Current Articles
2025, Volume 43, Issue 3
Display Method:
2025,
43(3):
769-781.
doi: 10.14027/j.issn.1000-0550.2023.143
Abstract:
Objective This study investigated the sorting movement and sedimentary characteristics of fine-grained sediments under the action of turbidity currents， and analyzed the controlled factors of their transport distance and the spatial distribution of sediment. Methods Based on a circular flume simulation， the transport and deposition process of fine-grained sediments carried by turbidity currents were simulated and analyzed by controlling three conditions： the initial fluid velocity， sediment concentration， and sand–mud ratio. Furthermore， the sedimentary dynamic mechanism was explored. Results （1） Fine-grained sediments transported by turbidity currents experience experimental phenomena such as “water jumps”， “double flow segmentation”， “lofting”， “head lifting”， and “new heads” during the flow process. （2） During fluid transportation， the movement speed and distance of fine-grained sediments are influenced by the concentration difference between the fluid and the environmental fluid. （3） Factors such as the initial flow velocity， water jumps， and lofting control the fluid flow velocity， fine-grained sediment transport distance， and spatial distribution. （4） The “new head” phenomenon causes sand bodies carried by the fluid to become discontinuous， isolated， or dispersed. Conclusions Based on the “new head” phenomenon in the simulation process， we offer insights on the causes of dispersed sand bodies. The results of this study can serve as a reference for studying the formation and distribution of dispersed sand bodies.
Objective This study investigated the sorting movement and sedimentary characteristics of fine-grained sediments under the action of turbidity currents， and analyzed the controlled factors of their transport distance and the spatial distribution of sediment. Methods Based on a circular flume simulation， the transport and deposition process of fine-grained sediments carried by turbidity currents were simulated and analyzed by controlling three conditions： the initial fluid velocity， sediment concentration， and sand–mud ratio. Furthermore， the sedimentary dynamic mechanism was explored. Results （1） Fine-grained sediments transported by turbidity currents experience experimental phenomena such as “water jumps”， “double flow segmentation”， “lofting”， “head lifting”， and “new heads” during the flow process. （2） During fluid transportation， the movement speed and distance of fine-grained sediments are influenced by the concentration difference between the fluid and the environmental fluid. （3） Factors such as the initial flow velocity， water jumps， and lofting control the fluid flow velocity， fine-grained sediment transport distance， and spatial distribution. （4） The “new head” phenomenon causes sand bodies carried by the fluid to become discontinuous， isolated， or dispersed. Conclusions Based on the “new head” phenomenon in the simulation process， we offer insights on the causes of dispersed sand bodies. The results of this study can serve as a reference for studying the formation and distribution of dispersed sand bodies.
2025,
43(3):
782-796.
doi: 10.14027/j.issn.1000-0550.2024.068
Abstract:
Objective During the sedimentation process of sandy braided rivers， the braided channels undergo frequent， rapid， and continuous shifts that lead to erosion and reworking within the preserved braided river deposits， such that deposited braided bars and braided channels are characterized by a fragmented morphology， relatively small scale， and undefined quantitative relationships. Traditional sedimentary models of sandy braided river sedimentation are inadequate to effectively guide the characterization of subsurface reservoirs. To clarify the sedimentary evolution mechanisms of sandy braided rivers and establish a reliable sedimentary architecture model with quantitative size relationships， this study conducted a flume experiment using constant boundary conditions to reproduce the formation and evolution of a sandy braided river. Methods Using a laser scanner， we obtained topographic data at regular time intervals and accurately reconstructed a three-dimensional sedimentary architecture model of the simulated braided river. Furthermore， the study analyzed sedimentary evolution mechanisms， dissected the sedimentary architecture， and constructed the quantitative size and relationship models for architecture elements. Results （1） In the initial stage of sandy braided river sedimentation， sediments undergo bedload transportation downstream， forming initial bars. The deflected flow converges into channels， further developing lobe-shaped initial bars， which are then reshaped and organized into a stable network of braided channels and bar patterns through the action of the braided channels. （2） Following the formation of the braided river， the braided channels and bars continually co-evolve， primarily through three mechanisms： lateral accretion of bars driven by braided channels， abandonment and infilling of braided channels overlaying existing bars， and scouring of the confluence by braided channels， which results in downstream bar reorganization. （3） During simulation， bars form within 1 to 6 run steps and grow to their maximum size before experiencing continuous erosion over 3 to 8 simulation periods， ultimately leading to preservation in only 36.28% of the area. （4） Upon completion of the simulation， the internal structure of the braided river deposit is dominated by braided channel deposits， accounting for approximately 57.9%， which can be classified into complex stacked， incised， and isolated channels. Bars often undergo erosion and reworking from channels， presen-ting as smaller， fragmented forms. （5） Within the preserved deposit， the average width-to-thickness ratio of braided channels is 14.1， with an internal accretion ratio of 13.7， whereas for bars， the ratio is 19.8， with an internal accretion ratio of 25.4. Conclusions This study constructed the complex sedimentary architecture formed within sandy braided river deposits after persistent and intensive erosional modification by the braided channel network， establishing a quantitative model of the size and relationships between internal architectural elements and providing a more geologically realistic and quantitative sedimentary architecture model for characterizing subsurface reservoirs.
Objective During the sedimentation process of sandy braided rivers， the braided channels undergo frequent， rapid， and continuous shifts that lead to erosion and reworking within the preserved braided river deposits， such that deposited braided bars and braided channels are characterized by a fragmented morphology， relatively small scale， and undefined quantitative relationships. Traditional sedimentary models of sandy braided river sedimentation are inadequate to effectively guide the characterization of subsurface reservoirs. To clarify the sedimentary evolution mechanisms of sandy braided rivers and establish a reliable sedimentary architecture model with quantitative size relationships， this study conducted a flume experiment using constant boundary conditions to reproduce the formation and evolution of a sandy braided river. Methods Using a laser scanner， we obtained topographic data at regular time intervals and accurately reconstructed a three-dimensional sedimentary architecture model of the simulated braided river. Furthermore， the study analyzed sedimentary evolution mechanisms， dissected the sedimentary architecture， and constructed the quantitative size and relationship models for architecture elements. Results （1） In the initial stage of sandy braided river sedimentation， sediments undergo bedload transportation downstream， forming initial bars. The deflected flow converges into channels， further developing lobe-shaped initial bars， which are then reshaped and organized into a stable network of braided channels and bar patterns through the action of the braided channels. （2） Following the formation of the braided river， the braided channels and bars continually co-evolve， primarily through three mechanisms： lateral accretion of bars driven by braided channels， abandonment and infilling of braided channels overlaying existing bars， and scouring of the confluence by braided channels， which results in downstream bar reorganization. （3） During simulation， bars form within 1 to 6 run steps and grow to their maximum size before experiencing continuous erosion over 3 to 8 simulation periods， ultimately leading to preservation in only 36.28% of the area. （4） Upon completion of the simulation， the internal structure of the braided river deposit is dominated by braided channel deposits， accounting for approximately 57.9%， which can be classified into complex stacked， incised， and isolated channels. Bars often undergo erosion and reworking from channels， presen-ting as smaller， fragmented forms. （5） Within the preserved deposit， the average width-to-thickness ratio of braided channels is 14.1， with an internal accretion ratio of 13.7， whereas for bars， the ratio is 19.8， with an internal accretion ratio of 25.4. Conclusions This study constructed the complex sedimentary architecture formed within sandy braided river deposits after persistent and intensive erosional modification by the braided channel network， establishing a quantitative model of the size and relationships between internal architectural elements and providing a more geologically realistic and quantitative sedimentary architecture model for characterizing subsurface reservoirs.
2025,
43(3):
797-812.
doi: 10.14027/j.issn.1000-0550.2024.032
Abstract:
Significance Physical simulation experimentation in a circular flume is an effective means of simulating the sedimentary process and revealing its formation mechanism. It is of great significance to research directions such as hydraulic engineering， environmental science， sedimentology， and hydrocarbon exploration. The circular flume sustains continuous fluid flow under the influence of inertial and shear forces， and is considered to approximate the transport and deposition of sediment over an infinitely long distance. Therefore， it approximately reproduces aspects of transport distance and fluid velocity that occur in environmental fluid flow， breaking through the application limitations of traditional flume simulations. Progress To meet the research needs of different application scenarios， circular flumes have gradually evolved into four types： conventional circular flumes， in situ circular flumes， mini circular flumes， and racetrack flumes. To date， physical simulations using circular flumes have achieved fruitful results in studying depositional characteristics， bedform morphology， and depositional mechanisms， among other aspects. However， there is still a relative scarcity of research in sedimentary physical simulation. With the development of tech-nology and equipment， research in sedimentary physical simulation has also made significant progress. For example， gravity flow deposition， the dynamics of fine-grained deposition transport， and tidal and wave deposition have become important research areas in physical simulations using circular flumes. It is recognized that there are several limitations in circular flume physical simulations， such as the influence of secondary circulation and the tracking of lateral deposition evolution， which will be optimized in subsequent research through improved experimental designs and enhanced measurement accuracy. Conclusions and Prospects In summary， systematically expanding the applicability of physical simulation with annular flumes based on sedimentology principles will contribute to the innovative development of basic sedimentological theories and many aspects such as fine-grained sedimentology and unconventional hydrocarbon sedimentology.
Significance Physical simulation experimentation in a circular flume is an effective means of simulating the sedimentary process and revealing its formation mechanism. It is of great significance to research directions such as hydraulic engineering， environmental science， sedimentology， and hydrocarbon exploration. The circular flume sustains continuous fluid flow under the influence of inertial and shear forces， and is considered to approximate the transport and deposition of sediment over an infinitely long distance. Therefore， it approximately reproduces aspects of transport distance and fluid velocity that occur in environmental fluid flow， breaking through the application limitations of traditional flume simulations. Progress To meet the research needs of different application scenarios， circular flumes have gradually evolved into four types： conventional circular flumes， in situ circular flumes， mini circular flumes， and racetrack flumes. To date， physical simulations using circular flumes have achieved fruitful results in studying depositional characteristics， bedform morphology， and depositional mechanisms， among other aspects. However， there is still a relative scarcity of research in sedimentary physical simulation. With the development of tech-nology and equipment， research in sedimentary physical simulation has also made significant progress. For example， gravity flow deposition， the dynamics of fine-grained deposition transport， and tidal and wave deposition have become important research areas in physical simulations using circular flumes. It is recognized that there are several limitations in circular flume physical simulations， such as the influence of secondary circulation and the tracking of lateral deposition evolution， which will be optimized in subsequent research through improved experimental designs and enhanced measurement accuracy. Conclusions and Prospects In summary， systematically expanding the applicability of physical simulation with annular flumes based on sedimentology principles will contribute to the innovative development of basic sedimentological theories and many aspects such as fine-grained sedimentology and unconventional hydrocarbon sedimentology.
2025,
43(3):
813-826.
doi: 10.14027/j.issn.1000-0550.2024.057
Abstract:
Objective To perform a numerical simulation of turbidity flow to demonstrate the effects of factors influencing the turbidity flow and sediment deposition. Methods A numerical calculation model of turbidity current was constructed based on the average layer thickness model. Initial particle size concentrations， inflow thickness and inflow velocity were modeled to assess the flow and deposition processes for suspended particles in a submarine turbidity current. Four particle sizes and a 3% flow-channel slope were simulated and the findings were analyzed. Results （1） In terms of thickness， the turbidity current began to thicken at the initial stage of its evolution as environmental water was entrained， then gradually thinned as sediment was introduced. （2） The flow velocity was observed to be in three stages： acceleration， uniform velocity， and deceleration. For the same initial thickness and sediment concentration， a higher content of fine-grained sediment resulted in a more stable turbidity current （i.e.， the current maintained a uniform flow for longer）. For similar sediment composition and concentration conditions， a thicker turbidity current was more stable. （3） The greatest accumulation of sediments occurred close to the source of the turbidity current and mainly at the central axis of the channel， decreasing monotonically with distance from the central axis. The deposition rate in a very thick， rapid turbidity current is smaller， but the overall quantity of deposited material is greater. Conclusions These results demonstrate that the method described is suitable for the study of field-scale turbidity currents and its future application is expected for naturally occurring turbidity currents.
Objective To perform a numerical simulation of turbidity flow to demonstrate the effects of factors influencing the turbidity flow and sediment deposition. Methods A numerical calculation model of turbidity current was constructed based on the average layer thickness model. Initial particle size concentrations， inflow thickness and inflow velocity were modeled to assess the flow and deposition processes for suspended particles in a submarine turbidity current. Four particle sizes and a 3% flow-channel slope were simulated and the findings were analyzed. Results （1） In terms of thickness， the turbidity current began to thicken at the initial stage of its evolution as environmental water was entrained， then gradually thinned as sediment was introduced. （2） The flow velocity was observed to be in three stages： acceleration， uniform velocity， and deceleration. For the same initial thickness and sediment concentration， a higher content of fine-grained sediment resulted in a more stable turbidity current （i.e.， the current maintained a uniform flow for longer）. For similar sediment composition and concentration conditions， a thicker turbidity current was more stable. （3） The greatest accumulation of sediments occurred close to the source of the turbidity current and mainly at the central axis of the channel， decreasing monotonically with distance from the central axis. The deposition rate in a very thick， rapid turbidity current is smaller， but the overall quantity of deposited material is greater. Conclusions These results demonstrate that the method described is suitable for the study of field-scale turbidity currents and its future application is expected for naturally occurring turbidity currents.
2025,
43(3):
827-845.
doi: 10.14027/j.issn.1000-0550.2024.074
Abstract:
Significance Deep-water gravity flow deposits are， in effect， records of extreme climatic events and tectonic activities （e.g. paleoseismic events）. Accumulations of these sediments significantly affect the number and extent of worldwide reserves of oil and gas resources. The event-driven nature of the deep-water gravity flow process， together with the unique nature of each deposition site， presents a significant challenge to direct observation in the field. At present， simulation of the dynamics and distribution patterns of deep-water gravity flow deposits is the primary approach. Progress This study reviews the advances in both physical and numerical simulation of the processes and patterns of deep-water gravity flow deposits. It begins with a summary of the principles and progress in monitoring technology and laboratory construction of physical simulation models， then examines the factors influencing such experiments： material composition and content， flow state and energy differences in the dynamics of the fluid flow. Analysis of the formation， transportation and depositional processes of deep-water gravity flow provides insights into the complex dynamics involved， in terms both of its behavior alone and when influenced by external factors （e.g.， contour currents）. The study also reviews advances in the simulation of sedimentary processes influenced by the structure of the fluid， taking account of hydrodynamic parameters and complex topography. Numerical simulation is also crucial to understanding deep-water gravity flow. This study provides a comprehensive review of the historical development of numerical simulation techniques and presently available numerical simulation platforms. Conclusions and Prospects The limited ability of physical models to simulate the intricate dynamics and complex interactions between sediment particles and fluid flow in deep-water gravity flow deposits are further discussed. The spatiotemporal scale of a laboratory setting hinders the ability to reproduce the behavior of deep-water gravity flow that exists in real-world conditions， and it is unlikely that hydrodynamic parameters （variation in water velocity， sediment concentration etc.） are accurately predicted by physical models. Numerical simulation offers a promising alternative for studying deep-water gravity flow deposits due to the mathematical ability to work at a scale consistent with real-world conditions. However， although computational fluid dynamics simulations provide valuable information about various depositional mechanisms that occur in deep-water environments， they have limited accuracy when applied to certain phenomena. In particular， the accurate capture of the behavior of high particle concentrations in turbidity currents and prediction of the amount of erosion they cause remain significant challenges due to the uncertainties associated with factors such as grain size distribution and bed composition. Interdisciplinary collaboration is crucial in confronting these challenges and advancing the understanding of deep-water gravity flow sedimentation. Deeper insights into the underlying mechanisms at play during these processes will best be obtained if key results from physical model simulation are integrated with outcomes from numerical simulation. This approach presents novel guidance for exploring oil and gas reserves in deep-water environments and preventing geological disasters.
Significance Deep-water gravity flow deposits are， in effect， records of extreme climatic events and tectonic activities （e.g. paleoseismic events）. Accumulations of these sediments significantly affect the number and extent of worldwide reserves of oil and gas resources. The event-driven nature of the deep-water gravity flow process， together with the unique nature of each deposition site， presents a significant challenge to direct observation in the field. At present， simulation of the dynamics and distribution patterns of deep-water gravity flow deposits is the primary approach. Progress This study reviews the advances in both physical and numerical simulation of the processes and patterns of deep-water gravity flow deposits. It begins with a summary of the principles and progress in monitoring technology and laboratory construction of physical simulation models， then examines the factors influencing such experiments： material composition and content， flow state and energy differences in the dynamics of the fluid flow. Analysis of the formation， transportation and depositional processes of deep-water gravity flow provides insights into the complex dynamics involved， in terms both of its behavior alone and when influenced by external factors （e.g.， contour currents）. The study also reviews advances in the simulation of sedimentary processes influenced by the structure of the fluid， taking account of hydrodynamic parameters and complex topography. Numerical simulation is also crucial to understanding deep-water gravity flow. This study provides a comprehensive review of the historical development of numerical simulation techniques and presently available numerical simulation platforms. Conclusions and Prospects The limited ability of physical models to simulate the intricate dynamics and complex interactions between sediment particles and fluid flow in deep-water gravity flow deposits are further discussed. The spatiotemporal scale of a laboratory setting hinders the ability to reproduce the behavior of deep-water gravity flow that exists in real-world conditions， and it is unlikely that hydrodynamic parameters （variation in water velocity， sediment concentration etc.） are accurately predicted by physical models. Numerical simulation offers a promising alternative for studying deep-water gravity flow deposits due to the mathematical ability to work at a scale consistent with real-world conditions. However， although computational fluid dynamics simulations provide valuable information about various depositional mechanisms that occur in deep-water environments， they have limited accuracy when applied to certain phenomena. In particular， the accurate capture of the behavior of high particle concentrations in turbidity currents and prediction of the amount of erosion they cause remain significant challenges due to the uncertainties associated with factors such as grain size distribution and bed composition. Interdisciplinary collaboration is crucial in confronting these challenges and advancing the understanding of deep-water gravity flow sedimentation. Deeper insights into the underlying mechanisms at play during these processes will best be obtained if key results from physical model simulation are integrated with outcomes from numerical simulation. This approach presents novel guidance for exploring oil and gas reserves in deep-water environments and preventing geological disasters.
2025,
43(3):
846-859.
doi: 10.14027/j.issn.1000-0550.2024.081
Abstract:
Objective Delta is not only an important part of sedimentological research， but also an important oil-gas enrichment layer in oil and gas exploration. The formation and development of deltas are completed by two or three sedimentary processes in rivers， tides， and waves simultaneously. With further research， tidal-controlled deltas have gradually become important targets for oil and gas exploration and sedimentary studies. However， owing to the influence of hydrodynamics， the distribution patterns of sediment bodies in tidal-controlled deltas are unclear， the sedimentary facies combinations are diverse， and the sedimentary systems and characteristics are complex， leading to significant differences in understanding the sedimentary characteristics and deposition models of tidal-controlled deltas. For the study of tidal-controlled deltas， traditional methods often lack field exposures， face difficulty in sedimentary dissections， and have low resolution logging interpretation data， resulting in a certain degree of bias in the understanding of tidal-controlled deltas. The application of numerical simulation method for sediment deposition is expected to solve the above problems. Methods To address these issues， sediment numerical simulation methods （Delft3D） were used to establish an idealized tidal-controlled delta model. By varying the conditions of river flow and tidal amplitudes， the study explored the evolutionary patterns and main control factors of tidal-controlled deltas. Although the hydrodynamic equation model used by Delft3D is smaller in simulation speed and spatiotemporal scale， it can more accurately describe the deposition process and meet the needs of simulation. This simulation model refers to tide-controlled deltas such as Ganges River Delta， which is used as the reference condition of sedimentary environment to determine the main parameters of the model. After the preliminary test and simulation of the parameters， the parameters were reasonably estimated， and the basic model and the corresponding set of parameter system were established， completing the model establishment. Furthermore， to explore the influence of the two variables of river discharge and tide on the development of the tide-controlled delta， the two variables of river discharge and tide amplitude were appropriately enlarged and reduced， and the dam body morphology and delta evolution law were observed by comparison and analysis with the basic simulation. Results The research results show that rivers and tides play different roles in the formation of tidal-controlled deltas. Rivers transport sediment from the upstream， which accumulates at the estuary， while tides transport and deposit sediment from the upstream towards the deep sea， forming sand bars. As the tidal amplitude increases， the bar body develops into a "flattened shape" towards the ocean. The morphology of the bar body and the area of the delta are determined by the river flow and tidal amplitudes. When the river flow and tidal amplitudes increase， their sediment-carrying capacity strengthens， allowing sediment to deposit further from the estuary， increasing the sand bar area. With the increase in tidal amplitudes， the existing bar bodies are eroded and remodeled， transporting the sand bodies towards the ocean， and increasing the average length of the bar body. Conclusions The evolution of tidal-controlled deltas can be divided into three periods： sediment accumulation at the river mouth； transportation of sediment by river-tidal interactions， forming bar bodies， and rapid delta development； and modification of bar bodies by river-tidal interactions， continued growth of delta area， but with a decreasing growth rate.
Objective Delta is not only an important part of sedimentological research， but also an important oil-gas enrichment layer in oil and gas exploration. The formation and development of deltas are completed by two or three sedimentary processes in rivers， tides， and waves simultaneously. With further research， tidal-controlled deltas have gradually become important targets for oil and gas exploration and sedimentary studies. However， owing to the influence of hydrodynamics， the distribution patterns of sediment bodies in tidal-controlled deltas are unclear， the sedimentary facies combinations are diverse， and the sedimentary systems and characteristics are complex， leading to significant differences in understanding the sedimentary characteristics and deposition models of tidal-controlled deltas. For the study of tidal-controlled deltas， traditional methods often lack field exposures， face difficulty in sedimentary dissections， and have low resolution logging interpretation data， resulting in a certain degree of bias in the understanding of tidal-controlled deltas. The application of numerical simulation method for sediment deposition is expected to solve the above problems. Methods To address these issues， sediment numerical simulation methods （Delft3D） were used to establish an idealized tidal-controlled delta model. By varying the conditions of river flow and tidal amplitudes， the study explored the evolutionary patterns and main control factors of tidal-controlled deltas. Although the hydrodynamic equation model used by Delft3D is smaller in simulation speed and spatiotemporal scale， it can more accurately describe the deposition process and meet the needs of simulation. This simulation model refers to tide-controlled deltas such as Ganges River Delta， which is used as the reference condition of sedimentary environment to determine the main parameters of the model. After the preliminary test and simulation of the parameters， the parameters were reasonably estimated， and the basic model and the corresponding set of parameter system were established， completing the model establishment. Furthermore， to explore the influence of the two variables of river discharge and tide on the development of the tide-controlled delta， the two variables of river discharge and tide amplitude were appropriately enlarged and reduced， and the dam body morphology and delta evolution law were observed by comparison and analysis with the basic simulation. Results The research results show that rivers and tides play different roles in the formation of tidal-controlled deltas. Rivers transport sediment from the upstream， which accumulates at the estuary， while tides transport and deposit sediment from the upstream towards the deep sea， forming sand bars. As the tidal amplitude increases， the bar body develops into a "flattened shape" towards the ocean. The morphology of the bar body and the area of the delta are determined by the river flow and tidal amplitudes. When the river flow and tidal amplitudes increase， their sediment-carrying capacity strengthens， allowing sediment to deposit further from the estuary， increasing the sand bar area. With the increase in tidal amplitudes， the existing bar bodies are eroded and remodeled， transporting the sand bodies towards the ocean， and increasing the average length of the bar body. Conclusions The evolution of tidal-controlled deltas can be divided into three periods： sediment accumulation at the river mouth； transportation of sediment by river-tidal interactions， forming bar bodies， and rapid delta development； and modification of bar bodies by river-tidal interactions， continued growth of delta area， but with a decreasing growth rate.
2025,
43(3):
860-879.
doi: 10.14027/j.issn.1000-0550.2024.086
Abstract:
Objective The integration of physical and numerical deposition simulations is an inevitable trend in the development of deposition simulation technology. In recent years， shoal water deltas have gradually become the focus of research by various experts and scholars. The main factors affecting the growth and development of shoal water deltas include ancient structures， topography， climate， and water flow. Previous scholars have conducted relevant research， but there is a lack of a more comprehensive quantitative analysis of the specific impact of the main controlling factors. In this study， the author takes the shoal water delta as an example for conducting a comparative study of physical and numerical deposition simulations， exploring the problems in the integration of the two. Methods Three influencing factors， namely sediment ratio， shoreline migration speed （lake level descent speed）， and inlet flow rate， were selected. Physical and numerical deposition simulation methods were used to analyze the deposition evolution of the shoal water delta and the influence of control factors. Quantitative analysis was conducted using indicators such as sediment aspect ratio， area， and front edge roughness. [Results and Conclusions ] （1） The physical and numerical simulation experiments of shoal water delta deposition show that sediment ratio， shoreline migration speed （lake level descent speed）， and inlet flow velocity have a significant impact on the aspect ratio， area， and front roughness changes， which are key factors affecting the development of shoal water deltas. （2） From a macro perspective， the results of physical and numerical simulations are consistent. Physical deposition simulations show that the inlet velocity of shoal water deltas is negatively correlated with aspect ratio， whereas numerical simulations provide a more detailed description of this. When the flow rate at the estuary is greater than 1000 m³/s but less than 1200 m³/s， the shoal water delta is in a period of morphological transformation， and the flow rate at the estuary is positively correlated with the aspect ratio of the shoal water delta. At speeds below 1000 m³/s and above 1200 m³/s， the flow velocity at the estuary is negatively correlated with the aspect ratio of shoal water deltas. Therefore， when using deposition simulations to predict the morphology and scale of shoal water deltas， low-cost numerical simulations can replace physical simulations for shoal water delta formation. （3） Physical and numerical simulations are different. Physical simulations indicate that there are two developmental mechanisms in shoal water deltas： the alternating growth of flower bodies and fan edges caused by the diversion of distributary channels and the alternating growth of flower bodies caused by the continuous diversion of river mouths. In numerical simulations， the growth of shoal water deltas is accompanied by breaches， abandonment of old distributary channels， and rapid formation of new distributary channels and estuarine sandbars （lobes）. These sandbars are mainly finger-shaped and rarely exhibit fan-shaped lobes. This study explores the combination of physical and numerical deposition simulations， which has important theoretical significance and practical value for promoting oil and gas reservoir exploration research. This study explores the integration of physical and numerical deposition simulations and has important theoretical significance and practical value in promoting exploration research of oil and gas reservoirs.
Objective The integration of physical and numerical deposition simulations is an inevitable trend in the development of deposition simulation technology. In recent years， shoal water deltas have gradually become the focus of research by various experts and scholars. The main factors affecting the growth and development of shoal water deltas include ancient structures， topography， climate， and water flow. Previous scholars have conducted relevant research， but there is a lack of a more comprehensive quantitative analysis of the specific impact of the main controlling factors. In this study， the author takes the shoal water delta as an example for conducting a comparative study of physical and numerical deposition simulations， exploring the problems in the integration of the two. Methods Three influencing factors， namely sediment ratio， shoreline migration speed （lake level descent speed）， and inlet flow rate， were selected. Physical and numerical deposition simulation methods were used to analyze the deposition evolution of the shoal water delta and the influence of control factors. Quantitative analysis was conducted using indicators such as sediment aspect ratio， area， and front edge roughness. [Results and Conclusions ] （1） The physical and numerical simulation experiments of shoal water delta deposition show that sediment ratio， shoreline migration speed （lake level descent speed）， and inlet flow velocity have a significant impact on the aspect ratio， area， and front roughness changes， which are key factors affecting the development of shoal water deltas. （2） From a macro perspective， the results of physical and numerical simulations are consistent. Physical deposition simulations show that the inlet velocity of shoal water deltas is negatively correlated with aspect ratio， whereas numerical simulations provide a more detailed description of this. When the flow rate at the estuary is greater than 1000 m³/s but less than 1200 m³/s， the shoal water delta is in a period of morphological transformation， and the flow rate at the estuary is positively correlated with the aspect ratio of the shoal water delta. At speeds below 1000 m³/s and above 1200 m³/s， the flow velocity at the estuary is negatively correlated with the aspect ratio of shoal water deltas. Therefore， when using deposition simulations to predict the morphology and scale of shoal water deltas， low-cost numerical simulations can replace physical simulations for shoal water delta formation. （3） Physical and numerical simulations are different. Physical simulations indicate that there are two developmental mechanisms in shoal water deltas： the alternating growth of flower bodies and fan edges caused by the diversion of distributary channels and the alternating growth of flower bodies caused by the continuous diversion of river mouths. In numerical simulations， the growth of shoal water deltas is accompanied by breaches， abandonment of old distributary channels， and rapid formation of new distributary channels and estuarine sandbars （lobes）. These sandbars are mainly finger-shaped and rarely exhibit fan-shaped lobes. This study explores the combination of physical and numerical deposition simulations， which has important theoretical significance and practical value for promoting oil and gas reservoir exploration research. This study explores the integration of physical and numerical deposition simulations and has important theoretical significance and practical value in promoting exploration research of oil and gas reservoirs.
2025,
43(3):
880-893.
doi: 10.14027/j.issn.1000-0550.2024.078
Abstract:
Objective River sediments are widely developed in natural strata， and meandering river sediments are an important part. The frequent channel migration that occurs during the development of meandering rivers results in a large number of lateral sedimentary deposits， complicating the superposition relationship of sand bodies at any particular deposit site. The analysis of factors influencing meandering river morphology is a highly significant aspect of the study of paleoclimate evolution and continental weathering intensity， and therefore important in the exploration and development of oil and gas reservoirs. In previous research， the initial conditions necessary for generating a meandering river have been proposed following observation of modern river sediments and assessment of the effects of clay mineral content， vegetation cover and initial saturation of the river bed. However， because in nature the development of river sediments takes place over very long periods of time， the dynamic sedimentation process cannot be definitely determined by field investigation or by the examination of outcrop sections. The history of a meandering river is susceptible to the influence of a range of environmental factors， and supporting quantitative data is usually lacking. Methods In this experimental study， the effects of single factor conditions on channel migration and dam body formation were investigated by flume sedimentation simulation. Three sets of experiments incorporating different particle size， water flow and clay mineral content were conducted， using high-precision 3D laser scanning to convert the data into a series of elevation models， enabling quantitative examination of the profile， structure and bed sediment changes. Results （1） The particle size of the source sand directly affected the curvature of the river meanders. For constant clay content and constant discharge， smaller particle size resulted in the meanders of the river having broader curvature. Also， obvious differences in the structure of the bank collapse were observed for different particle sizes. （2） When the sediment input rate and transport rate were in dynamic equilibrium， the discharge rate affected the sediment transport balance and the force of flow impact on the riverbank caused the riverbank to continuously erode and expand outwards， and the channel developed a meandering river form. （3） The addition of clay minerals to the river bank materials improved the resistance of the river bank by lowering its permeability. When the source sand grain size and flow rate remained unchanged， greater clay mineral content lowered the width-to-depth ratio of the river channel. Conclusions This study clarifies the influence of sand grain size， water discharge and clay mineral content on the morphological properties of a meandering river， and provides quantitative basic data for the study of meander evolution.
Objective River sediments are widely developed in natural strata， and meandering river sediments are an important part. The frequent channel migration that occurs during the development of meandering rivers results in a large number of lateral sedimentary deposits， complicating the superposition relationship of sand bodies at any particular deposit site. The analysis of factors influencing meandering river morphology is a highly significant aspect of the study of paleoclimate evolution and continental weathering intensity， and therefore important in the exploration and development of oil and gas reservoirs. In previous research， the initial conditions necessary for generating a meandering river have been proposed following observation of modern river sediments and assessment of the effects of clay mineral content， vegetation cover and initial saturation of the river bed. However， because in nature the development of river sediments takes place over very long periods of time， the dynamic sedimentation process cannot be definitely determined by field investigation or by the examination of outcrop sections. The history of a meandering river is susceptible to the influence of a range of environmental factors， and supporting quantitative data is usually lacking. Methods In this experimental study， the effects of single factor conditions on channel migration and dam body formation were investigated by flume sedimentation simulation. Three sets of experiments incorporating different particle size， water flow and clay mineral content were conducted， using high-precision 3D laser scanning to convert the data into a series of elevation models， enabling quantitative examination of the profile， structure and bed sediment changes. Results （1） The particle size of the source sand directly affected the curvature of the river meanders. For constant clay content and constant discharge， smaller particle size resulted in the meanders of the river having broader curvature. Also， obvious differences in the structure of the bank collapse were observed for different particle sizes. （2） When the sediment input rate and transport rate were in dynamic equilibrium， the discharge rate affected the sediment transport balance and the force of flow impact on the riverbank caused the riverbank to continuously erode and expand outwards， and the channel developed a meandering river form. （3） The addition of clay minerals to the river bank materials improved the resistance of the river bank by lowering its permeability. When the source sand grain size and flow rate remained unchanged， greater clay mineral content lowered the width-to-depth ratio of the river channel. Conclusions This study clarifies the influence of sand grain size， water discharge and clay mineral content on the morphological properties of a meandering river， and provides quantitative basic data for the study of meander evolution.
2025,
43(3):
894-911.
doi: 10.14027/j.issn.1000-0550.2024.087
Abstract:
Objective Recent research suggests that the basin water depth governs the morphodynamics of deltas that formed at the basin margin， because water depth affects the amount of subaerial and subaqueous sediment that are deposited. Shallow-water deltas contain more sediment than deep-water deltas in the subaerial region. As a result， aggradation of distributary channels takes place more rapidly in shallow-water deltas， making the channel more active in terms of migration and avulsion. The grade index （Gindex） model is proposed to quantitively illustrate this process. Methods This study elaborates the origin， theoretical modeling， experimental validation and application of the grade index model， and discusses its limitations. In this context， grade refers to the state of a river stream in which sedimentary material is all transported by the river flow without net deposition or erosion taking place. The grade index is defined as the ratio of the volume of sediment allocated subaerially to the total volume of sediment input in per unit time. By this definition， Gindex is a dimensionless number between 0 （no deposition subaerially） and 1 （complete deposition subaerially）. Results Theoretical analyses confirm a negative relationship between Gindex and water depth. It is also related to the geometry of the delta （e.g.， delta plain radius， topset slope and foreset slope）. In basins with deeper water， Gindex → 0， which means that decreasing volumes of sediment are deposited subaerially per unit time， forming a more stable channel that approaches the equilibrium condition or ‘state of grade’ of the alluvial river， when neither erosion nor deposition takes place. Conversely， Gindex → 1 for deltas developed in shallower water basins， and the delta plain becomes increasingly unstable. The value of Gindex reflects basic morphodynamic parameters of the delta （e.g.， rates of progradation， aggradation and channel migration， and the timescale of channel avulsion）. Each of these parameters can be calculated as the product or quotient between Gindex and their counterparts obtained with negligibly small basin water depth， while the former is determined by the delta’s geometrical parameters and basin water depth and the latter is determined by the delta’s geometrical parameters and total sediment supply rate. This means that for a particular deltaic system with specific geometrical parameters， sediment supply rate and basin water depth， it has theoretical values for the grade index and geomorphodynamic parameters， both of which can be calculated. This speculation was verified by tank experiment. The Gindex model is derived from the global mass balance of the deltaic system. Local and/or tentative depositional， erosional and dispersal processes （e.g.， backwater effect and coastal processes including waves， tides and longshore currents， as well as effects unrelated to the depositional system （vegetation and/or anthropogenic processes）） were not considered. Conclusions The grade index model isolates the effect of basin water depth from other variables in describing delta morphodynamics， and reveals the principal differences between the formation of deep-water and shallow-water delta landforms. It also goes some way toward explaining the influence of factors other than water depth. The model has the potential for general application to modern alluvial-deltaic systems. Its application to ancient systems has yet to be explored.
Objective Recent research suggests that the basin water depth governs the morphodynamics of deltas that formed at the basin margin， because water depth affects the amount of subaerial and subaqueous sediment that are deposited. Shallow-water deltas contain more sediment than deep-water deltas in the subaerial region. As a result， aggradation of distributary channels takes place more rapidly in shallow-water deltas， making the channel more active in terms of migration and avulsion. The grade index （Gindex） model is proposed to quantitively illustrate this process. Methods This study elaborates the origin， theoretical modeling， experimental validation and application of the grade index model， and discusses its limitations. In this context， grade refers to the state of a river stream in which sedimentary material is all transported by the river flow without net deposition or erosion taking place. The grade index is defined as the ratio of the volume of sediment allocated subaerially to the total volume of sediment input in per unit time. By this definition， Gindex is a dimensionless number between 0 （no deposition subaerially） and 1 （complete deposition subaerially）. Results Theoretical analyses confirm a negative relationship between Gindex and water depth. It is also related to the geometry of the delta （e.g.， delta plain radius， topset slope and foreset slope）. In basins with deeper water， Gindex → 0， which means that decreasing volumes of sediment are deposited subaerially per unit time， forming a more stable channel that approaches the equilibrium condition or ‘state of grade’ of the alluvial river， when neither erosion nor deposition takes place. Conversely， Gindex → 1 for deltas developed in shallower water basins， and the delta plain becomes increasingly unstable. The value of Gindex reflects basic morphodynamic parameters of the delta （e.g.， rates of progradation， aggradation and channel migration， and the timescale of channel avulsion）. Each of these parameters can be calculated as the product or quotient between Gindex and their counterparts obtained with negligibly small basin water depth， while the former is determined by the delta’s geometrical parameters and basin water depth and the latter is determined by the delta’s geometrical parameters and total sediment supply rate. This means that for a particular deltaic system with specific geometrical parameters， sediment supply rate and basin water depth， it has theoretical values for the grade index and geomorphodynamic parameters， both of which can be calculated. This speculation was verified by tank experiment. The Gindex model is derived from the global mass balance of the deltaic system. Local and/or tentative depositional， erosional and dispersal processes （e.g.， backwater effect and coastal processes including waves， tides and longshore currents， as well as effects unrelated to the depositional system （vegetation and/or anthropogenic processes）） were not considered. Conclusions The grade index model isolates the effect of basin water depth from other variables in describing delta morphodynamics， and reveals the principal differences between the formation of deep-water and shallow-water delta landforms. It also goes some way toward explaining the influence of factors other than water depth. The model has the potential for general application to modern alluvial-deltaic systems. Its application to ancient systems has yet to be explored.
2025,
43(3):
912-938.
doi: 10.14027/j.issn.1000-0550.2024.093
Abstract:
Objective Continental margins often develop fold and thrust belts， which have a major control over deep-water deposition processes， such as turbidity currents. These structures play a crucial role in shaping the seafloor and influencing sediment transport and deposition patterns. However， due to the difficulties in obtaining relevant geological data and conducting field measurements of turbidity currents， quantitative research on the hydraulic and depositional responses of turbidity currents to multi-segment folds is largely understudied. Methods In this study， computational fluid dynamics （CFD） and the finite volume method （FVM） were used to conduct a two-dimensional numerical simulation study on the hydraulic and depositional responses of turbidity currents to multi-segment parallel folds. Using the Flow-3D software and the Reynolds-Averaged Navier-Stokes （RANS） equations， six simulation experiments were designed by systematically varying fold morphology parameters （width， height， and spacing） and initial turbidity flow velocity. These parameters are based on in situ observations and physical flume experiments to ensure realistic input conditions. [Results and Conclusions] （1） under the influence of multi-segment parallel folds， reverse flows develop at the bottom of the turbidity current， including upstream-propagating reverse underflows generated by the blockage of the folds and downstream-propagating reverse under waves arising from perturbations after the turbidity current flows over the folds. （2） The propagation distance， velocity， and scale of the underflow reflect the extent to which the turbidity current is disturbed by the folds. By comparing the reverse flows， the turbidity current is shown to experience more severe disturbances at the back row folds than at the front row folds. This suggests that the spatial arrangement of the folds plays a critical role in modulating the flow dynamics and sedimentation patterns of turbidity currents. （3） The depocenters of turbidity currents on folded morphologies are primarily distributed on the upstream-facing slopes and in front of the folds， forming overlapping strata and gradually fining upstream. The deposition of turbidity currents is controlled both by the morphology of the folds and the hydraulic conditions of the turbidity current. Higher folds and slower flow velocities of the turbidity current promotes more deposition， indicating a strong coupling between the physical characteristics of the folds and the flow properties of the turbidity currents. Additionally， the front row folds accumulate more sediment than the back row folds， highlighting the influence of fold positioning on sediment dispersal. （4） The disturbance of the turbidity current by the front row folds and the separation distance between the two folds affect the hydraulic characteristics and depositional processes of the turbidity current flowing through the back row folds. When the turbidity current is disturbed by the front row folds and the separation distance between two folds is sufficiently small to maintain its perturbed state， the current is more likely to flow over the back row folds， further reducing the total amount of sediment deposited on the upstream-facing slope of the back row folds. The main findings of this study are consistent with those of previous studies focusing on natural examples. Therefore， this study helps to reveal the hydraulic and depositional patterns of turbidity currents occurring in multi-segment folds and provides a reference for oil and gas exploration in related regions.
Objective Continental margins often develop fold and thrust belts， which have a major control over deep-water deposition processes， such as turbidity currents. These structures play a crucial role in shaping the seafloor and influencing sediment transport and deposition patterns. However， due to the difficulties in obtaining relevant geological data and conducting field measurements of turbidity currents， quantitative research on the hydraulic and depositional responses of turbidity currents to multi-segment folds is largely understudied. Methods In this study， computational fluid dynamics （CFD） and the finite volume method （FVM） were used to conduct a two-dimensional numerical simulation study on the hydraulic and depositional responses of turbidity currents to multi-segment parallel folds. Using the Flow-3D software and the Reynolds-Averaged Navier-Stokes （RANS） equations， six simulation experiments were designed by systematically varying fold morphology parameters （width， height， and spacing） and initial turbidity flow velocity. These parameters are based on in situ observations and physical flume experiments to ensure realistic input conditions. [Results and Conclusions] （1） under the influence of multi-segment parallel folds， reverse flows develop at the bottom of the turbidity current， including upstream-propagating reverse underflows generated by the blockage of the folds and downstream-propagating reverse under waves arising from perturbations after the turbidity current flows over the folds. （2） The propagation distance， velocity， and scale of the underflow reflect the extent to which the turbidity current is disturbed by the folds. By comparing the reverse flows， the turbidity current is shown to experience more severe disturbances at the back row folds than at the front row folds. This suggests that the spatial arrangement of the folds plays a critical role in modulating the flow dynamics and sedimentation patterns of turbidity currents. （3） The depocenters of turbidity currents on folded morphologies are primarily distributed on the upstream-facing slopes and in front of the folds， forming overlapping strata and gradually fining upstream. The deposition of turbidity currents is controlled both by the morphology of the folds and the hydraulic conditions of the turbidity current. Higher folds and slower flow velocities of the turbidity current promotes more deposition， indicating a strong coupling between the physical characteristics of the folds and the flow properties of the turbidity currents. Additionally， the front row folds accumulate more sediment than the back row folds， highlighting the influence of fold positioning on sediment dispersal. （4） The disturbance of the turbidity current by the front row folds and the separation distance between the two folds affect the hydraulic characteristics and depositional processes of the turbidity current flowing through the back row folds. When the turbidity current is disturbed by the front row folds and the separation distance between two folds is sufficiently small to maintain its perturbed state， the current is more likely to flow over the back row folds， further reducing the total amount of sediment deposited on the upstream-facing slope of the back row folds. The main findings of this study are consistent with those of previous studies focusing on natural examples. Therefore， this study helps to reveal the hydraulic and depositional patterns of turbidity currents occurring in multi-segment folds and provides a reference for oil and gas exploration in related regions.
2025,
43(3):
939-960.
doi: 10.14027/j.issn.1000-0550.2024.116
Abstract:
Objective The shelf-edge trajectory is the pathway taken by the shelf-edge during the development of a series of accreting clinoforms and it records the migration of the shelf-edge system over time. The autoretreat theory， which considers the fluvial deltas as the main subject of discussion， is also applicable to the shelf-edge trajectory. First， the geometric characteristics of the sediment-wedge in shelf-edge system are similar to fluvial-delta system. Second， the shelf-edge trajectory is commonly recognized as formed through repeated cross-shelf transits of shorelines. When the low-frequency rise rate of base level is kept constant， the growth conditions of the shelf edge are similar to the conditions for shoreline autoretreat. Therefore， if the low-frequency rise rate is kept constant during base level rise of a zigzag pattern， the shelf-edge trajectory should experience autoretreat. Methods To verify the existence of autoretreat of the shelf-edge trajectory， sedimentary numerical simulation software DionisosFlow， which is based on the sediment diffusion equation， was applied to conduct a two-dimensional （2D） numerical simulation of the growth of shelf-edge during base level rise of a zigzag pattern and model shelf edge migration. In addition， 2D numerical simulations of the shoreline trajectory under the steady rise of base level was set for comparison. The simulation includes two groups： （1） To simulate the migration of the shelf-edge， the base-level rise occurred in a zigzag pattern； the rise rate （Rblr） and fall rate （Rblf） are different during the cycle； however， the rise period （Tblr） and fall period （Tblf） are the same. （2） To simulate the migration of the shoreline， the base level rises at a steady rate. Six simulations were run in this study. [Results and Conclusions] The simulation results suggests that for a constant low frequency rise rate and constant sediment input， during the latest stage of each base-level fall， the delta progrades to the farthest end， and the shelf-slope break （shelf edge） is formed； then， the base-level rise preserves the newly formed shelf edge. For the zigzag rise of the base level， the shelf-edge trajectory shows early seaward advance and late landward retreat， which is the autoretreat phenomenon of the shelf-edge trajectory. The autoretreat of shelf-edge during base level rise of a zigzag pattern has the following characteristics： （1） It follows the same theoretical trajectory as the autoretreat of the shoreline. （2） Compared with coastal system with the same external conditions but with steady base-level rise， at the end of the base0level fall， the shelf-edge system forms a steeper topset due to degradation， resulting in the autoretreat phenomenon occurring later. （3） The autoretreat of the shelf-edge is primarily controlled by the initial geometric characteristics of the basin and the low-frequency rise of base level （or subsidence rate）. When other external factors remain constant， a smaller initial slope of the alluvial plain or higher low-frequency rise rate of base level （or subsidence rate） lead to the autoretreat and autobreak phenomenon occurring more quickly. For the opposite conditions， these events occur later. The Hanjiang Formation of the Middle Miocene and the Wanshan Formation of the Pliocene in the Pearl River Mouth Basin in the northern South China Sea are possible examples of the shelf-edge autoretreat. Verifying the autoretreat of shelf-edge trajectory and understanding its characteristics helps to explain the migration of continental shelf edge in passive continental margin basins with continuous subsidence.
Objective The shelf-edge trajectory is the pathway taken by the shelf-edge during the development of a series of accreting clinoforms and it records the migration of the shelf-edge system over time. The autoretreat theory， which considers the fluvial deltas as the main subject of discussion， is also applicable to the shelf-edge trajectory. First， the geometric characteristics of the sediment-wedge in shelf-edge system are similar to fluvial-delta system. Second， the shelf-edge trajectory is commonly recognized as formed through repeated cross-shelf transits of shorelines. When the low-frequency rise rate of base level is kept constant， the growth conditions of the shelf edge are similar to the conditions for shoreline autoretreat. Therefore， if the low-frequency rise rate is kept constant during base level rise of a zigzag pattern， the shelf-edge trajectory should experience autoretreat. Methods To verify the existence of autoretreat of the shelf-edge trajectory， sedimentary numerical simulation software DionisosFlow， which is based on the sediment diffusion equation， was applied to conduct a two-dimensional （2D） numerical simulation of the growth of shelf-edge during base level rise of a zigzag pattern and model shelf edge migration. In addition， 2D numerical simulations of the shoreline trajectory under the steady rise of base level was set for comparison. The simulation includes two groups： （1） To simulate the migration of the shelf-edge， the base-level rise occurred in a zigzag pattern； the rise rate （Rblr） and fall rate （Rblf） are different during the cycle； however， the rise period （Tblr） and fall period （Tblf） are the same. （2） To simulate the migration of the shoreline， the base level rises at a steady rate. Six simulations were run in this study. [Results and Conclusions] The simulation results suggests that for a constant low frequency rise rate and constant sediment input， during the latest stage of each base-level fall， the delta progrades to the farthest end， and the shelf-slope break （shelf edge） is formed； then， the base-level rise preserves the newly formed shelf edge. For the zigzag rise of the base level， the shelf-edge trajectory shows early seaward advance and late landward retreat， which is the autoretreat phenomenon of the shelf-edge trajectory. The autoretreat of shelf-edge during base level rise of a zigzag pattern has the following characteristics： （1） It follows the same theoretical trajectory as the autoretreat of the shoreline. （2） Compared with coastal system with the same external conditions but with steady base-level rise， at the end of the base0level fall， the shelf-edge system forms a steeper topset due to degradation， resulting in the autoretreat phenomenon occurring later. （3） The autoretreat of the shelf-edge is primarily controlled by the initial geometric characteristics of the basin and the low-frequency rise of base level （or subsidence rate）. When other external factors remain constant， a smaller initial slope of the alluvial plain or higher low-frequency rise rate of base level （or subsidence rate） lead to the autoretreat and autobreak phenomenon occurring more quickly. For the opposite conditions， these events occur later. The Hanjiang Formation of the Middle Miocene and the Wanshan Formation of the Pliocene in the Pearl River Mouth Basin in the northern South China Sea are possible examples of the shelf-edge autoretreat. Verifying the autoretreat of shelf-edge trajectory and understanding its characteristics helps to explain the migration of continental shelf edge in passive continental margin basins with continuous subsidence.
2025,
43(3):
961-975.
doi: 10.14027/j.issn.1000-0550.2023.053
Abstract:
Objective The Otindag sandy land， located at the boundary of the East Asian monsoon region in east-central Inner Mongolia， is an ideal area for studying climate change since the Last Glacial Maximum owing to its unique geographical environment and extensive development of aeolian sand stratigraphy. Previous studies on the chronology of the Otindag sandy land have focused on the Holocene， and relatively few studies have been conducted since the Last Glacial Maximum owing to the lack of a systematic stratigraphic chronology framework， and the scientific issue of whether the Holocene Climate Optimum in the sandy land began in the Early or Middle Holocene. This remains controversial， based on different dating methods and research objects. Methods In this study， two aeolian sand sedimentary sequences on the southern edge of the Otindag sandy land， Lanqi South （LQS） and Baleng Mountain （BLS）， were studied， and the stratigraphic chronological framework was determined by the single-aliquot regenerative-dose （SAR） method with the optical stimulated luminescence （OSL） dating method. Combined with the sedimentary characteristics， grain size and quartz grain surface morphological features were integrated for analysis. Results The results show that： from 18 to 11.5 ka， solar radiation and East Asian summer monsoon gradually increased， aeolian sand and sandy loess interstratification were developed， with a cold and dry climate， strong sandstorm activity， and millennial-scale climate fluctuations. The aeolian sand and sand loess， which developed at 15.9 and 12.2 ka， correspond well to two significant cooling and dehumidification events during the temperature warming of the last deglaciation period. Between 11.5 ka and 8.2 ka， the temperature fluctuated and increased， with a relatively dry and cold climate and primarily developed aeolian sands with sandy paleosols. The sandy paleosoil developed at 8.2 ka and 8.94 ka indicated the early Holocene， and the sandy climate gradually changed from cold and dry to warm and wet. The lacustrine and aeolian sand developed at approximately 10 ka are contemporaneous heterogeneous sediments， both indicating a cold and dry climate， and their formation was influenced by three depositional dynamics： wind， river and lake. From 8.2 to 2.7 ka， solar radiation reached its maximum， the East Asian summer monsoon strengthened， and the climate was the warmest and wetter. The sandy palaeosols were developed in both profiles. Since 2.7 ka， the solar radiation has weakened， the East Asian winter monsoon has strengthened， the climate has become mild and dry， and weak sandy paleosols have developed. The sandy paleosols developed at approximately 1 ka are consistent with the medieval warm period. The formation of lacustrine sediments in LQS profile was mainly influenced by local geomorphology， which is similar to the coexistence of dunes and lakes in modern sandy land. Conclusions In general， the Holocene Climate Optimum in Otindag sandy land was in the middle of Holocene. The rapid climate change since the Last Glacial Maximum in the Otindag sandy land has global and universal characteristics， which are a regional response to global climate change and closely related to the East Asian monsoon， driven by solar radiation and global ice volume.
Objective The Otindag sandy land， located at the boundary of the East Asian monsoon region in east-central Inner Mongolia， is an ideal area for studying climate change since the Last Glacial Maximum owing to its unique geographical environment and extensive development of aeolian sand stratigraphy. Previous studies on the chronology of the Otindag sandy land have focused on the Holocene， and relatively few studies have been conducted since the Last Glacial Maximum owing to the lack of a systematic stratigraphic chronology framework， and the scientific issue of whether the Holocene Climate Optimum in the sandy land began in the Early or Middle Holocene. This remains controversial， based on different dating methods and research objects. Methods In this study， two aeolian sand sedimentary sequences on the southern edge of the Otindag sandy land， Lanqi South （LQS） and Baleng Mountain （BLS）， were studied， and the stratigraphic chronological framework was determined by the single-aliquot regenerative-dose （SAR） method with the optical stimulated luminescence （OSL） dating method. Combined with the sedimentary characteristics， grain size and quartz grain surface morphological features were integrated for analysis. Results The results show that： from 18 to 11.5 ka， solar radiation and East Asian summer monsoon gradually increased， aeolian sand and sandy loess interstratification were developed， with a cold and dry climate， strong sandstorm activity， and millennial-scale climate fluctuations. The aeolian sand and sand loess， which developed at 15.9 and 12.2 ka， correspond well to two significant cooling and dehumidification events during the temperature warming of the last deglaciation period. Between 11.5 ka and 8.2 ka， the temperature fluctuated and increased， with a relatively dry and cold climate and primarily developed aeolian sands with sandy paleosols. The sandy paleosoil developed at 8.2 ka and 8.94 ka indicated the early Holocene， and the sandy climate gradually changed from cold and dry to warm and wet. The lacustrine and aeolian sand developed at approximately 10 ka are contemporaneous heterogeneous sediments， both indicating a cold and dry climate， and their formation was influenced by three depositional dynamics： wind， river and lake. From 8.2 to 2.7 ka， solar radiation reached its maximum， the East Asian summer monsoon strengthened， and the climate was the warmest and wetter. The sandy palaeosols were developed in both profiles. Since 2.7 ka， the solar radiation has weakened， the East Asian winter monsoon has strengthened， the climate has become mild and dry， and weak sandy paleosols have developed. The sandy paleosols developed at approximately 1 ka are consistent with the medieval warm period. The formation of lacustrine sediments in LQS profile was mainly influenced by local geomorphology， which is similar to the coexistence of dunes and lakes in modern sandy land. Conclusions In general， the Holocene Climate Optimum in Otindag sandy land was in the middle of Holocene. The rapid climate change since the Last Glacial Maximum in the Otindag sandy land has global and universal characteristics， which are a regional response to global climate change and closely related to the East Asian monsoon， driven by solar radiation and global ice volume.
2025,
43(3):
976-995.
doi: 10.14027/j.issn.1000-0550.2023.084
Abstract:
Objective The climate records of the Late Paleozoic ice chamber， which developed mainly in the Gondwana continent， are quite similar to the evolution of the current climate. It has become a focus for comparative studies of Quaternary ice ages and ice chamber climate. The Late Paleozoic ice age was a glacial event with the most widely ranging influence and the richest geological record since the Phanerozoic. Its evidence of the complete greenhouse-icehouse-greenhouse climate change process is of great significance for an understanding of the evolution of the present climate on Earth. The Lhasa Block was located at the northeastern margin of the Gondwana continent during the Late Paleozoic. Although many studies have been conducted on the spatial and temporal evolution and controlling factors of the Late Paleozoic ice age， the sedimentary evolution history of the Lhasa Block during that time remained unclear. Methods In view of this， in this study the Late Paleozoic strata in the Xainza area of the Lhasa Block was selected for a 1：200 scale profile survey， which included rock color， lithological characteristics， rock thickness， sedimentary structures， fossils and contact relationships. Lithofacies and their associations were classified for glacial development， and sedimentary architecture analysis was applied to find the lateral and vertical changes of sedimentary facies that would identify the sedimentary environment and restore the glacial sedimentary system. Results The study showed that the Late Paleozoic ice age records in the Lhasa Block are mainly evident at the Lagar Formation， with the age constrained between the Late Carboniferous and Early Permian. The glacial deposits of the Lagar Formation indicate twenty lithofacies and sixteen typical lithofacies associations indicating six sedimentary environments： shallow sea shelf， baseline fan， subglacial， ice river， ice lake and outwash fan. Conclusions The Late Paleozoic glaciers in the central part of the Lhasa Block were located in a nearshore glaciomarine environment， and the glacial deposition system was mainly divided into marine and terrestrial phases. In addition， a number of small glacial-interglacial cyclones were delineated in both the Early and late evolutionary stages of the Lagar Formation， based on vertical variation of glacial and non-glacial environments. The sedimentary system analysis for the Lagar Formation sedimentary sequences indicates that the Late Paleozoic ice age in the Xainza area of the Lhasa Block experienced a transition from early marine to late terrestrial glaciations， indicating a global trend of gradual climate warming from the Late Carboniferous to the Early Permian consistent with global Late Paleozoic ice age evolutionary features. The Late Paleozoic ice age was the closest global ice age to the Quaternary ice age and is an important window for understanding future climate shifts such as glacial melting and global warming. Conducting research into Late Paleozoic sedimentary records in the Lhasa Block is greatly significant for exploration of the spatial and temporal evolution， climate change and driving mechanisms of the global Late Paleozoic ice age.
Objective The climate records of the Late Paleozoic ice chamber， which developed mainly in the Gondwana continent， are quite similar to the evolution of the current climate. It has become a focus for comparative studies of Quaternary ice ages and ice chamber climate. The Late Paleozoic ice age was a glacial event with the most widely ranging influence and the richest geological record since the Phanerozoic. Its evidence of the complete greenhouse-icehouse-greenhouse climate change process is of great significance for an understanding of the evolution of the present climate on Earth. The Lhasa Block was located at the northeastern margin of the Gondwana continent during the Late Paleozoic. Although many studies have been conducted on the spatial and temporal evolution and controlling factors of the Late Paleozoic ice age， the sedimentary evolution history of the Lhasa Block during that time remained unclear. Methods In view of this， in this study the Late Paleozoic strata in the Xainza area of the Lhasa Block was selected for a 1：200 scale profile survey， which included rock color， lithological characteristics， rock thickness， sedimentary structures， fossils and contact relationships. Lithofacies and their associations were classified for glacial development， and sedimentary architecture analysis was applied to find the lateral and vertical changes of sedimentary facies that would identify the sedimentary environment and restore the glacial sedimentary system. Results The study showed that the Late Paleozoic ice age records in the Lhasa Block are mainly evident at the Lagar Formation， with the age constrained between the Late Carboniferous and Early Permian. The glacial deposits of the Lagar Formation indicate twenty lithofacies and sixteen typical lithofacies associations indicating six sedimentary environments： shallow sea shelf， baseline fan， subglacial， ice river， ice lake and outwash fan. Conclusions The Late Paleozoic glaciers in the central part of the Lhasa Block were located in a nearshore glaciomarine environment， and the glacial deposition system was mainly divided into marine and terrestrial phases. In addition， a number of small glacial-interglacial cyclones were delineated in both the Early and late evolutionary stages of the Lagar Formation， based on vertical variation of glacial and non-glacial environments. The sedimentary system analysis for the Lagar Formation sedimentary sequences indicates that the Late Paleozoic ice age in the Xainza area of the Lhasa Block experienced a transition from early marine to late terrestrial glaciations， indicating a global trend of gradual climate warming from the Late Carboniferous to the Early Permian consistent with global Late Paleozoic ice age evolutionary features. The Late Paleozoic ice age was the closest global ice age to the Quaternary ice age and is an important window for understanding future climate shifts such as glacial melting and global warming. Conducting research into Late Paleozoic sedimentary records in the Lhasa Block is greatly significant for exploration of the spatial and temporal evolution， climate change and driving mechanisms of the global Late Paleozoic ice age.
2025,
43(3):
996-1006.
doi: 10.14027/j.issn.1000-0550.2023.067
Abstract:
Objective The paper explores the geochemical and genetic evolution characteristics of deep potassium-rich brine in Lop Nur and investigates the potassium salt mineralization model， aiming to provide a scientific basis for subsequent target selection of deep potassium-rich brine resources in Lop Nur. Methods Based on the petrological analysis of the brine reservoir and analysis on the normal and trace elements and isotopes of the brine， using the means of phase diagram and element correlation analysis. [Results and Conclusions] It is found that the brine of 200 m to 500 m from the Early to Middle Pleistocene in well LDK02 in Lop Nur area is mainly sulphate-type， and the content of K+ is far more than 3g/L， reaching the K+ alone mining and utilization standard. The sodium chloride coefficient coefficient is close to 1， and the boron isotopes are close to the marine sediments， which indicates the brine is mainly of Marine salt origin. The positive correlation between K+ and HBO2 indicates that the filtration salt bed provides a certain amount of K+ in brine. The characteristics of strontium isotopes are similar to those of Miocene saline formations， the positive drift of D and O isotopes， which indicates that the brine was mainly leached from the Miocene saline formations and had undergone a concentrated evaporation process. Combined with previous studies on the tectonic evolution in the Early and Middle Pleistocene and the formation history of modern runoff system in Lop Nur， the soluble salt from the marine and marine-terrestrial salt-bearing strata in the Paleogene- Neogene， especially Miocene saline strata， which are carried by the Tarim River into Lop Nur， are the important source of brine K+. In addition， considering the tectonic movement background of the western region in the Pleistocene， indicates that the K-rich and Li-rich hydrothermal fluids and the dissolution of volcanic detritus related to tectonic movement also provide an important source of K in the brine. Based on this， a binary model of “deep material recharge + paleo-salt dissolution and filtration” for potassium-bearing brine from the 200 -500 m in the early-middle Pleistocene in Lop Nur has been established.
Objective The paper explores the geochemical and genetic evolution characteristics of deep potassium-rich brine in Lop Nur and investigates the potassium salt mineralization model， aiming to provide a scientific basis for subsequent target selection of deep potassium-rich brine resources in Lop Nur. Methods Based on the petrological analysis of the brine reservoir and analysis on the normal and trace elements and isotopes of the brine， using the means of phase diagram and element correlation analysis. [Results and Conclusions] It is found that the brine of 200 m to 500 m from the Early to Middle Pleistocene in well LDK02 in Lop Nur area is mainly sulphate-type， and the content of K+ is far more than 3g/L， reaching the K+ alone mining and utilization standard. The sodium chloride coefficient coefficient is close to 1， and the boron isotopes are close to the marine sediments， which indicates the brine is mainly of Marine salt origin. The positive correlation between K+ and HBO2 indicates that the filtration salt bed provides a certain amount of K+ in brine. The characteristics of strontium isotopes are similar to those of Miocene saline formations， the positive drift of D and O isotopes， which indicates that the brine was mainly leached from the Miocene saline formations and had undergone a concentrated evaporation process. Combined with previous studies on the tectonic evolution in the Early and Middle Pleistocene and the formation history of modern runoff system in Lop Nur， the soluble salt from the marine and marine-terrestrial salt-bearing strata in the Paleogene- Neogene， especially Miocene saline strata， which are carried by the Tarim River into Lop Nur， are the important source of brine K+. In addition， considering the tectonic movement background of the western region in the Pleistocene， indicates that the K-rich and Li-rich hydrothermal fluids and the dissolution of volcanic detritus related to tectonic movement also provide an important source of K in the brine. Based on this， a binary model of “deep material recharge + paleo-salt dissolution and filtration” for potassium-bearing brine from the 200 -500 m in the early-middle Pleistocene in Lop Nur has been established.
2025,
43(3):
1007-1018.
doi: 10.14027/j.issn.1000-0550.2023.066
Abstract:
Objective The Shizigou anticline structure is located in the western part of Qaidam Basin. The upper section of the Paleogene Lower Ganchaigou Formation， with high contents of K， B， and Li， and has development prospects. Methods By systematically analyzing the geochemical characteristics of this set of brine， halite， trace elements and strontium isotopes， the source and metallogenic model of potassium-rich brine are explored. Results （1） The content of K+ in the brine in the study area is 1.06~15.87 g/L， of which 70% exceeds 3 g/L； the chemical type of brine is mainly chloride type； （2） By calculating the characteristic coefficient of brine and combining with the phase diagram analysis of water-salt system， it is found that the leaching salt layer is the main cause of the high salinity brine； （3） At the same time， the relationship between the strontium isotope characteristics of the brine and the halite layer and the correlation between K+ and Li+ reflect that the deep thermal fluid source K also has a certain contribution. Conclusions The metallogenic model of brine potassium in the study area was preliminarily established. During the Lower Ganchaigou period of Paleogene， the Shizigou area was in a weak extensional environment， and the sedimentary environment was relatively stable. The upper part of the Late Eocene Lower Ganchaigou Formation was deposited with halite and other salts； In the later period， the tectonic activity intensified， and the potassium-rich thermal fluid rose into the lake along the tensile fault， providing some deep material source K， At the same time， it caused the dissolution of the existing potassium-containing salt minerals and some halite deposits， which in turn provided another important source of dissolved potassium for the brine in this area.
Objective The Shizigou anticline structure is located in the western part of Qaidam Basin. The upper section of the Paleogene Lower Ganchaigou Formation， with high contents of K， B， and Li， and has development prospects. Methods By systematically analyzing the geochemical characteristics of this set of brine， halite， trace elements and strontium isotopes， the source and metallogenic model of potassium-rich brine are explored. Results （1） The content of K+ in the brine in the study area is 1.06~15.87 g/L， of which 70% exceeds 3 g/L； the chemical type of brine is mainly chloride type； （2） By calculating the characteristic coefficient of brine and combining with the phase diagram analysis of water-salt system， it is found that the leaching salt layer is the main cause of the high salinity brine； （3） At the same time， the relationship between the strontium isotope characteristics of the brine and the halite layer and the correlation between K+ and Li+ reflect that the deep thermal fluid source K also has a certain contribution. Conclusions The metallogenic model of brine potassium in the study area was preliminarily established. During the Lower Ganchaigou period of Paleogene， the Shizigou area was in a weak extensional environment， and the sedimentary environment was relatively stable. The upper part of the Late Eocene Lower Ganchaigou Formation was deposited with halite and other salts； In the later period， the tectonic activity intensified， and the potassium-rich thermal fluid rose into the lake along the tensile fault， providing some deep material source K， At the same time， it caused the dissolution of the existing potassium-containing salt minerals and some halite deposits， which in turn provided another important source of dissolved potassium for the brine in this area.
2025,
43(3):
1019-1036.
doi: 10.14027/j.issn.1000-0550.2023.065
Abstract:
Objective Laminations are sedimentary structures that result from the slow deposition of fine-grained materials under stratified conditions in lakes. Among the various types of laminations， carbonate laminations are particularly sensitive indicators of changes in water salinity， alkalinity， and biological activity. They supply important evidence for reconstructing past continental climates and hydrology， and the study of lacustrine carbonate laminations can provide valuable information on the evolution of lake systems and associated environmental changes. However， research on lacustrine carbonate laminations has been relatively limited. By studying the lacustrine carbonate laminations in the Qaidam Basin， particularly the genesis of aragonite and calcite in the carbonate laminations and the mechanisms of their formation， we aim to reveal the climate and environmental changes in the northern Tibetan Plateau during the Eocene. Methods Taking the Upper Oligocene Gangchaigou Formation in the Xichagou section of the Qaidam Basin as an example， we conducted observations using conventional thin sections， fluorescence thin sections， and scanning electron microscopy， as well as X-ray powder diffraction and carbon-oxygen isotope analysis. Based on the analysis of petrological and carbon-oxygen isotopic characteristics， we investigated the vertical variations of carbonate mineral content and carbon-oxygen isotopes in the Gangchaigou Formation of the Xichagou section. Results The Gangchaigou Formation in the Xichagou section consists of three types of laminations： silt， carbonate， and clay. Among them， aragonite， calcite， and dolomite are alternately enriched in the carbonate laminations. Samples with high aragonite content have relatively positive carbon isotope ratios， whereas samples enriched in dolomite have relatively higher oxygen isotope ratios. Moreover， there are certain regularities in the vertical variations of carbonate mineral content and carbon-oxygen isotopes in the Gangchaigou Formation in the Xichagou section. Conclusion （1） The Upper Gangchaigou Formation in the Qaidam Basin contains various types of lacustrine laminations， primarily interbedded carbonate and feldspar laminations. The mineral compositions of most laminations are impure， with a mixture of terrestrial debris and authigenic carbonate minerals. （2） The formation and preservation of aragonite， calcite， and dolomite in the laminations of the Upper Gangchaigou Formation are related to the chemical composition of the water （such as the Mg/Ca ratio） and algal biological activity. Under the overall brackish water environment， when the external water supply exceeds the evaporation rate， the Mg/Ca value in the water decreases， the salinity decreases， and the nutrient input increases. As a result， calcite and aragonite minerals begin to precipitate and transform. The preservation of aragonite in the Eocene strata is related to the blooming of algae and the abundance of organic matter. When the evaporation rate exceeds the water supply， the Mg/Ca value in the water increases， the salinity increases， and dolomite forms through the replacement of calcite or aragonite or by precipitation. （3） During the Eocene， the climate in the Qaidam Basin was consistent with global climate change， with a humid climate prevailing in the early period and a semi-arid climate prevailing in the late period. The lakes in the Xichagou area experienced an evolution from low to high water levels and then back to low water levels. The early low water level stage represents shallow， brackish water sedimentation with a high input of terrestrial debris. The middle high water level stage represents brackish water sedimentation with well-developed calcite and aragonite. The late low water level stage represents shallow， saline water sedimentation with a low input of terrestrial debris.
Objective Laminations are sedimentary structures that result from the slow deposition of fine-grained materials under stratified conditions in lakes. Among the various types of laminations， carbonate laminations are particularly sensitive indicators of changes in water salinity， alkalinity， and biological activity. They supply important evidence for reconstructing past continental climates and hydrology， and the study of lacustrine carbonate laminations can provide valuable information on the evolution of lake systems and associated environmental changes. However， research on lacustrine carbonate laminations has been relatively limited. By studying the lacustrine carbonate laminations in the Qaidam Basin， particularly the genesis of aragonite and calcite in the carbonate laminations and the mechanisms of their formation， we aim to reveal the climate and environmental changes in the northern Tibetan Plateau during the Eocene. Methods Taking the Upper Oligocene Gangchaigou Formation in the Xichagou section of the Qaidam Basin as an example， we conducted observations using conventional thin sections， fluorescence thin sections， and scanning electron microscopy， as well as X-ray powder diffraction and carbon-oxygen isotope analysis. Based on the analysis of petrological and carbon-oxygen isotopic characteristics， we investigated the vertical variations of carbonate mineral content and carbon-oxygen isotopes in the Gangchaigou Formation of the Xichagou section. Results The Gangchaigou Formation in the Xichagou section consists of three types of laminations： silt， carbonate， and clay. Among them， aragonite， calcite， and dolomite are alternately enriched in the carbonate laminations. Samples with high aragonite content have relatively positive carbon isotope ratios， whereas samples enriched in dolomite have relatively higher oxygen isotope ratios. Moreover， there are certain regularities in the vertical variations of carbonate mineral content and carbon-oxygen isotopes in the Gangchaigou Formation in the Xichagou section. Conclusion （1） The Upper Gangchaigou Formation in the Qaidam Basin contains various types of lacustrine laminations， primarily interbedded carbonate and feldspar laminations. The mineral compositions of most laminations are impure， with a mixture of terrestrial debris and authigenic carbonate minerals. （2） The formation and preservation of aragonite， calcite， and dolomite in the laminations of the Upper Gangchaigou Formation are related to the chemical composition of the water （such as the Mg/Ca ratio） and algal biological activity. Under the overall brackish water environment， when the external water supply exceeds the evaporation rate， the Mg/Ca value in the water decreases， the salinity decreases， and the nutrient input increases. As a result， calcite and aragonite minerals begin to precipitate and transform. The preservation of aragonite in the Eocene strata is related to the blooming of algae and the abundance of organic matter. When the evaporation rate exceeds the water supply， the Mg/Ca value in the water increases， the salinity increases， and dolomite forms through the replacement of calcite or aragonite or by precipitation. （3） During the Eocene， the climate in the Qaidam Basin was consistent with global climate change， with a humid climate prevailing in the early period and a semi-arid climate prevailing in the late period. The lakes in the Xichagou area experienced an evolution from low to high water levels and then back to low water levels. The early low water level stage represents shallow， brackish water sedimentation with a high input of terrestrial debris. The middle high water level stage represents brackish water sedimentation with well-developed calcite and aragonite. The late low water level stage represents shallow， saline water sedimentation with a low input of terrestrial debris.
2025,
43(3):
1037-1048.
doi: 10.14027/j.issn.1000-0550.2023.110
Abstract:
Objective The surface environment of the Zoige Basin is very complex， which is located in a climate-sensitive area. It is of great significance to reveal the response of the surface processes to environmental changes in the Zoige Basin since the last glaciation， as well as the response of environmental changes and surface processes on the Tibetan Plateau to global changes. Methods Through extensive investigation， a complete stratigraphic profile of sedimentary sequence was found and systematically sampled on the high platform in the front of the glacial- alluvial fan in Maqu reach of the Zoige Basin， and the sedimentary environment and surface process changes since the last glaciation in the Zoige Basin were studied by particle size analysis and optically stimulated luminescence （OSL） dating. Results During the last glacial period before 14.5 ka， the ice meltwater and flash flood process in the Warihe River at the east end of Xiqing Mountain was very active and accumulated rapidly in the foothills， forming a thick glacial-alluvial fan sand and gravel layer. During the Bølling-Allerød warm period of 14.5~11.7 ka， the climate was warm and humid， and the silty swamp environment formed in the depressions at the front of the glacial-alluvial fans and developed gray-green sandy sediments. However， during the Younger Dryas period， the climate suddenly worsened， and the upper part of the gray-green bog soil layer in the shallow depression was folded and deformed due to surface freeze-thaw action. In the early Holocene period from 11.7 ka to 8.5 ka， the climate was relatively dry and the aeolian sand was prevalent， the coarse silt accumulated in the shallow depression and the interbedded sedimentary facies of aeolian sand and bog soil developed under the strong wind power of the plateau surface. During the warm and humid period of 8.5 ka to 3.1 ka， the pedogenesis was strong， and the clay content in sediments increased significantly and developed into the paleosol. In the late Holocene from 3.1 ka， the climate was relatively dry and aeolian sand activities were prevalent. The coarse silt accumulated in the late Holocene was transformed into subalpine meadow black soil due to the rising temperature and humidity. Conclusions It indicated that the sedimentary environment and surface processes of the Zoige Basin since the last deglaciation are important information carriers to reveal regional environmental evolution， and responded to the evolution law of global environmental change.
Objective The surface environment of the Zoige Basin is very complex， which is located in a climate-sensitive area. It is of great significance to reveal the response of the surface processes to environmental changes in the Zoige Basin since the last glaciation， as well as the response of environmental changes and surface processes on the Tibetan Plateau to global changes. Methods Through extensive investigation， a complete stratigraphic profile of sedimentary sequence was found and systematically sampled on the high platform in the front of the glacial- alluvial fan in Maqu reach of the Zoige Basin， and the sedimentary environment and surface process changes since the last glaciation in the Zoige Basin were studied by particle size analysis and optically stimulated luminescence （OSL） dating. Results During the last glacial period before 14.5 ka， the ice meltwater and flash flood process in the Warihe River at the east end of Xiqing Mountain was very active and accumulated rapidly in the foothills， forming a thick glacial-alluvial fan sand and gravel layer. During the Bølling-Allerød warm period of 14.5~11.7 ka， the climate was warm and humid， and the silty swamp environment formed in the depressions at the front of the glacial-alluvial fans and developed gray-green sandy sediments. However， during the Younger Dryas period， the climate suddenly worsened， and the upper part of the gray-green bog soil layer in the shallow depression was folded and deformed due to surface freeze-thaw action. In the early Holocene period from 11.7 ka to 8.5 ka， the climate was relatively dry and the aeolian sand was prevalent， the coarse silt accumulated in the shallow depression and the interbedded sedimentary facies of aeolian sand and bog soil developed under the strong wind power of the plateau surface. During the warm and humid period of 8.5 ka to 3.1 ka， the pedogenesis was strong， and the clay content in sediments increased significantly and developed into the paleosol. In the late Holocene from 3.1 ka， the climate was relatively dry and aeolian sand activities were prevalent. The coarse silt accumulated in the late Holocene was transformed into subalpine meadow black soil due to the rising temperature and humidity. Conclusions It indicated that the sedimentary environment and surface processes of the Zoige Basin since the last deglaciation are important information carriers to reveal regional environmental evolution， and responded to the evolution law of global environmental change.
2025,
43(3):
1049-1058.
doi: 10.14027/j.issn.1000-0550.2023.050
Abstract:
Objective The reticulated laterite in southern China is important for the reconstruction of the Quaternary climatic environment in the south， but micro recognition of the reticulated laterite process is still relatively weak. Methods We combined micro-area analysis techniques with geostatistical and factor analyses to conduct element geochemical analysis on the white vein micro-area and the transitional micro-area of the red and white vein profile in Langxi （30°58′24″ N， 119°7′43″ E）. Results （1） The content of iron group elements such as Fe2O3（3.43%-16.97%）， Mn（0.01×10-6-0.37×10-6） and Co（21×10-6-230×10-6） showed a trend of low value area in the center of the vein and high value area in the periphery， gradually increasing from the center to the periphery. However， K2O（0.78%-1.48%）， MgO（0.18%-0.45%）， and other constant elements， as well as Ti（4 054×10-6-7 190×10-6）、Zr（310×10-6-330×10-6）， and other elements differ from the distribution trend. （2） The common feature of factors in the white vein micro-area and the red-white transition micro-area is that they are mainly factor 1， which reflects the leaching migration of iron and iron group elements in the white vein， as well as the relative enrichment process of soluble constant elements such as K， Ca， and Mg and stable elements such as Ti and Zr， while factor 2 may be related to the deposition of iron. In addition， there may be adsorption processes of iron oxides on Cu， Zn， etc. Conclusions Through the micro-area technical method and factor analysis， the interior of the white area was found to be inhomogeneous， and there is a gradual change from the center of the vein to the periphery. The variation of elemental content from the white to red vein also showed a gradual change， similar to that in the white vein micro-area. Reticulation is a continuous developmental process. During reticulation， the leaching migration of iron and iron elements are dominant， the deposition and leaching migration of iron and iron group elements coexist， and the reticulation process is relatively complicated.
Objective The reticulated laterite in southern China is important for the reconstruction of the Quaternary climatic environment in the south， but micro recognition of the reticulated laterite process is still relatively weak. Methods We combined micro-area analysis techniques with geostatistical and factor analyses to conduct element geochemical analysis on the white vein micro-area and the transitional micro-area of the red and white vein profile in Langxi （30°58′24″ N， 119°7′43″ E）. Results （1） The content of iron group elements such as Fe2O3（3.43%-16.97%）， Mn（0.01×10-6-0.37×10-6） and Co（21×10-6-230×10-6） showed a trend of low value area in the center of the vein and high value area in the periphery， gradually increasing from the center to the periphery. However， K2O（0.78%-1.48%）， MgO（0.18%-0.45%）， and other constant elements， as well as Ti（4 054×10-6-7 190×10-6）、Zr（310×10-6-330×10-6）， and other elements differ from the distribution trend. （2） The common feature of factors in the white vein micro-area and the red-white transition micro-area is that they are mainly factor 1， which reflects the leaching migration of iron and iron group elements in the white vein， as well as the relative enrichment process of soluble constant elements such as K， Ca， and Mg and stable elements such as Ti and Zr， while factor 2 may be related to the deposition of iron. In addition， there may be adsorption processes of iron oxides on Cu， Zn， etc. Conclusions Through the micro-area technical method and factor analysis， the interior of the white area was found to be inhomogeneous， and there is a gradual change from the center of the vein to the periphery. The variation of elemental content from the white to red vein also showed a gradual change， similar to that in the white vein micro-area. Reticulation is a continuous developmental process. During reticulation， the leaching migration of iron and iron elements are dominant， the deposition and leaching migration of iron and iron group elements coexist， and the reticulation process is relatively complicated.
2025,
43(3):
1059-1071.
doi: 10.14027/j.issn.1000-0550.2023.057
Abstract:
Objective The Upper Permian Wutonggou Formation in the Lukeqin area of the Turpan-Hami Basin has good oil and gas exploration potential， making it a key deep exploration target in the Turpan-Hami Basin. Diagenetic analysis shows that calcite cement is one of the main authigenic minerals developed in the reservoir of the Wutonggou Formation in this area， but more work on the precise analysis is still recommended to improve our understanding of its diagenetic period and how it affects the reservoir quality. Methods Because the calcite cement is an abundant authigenic cements in most clastic rocks， it is also the product of fluid rock interaction during diagenesis， during which its relative content， occurrence type， occurrence， state and formation mechanism would likely exert huge impacts on reservoir quality. Combined with the previous study that concluded that mechanical compaction and cementation under deep burial conditions are the two main factors affecting the quality of the Wutonggou Formation sandstone reservoir in the Lukeqin area， we present the thin section identification， physical property analysis， scanning electron microscopy， cathodoluminescence， and other testing methods of the Wutonggou Formation in the Lukeqin area， Turpan-Hami Basin. We systematically investigated the period and diagenetic evolution of common calcite cements in the deep sandstone reservoir of this period and discussed the influence of calcite cement on reservoir quality. Results The photomicrographs and statistics show a clear positive correlation between the porosity and permeability， indicating that the sandstone reservoir of the Wutonggou Formation is porous. The calcite cement content most favorable for reservoir development of the Wutonggou Formation reservoir in Lukeqin area is 1%-8%. More than 8.0% samples show that the primary pores are almost filled with calcite， while less than 1.0% samples indicate that the compaction is too strong and unfavorable for reservoir development； Photomicrographs also exhibit a filling relationship that indicates three stages of calcite cement； the first stage is argillaceous calcite with 25%； the second stage is calcite cemented by continuous crystal with 60%； and stage Ⅲ is calcite filled with feldspar and other intragranular solution pores with 15%. There is no distinct positive or negative correlation between calcite cement and physical properties， which indicates that it belongs to ret entive diagenesis in the form of pore filling， which could occupy the remaining intergranular pores while enhancing their ability to resist compaction of the clastic particle skeleton. This is also consistent with a large number of earlier studies that the calcite cement formed in the early diagenetic stage before the main compaction can preserve the primary pores in the sandstone， which may further dissolve and release the secondary pores to improve the reservoir quality in the later diagenetic process. Conclusions Therefore， we suggest that the calcite cement is the key factor for the development of deep sandstone reservoirs of the Wutonggou Formation in the Lukeqin area.
Objective The Upper Permian Wutonggou Formation in the Lukeqin area of the Turpan-Hami Basin has good oil and gas exploration potential， making it a key deep exploration target in the Turpan-Hami Basin. Diagenetic analysis shows that calcite cement is one of the main authigenic minerals developed in the reservoir of the Wutonggou Formation in this area， but more work on the precise analysis is still recommended to improve our understanding of its diagenetic period and how it affects the reservoir quality. Methods Because the calcite cement is an abundant authigenic cements in most clastic rocks， it is also the product of fluid rock interaction during diagenesis， during which its relative content， occurrence type， occurrence， state and formation mechanism would likely exert huge impacts on reservoir quality. Combined with the previous study that concluded that mechanical compaction and cementation under deep burial conditions are the two main factors affecting the quality of the Wutonggou Formation sandstone reservoir in the Lukeqin area， we present the thin section identification， physical property analysis， scanning electron microscopy， cathodoluminescence， and other testing methods of the Wutonggou Formation in the Lukeqin area， Turpan-Hami Basin. We systematically investigated the period and diagenetic evolution of common calcite cements in the deep sandstone reservoir of this period and discussed the influence of calcite cement on reservoir quality. Results The photomicrographs and statistics show a clear positive correlation between the porosity and permeability， indicating that the sandstone reservoir of the Wutonggou Formation is porous. The calcite cement content most favorable for reservoir development of the Wutonggou Formation reservoir in Lukeqin area is 1%-8%. More than 8.0% samples show that the primary pores are almost filled with calcite， while less than 1.0% samples indicate that the compaction is too strong and unfavorable for reservoir development； Photomicrographs also exhibit a filling relationship that indicates three stages of calcite cement； the first stage is argillaceous calcite with 25%； the second stage is calcite cemented by continuous crystal with 60%； and stage Ⅲ is calcite filled with feldspar and other intragranular solution pores with 15%. There is no distinct positive or negative correlation between calcite cement and physical properties， which indicates that it belongs to ret entive diagenesis in the form of pore filling， which could occupy the remaining intergranular pores while enhancing their ability to resist compaction of the clastic particle skeleton. This is also consistent with a large number of earlier studies that the calcite cement formed in the early diagenetic stage before the main compaction can preserve the primary pores in the sandstone， which may further dissolve and release the secondary pores to improve the reservoir quality in the later diagenetic process. Conclusions Therefore， we suggest that the calcite cement is the key factor for the development of deep sandstone reservoirs of the Wutonggou Formation in the Lukeqin area.
2025,
43(3):
1072-1090.
doi: 10.14027/j.issn.1000-0550.2023.083
Abstract:
Objective The Early Triassic was a special geological period after the mass extinction of organisms， during which oolitic and giant oolitic deposits were widely developed in shallow carbonate platforms worldwide. However， there is still significant controversy regarding the origin and paleomarine environmental significance of oolitic and giant oolitic deposits. Methods Based on field and core observations， this study utilized petrological， mineralogical， and geochemical analyses to explore the sedimentary characteristics， genesis， and paleoenvironmental significance of the Early Triassic Feixianguan Formation oolites and giant oolites in the Yuanba area. Results Research shows that the oolites and giant oolites of the Feixianguan Formation in the Yuanba area primarily developed in the margin zone of the section 2 of Feixianguan Formation. The types of oolites are concentric and single crystal oolites， which are developed in the middle and upper part of the meter scale sedimentary cycle and are produced in thick layers and blocks， indicating that they were formed in a shallow water environment with strong hydrodynamic forces and easy exposure. Giant ooids are primarily composed of concentric ooids， which are developed in the upper part of the meter scale sedimentary cycle and the lower part of the mud crystal limestone. They are produced in a thin layer and have clear erosion at the bottom， indicating that they were formed under intermittent strong hydrodynamic conditions， mostly due to storm action. Based on geochemical analysis， the Sr content in the concentric layer of oolites is found to be high， and the crystal structure is mostly needle-like or rod-shaped， indicating that the original minerals are aragonite deposits. However， the Sr content in the concentric layers of giant ooids is relatively low， and their crystal structure is irregularly inlaid， indicating that their original minerals are calcite deposits. In addition， the concentric layer of oolites has characteristics such as high Fe content， weak positive Ce anomaly， clear positive Eu anomaly， enrichment of light rare earth element （LREE） relative to heavy rare earth element （HREE）， and low Y/Ho values， indicating that it was formed in a reducing environment of iron mineralization. Giant ooids have characteristics such as low Fe content， weak negative Ce anomalies， relative HREE depletion of LREE， and high Y/Ho values， indicating that they were formed in a weakly oxidizing environment. Conclusions Comprehensive analysis suggests that during the sedimentary period of the Early Triassic Feixianguan Formation， the seawater was mainly characterized by the anoxic aragonite sea. However， in the context of gradual atmospheric oxidation and strengthened continental weathering， intermittent storm action increased the input of terrestrial materials （particularly Ca2+） and oxidants， resulting in a decrease in Mg/Ca in shallow seawater and weak oxidation， as well as the development of a transient weak oxidation calcite sea. This may be the cause for the gradual improvement of the marine environment and slow biological recovery in the Early Triassic.
Objective The Early Triassic was a special geological period after the mass extinction of organisms， during which oolitic and giant oolitic deposits were widely developed in shallow carbonate platforms worldwide. However， there is still significant controversy regarding the origin and paleomarine environmental significance of oolitic and giant oolitic deposits. Methods Based on field and core observations， this study utilized petrological， mineralogical， and geochemical analyses to explore the sedimentary characteristics， genesis， and paleoenvironmental significance of the Early Triassic Feixianguan Formation oolites and giant oolites in the Yuanba area. Results Research shows that the oolites and giant oolites of the Feixianguan Formation in the Yuanba area primarily developed in the margin zone of the section 2 of Feixianguan Formation. The types of oolites are concentric and single crystal oolites， which are developed in the middle and upper part of the meter scale sedimentary cycle and are produced in thick layers and blocks， indicating that they were formed in a shallow water environment with strong hydrodynamic forces and easy exposure. Giant ooids are primarily composed of concentric ooids， which are developed in the upper part of the meter scale sedimentary cycle and the lower part of the mud crystal limestone. They are produced in a thin layer and have clear erosion at the bottom， indicating that they were formed under intermittent strong hydrodynamic conditions， mostly due to storm action. Based on geochemical analysis， the Sr content in the concentric layer of oolites is found to be high， and the crystal structure is mostly needle-like or rod-shaped， indicating that the original minerals are aragonite deposits. However， the Sr content in the concentric layers of giant ooids is relatively low， and their crystal structure is irregularly inlaid， indicating that their original minerals are calcite deposits. In addition， the concentric layer of oolites has characteristics such as high Fe content， weak positive Ce anomaly， clear positive Eu anomaly， enrichment of light rare earth element （LREE） relative to heavy rare earth element （HREE）， and low Y/Ho values， indicating that it was formed in a reducing environment of iron mineralization. Giant ooids have characteristics such as low Fe content， weak negative Ce anomalies， relative HREE depletion of LREE， and high Y/Ho values， indicating that they were formed in a weakly oxidizing environment. Conclusions Comprehensive analysis suggests that during the sedimentary period of the Early Triassic Feixianguan Formation， the seawater was mainly characterized by the anoxic aragonite sea. However， in the context of gradual atmospheric oxidation and strengthened continental weathering， intermittent storm action increased the input of terrestrial materials （particularly Ca2+） and oxidants， resulting in a decrease in Mg/Ca in shallow seawater and weak oxidation， as well as the development of a transient weak oxidation calcite sea. This may be the cause for the gradual improvement of the marine environment and slow biological recovery in the Early Triassic.
2025,
43(3):
1091-1102.
doi: 10.14027/j.issn.1000-0550.2023.098
Abstract:
Objective The purpose of this study is to study the development characteristics of the Ordovician stormrock in the northern margin of the Upper Yangtze Plate， and the sedimentary environment， paleomarine conditions， paleogeography and sedimentary paleogeomorphology of the Lower Ordovician in this area. Methods The typical storm rocks in Fenxiang Formation of Houping section in Chengkou area of the upper Yangtze Platform are studied. Detailed field profile survey and microscopic thin section identification are carried out to study the sedimentary sequence and sedimentary model of Fenxiang Formation and reveal its geological significance. Results The tempestite sedimentary structures of the Fenxiang Formation in the Chengkou area include bottom scour structure， storm gravel layer， grain sequence bedding， and mound cross-bedding. In total， five tempestite sedimentary sequences were identified： Sequence I was composed of a bottom erosion and gravel layer （A）， grain sequence （B）， and parallel bedding segment （C） and developed in the platform margin facies； Sequence II consisted of a grain sequence （B） and parallel bedding segment （C）， which developed in the platform margin facies near the slope. Sequence III was composed of a bottom erosion and gravel layer （A）， grain sequence layer （B）， parallel bedding （C）， and argillaceous limestone segment （E） and primarily deposited in the fore-platform slope facies zone. Sequence Ⅳ consisted of a grain sequence segment （B） and argillaceous micrite segment （E）， which were primarily deposited in the lower the fore-platform slope. Sequence V was composed of a grain sequence （B）， mound bedding segment （D）， and argillaceous micrite segment （E）， which mainly developed in the deepwater shelf. The development of tempestites indicate that the Upper Yangtze platform was located at a low latitude in the Early Ordovician， and the Chengkou area was dominated by platform margin and slope deposits. The bottom-up sedimentary environment evolved into platform margin → platform front slope → deep water shelf. Conclusions The development of storm rock of Fenxiang Formation in Chengkou area of Upper Yangtze Platform indicates that the Upper Yangtze platform was near the equator of low latitude in Ordovician period， and the sedimentary environment was platform margin zone with geological conditions for developing large-scale platform margin shoals.
Objective The purpose of this study is to study the development characteristics of the Ordovician stormrock in the northern margin of the Upper Yangtze Plate， and the sedimentary environment， paleomarine conditions， paleogeography and sedimentary paleogeomorphology of the Lower Ordovician in this area. Methods The typical storm rocks in Fenxiang Formation of Houping section in Chengkou area of the upper Yangtze Platform are studied. Detailed field profile survey and microscopic thin section identification are carried out to study the sedimentary sequence and sedimentary model of Fenxiang Formation and reveal its geological significance. Results The tempestite sedimentary structures of the Fenxiang Formation in the Chengkou area include bottom scour structure， storm gravel layer， grain sequence bedding， and mound cross-bedding. In total， five tempestite sedimentary sequences were identified： Sequence I was composed of a bottom erosion and gravel layer （A）， grain sequence （B）， and parallel bedding segment （C） and developed in the platform margin facies； Sequence II consisted of a grain sequence （B） and parallel bedding segment （C）， which developed in the platform margin facies near the slope. Sequence III was composed of a bottom erosion and gravel layer （A）， grain sequence layer （B）， parallel bedding （C）， and argillaceous limestone segment （E） and primarily deposited in the fore-platform slope facies zone. Sequence Ⅳ consisted of a grain sequence segment （B） and argillaceous micrite segment （E）， which were primarily deposited in the lower the fore-platform slope. Sequence V was composed of a grain sequence （B）， mound bedding segment （D）， and argillaceous micrite segment （E）， which mainly developed in the deepwater shelf. The development of tempestites indicate that the Upper Yangtze platform was located at a low latitude in the Early Ordovician， and the Chengkou area was dominated by platform margin and slope deposits. The bottom-up sedimentary environment evolved into platform margin → platform front slope → deep water shelf. Conclusions The development of storm rock of Fenxiang Formation in Chengkou area of Upper Yangtze Platform indicates that the Upper Yangtze platform was near the equator of low latitude in Ordovician period， and the sedimentary environment was platform margin zone with geological conditions for developing large-scale platform margin shoals.
2025,
43(3):
1103-1115.
doi: 10.14027/j.issn.1000-0550.2023.063
Abstract:
Objective To understand the sedimentary characteristics of shell limestone-shale mixed strata in the Da’anzhai member of Sichuan Basin and its influence on favorable shale oil horizon. Methods Field profiles in Dazhou Tieshan Jinwo and Liangping Fuluzhen of the northeast Sichuan Basin were studied. The lithology and sequence， source and reservoir quality， and favorable strata of the Da’anzhai member were evaluated in detail by using rock thin sections， X-ray diffraction （XRD） whole rock and organic geochemical analyses. Results （1） The Da’anzhai member is a set of limestone-shale mixed strata， and different lithologies are superimposed in an orderly way to form a variety of upward shallower sequences. From shallow lake to semi-deep lake-deep lake， six kinds of upward shallower decimeter to meter lithofacies sequences are identified： ①shale-shell shale， ②shale-thin shell limestone， ③shale-medium shell limestone， ④shale-nodular micrite， ⑤thin shale-shell limestone-crystalline limestone， and ⑥shell limestone-siltstone/fine sandstone. （2） The quality of source and reservoir varies greatly among different lithologic sequences. Black shales in sequence ①-③ are developed with the best source quality. The organic carbon content of black shales in a single sequence shows a trend of higher and lower organic carbon content， and total organic carbon （TOC） gradually decreases with the increase of shell limestone. Different lithologic properties vary greatly. The porosity of shale is higher than that of limestone and siltstone， but the clay content is high， the pore size is small， and the seepage capacity is poor. Limestone easily develops joint fractures， and the density of joints decreases exponentially with the increase of limestone thickness. Therefore， Sequence ②-④ developed middle and thin layer limestone has better reservoir performance. （3） The field oil seedling shows that the shale oil reservoir of the Da’anzhai member is characterized by the separation of source and reservoir and thin high-quality reservoir. The shale oil seepages in the field are mainly distributed near the joints of the medium-thin layer shell limestone. The favorable reservoir is primarily controlled by the sedimentary conditions， micro-fractures， and configuration of source and reservoir. Conclusions Sequences ② and ③ have the best source and reservoir configuration conditions， which are favorable intervals for shale oil.
Objective To understand the sedimentary characteristics of shell limestone-shale mixed strata in the Da’anzhai member of Sichuan Basin and its influence on favorable shale oil horizon. Methods Field profiles in Dazhou Tieshan Jinwo and Liangping Fuluzhen of the northeast Sichuan Basin were studied. The lithology and sequence， source and reservoir quality， and favorable strata of the Da’anzhai member were evaluated in detail by using rock thin sections， X-ray diffraction （XRD） whole rock and organic geochemical analyses. Results （1） The Da’anzhai member is a set of limestone-shale mixed strata， and different lithologies are superimposed in an orderly way to form a variety of upward shallower sequences. From shallow lake to semi-deep lake-deep lake， six kinds of upward shallower decimeter to meter lithofacies sequences are identified： ①shale-shell shale， ②shale-thin shell limestone， ③shale-medium shell limestone， ④shale-nodular micrite， ⑤thin shale-shell limestone-crystalline limestone， and ⑥shell limestone-siltstone/fine sandstone. （2） The quality of source and reservoir varies greatly among different lithologic sequences. Black shales in sequence ①-③ are developed with the best source quality. The organic carbon content of black shales in a single sequence shows a trend of higher and lower organic carbon content， and total organic carbon （TOC） gradually decreases with the increase of shell limestone. Different lithologic properties vary greatly. The porosity of shale is higher than that of limestone and siltstone， but the clay content is high， the pore size is small， and the seepage capacity is poor. Limestone easily develops joint fractures， and the density of joints decreases exponentially with the increase of limestone thickness. Therefore， Sequence ②-④ developed middle and thin layer limestone has better reservoir performance. （3） The field oil seedling shows that the shale oil reservoir of the Da’anzhai member is characterized by the separation of source and reservoir and thin high-quality reservoir. The shale oil seepages in the field are mainly distributed near the joints of the medium-thin layer shell limestone. The favorable reservoir is primarily controlled by the sedimentary conditions， micro-fractures， and configuration of source and reservoir. Conclusions Sequences ② and ③ have the best source and reservoir configuration conditions， which are favorable intervals for shale oil.
2025,
43(3):
1130-1144.
doi: 10.14027/j.issn.1000-0550.2023.068
Abstract:
Objective The pressure differences between source and reservoir rocks is not only the driving force for unconventional oil and gas accumulation， but also indispensable key content in the study of the genesis of shale oil sweet spots. In addition， laminar structures are widely developed in continental shale， and the degree of development results in differences in the accumulation dynamics of reservoir rocks， which affect the accumulation of shale oil and gas. However， there are relatively few studies on the accumulation dynamics of shale oil. The sweet spot section of the Permian Lucaogou Formation in the Jimusar Sag was taken as the research object， and the intrinsic relationship between the development degree of laminar structure and shale oil and gas accumulation was revealed from the perspective of accumulation dynamics. Methods Through the evaluation of source rocks， classification of petrographic types and characterization of pores， etc.， the characteristics of the source rocks， different types of reservoir rocks， and source-reservoir assemblages in the study area were obtained. Using the equivalent depth method and fluid inclusion simulation， the pressure difference between source and reservoir rocks during the accumulation period was recovered， and the accumulation dynamics of different types of reservoir rocks were obtained. Results The results show that the study area is dominated by source-reservoir interbedded combinations， and the hydrocarbon generation of high-quality source rocks creates a strong source-reservoir pressure difference between the source and reservoir， promoting the continuous migration of oil and gas to adjacent reservoir spaces. Interbedded silty and argillaceous laminae are widely developed in the reservoir rocks， which constitute a large area of frequent contact between the source and reservoir. The degree of development results in differences in the accumulation dynamics of different types of reservoir rocks， the laminar reservoir has developed laminar structure， and the migration distance of oil and gas is shortened； thus， it has stronger accumulation power and oil-bearing properties. Conclusions The interaction between the pressure difference between source and reservoir rocks and the laminar structure causes the difference in the accumulation effect of oil and gas in the reservoir rocks，and the development of laminar reservoir rocks in the lower sweet spot is a favorable area for studying oil and gas migration and accumulation in the shale sweet spot.
Objective The pressure differences between source and reservoir rocks is not only the driving force for unconventional oil and gas accumulation， but also indispensable key content in the study of the genesis of shale oil sweet spots. In addition， laminar structures are widely developed in continental shale， and the degree of development results in differences in the accumulation dynamics of reservoir rocks， which affect the accumulation of shale oil and gas. However， there are relatively few studies on the accumulation dynamics of shale oil. The sweet spot section of the Permian Lucaogou Formation in the Jimusar Sag was taken as the research object， and the intrinsic relationship between the development degree of laminar structure and shale oil and gas accumulation was revealed from the perspective of accumulation dynamics. Methods Through the evaluation of source rocks， classification of petrographic types and characterization of pores， etc.， the characteristics of the source rocks， different types of reservoir rocks， and source-reservoir assemblages in the study area were obtained. Using the equivalent depth method and fluid inclusion simulation， the pressure difference between source and reservoir rocks during the accumulation period was recovered， and the accumulation dynamics of different types of reservoir rocks were obtained. Results The results show that the study area is dominated by source-reservoir interbedded combinations， and the hydrocarbon generation of high-quality source rocks creates a strong source-reservoir pressure difference between the source and reservoir， promoting the continuous migration of oil and gas to adjacent reservoir spaces. Interbedded silty and argillaceous laminae are widely developed in the reservoir rocks， which constitute a large area of frequent contact between the source and reservoir. The degree of development results in differences in the accumulation dynamics of different types of reservoir rocks， the laminar reservoir has developed laminar structure， and the migration distance of oil and gas is shortened； thus， it has stronger accumulation power and oil-bearing properties. Conclusions The interaction between the pressure difference between source and reservoir rocks and the laminar structure causes the difference in the accumulation effect of oil and gas in the reservoir rocks，and the development of laminar reservoir rocks in the lower sweet spot is a favorable area for studying oil and gas migration and accumulation in the shale sweet spot.
2025,
43(3):
1145-1162.
doi: 10.14027/j.issn.1000-0550.2023.079
Abstract:
Objective After more than 50 years of exploration， Langgu Sag has entered the stage of oil and gas exploration and development with lithologic and structural-lithologic reservoirs as the main targets. Previous studies have been carried out on the large-scale sedimentary characteristics， hydrocarbon accumulation factors and models of Langgu Sag. However， relatively little is known of the spatial distribution characteristics and the distribution rules of the high-quality sand bodies. The main controlling factors of hydrocarbon accumulation and their distribution are not uniform， which restricts the evaluation and production of subtle reservoirs. Methods This study comprehensively used core data， well logging， seismic data， analytical tests and production data to systematically study the Shahejie Formation in the Jiuzhou-Wanzhuang area. The study aims to identify and classify sedimentary facies and microfacies types， accurately characterize the spatial distribution of sand bodies， and analyze reservoirs formation control factors such as source rocks， traps and fault conduit systems. The hydrocarbon accumulation model is established， leading to the prediction of favorable concealed lithologic or structural-lithologic reservoirs distribution zones. Results The lithology is mainly fine-grained clastic rock； the sedimentary sequence is not typical， a deformation structure is clearly developed， and floating mud gravel of sandy clastic flow origin can be seen. This reflects the characteristics of the dynamic conditions of traction flow in the distal fan delta. In the study area， there are two provenance supply systems in the south and north， and a braided channel extends from the SE of the Daxing Fault to the interior of the lake in a finger-like way， forming two depositional centers in Jiuzhou and Wanzhuang. In the study area， an underwater distri-butary channel at the front of the fan delta extends for some distance and migrates frequently. The estuary is unstable， with an underdeveloped or small-scale estuarine bar. Mature source rocks， effective traps and fault conduit systems are the main controls of hydrocarbon accumulation in the middle submember of Shahejie Formation 3rd member in the study area. The abundance of organic matter shows that the oil source of the lower submember of Shahejie Formation 3rd member in the study area comes from underlying source rocks of the lower submember of Shahejie Formation 3rd member. Using forward modeling and RGB （Red-Green-Blue） attribute fusion， sensitive attribute optimization was performed to predict the distribution range of high-quality sandstone reservoirs combined with a series of anticlinal tectonic settings to form good structural traps along with lithologic up-dip pinch-out traps. As oil source faults， the Daxing and Jiuzhou Faults and their secondary branches are the main channels connecting the oil and gas resources of the lower submember of Shahejie Formation 3rd member and the reservoirs of the middle submember of Shahejie Formation 3rd member， and they also control the formation of traps as a whole. Conclusions The results show that the study area is primarily characterized by fan-delta systems and lake systems. Within the fan-delta system， various microfacies types were identified （e.g.， braided channels， submarine distributary channels， delta front sandbars， and sheet-like sands）. The spatial distribution of sand bodies is characterized by thick layers of distributary channel-sandbar complexes with finger-like distribution and continuous thin sheet-like sands. The organic configurations of oil source faults， structures and even lithologic traps are the main causes of hydrocarbon accumulation in the study area， and the reservoir lithology within the traps determines the oil， gas and water distribution. Ultimately， four favorable development zones for lithologic or structural-lithologic reservoirs were predicted in the SE and NW wings of the jiuzhou plunging nose structure and the NE wing of the Tongxi paleo-structural ridge.
Objective After more than 50 years of exploration， Langgu Sag has entered the stage of oil and gas exploration and development with lithologic and structural-lithologic reservoirs as the main targets. Previous studies have been carried out on the large-scale sedimentary characteristics， hydrocarbon accumulation factors and models of Langgu Sag. However， relatively little is known of the spatial distribution characteristics and the distribution rules of the high-quality sand bodies. The main controlling factors of hydrocarbon accumulation and their distribution are not uniform， which restricts the evaluation and production of subtle reservoirs. Methods This study comprehensively used core data， well logging， seismic data， analytical tests and production data to systematically study the Shahejie Formation in the Jiuzhou-Wanzhuang area. The study aims to identify and classify sedimentary facies and microfacies types， accurately characterize the spatial distribution of sand bodies， and analyze reservoirs formation control factors such as source rocks， traps and fault conduit systems. The hydrocarbon accumulation model is established， leading to the prediction of favorable concealed lithologic or structural-lithologic reservoirs distribution zones. Results The lithology is mainly fine-grained clastic rock； the sedimentary sequence is not typical， a deformation structure is clearly developed， and floating mud gravel of sandy clastic flow origin can be seen. This reflects the characteristics of the dynamic conditions of traction flow in the distal fan delta. In the study area， there are two provenance supply systems in the south and north， and a braided channel extends from the SE of the Daxing Fault to the interior of the lake in a finger-like way， forming two depositional centers in Jiuzhou and Wanzhuang. In the study area， an underwater distri-butary channel at the front of the fan delta extends for some distance and migrates frequently. The estuary is unstable， with an underdeveloped or small-scale estuarine bar. Mature source rocks， effective traps and fault conduit systems are the main controls of hydrocarbon accumulation in the middle submember of Shahejie Formation 3rd member in the study area. The abundance of organic matter shows that the oil source of the lower submember of Shahejie Formation 3rd member in the study area comes from underlying source rocks of the lower submember of Shahejie Formation 3rd member. Using forward modeling and RGB （Red-Green-Blue） attribute fusion， sensitive attribute optimization was performed to predict the distribution range of high-quality sandstone reservoirs combined with a series of anticlinal tectonic settings to form good structural traps along with lithologic up-dip pinch-out traps. As oil source faults， the Daxing and Jiuzhou Faults and their secondary branches are the main channels connecting the oil and gas resources of the lower submember of Shahejie Formation 3rd member and the reservoirs of the middle submember of Shahejie Formation 3rd member， and they also control the formation of traps as a whole. Conclusions The results show that the study area is primarily characterized by fan-delta systems and lake systems. Within the fan-delta system， various microfacies types were identified （e.g.， braided channels， submarine distributary channels， delta front sandbars， and sheet-like sands）. The spatial distribution of sand bodies is characterized by thick layers of distributary channel-sandbar complexes with finger-like distribution and continuous thin sheet-like sands. The organic configurations of oil source faults， structures and even lithologic traps are the main causes of hydrocarbon accumulation in the study area， and the reservoir lithology within the traps determines the oil， gas and water distribution. Ultimately， four favorable development zones for lithologic or structural-lithologic reservoirs were predicted in the SE and NW wings of the jiuzhou plunging nose structure and the NE wing of the Tongxi paleo-structural ridge.
