the source containing predominantly lower aquatic organisms combined with a small amount terrestrial higher plant deposited in a marine environment. The maturity stduy indicates methylnaphthalene index due to mixed source influence and cannot be used alone for maturity evaluation, but methylphenanthrene index and methyldibenzothiophene index are effective parameter for the maturity research of crude oil in Qiangtang Basin. Applying maturity parameters of methylnaphthalene, methylphenanthrene and methyldibenzothiophene from the aromatic hydrocarbon to the study of the maturity of oil from Longeni erea indicates that the maturity has reached the matrue stage in Qiangtang Basin.
As an ipmortance component of crude oil and source rocks, aromatic biomarkers have been analysed for source, depositional envirment and maturity. Particularly, it’s more difficult biodegradation than the saturated hydrocarbon, so aromatic biomarkers perhaps will be widely used for the study of biodegradation oil. The biodegradation oil exsits widely in the Qiangtang Basin, Tibet plateau. In order to effectively carry out the oil source correlation analysis, aromatic fractions of six oils from Longeni area of Qiangtang Basin were analyzed using GC-MS techique. Fifteen aromatic series of hydrocarbon detected such as naphthalene, phenanthrene, terfluorene( more than One hundred and seventy aromatic hydrocarbon compounds) were used to analyze the origin and maturity of the oil. Oils are characterized by a high abundance of phenanthrene and low of naphthalene, in the meantime, a certain amount of components regarded as the marker of terrestrial high plant were detected, such as cadalene, pimanthrene, retene and so on, which indicate the oil have derived from the source containing predominantly lower aquatic organisms combined with a small amount terrestrial higher plant deposited in a marine environment. The maturity stduy indicates methylnaphthalene index due to mixed source influence and cannot be used alone for maturity evaluation, but methylphenanthrene index and methyldibenzothiophene index are effective parameter for the maturity research of crude oil in Qiangtang Basin. Applying maturity parameters of methylnaphthalene, methylphenanthrene and methyldibenzothiophene from the aromatic hydrocarbon to the study of the maturity of oil from Longeni erea indicates that the maturity has reached the matrue stage in Qiangtang Basin.
