2022 Vol. 47, No. 7
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2022, 47(7): 2287-2302.
doi: 10.3799/dqkx.2022.135
Abstract:
Based on the interpretation and analysis of 1 000 km long deep reflection seismic sections across the conjugate passive continental margins in the V-shaped tip of the Southwest sub-basin of the South China Sea, in this paper it presents a study on the basin structure, tectonic style and the extension progress of continental lithosphere in the final breakup area of South China Sea. Three first order surfaces can be recognized in the SW South China Sea: seafloor, Tg/Tm and Moho. The relationship between these three surfaces can be used to define the box-shape domain, necking domain, wedge shape domain and thin box-shape domain. In the V-shaped SW sub-basin, T50/Tm corresponds to the lithosphere breakup surface, which is also named as the breakup unconformity. This interface and the basement surface (Tg/Tm) define the syn-rifting deposition filling sequence of the continental margin basin. Two important episodic structures, T70 and T60, have developed within it. The surfaces of Tg and T70 constrained the formation of early faulted basin system which was controlled by high-angle normal faults. The surfaces of T70 and T60 controlled the development of detachment basin. The surfaces of T60 and T50 constrained the formation of sag basins. In this paper it shows that the thin box-shape domain belongs to the proto-oceanic domain. The nature of this area consists of magmatic ocean, representing the final breakup process before the formation of mantle convection system in which the lithosphere was close to disintegration and separation, but the steady-state seafloor spreading had not been fully established. The thin box-shape domain developed between the T60 and Tm. Considering the initial crustal thickness, fault activity, and basin prototypes during different periods, and applying the balanced profile technology, the development progress of V-shaped tip at the SW sub-basin has been reconstructed. The structure-stratigraphic-magma interaction model of the final breakup domain in the SW sub-basin of the South China Sea has been established, revealing the extension and breakup mechanism of the continental margin lithosphere in the South China Sea. This mechanism has important theoretical significance, and has great practical application value for deep-water oil and gas exploration in the South China Sea.
Based on the interpretation and analysis of 1 000 km long deep reflection seismic sections across the conjugate passive continental margins in the V-shaped tip of the Southwest sub-basin of the South China Sea, in this paper it presents a study on the basin structure, tectonic style and the extension progress of continental lithosphere in the final breakup area of South China Sea. Three first order surfaces can be recognized in the SW South China Sea: seafloor, Tg/Tm and Moho. The relationship between these three surfaces can be used to define the box-shape domain, necking domain, wedge shape domain and thin box-shape domain. In the V-shaped SW sub-basin, T50/Tm corresponds to the lithosphere breakup surface, which is also named as the breakup unconformity. This interface and the basement surface (Tg/Tm) define the syn-rifting deposition filling sequence of the continental margin basin. Two important episodic structures, T70 and T60, have developed within it. The surfaces of Tg and T70 constrained the formation of early faulted basin system which was controlled by high-angle normal faults. The surfaces of T70 and T60 controlled the development of detachment basin. The surfaces of T60 and T50 constrained the formation of sag basins. In this paper it shows that the thin box-shape domain belongs to the proto-oceanic domain. The nature of this area consists of magmatic ocean, representing the final breakup process before the formation of mantle convection system in which the lithosphere was close to disintegration and separation, but the steady-state seafloor spreading had not been fully established. The thin box-shape domain developed between the T60 and Tm. Considering the initial crustal thickness, fault activity, and basin prototypes during different periods, and applying the balanced profile technology, the development progress of V-shaped tip at the SW sub-basin has been reconstructed. The structure-stratigraphic-magma interaction model of the final breakup domain in the SW sub-basin of the South China Sea has been established, revealing the extension and breakup mechanism of the continental margin lithosphere in the South China Sea. This mechanism has important theoretical significance, and has great practical application value for deep-water oil and gas exploration in the South China Sea.
2022, 47(7): 2303-2316.
doi: 10.3799/dqkx.2022.064
Abstract:
The structure of faulted basins is mainly controlled by the tectonic action of boundary faults, but when magmatism occurs in different degrees during the development of basins, the structure of faulted basins will be significantly transformed and influenced. Based on the description and analysis of the differential evolution characteristics of fault depression structure in Baiyun Sag, Pearl River Mouth Basin, which is located in the northern margin of the South China Sea, in this paper it discusses the influence of the participation of magmatism on the structural style of the sag and the evolution of fault depression structure-stratum-sediment in the process of continental margin extension. The research shows that during the intense extension of the main depression in Baiyun Sag, magmatism was not obvious, brittle fracture occurred in the upper crust, and ductile extension thinning occurred in the middle and lower crust, resulting in the broad and deep fault depression controlled by crust-mantle detachment fault, and tectonism, namely, crustal extension detachment thinning, was the main mechanism of fault depression development. However, in the eastern depression of Baiyun Sag, after the early brittle fracture, a remarkable magmatic upwelling took place, which changed the structural strength of the upper crust, and the brittle-ductile transition plane moved upward, resulting in a broad and shallow fault depression controlled by the upper crust detachment fault. The fault depression structure was transformed by magmatic upwelling, showing a semi-graben system controlled by the slope-flat detachment fault, and the sedimentary center moved regularly. Tetconism and magmatism were the mechanism of fault depression development. The different degrees of magmatism participation between the main depression of Baiyun Sag and the eastern depression of Baiyun Sag not only led to the different structural styles and evolution process of the depression, but also the significant differences in the sedimentary filling system in the fault depression. In the broad and deep fault depressions that constitute the main depression of Baiyun sag, there were extremely thick strata of Upper Wenchang Formation-Enping Formation in the Middle and Late Eocene. In the gentle slope in the north and deep depression in the south, this stratum is composed of large delta system and deep lacustrine sedimentary system in turn. The eastern depression of Baiyun Sag was transformed by magma upwelling, which developed a broad-shallow fault depression with many uplifts and depressions, forming a small delta-shallow lake sedimentary system with several small sources, and the sediments were rich in pyroclastic rocks. The results are not only of great significance for the study of basin-forming mechanism in Baiyun Sag, and but also of important practical application value for oil and gas exploration in this sag.
The structure of faulted basins is mainly controlled by the tectonic action of boundary faults, but when magmatism occurs in different degrees during the development of basins, the structure of faulted basins will be significantly transformed and influenced. Based on the description and analysis of the differential evolution characteristics of fault depression structure in Baiyun Sag, Pearl River Mouth Basin, which is located in the northern margin of the South China Sea, in this paper it discusses the influence of the participation of magmatism on the structural style of the sag and the evolution of fault depression structure-stratum-sediment in the process of continental margin extension. The research shows that during the intense extension of the main depression in Baiyun Sag, magmatism was not obvious, brittle fracture occurred in the upper crust, and ductile extension thinning occurred in the middle and lower crust, resulting in the broad and deep fault depression controlled by crust-mantle detachment fault, and tectonism, namely, crustal extension detachment thinning, was the main mechanism of fault depression development. However, in the eastern depression of Baiyun Sag, after the early brittle fracture, a remarkable magmatic upwelling took place, which changed the structural strength of the upper crust, and the brittle-ductile transition plane moved upward, resulting in a broad and shallow fault depression controlled by the upper crust detachment fault. The fault depression structure was transformed by magmatic upwelling, showing a semi-graben system controlled by the slope-flat detachment fault, and the sedimentary center moved regularly. Tetconism and magmatism were the mechanism of fault depression development. The different degrees of magmatism participation between the main depression of Baiyun Sag and the eastern depression of Baiyun Sag not only led to the different structural styles and evolution process of the depression, but also the significant differences in the sedimentary filling system in the fault depression. In the broad and deep fault depressions that constitute the main depression of Baiyun sag, there were extremely thick strata of Upper Wenchang Formation-Enping Formation in the Middle and Late Eocene. In the gentle slope in the north and deep depression in the south, this stratum is composed of large delta system and deep lacustrine sedimentary system in turn. The eastern depression of Baiyun Sag was transformed by magma upwelling, which developed a broad-shallow fault depression with many uplifts and depressions, forming a small delta-shallow lake sedimentary system with several small sources, and the sediments were rich in pyroclastic rocks. The results are not only of great significance for the study of basin-forming mechanism in Baiyun Sag, and but also of important practical application value for oil and gas exploration in this sag.
2022, 47(7): 2317-2327.
doi: 10.3799/dqkx.2021.247
Abstract:
The characteristics and tectonic evolution of Mesozoic continental margin magmatic arc are crucial to the buried hill exploration and research in Pearl River Mouth Basin. By integrating studies of structural geology, petrology, geochronology, geochemistry and geophysics, it is confirmed that the basement is mainly Yanshan period complex, the lithology is mostly intermediate-acidic igneous and the most intense magmatic event is between 105-165 Ma. Regional tectonic studies suggest that during Mesozoic period, Pearl River Mouth Basin was in the margin magmatic arc environment caused by the subducted paleo-Pacific Ocean Plate. The magmatic rocks are enriched with fluid-indication elements and depleted in Ta-Nb-Ti. "Double layers" of composite volcanic rocks and deep igneous rocks developed. This study has reconstructed five episodes of formation and tectonic evolution of Mesozoic continental margin volcanic arc in Pearl River Mouth Basin, and revealed the orogenic foundation of buried hills in Pearl River Mouth Basin.
The characteristics and tectonic evolution of Mesozoic continental margin magmatic arc are crucial to the buried hill exploration and research in Pearl River Mouth Basin. By integrating studies of structural geology, petrology, geochronology, geochemistry and geophysics, it is confirmed that the basement is mainly Yanshan period complex, the lithology is mostly intermediate-acidic igneous and the most intense magmatic event is between 105-165 Ma. Regional tectonic studies suggest that during Mesozoic period, Pearl River Mouth Basin was in the margin magmatic arc environment caused by the subducted paleo-Pacific Ocean Plate. The magmatic rocks are enriched with fluid-indication elements and depleted in Ta-Nb-Ti. "Double layers" of composite volcanic rocks and deep igneous rocks developed. This study has reconstructed five episodes of formation and tectonic evolution of Mesozoic continental margin volcanic arc in Pearl River Mouth Basin, and revealed the orogenic foundation of buried hills in Pearl River Mouth Basin.
Late Mesozoic Magmatic Arc: Constraints from Well KP1-1-1 Detrital Zircon U-Pb Data, South China Sea
2022, 47(7): 2328-2336.
doi: 10.3799/dqkx.2022.033
Abstract:
The Late Mesozoic is an important tectonic episode for Paleo-Pacific slab subduction and magmatic arc evolution in the South China Sea. The low-metamorphosed sandstone drilled by KP1-1-1 belongs to a proximal deposition which helps to reveal tectonic characteristics of the magmatic arc provenance. Based on LA-ICPMS detrital zircon analysis, age components of 129-155 Ma, 155-172 Ma, and 172-196 Ma are identified from KP1-1-1 sandstone in the western Pearl River Mouth Basin, in accordance with regional tectono-magmatic events. These magmatic zircons which derive from arc-related magmatic source are characterized by low-temperature (551-786℃), enrichment of fluid-mobile elements (U, Th) and depletion of high field-strength elements (Nb, Hf and Ti). They are characterized by high element ratios of U/Yb (0.34-3.92), Sc/Yb (0.48-2.28), Hf/Th (14.4-186.6), and Th/Nb (24.3-462.7), indicating the related magmatism in a continental arc environment. The age component of 172-196 Ma from the sandstone registers the Early Jurassic Dongsha-Talun-Yandang magmatic arc further stretching southwest in East to South China Seas, as a result of oblique initial subduction of the Paleo-Pacific slab. The major component of 155-172 Ma reveals an intensified slab subduction and arc-related magmatism in South China Sea, comparable to voluminous granitic magmatism (165-150 Ma) in South China. The minor component of 129-155 Ma found, however, implies a reduced arc-related magmatism due to slow subduction or slab rollback, sharply in contrast to intensified rhyolite volcanism (120-160 Ma) developed in Zhejiang to Fujian coastal areas. The minimum U-Pb age 128.8 Ma of detrital zircon defines the stratigraphic age of KP1-1-1 sandstone as Cretaceous, not the latest Late Proterozoic to Early Paleozoic as traditionally treated.
The Late Mesozoic is an important tectonic episode for Paleo-Pacific slab subduction and magmatic arc evolution in the South China Sea. The low-metamorphosed sandstone drilled by KP1-1-1 belongs to a proximal deposition which helps to reveal tectonic characteristics of the magmatic arc provenance. Based on LA-ICPMS detrital zircon analysis, age components of 129-155 Ma, 155-172 Ma, and 172-196 Ma are identified from KP1-1-1 sandstone in the western Pearl River Mouth Basin, in accordance with regional tectono-magmatic events. These magmatic zircons which derive from arc-related magmatic source are characterized by low-temperature (551-786℃), enrichment of fluid-mobile elements (U, Th) and depletion of high field-strength elements (Nb, Hf and Ti). They are characterized by high element ratios of U/Yb (0.34-3.92), Sc/Yb (0.48-2.28), Hf/Th (14.4-186.6), and Th/Nb (24.3-462.7), indicating the related magmatism in a continental arc environment. The age component of 172-196 Ma from the sandstone registers the Early Jurassic Dongsha-Talun-Yandang magmatic arc further stretching southwest in East to South China Seas, as a result of oblique initial subduction of the Paleo-Pacific slab. The major component of 155-172 Ma reveals an intensified slab subduction and arc-related magmatism in South China Sea, comparable to voluminous granitic magmatism (165-150 Ma) in South China. The minor component of 129-155 Ma found, however, implies a reduced arc-related magmatism due to slow subduction or slab rollback, sharply in contrast to intensified rhyolite volcanism (120-160 Ma) developed in Zhejiang to Fujian coastal areas. The minimum U-Pb age 128.8 Ma of detrital zircon defines the stratigraphic age of KP1-1-1 sandstone as Cretaceous, not the latest Late Proterozoic to Early Paleozoic as traditionally treated.
2022, 47(7): 2337-2353.
doi: 10.3799/dqkx.2021.208
Abstract:
The northern continental margin of the South China Sea (SCS) developed a diagnostic crustal structure in the distal domain, which is characterized by "wide rift, thick basement, and prominent topographic variations of the top basement". These characteristics are significantly different from those of the typical magma-poor and magma-rich rifted margins. In order to decipher the origin of such crustal structure in the northern SCS, in this study it defines the nature of the basement in the distal margin based on the latest research progresses and the drilling results of the International Ocean Discovery Program (IODP), and discusses the detachment faults, magmatic additions and the tectono-magmatic interaction. The results suggest that several large-scale core complex structures were developed in the northern SCS during the early rifting (before 38 Ma), which was accompanied by voluminous magma intruding into the mid-lower crust. On the one hand, the emplacement of the syn-rift magma enhanced the ductile deformation of the mid-lower crust, resulting in the delocalization of the strain and the occurrence of the detachment in many places almost at the same time. On the other hand, the magmatism strongly affected the geometries of the detachment faults, resulting in the thickened basement. Finally, the syn-rift magmatism and the ductile flow of mid-lower crust are considered as the key factors to produce the wide rift in the northern SCS. The results would help to deepen the understanding of the crustal structure, deformation process and lithospheric thinning mechanism during the development of the rifted margins.
The northern continental margin of the South China Sea (SCS) developed a diagnostic crustal structure in the distal domain, which is characterized by "wide rift, thick basement, and prominent topographic variations of the top basement". These characteristics are significantly different from those of the typical magma-poor and magma-rich rifted margins. In order to decipher the origin of such crustal structure in the northern SCS, in this study it defines the nature of the basement in the distal margin based on the latest research progresses and the drilling results of the International Ocean Discovery Program (IODP), and discusses the detachment faults, magmatic additions and the tectono-magmatic interaction. The results suggest that several large-scale core complex structures were developed in the northern SCS during the early rifting (before 38 Ma), which was accompanied by voluminous magma intruding into the mid-lower crust. On the one hand, the emplacement of the syn-rift magma enhanced the ductile deformation of the mid-lower crust, resulting in the delocalization of the strain and the occurrence of the detachment in many places almost at the same time. On the other hand, the magmatism strongly affected the geometries of the detachment faults, resulting in the thickened basement. Finally, the syn-rift magmatism and the ductile flow of mid-lower crust are considered as the key factors to produce the wide rift in the northern SCS. The results would help to deepen the understanding of the crustal structure, deformation process and lithospheric thinning mechanism during the development of the rifted margins.
2022, 47(7): 2354-2373.
doi: 10.3799/dqkx.2022.035
Abstract:
Crust-mantle detachment faults and its sedimentary system response are the hotspots of the study on continental margin evolution in the world. In this paper it focuses on the Baiyun Sag in the Pearl River Mouth Basin under a systematic dissection. Combined with the new progress in the evolution of continental margins, it is revealed through long cable three-dimensional seismic data and comprehensive drilling interpretation that the main control fault zone in the southern Baiyun Sag is mainly composed of 4 rows of NEE-NE trending high-angle shovel-type crust-mantle detachment faults, which reach to the Moho Surface. Three stages of tectonic activities were identified, as isostatic rifting, detachment rifting, and fault-depression transformation. During the isostatic rifting stage (Lower Wenchang Formation), when the depression-controlling fault had not extended to the Moho Surface, axial steep-slope braided river delta-lacustrine deposition systems were developed, while the gentle slope provenance system was not well developed. During the detachment rifting stage (Upper Wenchang Formation), crust-mantle detachment faulted to the Moho Surface, showing strong horizontal extension and vertical drop, which led to the strong rotation, warping, uplifting and denudation of the hanging wall, and became the main source system of gentle slopes where large delta system developed. At the meantime, the north downshrown side of the fault became deep lake. During the fault-depression transition stage (Enping Formation), the detachment effect weakened and the subsidence increased significantly, which controlled the development of the large delta-lacustrine sedimentary system advancing in the NW-SE direction and the flexure of the gentle slope in the north. As a result, the tectonic evolution of the main control fault in the Baiyun Sag led the depositional systems transferred from the east-west axial braided river deltas in Lower Wenchang Formation to large deltas developed in gentle slopes in the Enping Formation, and fan delta sandstone developed as well in the steep slope belts around the sags consistently. Three types of large-scale reservoirs and lacustrine mudstone combinations have been identified, so the deep-water exploration targets have expanded to the middle and deep layers.
Crust-mantle detachment faults and its sedimentary system response are the hotspots of the study on continental margin evolution in the world. In this paper it focuses on the Baiyun Sag in the Pearl River Mouth Basin under a systematic dissection. Combined with the new progress in the evolution of continental margins, it is revealed through long cable three-dimensional seismic data and comprehensive drilling interpretation that the main control fault zone in the southern Baiyun Sag is mainly composed of 4 rows of NEE-NE trending high-angle shovel-type crust-mantle detachment faults, which reach to the Moho Surface. Three stages of tectonic activities were identified, as isostatic rifting, detachment rifting, and fault-depression transformation. During the isostatic rifting stage (Lower Wenchang Formation), when the depression-controlling fault had not extended to the Moho Surface, axial steep-slope braided river delta-lacustrine deposition systems were developed, while the gentle slope provenance system was not well developed. During the detachment rifting stage (Upper Wenchang Formation), crust-mantle detachment faulted to the Moho Surface, showing strong horizontal extension and vertical drop, which led to the strong rotation, warping, uplifting and denudation of the hanging wall, and became the main source system of gentle slopes where large delta system developed. At the meantime, the north downshrown side of the fault became deep lake. During the fault-depression transition stage (Enping Formation), the detachment effect weakened and the subsidence increased significantly, which controlled the development of the large delta-lacustrine sedimentary system advancing in the NW-SE direction and the flexure of the gentle slope in the north. As a result, the tectonic evolution of the main control fault in the Baiyun Sag led the depositional systems transferred from the east-west axial braided river deltas in Lower Wenchang Formation to large deltas developed in gentle slopes in the Enping Formation, and fan delta sandstone developed as well in the steep slope belts around the sags consistently. Three types of large-scale reservoirs and lacustrine mudstone combinations have been identified, so the deep-water exploration targets have expanded to the middle and deep layers.
2022, 47(7): 2374-2390.
doi: 10.3799/dqkx.2021.258
Abstract:
There is still a lack of systematic understanding of the evolution process of the Pearl River Mouth Basin since the Mesozoic and its response to the evolution of sedimentary environment. Based on the comparative analysis of the magmatic activity, architectural style of depression and its modification, typical structural deformation style and migration of sedimentary centers, the tectonic evolution of the Pearl River Mouth Basin in Meso-Cenozoic can be divided into 4 stages and 7 periods: (1) the evolution stage of the continental-margin magmatic arc and forearc basin, dominated by paleo-Pacific plate subduction, from Middle Jurassic to early Late Cretaceous (~170-90 Ma); (2) the evolution stage of peripheral foreland basin/post-orogenic collapse to active rift basin in back-arc area, dominated by the subduction retreat of Pacific plate, from Late Cretaceous to Middle Eocene (~90-43 Ma); (3) the evolution stage of passive continental margin, dominated by South China block's extrusion and proto-South China Sea subduction, from Middle Eocene to Middle Miocene (~43-10 Ma); (4) the evolution stage of compression and tensional-shear faults, dominated by NWW upward thrust of the Philippine Sea Plate, since the Late Miocene (~10-0 Ma).~90 Ma, ~43 Ma and~10 Ma are three important periods of tectonic transformation. The subduction of the West Pacific transformed from Andean-type subduction to West Pacific-type subduction in~90 Ma, and the rifting transformed from active rift to passive continental margin extension in ~43 Ma, and the tectonic environment transformed from passive continental margin extension to compression and wrench in ~10 Ma. In this process, with the development and extinction of the proto-South China Sea and the South China Sea, the sedimentary environment in the Cenozoic rifting period gradually transgressed from east to west and from south to north. In the post-rifting period, under the control of phased differential subsidence from south to north, depositional environment transformed from shallow water to deep water, which resulted in significant zoning differences of the petroleum geological conditions in Zhu Ⅰ/Ⅲ, Zhu Ⅱ and Zhu Ⅳ depressions.
There is still a lack of systematic understanding of the evolution process of the Pearl River Mouth Basin since the Mesozoic and its response to the evolution of sedimentary environment. Based on the comparative analysis of the magmatic activity, architectural style of depression and its modification, typical structural deformation style and migration of sedimentary centers, the tectonic evolution of the Pearl River Mouth Basin in Meso-Cenozoic can be divided into 4 stages and 7 periods: (1) the evolution stage of the continental-margin magmatic arc and forearc basin, dominated by paleo-Pacific plate subduction, from Middle Jurassic to early Late Cretaceous (~170-90 Ma); (2) the evolution stage of peripheral foreland basin/post-orogenic collapse to active rift basin in back-arc area, dominated by the subduction retreat of Pacific plate, from Late Cretaceous to Middle Eocene (~90-43 Ma); (3) the evolution stage of passive continental margin, dominated by South China block's extrusion and proto-South China Sea subduction, from Middle Eocene to Middle Miocene (~43-10 Ma); (4) the evolution stage of compression and tensional-shear faults, dominated by NWW upward thrust of the Philippine Sea Plate, since the Late Miocene (~10-0 Ma).~90 Ma, ~43 Ma and~10 Ma are three important periods of tectonic transformation. The subduction of the West Pacific transformed from Andean-type subduction to West Pacific-type subduction in~90 Ma, and the rifting transformed from active rift to passive continental margin extension in ~43 Ma, and the tectonic environment transformed from passive continental margin extension to compression and wrench in ~10 Ma. In this process, with the development and extinction of the proto-South China Sea and the South China Sea, the sedimentary environment in the Cenozoic rifting period gradually transgressed from east to west and from south to north. In the post-rifting period, under the control of phased differential subsidence from south to north, depositional environment transformed from shallow water to deep water, which resulted in significant zoning differences of the petroleum geological conditions in Zhu Ⅰ/Ⅲ, Zhu Ⅱ and Zhu Ⅳ depressions.
2022, 47(7): 2391-2409.
doi: 10.3799/dqkx.2022.215
Abstract:
The Pearl River Mouth Basin developed many types of Cenozoic detachment depressions from shallow-water area to deep-water area. Among them, the detachment depression in continental shelf shallow water area is an important window to explore the detachment structural deformation and its sedimentary filling response. Based on the detailed analysis of seismic and drilling data, the characteristics of low-angle detachment fault system in Enping Sag are studied, and the control factors, deformation process and sedimentary filling response mechanism of structural deformation in detachment fault depression are discussed. The research shows that the low-angle boundary normal fault in Enping Sag is an inter-crust detachment fault, with a length of about 50 km and an average dip angle of 17.5°, deepest reaches to the middle-lower crust. During the rifting period, the fault-dip transformed from medium-low angle to low angle. The detachment fault was formed on the basis of the pre-existing thrust fault in the Mesozoic era, associated with the ductile shear dome of the middle-lower crust and the boundary regulating strike slip fault, and jointly controlled the formation of three types of subbasin structures, such as balanced deep detachment, forward spreading wide detachment and migration compound detachment subbasin. It can be divided into three rifting stages with different sedimentary filling responses due to different structural deformation. (1) In the homogeneous rifting stage at Early Wenchang period, the extension stress was concentrated on the weak surface of the pre-existing thrust fault, and the rapid rift formed narrow and deep homogeneous half-grabens, which developed thick medium-deep lakes. (2) In the detachment extensional stage at late Wenchang period, the sag developed into a wide and shallow fault depression with differential sedimentation and filling in the east and west due to differential structural deformation. In the western sag, the weak uplift of the ductile shear dome and the strong strike slip of the boundary strike slip fault controlled self migrating medium-deep lacustrine source rocks and large-scale braided river delta turbidite sedimentary system developed in Enping 17 Subsag. In the western sag, the strong uplift of ductile shear dome controlled the jumping and allochthonous migration of sedimentary center from Enping 12 Subsag to Enping 18 Subsag. A large fan delta was developed in the transition trending slope. (3) In the detachment-depression transition stage at Enping period, the structure changed from simple shear to pure shear deformation, and the sedimentation changed from internally drainage to large shallow braided river delta lacustrine filling dominated by externally drained conditions. The low-angle detachment depression has different structural deformation and sedimentary filling from the high-angle brittle fault depression. The research results have significance guiding value for the prediction of source rocks and deep reservoirs in Enping Sag, and for the study of structural deformation and sedimentary filling of similar detachment fault depressions in the northern continental margin of the South China Sea.
The Pearl River Mouth Basin developed many types of Cenozoic detachment depressions from shallow-water area to deep-water area. Among them, the detachment depression in continental shelf shallow water area is an important window to explore the detachment structural deformation and its sedimentary filling response. Based on the detailed analysis of seismic and drilling data, the characteristics of low-angle detachment fault system in Enping Sag are studied, and the control factors, deformation process and sedimentary filling response mechanism of structural deformation in detachment fault depression are discussed. The research shows that the low-angle boundary normal fault in Enping Sag is an inter-crust detachment fault, with a length of about 50 km and an average dip angle of 17.5°, deepest reaches to the middle-lower crust. During the rifting period, the fault-dip transformed from medium-low angle to low angle. The detachment fault was formed on the basis of the pre-existing thrust fault in the Mesozoic era, associated with the ductile shear dome of the middle-lower crust and the boundary regulating strike slip fault, and jointly controlled the formation of three types of subbasin structures, such as balanced deep detachment, forward spreading wide detachment and migration compound detachment subbasin. It can be divided into three rifting stages with different sedimentary filling responses due to different structural deformation. (1) In the homogeneous rifting stage at Early Wenchang period, the extension stress was concentrated on the weak surface of the pre-existing thrust fault, and the rapid rift formed narrow and deep homogeneous half-grabens, which developed thick medium-deep lakes. (2) In the detachment extensional stage at late Wenchang period, the sag developed into a wide and shallow fault depression with differential sedimentation and filling in the east and west due to differential structural deformation. In the western sag, the weak uplift of the ductile shear dome and the strong strike slip of the boundary strike slip fault controlled self migrating medium-deep lacustrine source rocks and large-scale braided river delta turbidite sedimentary system developed in Enping 17 Subsag. In the western sag, the strong uplift of ductile shear dome controlled the jumping and allochthonous migration of sedimentary center from Enping 12 Subsag to Enping 18 Subsag. A large fan delta was developed in the transition trending slope. (3) In the detachment-depression transition stage at Enping period, the structure changed from simple shear to pure shear deformation, and the sedimentation changed from internally drainage to large shallow braided river delta lacustrine filling dominated by externally drained conditions. The low-angle detachment depression has different structural deformation and sedimentary filling from the high-angle brittle fault depression. The research results have significance guiding value for the prediction of source rocks and deep reservoirs in Enping Sag, and for the study of structural deformation and sedimentary filling of similar detachment fault depressions in the northern continental margin of the South China Sea.
2022, 47(7): 2410-2420.
doi: 10.3799/dqkx.2022.002
Abstract:
The Tibetan Uplift and its corresponding environmental effect are widely considered as one of the most significant global geological events during the Cenozoic. Specifically, the generation of loess and continental-scale drainage networks within the East Asia has attracted increasing attention. As the link connecting the South China Continent and the northern South China Sea (SCS) of the "source-to-sink" system, the Pearl River is the focus of sedimentology and petroleum geology research. Its evolutionary process and controlling factors are of great significance in revealing the landform development of both Yunnan-Guizhou Uplift and SE Tibetan margin. Based on the combination of elemental geochemistry and detrital zircon U-Pb dating results, in this paper it provides a research synthesis of the Pearl River tributaries and the Pearl River Mouth Basin to unravel the birth and development history of the Pearl River system in detail. The Pearl River system was initially formed in the Early Oligocene, and the drainage basin was limited to the South China coastal areas. In the Late Oligocene, the Pearl River eroded westward greatly reaching the eastern margin of the Yunnan-Guizhou uplift. Since the Miocene, the Pearl River largely expanded westward and northward, and deeply cut across gorges within the hinterland of the Yunnan-Guizhou uplift. Since then, the Pearl River has established its general framework over the South China Continent. The rapid expansion of the Pearl River at the Oligocene/Miocene boundary (23 Ma) is in consistence with the contemporaneous Three Gorges connection of the Yangtze River and the loess formation. These events are not only closely related to the dramatic uplift of the Tibetan Plateau during this time, but also substantial geological records of the west-high-east-low landform generation in the East Asia region.
The Tibetan Uplift and its corresponding environmental effect are widely considered as one of the most significant global geological events during the Cenozoic. Specifically, the generation of loess and continental-scale drainage networks within the East Asia has attracted increasing attention. As the link connecting the South China Continent and the northern South China Sea (SCS) of the "source-to-sink" system, the Pearl River is the focus of sedimentology and petroleum geology research. Its evolutionary process and controlling factors are of great significance in revealing the landform development of both Yunnan-Guizhou Uplift and SE Tibetan margin. Based on the combination of elemental geochemistry and detrital zircon U-Pb dating results, in this paper it provides a research synthesis of the Pearl River tributaries and the Pearl River Mouth Basin to unravel the birth and development history of the Pearl River system in detail. The Pearl River system was initially formed in the Early Oligocene, and the drainage basin was limited to the South China coastal areas. In the Late Oligocene, the Pearl River eroded westward greatly reaching the eastern margin of the Yunnan-Guizhou uplift. Since the Miocene, the Pearl River largely expanded westward and northward, and deeply cut across gorges within the hinterland of the Yunnan-Guizhou uplift. Since then, the Pearl River has established its general framework over the South China Continent. The rapid expansion of the Pearl River at the Oligocene/Miocene boundary (23 Ma) is in consistence with the contemporaneous Three Gorges connection of the Yangtze River and the loess formation. These events are not only closely related to the dramatic uplift of the Tibetan Plateau during this time, but also substantial geological records of the west-high-east-low landform generation in the East Asia region.
2022, 47(7): 2421-2432.
doi: 10.3799/dqkx.2022.157
Abstract:
The sedimentary system controlled by the narrow continental shelf-faulted continental slope in the northern South China Sea is very poorly studied. Guided by the coupling idea of "source-conduit-sink" and based on petrological characteristics, logging facies and seismic facies analysis, the vertical superposition and lateral migration characteristics of submarine fan sand bodies of the Zhuhai Formation in Jieyang Sag are characterized, and its evolution history is divided into the initial formation period of Member Ⅳ of Zhuhai Formation, the development and expansion period of Member Ⅲ-Ⅱ of Zhuhai Formation and the shrinkage and extinction period of Member Ⅰ of Zhuhai Formation. It is considered that the formation of large submarine fan of Zhuhai Formation in Jieyang Sag was controlled by the coupling effect of three key factors: easily eroded Mesozoic provenance, multi-stage rapid decline of relative sea level, favorable geomorphology of the narrow continental shelf -faulted continental slope. Under the background of rapid decline of regional third order relative sea level, the sand-prone Lower Cretaceous was rapidly eroded from the Dongsha uplift on the north side of Jieyang Sag. The sediments were transported directly along the erosion downcut valley or the underwater distributary channel of the small shelf-margin delta in the narrow continental shelf area, adjusted along the fault slope break zone or structural transition zone, and continued to be transported to the lower slope basin in the form of gravity flow through the canyon channels to form a large submarine fan.
The sedimentary system controlled by the narrow continental shelf-faulted continental slope in the northern South China Sea is very poorly studied. Guided by the coupling idea of "source-conduit-sink" and based on petrological characteristics, logging facies and seismic facies analysis, the vertical superposition and lateral migration characteristics of submarine fan sand bodies of the Zhuhai Formation in Jieyang Sag are characterized, and its evolution history is divided into the initial formation period of Member Ⅳ of Zhuhai Formation, the development and expansion period of Member Ⅲ-Ⅱ of Zhuhai Formation and the shrinkage and extinction period of Member Ⅰ of Zhuhai Formation. It is considered that the formation of large submarine fan of Zhuhai Formation in Jieyang Sag was controlled by the coupling effect of three key factors: easily eroded Mesozoic provenance, multi-stage rapid decline of relative sea level, favorable geomorphology of the narrow continental shelf -faulted continental slope. Under the background of rapid decline of regional third order relative sea level, the sand-prone Lower Cretaceous was rapidly eroded from the Dongsha uplift on the north side of Jieyang Sag. The sediments were transported directly along the erosion downcut valley or the underwater distributary channel of the small shelf-margin delta in the narrow continental shelf area, adjusted along the fault slope break zone or structural transition zone, and continued to be transported to the lower slope basin in the form of gravity flow through the canyon channels to form a large submarine fan.
2022, 47(7): 2433-2453.
doi: 10.3799/dqkx.2022.156
Abstract:
Based on 3D seismic data, drilling and logging data, the tectonic evolution and its controlled sedimentary filling process of Wenchang Formation in Baiyun Sag were studied in detail by using new methods such as the restoration of original form structure section, enhanced seismic facies analysis and seismic scanning interpretation of sand body in order to explore the structure-sedimentary response relationship of faulted lake basin. The study shows that in response to the activity process of "weak-very strong-relatively strong-weak" of sag-controlling faults, Baiyun Sag experienced four tectonic evolution stages during the Wenchang Formation: initial fault depression stage (WCSQ1), early stage of strong fault depression (WCSQ2), late stage of strong fault depression (WCSQ3) and weak fault depression stage (WCSQ4, WCSQ5). Correspondingly, Baiyun Main Sag underwent the sedimentary evolution processes of fluvial-lacustrine, ultra-deep lake occurrence, ultra-deep lake filling, deep lake-shallow lake occurrence. The northern gentle slope zone located on the tilting side of rotating fault block mainly developed a fluvial-shallow lake transitional environment and a braided river delta depositional system of large-medium scale. The southern steep slope zone located on the plunging side of rotating fault block mainly developed a semi-deep lacustrine to deep lacustrine environment and a nearshore subaqueous fan-fan delta depositional system. The center of lake basin mainly developed a deep lake-ultra-deep lake environment and argillaceous deposits. The deposits of turbidite fan were developed around the deep lake. However, the Baiyun East Sag appeared as a landform of multiple uplift-depression formed by steep slope and magmatic underplating, and mainly developed small-scale inshore subaqueous fan-fan delta sedimentary system with volcaniclastic sediments. The porosity of sand bodies of Wenchang Formation was jointly controlled by the activity intensity of sag-controlling faults and magma, provenance system and paleogeographic characteristics of secondary depressions in Baiyun Sag.
Based on 3D seismic data, drilling and logging data, the tectonic evolution and its controlled sedimentary filling process of Wenchang Formation in Baiyun Sag were studied in detail by using new methods such as the restoration of original form structure section, enhanced seismic facies analysis and seismic scanning interpretation of sand body in order to explore the structure-sedimentary response relationship of faulted lake basin. The study shows that in response to the activity process of "weak-very strong-relatively strong-weak" of sag-controlling faults, Baiyun Sag experienced four tectonic evolution stages during the Wenchang Formation: initial fault depression stage (WCSQ1), early stage of strong fault depression (WCSQ2), late stage of strong fault depression (WCSQ3) and weak fault depression stage (WCSQ4, WCSQ5). Correspondingly, Baiyun Main Sag underwent the sedimentary evolution processes of fluvial-lacustrine, ultra-deep lake occurrence, ultra-deep lake filling, deep lake-shallow lake occurrence. The northern gentle slope zone located on the tilting side of rotating fault block mainly developed a fluvial-shallow lake transitional environment and a braided river delta depositional system of large-medium scale. The southern steep slope zone located on the plunging side of rotating fault block mainly developed a semi-deep lacustrine to deep lacustrine environment and a nearshore subaqueous fan-fan delta depositional system. The center of lake basin mainly developed a deep lake-ultra-deep lake environment and argillaceous deposits. The deposits of turbidite fan were developed around the deep lake. However, the Baiyun East Sag appeared as a landform of multiple uplift-depression formed by steep slope and magmatic underplating, and mainly developed small-scale inshore subaqueous fan-fan delta sedimentary system with volcaniclastic sediments. The porosity of sand bodies of Wenchang Formation was jointly controlled by the activity intensity of sag-controlling faults and magma, provenance system and paleogeographic characteristics of secondary depressions in Baiyun Sag.
2022, 47(7): 2454-2467.
doi: 10.3799/dqkx.2022.017
Abstract:
The Zhuhai Formation and Enping Formation in Baiyun Sag of Pearl River Mouth Basin are important strata for deep oil and gas exploration. Understanding the basic characteristics of deep reservoirs and analyzing the development characteristics and controlling factors of effective reservoirs can provide necessary guidance and support for deep oil and gas exploration to find favorable target layers and target areas. Based on the analyses of petrology and mineralogy, diagenesis, pore development characteristics and sedimentary facies types of deep reservoirs, the basic characteristics of deep reservoirs are clarified. Deep reservoirs are mainly low porosity-low permeability (LL) and tight reservoirs. Compaction is the main reason for the deterioration of deep reservoir, and carbonate cementation and overgrowth of quartz are the main authigenic minerals. Pore types are mainly intergranular dissolved pores and intragranular dissolved pores. Effective reservoirs are mainly LL reservoirs and reservoirs that are better than LL reservoirs. Porosity is generally maintained at about 10%, and permeability varies widely. Sedimentary facies, dissolution and overpressure are the main controlling factors of deep effective reservoir. Medium- and coarse-grained sandstones have better development conditions of primary and secondary pores, higher permeability, weaker porosity reduction by cementation and stronger porosity increase by dissolution. Dissolution is the key constructive diagenesis in deep reservoir, and dissolution pores are the dominate pore type in deep layer. Overpressure conduction is conducive to the activity of acid fluid and the migration of dissolved substances, which is of positive significance to the formation of dissolution pores. Distributary channel and subaqueous distributary channel sandbodies are the main carriers of medium and coarse-grained sandstone and should be the preferred target of deep oil and gas exploration.
The Zhuhai Formation and Enping Formation in Baiyun Sag of Pearl River Mouth Basin are important strata for deep oil and gas exploration. Understanding the basic characteristics of deep reservoirs and analyzing the development characteristics and controlling factors of effective reservoirs can provide necessary guidance and support for deep oil and gas exploration to find favorable target layers and target areas. Based on the analyses of petrology and mineralogy, diagenesis, pore development characteristics and sedimentary facies types of deep reservoirs, the basic characteristics of deep reservoirs are clarified. Deep reservoirs are mainly low porosity-low permeability (LL) and tight reservoirs. Compaction is the main reason for the deterioration of deep reservoir, and carbonate cementation and overgrowth of quartz are the main authigenic minerals. Pore types are mainly intergranular dissolved pores and intragranular dissolved pores. Effective reservoirs are mainly LL reservoirs and reservoirs that are better than LL reservoirs. Porosity is generally maintained at about 10%, and permeability varies widely. Sedimentary facies, dissolution and overpressure are the main controlling factors of deep effective reservoir. Medium- and coarse-grained sandstones have better development conditions of primary and secondary pores, higher permeability, weaker porosity reduction by cementation and stronger porosity increase by dissolution. Dissolution is the key constructive diagenesis in deep reservoir, and dissolution pores are the dominate pore type in deep layer. Overpressure conduction is conducive to the activity of acid fluid and the migration of dissolved substances, which is of positive significance to the formation of dissolution pores. Distributary channel and subaqueous distributary channel sandbodies are the main carriers of medium and coarse-grained sandstone and should be the preferred target of deep oil and gas exploration.
2022, 47(7): 2468-2480.
doi: 10.3799/dqkx.2022.239
Abstract:
How the geothermal gradient affects the diagenetic evolution of sandstone and the change of reservoir physical properties is a hot issue in the field of geosciences. Taking the Baiyun deep water area with a highly variable geothermal gradient distribution as an example, through the analysis of a large number of samples from different geothermal gradient areas, with a geothermal gradient of 0.1 ℃/100 m as the progressive interval, in this paper it compares and analyzes the variation trend of the permeability of sandstone reservoirs of different grain sizes with burial depth in different geothermal gradient intervals, establishes a quantitative geological prediction model of sandstone permeability and shows the inherent relationship between the reservoir properties of sandstone and the stratum geothermal gradient.The results show that within a certain buried depth range, with the increase of geothermal gradient, the difference of lower buried depth decreases step by step with the decrease of permeability by an order of magnitude. In the same geothermal gradient range, for pebbly sandstone, coarse-grained sandstone, medium-sized sandstone and fine-grained sandstone with high composition maturity and low plastic debris, the difference of lower limit of equal permeability between adjacent grain size sandstones is similar. With the increase of geothermal gradient, the difference of lower limit of equal permeability between adjacent grain size sandstones decreases regularly. The thickness of low permeability and ultra-low permeability sandstone reservoirs decreases with the increase of geothermal gradient, and the ultra-low permeability lower limit of coarse-grained sandstone can become the limit depth of deepwater conventional exploration. This study has important scientific significance for revealing the influence of geothermal gradient on the diagenetic evolution of sandstone and physical property evolution effect, and has a positive guiding role for oil and gas exploration.
How the geothermal gradient affects the diagenetic evolution of sandstone and the change of reservoir physical properties is a hot issue in the field of geosciences. Taking the Baiyun deep water area with a highly variable geothermal gradient distribution as an example, through the analysis of a large number of samples from different geothermal gradient areas, with a geothermal gradient of 0.1 ℃/100 m as the progressive interval, in this paper it compares and analyzes the variation trend of the permeability of sandstone reservoirs of different grain sizes with burial depth in different geothermal gradient intervals, establishes a quantitative geological prediction model of sandstone permeability and shows the inherent relationship between the reservoir properties of sandstone and the stratum geothermal gradient.The results show that within a certain buried depth range, with the increase of geothermal gradient, the difference of lower buried depth decreases step by step with the decrease of permeability by an order of magnitude. In the same geothermal gradient range, for pebbly sandstone, coarse-grained sandstone, medium-sized sandstone and fine-grained sandstone with high composition maturity and low plastic debris, the difference of lower limit of equal permeability between adjacent grain size sandstones is similar. With the increase of geothermal gradient, the difference of lower limit of equal permeability between adjacent grain size sandstones decreases regularly. The thickness of low permeability and ultra-low permeability sandstone reservoirs decreases with the increase of geothermal gradient, and the ultra-low permeability lower limit of coarse-grained sandstone can become the limit depth of deepwater conventional exploration. This study has important scientific significance for revealing the influence of geothermal gradient on the diagenetic evolution of sandstone and physical property evolution effect, and has a positive guiding role for oil and gas exploration.
2022, 47(7): 2481-2493.
doi: 10.3799/dqkx.2022.254
Abstract:
The Paleogene oil and gas accumulation in Lufeng Sag of the Pearl River Mouth Basin is jointly controlled by a variety of dynamic factors, so the favorable reservoir forming area can not be predicted completely according to the classical buoyancy reservoir forming theory. By analyzing the discovered oil and gas reservoirs in the study area, in this paper it reveals that three driving forces play a key role in oil and gas accumulation, including low-level energy (anticline oil and gas reservoir), low-pressure energy (fault block oil and gas reservoir) and low interface energy (lithologic stratigraphic oil and gas reservoir). Under each dynamic action, oil and gas accumulation is controlled by four functional elements and their temporal and spatial combination: effective source rock, excellent facies reservoir, regional cap rock and low potential zone. By establishing a multi⁃dynamic⁃factor composite reservoir forming model, the favorable reservoir forming zones of four target layers in Lufeng Sag are predicted and evaluated, and 10 most favorable targets are selected, which provides a scientific basis for deepening oil and gas exploration and optimizing drilling targets in the study area.
The Paleogene oil and gas accumulation in Lufeng Sag of the Pearl River Mouth Basin is jointly controlled by a variety of dynamic factors, so the favorable reservoir forming area can not be predicted completely according to the classical buoyancy reservoir forming theory. By analyzing the discovered oil and gas reservoirs in the study area, in this paper it reveals that three driving forces play a key role in oil and gas accumulation, including low-level energy (anticline oil and gas reservoir), low-pressure energy (fault block oil and gas reservoir) and low interface energy (lithologic stratigraphic oil and gas reservoir). Under each dynamic action, oil and gas accumulation is controlled by four functional elements and their temporal and spatial combination: effective source rock, excellent facies reservoir, regional cap rock and low potential zone. By establishing a multi⁃dynamic⁃factor composite reservoir forming model, the favorable reservoir forming zones of four target layers in Lufeng Sag are predicted and evaluated, and 10 most favorable targets are selected, which provides a scientific basis for deepening oil and gas exploration and optimizing drilling targets in the study area.
2022, 47(7): 2494-2508.
doi: 10.3799/dqkx.2022.253
Abstract:
Many types of oil and gas resources have been developed in the Paleogene of Lufeng Depression, Pearl River Mouth Basin, especially the complex and reformed oil and gas reservoirs with various characteristics. It is difficult to explain the genetic mechanism and distribution law of oil and gas reservoirs by using the classical "petroleum system" theory. Based on the new concept of the whole petroleum system, in this paper it expounds their formation and distribution. It is found that during the tight evolution of Paleogene reservoirs, the two sets of source rocks of Wenchang Formation and Enping Formation provided three kinds of original hydrocarbon quantities: early discharged hydrocarbon, late discharged hydrocarbon and retained hydrocarbon in the source. Due to the diagenetic compaction difference, the sandstone reservoirs inside and around the source rock developed oil and gas free dynamic field, limited dynamic field and bound dynamic field, The coupling effect of three kinds of original hydrocarbon quantities and three dynamic fields in the whole oil and gas system forms an orderly distribution of "shale oil and gas, tight oil and gas and conventional oil and gas" from bottom to top. This understanding of regularity has important guiding significance for the distribution prediction and exploration of different types of oil and gas resources in the study area.
Many types of oil and gas resources have been developed in the Paleogene of Lufeng Depression, Pearl River Mouth Basin, especially the complex and reformed oil and gas reservoirs with various characteristics. It is difficult to explain the genetic mechanism and distribution law of oil and gas reservoirs by using the classical "petroleum system" theory. Based on the new concept of the whole petroleum system, in this paper it expounds their formation and distribution. It is found that during the tight evolution of Paleogene reservoirs, the two sets of source rocks of Wenchang Formation and Enping Formation provided three kinds of original hydrocarbon quantities: early discharged hydrocarbon, late discharged hydrocarbon and retained hydrocarbon in the source. Due to the diagenetic compaction difference, the sandstone reservoirs inside and around the source rock developed oil and gas free dynamic field, limited dynamic field and bound dynamic field, The coupling effect of three kinds of original hydrocarbon quantities and three dynamic fields in the whole oil and gas system forms an orderly distribution of "shale oil and gas, tight oil and gas and conventional oil and gas" from bottom to top. This understanding of regularity has important guiding significance for the distribution prediction and exploration of different types of oil and gas resources in the study area.
2022, 47(7): 2509-2520.
doi: 10.3799/dqkx.2022.154
Abstract:
From the Early Paleocene to the end of the Oligocene, Wushi Sag of the Beibuwan Basin experienced multiple phases of extension. A group of extensional decollement faults formed during the 2nd phase of rifting, but their formation mechanism and evolution process are not clear. Based on the new high-quality 3-D seismic data obtained in the process of petroleum exploration, an in-depth analysis of the extensional decollement faults in the Wushi East subsag is conducted in this study. The results show that there are 7 extensional decollement faults (Fa‒Fg) in the Wushi East subsag, which are distributed in the near E-W or NE-SW direction. These decollement faults, together with north-dipping No.7 boundary fault, controlled sedimentation from the 1st Member of Liushagang Formation to the 1st Member of Weizhou Formation, which formed a huge rollover anticline. In terms of evolution, during the Early-Middle Eocene, the basin was a graben or half-graben controlled by the NE-SW No.7 boundary fault and other local small basement faults. The 3rd Member of Liushagang Formation strata was discretely distributed and was overlain by thick layer oil shale of the 2nd Member of Liushagang Formation. From the Late Eocene to the Late Oligocene, 1st Member of Liushagang Formation to the 1st Member of Weizhou Formation deposited in the basin, which was controlled by the oppositely dipping extensional decollement faults and the No.7 boundary fault. From the Early Miocene to the present, the basin changed into a sag basin. This study has depicted the geometry of extensional decollement structure which formed during the second episodic rift phase of Wushi East subsag, analyzed the growth and linkage pattern of decollement faults, and proposed the decollement faults upslope-ward migration model, which has a great significance for solving the problems of oil and gas migration, storage and preservation.
From the Early Paleocene to the end of the Oligocene, Wushi Sag of the Beibuwan Basin experienced multiple phases of extension. A group of extensional decollement faults formed during the 2nd phase of rifting, but their formation mechanism and evolution process are not clear. Based on the new high-quality 3-D seismic data obtained in the process of petroleum exploration, an in-depth analysis of the extensional decollement faults in the Wushi East subsag is conducted in this study. The results show that there are 7 extensional decollement faults (Fa‒Fg) in the Wushi East subsag, which are distributed in the near E-W or NE-SW direction. These decollement faults, together with north-dipping No.7 boundary fault, controlled sedimentation from the 1st Member of Liushagang Formation to the 1st Member of Weizhou Formation, which formed a huge rollover anticline. In terms of evolution, during the Early-Middle Eocene, the basin was a graben or half-graben controlled by the NE-SW No.7 boundary fault and other local small basement faults. The 3rd Member of Liushagang Formation strata was discretely distributed and was overlain by thick layer oil shale of the 2nd Member of Liushagang Formation. From the Late Eocene to the Late Oligocene, 1st Member of Liushagang Formation to the 1st Member of Weizhou Formation deposited in the basin, which was controlled by the oppositely dipping extensional decollement faults and the No.7 boundary fault. From the Early Miocene to the present, the basin changed into a sag basin. This study has depicted the geometry of extensional decollement structure which formed during the second episodic rift phase of Wushi East subsag, analyzed the growth and linkage pattern of decollement faults, and proposed the decollement faults upslope-ward migration model, which has a great significance for solving the problems of oil and gas migration, storage and preservation.
2022, 47(7): 2521-2535.
doi: 10.3799/dqkx.2022.106
Abstract:
Lacustrine rift basin is characterized by multiple input systems and complex paleo-geomorphology, and a source-to-sink analysis can help improve sandstone prediction. Based on logging and 3D seismic data, this study distinguishes concordant and discordant input systems and establishes the spatio-temporal distribution pattern of depositional systems within the C Sag, Weixinan Depression. The results indicate that the C Sag was supplied by the northern and southern transverse input systems as well as the western axial system during deposition of the third member of Liushagang Formation, and the southern system can be further divided into three second-order subsystems (i.e., subsystems S-Ⅰ, S-Ⅱ, S-Ⅲ). The axial system with gentle catchment and wide valley was characterized as a concordant input system with steady flux and tractive flow, as manifested by a braided delta with correlative grain size and sand ratio. In contrast, the discordant transverse input system, with a steep catchment and incised valleys (e.g., sub-system S-Ⅱ) was characterized by sediment pulse and gravity flow, as manifested by basin floor fan and fan delta with thick mudstone intercalated with thin conglomerate-bearing layer. The axial braided delta developed in the lower part of third member of Liushagang Formation was distributed mostly in the northern C Sag, as a result of intensive transverse sediment contributions from southern Weixinan Low Uplift. The reduced sediment flux from transverse input system, however, resulted in southward shifted axial delta in the upper part of third member of Liushagang Formation. Through a source-to-sink analysis of the C Sag, this study demonstrates that different input systems and interactions between depositional systems have exerted important controls on the spatio-temporal distribution patterns of favorable sandstone, with implications for hydrocarbon explorations in C Sag and other lacustrine rift basins with similar characteristics.
Lacustrine rift basin is characterized by multiple input systems and complex paleo-geomorphology, and a source-to-sink analysis can help improve sandstone prediction. Based on logging and 3D seismic data, this study distinguishes concordant and discordant input systems and establishes the spatio-temporal distribution pattern of depositional systems within the C Sag, Weixinan Depression. The results indicate that the C Sag was supplied by the northern and southern transverse input systems as well as the western axial system during deposition of the third member of Liushagang Formation, and the southern system can be further divided into three second-order subsystems (i.e., subsystems S-Ⅰ, S-Ⅱ, S-Ⅲ). The axial system with gentle catchment and wide valley was characterized as a concordant input system with steady flux and tractive flow, as manifested by a braided delta with correlative grain size and sand ratio. In contrast, the discordant transverse input system, with a steep catchment and incised valleys (e.g., sub-system S-Ⅱ) was characterized by sediment pulse and gravity flow, as manifested by basin floor fan and fan delta with thick mudstone intercalated with thin conglomerate-bearing layer. The axial braided delta developed in the lower part of third member of Liushagang Formation was distributed mostly in the northern C Sag, as a result of intensive transverse sediment contributions from southern Weixinan Low Uplift. The reduced sediment flux from transverse input system, however, resulted in southward shifted axial delta in the upper part of third member of Liushagang Formation. Through a source-to-sink analysis of the C Sag, this study demonstrates that different input systems and interactions between depositional systems have exerted important controls on the spatio-temporal distribution patterns of favorable sandstone, with implications for hydrocarbon explorations in C Sag and other lacustrine rift basins with similar characteristics.
2022, 47(7): 2536-2548.
doi: 10.3799/dqkx.2021.246
Abstract:
In order to clarify the tectono-stratigraphic framework and genetic mechanism of the Nansha trough basin, in this paper, the quantitative calculation of fault activity and subsidence history is carried out based on the interpretation of regional 2D seismic data in the Nansha trough. Four first-order sequence interfaces (Tg, T60, T50 and T0) have been identified in the Nansha trough basin. On the basis of these four first-order sequence interfaces, the Nansha trough basin can be divided into three basin prototypes: the Paleocene-Oligocene (Tg‒T60) rift basin, the Early Miocene (T60‒T50) depression basin and the Middle Miocene (T50‒T0) foreland basin. From the Cenozoic, the Nansha trough basin has gradually migrated from NW to SE. Comparative analysis from the previous study shows that the Nansha trough foreland basin is formed by the superposition of multi-phased foreland basins. Bounded by the Sarawak orogenic unconformity, the deep regional unconformity and the shallow regional unconformity, the Nansha trough foreland basin can be divided into three stages of the foreland basin: the Early Oligocene to Miocene, the Middle Miocene to the Early Pliocene and the Late Pliocene to present. The Nansha trough belongs to the third phase of the whole foreland basin and is still developing now.
In order to clarify the tectono-stratigraphic framework and genetic mechanism of the Nansha trough basin, in this paper, the quantitative calculation of fault activity and subsidence history is carried out based on the interpretation of regional 2D seismic data in the Nansha trough. Four first-order sequence interfaces (Tg, T60, T50 and T0) have been identified in the Nansha trough basin. On the basis of these four first-order sequence interfaces, the Nansha trough basin can be divided into three basin prototypes: the Paleocene-Oligocene (Tg‒T60) rift basin, the Early Miocene (T60‒T50) depression basin and the Middle Miocene (T50‒T0) foreland basin. From the Cenozoic, the Nansha trough basin has gradually migrated from NW to SE. Comparative analysis from the previous study shows that the Nansha trough foreland basin is formed by the superposition of multi-phased foreland basins. Bounded by the Sarawak orogenic unconformity, the deep regional unconformity and the shallow regional unconformity, the Nansha trough foreland basin can be divided into three stages of the foreland basin: the Early Oligocene to Miocene, the Middle Miocene to the Early Pliocene and the Late Pliocene to present. The Nansha trough belongs to the third phase of the whole foreland basin and is still developing now.
2022, 47(7): 2549-2561.
doi: 10.3799/dqkx.2022.073
Abstract:
In the context of the fracture, collision, and splicing of microplates during the expansion of the South China Sea, carbonate platforms and reefs have developed in the southern South China Sea since the Miocene. After later diagenetic transformation, a large number of carbonate reservoirs have been formed and contain rich hydrocarbon resources. In order to understand the development characteristics and genetic mechanism of carbonate reservoirs in this area, a systematic study was carried out on the types, storage spaces, diagenesis and control factors of carbonate reservoirs in this area based on high-precision 2D seismic data and combined with core and thin section data. The analysis shows that there are many types of carbonate reservoirs in the southern part of the South China Sea, and there are mainly three types, namely reef and shoal reservoir, karst reservoir and dolomite reservoir. A variety of pore types are developed, including primary pore and secondary pore, which is dominated by secondary pore, including mold pore, intracrystalline dissolved pore, intergranular pore and intracrystalline pore. The carbonate reservoir space in this region is mainly reconstructed by chalkization, dissolution and dolomization. The development of carbonate reservoirs is mainly controlled by tectonic, sedimentary, paleoclimate and fluid activities, and can be used as a good reservoir. The Beikang Basin has favorable hydrocarbon conditions and can form carbonate hydrocarbon reservoirs with "lower generation and upper storage".
In the context of the fracture, collision, and splicing of microplates during the expansion of the South China Sea, carbonate platforms and reefs have developed in the southern South China Sea since the Miocene. After later diagenetic transformation, a large number of carbonate reservoirs have been formed and contain rich hydrocarbon resources. In order to understand the development characteristics and genetic mechanism of carbonate reservoirs in this area, a systematic study was carried out on the types, storage spaces, diagenesis and control factors of carbonate reservoirs in this area based on high-precision 2D seismic data and combined with core and thin section data. The analysis shows that there are many types of carbonate reservoirs in the southern part of the South China Sea, and there are mainly three types, namely reef and shoal reservoir, karst reservoir and dolomite reservoir. A variety of pore types are developed, including primary pore and secondary pore, which is dominated by secondary pore, including mold pore, intracrystalline dissolved pore, intergranular pore and intracrystalline pore. The carbonate reservoir space in this region is mainly reconstructed by chalkization, dissolution and dolomization. The development of carbonate reservoirs is mainly controlled by tectonic, sedimentary, paleoclimate and fluid activities, and can be used as a good reservoir. The Beikang Basin has favorable hydrocarbon conditions and can form carbonate hydrocarbon reservoirs with "lower generation and upper storage".
2022, 47(7): 2562-2572.
doi: 10.3799/dqkx.2022.244
Abstract:
The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine- and terrestrial-facies sediments during Cenozoic. It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings. Therein, the Lishui Depression formed fan delta, fluvial delta and littoral-to-neritic facies sediments during Paleocene-Eocene, and the research on its sedimentary environment and sediment source has been controversial. Combining detrital zircon U-Pb age spectra patterns with paleontological assemblages, a source-to-sink comparative analysis was conducted to restore the sedimentary environment and provenance evolution of the Lishui Depression during Paleocene-Eocene. In general, the Lishui Depression was dominated by littoral and neritic-facies environment during this time, corroborated by large abundance of benthic foraminifera, calcareous nannofossils and dinoflagellates. In addition, the eastern basin was featured with deeper water depths. The Lishui Depression was mainly influenced from the surrounding paleo-uplifts of Yanshanian magmatic rocks. However, its eastern area partly shows Indosinian populations compared to the dominance of Yanshanian clusters in the west. In particular, the Eocene Wenzhou sediments are characterized by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks, indicating a possible impact from the Yushan Low Uplift to the east. Therefore, it is likely that the eastern Lishui Depression generated large river systems as well as deltas during this time. Due to the Yuquan Movement, the Lishui Depression experienced uplifting and exhumation in the late stage of the Late Eocene and sediments had not been deposited until Miocene. With transitional-facies depositions of Paleocene-Eocene, the Lishui Depression has great potential for source rock and oil-gas reservoir accumulation.
The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine- and terrestrial-facies sediments during Cenozoic. It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings. Therein, the Lishui Depression formed fan delta, fluvial delta and littoral-to-neritic facies sediments during Paleocene-Eocene, and the research on its sedimentary environment and sediment source has been controversial. Combining detrital zircon U-Pb age spectra patterns with paleontological assemblages, a source-to-sink comparative analysis was conducted to restore the sedimentary environment and provenance evolution of the Lishui Depression during Paleocene-Eocene. In general, the Lishui Depression was dominated by littoral and neritic-facies environment during this time, corroborated by large abundance of benthic foraminifera, calcareous nannofossils and dinoflagellates. In addition, the eastern basin was featured with deeper water depths. The Lishui Depression was mainly influenced from the surrounding paleo-uplifts of Yanshanian magmatic rocks. However, its eastern area partly shows Indosinian populations compared to the dominance of Yanshanian clusters in the west. In particular, the Eocene Wenzhou sediments are characterized by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks, indicating a possible impact from the Yushan Low Uplift to the east. Therefore, it is likely that the eastern Lishui Depression generated large river systems as well as deltas during this time. Due to the Yuquan Movement, the Lishui Depression experienced uplifting and exhumation in the late stage of the Late Eocene and sediments had not been deposited until Miocene. With transitional-facies depositions of Paleocene-Eocene, the Lishui Depression has great potential for source rock and oil-gas reservoir accumulation.
2022, 47(7): 2573-2585.
doi: 10.3799/dqkx.2021.240
Abstract:
Rapid uplift period of formation of the eastern Himalayan syntaxis and the hypothesis of Tsangpo-Irrawaddy River connection have been debated for over half a century. A combination of detrital zircon U-Pb chronology and heavy mineral assemblages was employed to investigate the "source to sink" pathways of Cenozoic strata in Central Myanmar Basin (CMB). The Eocene sediments indicate an intrabasinal provenance and no uniform source area with the presence of large amounts of Chromian spinel as well as the heterogeneity of zircon age spectra between all depressions. Since Oligocene, it is found that local-derived source was gradually replaced by Mogok Metamorphic Belt(MMB) and Irrawaddy River began to develop, which is revealed by zircon age spectra in all depressions tending to be identical (with 40-70 Ma at major peaks and 80-110 Ma at secondary peaks) and heavy mineral assemblages derived from regional metamorphic rock constantly increasing. In addition, due to lack of signal of Himalayan orogenic belt in Central Myanmar Basin, it is believed that there is no possibility of Tsangpo-Irrawaddy connection during Oligocene and Early Miocene. In Late Miocene-Pleistocene, the occurrence of granatite and kyanite and 110-130 Ma age peaks representing Himalayan orogenic belt suggest that the Irrawaddy River had eroded to the eastern Himalayan syntaxis and attained a near-modern configuration of drainage networks. Consequently, rapid uplift of eastern Himalayan syntaxis should have occurred in the Late Miocene-Pleistocene.
Rapid uplift period of formation of the eastern Himalayan syntaxis and the hypothesis of Tsangpo-Irrawaddy River connection have been debated for over half a century. A combination of detrital zircon U-Pb chronology and heavy mineral assemblages was employed to investigate the "source to sink" pathways of Cenozoic strata in Central Myanmar Basin (CMB). The Eocene sediments indicate an intrabasinal provenance and no uniform source area with the presence of large amounts of Chromian spinel as well as the heterogeneity of zircon age spectra between all depressions. Since Oligocene, it is found that local-derived source was gradually replaced by Mogok Metamorphic Belt(MMB) and Irrawaddy River began to develop, which is revealed by zircon age spectra in all depressions tending to be identical (with 40-70 Ma at major peaks and 80-110 Ma at secondary peaks) and heavy mineral assemblages derived from regional metamorphic rock constantly increasing. In addition, due to lack of signal of Himalayan orogenic belt in Central Myanmar Basin, it is believed that there is no possibility of Tsangpo-Irrawaddy connection during Oligocene and Early Miocene. In Late Miocene-Pleistocene, the occurrence of granatite and kyanite and 110-130 Ma age peaks representing Himalayan orogenic belt suggest that the Irrawaddy River had eroded to the eastern Himalayan syntaxis and attained a near-modern configuration of drainage networks. Consequently, rapid uplift of eastern Himalayan syntaxis should have occurred in the Late Miocene-Pleistocene.
2022, 47(7): 2586-2601.
doi: 10.3799/dqkx.2021.093
Abstract:
In order to further explain the geochemical characteristics and genesis of polymetallic nodules (crusts) in different regions of the South China Sea, X-ray diffraction, X-ray fluorescence spectroscopy, SEM-EDS analysis and X-Series analysis were carried out on the newly obtained polymetallic nodules (crusts) from the Huangyan-Zhenbei seamount chain in the eastern Subbasin. The mineral composition and geochemical characteristics of polymetallic nodules (crusts) were analyzed by ICP-MS. The results show that the mineral compositions of polymetallic nodules (crusts) are hydroxidite, quartz and plagioclase, and the main rock forming elements are Si and Al. It is rich in Mn, Fe, Co, Ti, Ni, Pb, Sr, Cu and other metal elements. Compared with other areas in the South China Sea, it has the characteristics of medium Fe and Mn contents, and the geochemical element characteristics are similar to those of ferromanganese nodules (crusts) found in the northwest slope of the South China Sea. The REE content of nodules (crusts) in the study area is high (average 2 070.01×10-6), which is higher than other samples in the northern South China Sea, and close to the industrial grade of crusts in the West Pacific, indicating its important rare earth resource prospect. The results of Be isotope indicate that the age of Fe Mn nodules in this area is 1.17‒8.51 Ma, which was formed after a large number of volcanic eruptions in the Late Miocene. Therefore, the hydrogenesis is the main control of the seamount chain nodules (crusts) in the eastern Subbasin of the South China Sea, and the input of terrigenous materials, volcanism and leaching of high-pressure hydrogen rich seawater all provide favorable conditions for the formation of nodules (crusts).
In order to further explain the geochemical characteristics and genesis of polymetallic nodules (crusts) in different regions of the South China Sea, X-ray diffraction, X-ray fluorescence spectroscopy, SEM-EDS analysis and X-Series analysis were carried out on the newly obtained polymetallic nodules (crusts) from the Huangyan-Zhenbei seamount chain in the eastern Subbasin. The mineral composition and geochemical characteristics of polymetallic nodules (crusts) were analyzed by ICP-MS. The results show that the mineral compositions of polymetallic nodules (crusts) are hydroxidite, quartz and plagioclase, and the main rock forming elements are Si and Al. It is rich in Mn, Fe, Co, Ti, Ni, Pb, Sr, Cu and other metal elements. Compared with other areas in the South China Sea, it has the characteristics of medium Fe and Mn contents, and the geochemical element characteristics are similar to those of ferromanganese nodules (crusts) found in the northwest slope of the South China Sea. The REE content of nodules (crusts) in the study area is high (average 2 070.01×10-6), which is higher than other samples in the northern South China Sea, and close to the industrial grade of crusts in the West Pacific, indicating its important rare earth resource prospect. The results of Be isotope indicate that the age of Fe Mn nodules in this area is 1.17‒8.51 Ma, which was formed after a large number of volcanic eruptions in the Late Miocene. Therefore, the hydrogenesis is the main control of the seamount chain nodules (crusts) in the eastern Subbasin of the South China Sea, and the input of terrigenous materials, volcanism and leaching of high-pressure hydrogen rich seawater all provide favorable conditions for the formation of nodules (crusts).
2022, 47(7): 2602-2615.
doi: 10.3799/dqkx.2021.114
Abstract:
Deciphering the evolution of global hydroclimate during the last deglaciation is of great significance for understanding the response of the climate system to the internal and external forces. Based on planktonic foraminiferal Globigerinodes ruber and Pulleniatina obliquiloculata shell Mg/Ca ratio obtained from core OKI02, we reconstructed a 19 000-year record of Sea Surface Temperature (SST) and Thermocline Water Temperature (TWT) to unveil the characteristics and process of upper water temperature in the Middle Okinawa Trough during the last deglaciation. The results imply that the SST was significantly low (about 23.7 ℃ on average) during the Last Glacial Maximum (LGM, about 19-18 ka BP), and was of obvious millennial-scale variation features during the last deglaciation. Heinrich Stadial 1(HS1), Bølling-Allerød (B/A) and Younger Dryas (YD) events could be identified obviously in the record of SST.TWT shows a rising trend, with frequent and strong fluctuation since 19 ka BP. TWT is relatively low (about 20.3 ℃ on average) during the last deglaciation, without apparent significant millennial-scale changes. During the last deglaciation, the beginning time of SST rising in the Okinawa Trough was consistent with the SST record in high latitudes of the northern hemisphere, while lagged significantly behind SST record of the tropical western Pacific. Meanwhile, the SST change pattern in the Okinawa Trough was different from the continuous and stable warming process of the tropical western Pacific, but more similar to the climate change of the northern hemisphere high latitudes. In contrast, the warming time of TWT was earlier than that happened in the northern high latitudes but close to the tropical western Pacific. Moreover, the rising and fluctuating mode of TWT was different from the former and was more similar to the variation pattern of the tropical Pacific. The differentiated evolution of SST and TWT demonstrates that the influence of Atlantic Meridional Overturning Circulation (AMOC) on the atmospheric circulation may control the SST in the trough area through the changes of the East Asian winter monsoon. However, the tropical Pacific ENSO process probably plays an important role in the evolution of the regional TWT through the changes of the Kuroshio during the last deglaciation. The trend of the decoupling change in SST and TWT in the middle of the Okinawa Trough implies its intimate connection with high and low latitude oceans and climate change.
Deciphering the evolution of global hydroclimate during the last deglaciation is of great significance for understanding the response of the climate system to the internal and external forces. Based on planktonic foraminiferal Globigerinodes ruber and Pulleniatina obliquiloculata shell Mg/Ca ratio obtained from core OKI02, we reconstructed a 19 000-year record of Sea Surface Temperature (SST) and Thermocline Water Temperature (TWT) to unveil the characteristics and process of upper water temperature in the Middle Okinawa Trough during the last deglaciation. The results imply that the SST was significantly low (about 23.7 ℃ on average) during the Last Glacial Maximum (LGM, about 19-18 ka BP), and was of obvious millennial-scale variation features during the last deglaciation. Heinrich Stadial 1(HS1), Bølling-Allerød (B/A) and Younger Dryas (YD) events could be identified obviously in the record of SST.TWT shows a rising trend, with frequent and strong fluctuation since 19 ka BP. TWT is relatively low (about 20.3 ℃ on average) during the last deglaciation, without apparent significant millennial-scale changes. During the last deglaciation, the beginning time of SST rising in the Okinawa Trough was consistent with the SST record in high latitudes of the northern hemisphere, while lagged significantly behind SST record of the tropical western Pacific. Meanwhile, the SST change pattern in the Okinawa Trough was different from the continuous and stable warming process of the tropical western Pacific, but more similar to the climate change of the northern hemisphere high latitudes. In contrast, the warming time of TWT was earlier than that happened in the northern high latitudes but close to the tropical western Pacific. Moreover, the rising and fluctuating mode of TWT was different from the former and was more similar to the variation pattern of the tropical Pacific. The differentiated evolution of SST and TWT demonstrates that the influence of Atlantic Meridional Overturning Circulation (AMOC) on the atmospheric circulation may control the SST in the trough area through the changes of the East Asian winter monsoon. However, the tropical Pacific ENSO process probably plays an important role in the evolution of the regional TWT through the changes of the Kuroshio during the last deglaciation. The trend of the decoupling change in SST and TWT in the middle of the Okinawa Trough implies its intimate connection with high and low latitude oceans and climate change.
2022, 47(7): 2616-2630.
doi: 10.3799/dqkx.2021.057
Abstract:
There is a wide range of heterogeneity in the oceanic mantle, which can be caused by a variety of models, among which the subduction cycle has an important influence on the composition of the mantle. In order to clarify the relative contribution of each cyclic component to the reformation of depleted mantle and the enrichment source region, in this paper it systematically summarizes the average trace element characteristics of different cyclic components (pelagic sediments, subducted oceanic crust, continental crust), and the cyclic components undergone chemical changes during subduction are calculated. Based on the modified cyclic components, the mixing and melting simulations with depleted mantle sources are carried out. It is found that the HIMU basalt can be formed by a low degree of melting (0.5%-1.5%) in the mantle formed by the mixing of pure subducted oceanic crust (≤10%) and depleted mantle (≥90%). The EMI basalts can be formed by a low degree of melting (1%-2%) in the mantle formed by the mixing of subducted oceanic crust (≤10%), low continental crust (≤3%) and depleted mantle (≥90%). The EMII basalts can be formed by a low degree of melting (1%-1.5%) in the mantle formed by the mixing of subducted oceanic crust (≤10%), GLOSS-II(global subducting sediment) or upper continental crust (≤0.8%) and depleted mantle (≥90%).
There is a wide range of heterogeneity in the oceanic mantle, which can be caused by a variety of models, among which the subduction cycle has an important influence on the composition of the mantle. In order to clarify the relative contribution of each cyclic component to the reformation of depleted mantle and the enrichment source region, in this paper it systematically summarizes the average trace element characteristics of different cyclic components (pelagic sediments, subducted oceanic crust, continental crust), and the cyclic components undergone chemical changes during subduction are calculated. Based on the modified cyclic components, the mixing and melting simulations with depleted mantle sources are carried out. It is found that the HIMU basalt can be formed by a low degree of melting (0.5%-1.5%) in the mantle formed by the mixing of pure subducted oceanic crust (≤10%) and depleted mantle (≥90%). The EMI basalts can be formed by a low degree of melting (1%-2%) in the mantle formed by the mixing of subducted oceanic crust (≤10%), low continental crust (≤3%) and depleted mantle (≥90%). The EMII basalts can be formed by a low degree of melting (1%-1.5%) in the mantle formed by the mixing of subducted oceanic crust (≤10%), GLOSS-II(global subducting sediment) or upper continental crust (≤0.8%) and depleted mantle (≥90%).
2022, 47(7): 2631-2645.
doi: 10.3799/dqkx.2021.084
Abstract:
Establishment of high-resolution volcano-stratigraphic frameworks (HRVF) of buried volcanoes is important for understanding the evolution of the volcanic system and its potential to form volcanic reservoirs. Taking Miocene Kora volcano in Taranaki Basin, New Zealand as an example, in this paper it uses wavelet transform and well-seismic correlation to analyze the HRVF. It mapped 20 units that include predominately deposits from pyroclastic eruptions, together with reworked debris deposits. The Kora Volcano can be divided into five parts according to major unconformities that are related with active and quiescent eruptive periods and with the formation and migration of distinctive eruptive centers. The outline framework can be built by using the conventional 3D seismic data, and the HRVF can be built by using the wells and conventional 3D seismic data. The better choice for building the HRVF of the buried volcano is in relative age.
Establishment of high-resolution volcano-stratigraphic frameworks (HRVF) of buried volcanoes is important for understanding the evolution of the volcanic system and its potential to form volcanic reservoirs. Taking Miocene Kora volcano in Taranaki Basin, New Zealand as an example, in this paper it uses wavelet transform and well-seismic correlation to analyze the HRVF. It mapped 20 units that include predominately deposits from pyroclastic eruptions, together with reworked debris deposits. The Kora Volcano can be divided into five parts according to major unconformities that are related with active and quiescent eruptive periods and with the formation and migration of distinctive eruptive centers. The outline framework can be built by using the conventional 3D seismic data, and the HRVF can be built by using the wells and conventional 3D seismic data. The better choice for building the HRVF of the buried volcano is in relative age.
2022, 47(7): 2646-2666.
doi: 10.3799/dqkx.2021.192
Abstract:
As the boundary fault of the Hongqi Sag, the Hongxi fault has long controlled the formation and evolution of the depression and hydrocarbon accumulation. At present, there are still many shortcomings in the recognition and description of faults and the understanding of growth patterns. Therefore, based on the defined interpretation of the seismic profile, the geometric characteristics and boundary conditions of the Hongqi Sag are determined, and multiple sets of structural physical simulation experiments were carried out in combination with the controlled variable method. Then, comparing the experimental results with the parameters of the tectonic map of the top surface of the Hongqi Sag basement, the evolution pattern of Hongxi fault controlled by the scale of the pre-existing structures can be established finally. Experimental results show that the total length of the pre-existing structures in the Hongqi Sag is 34 kilometers, which accounts for 50% of the current length about the entire boundary fault at least. The structural evolution of the Hongxi Fault has a growth pattern characterized by isolated fault segmentation (pre-existing structures) →"soft connection"→"hard connection", meanwhile, there are typical relay structures at the transition site of Hongxi fault.
As the boundary fault of the Hongqi Sag, the Hongxi fault has long controlled the formation and evolution of the depression and hydrocarbon accumulation. At present, there are still many shortcomings in the recognition and description of faults and the understanding of growth patterns. Therefore, based on the defined interpretation of the seismic profile, the geometric characteristics and boundary conditions of the Hongqi Sag are determined, and multiple sets of structural physical simulation experiments were carried out in combination with the controlled variable method. Then, comparing the experimental results with the parameters of the tectonic map of the top surface of the Hongqi Sag basement, the evolution pattern of Hongxi fault controlled by the scale of the pre-existing structures can be established finally. Experimental results show that the total length of the pre-existing structures in the Hongqi Sag is 34 kilometers, which accounts for 50% of the current length about the entire boundary fault at least. The structural evolution of the Hongxi Fault has a growth pattern characterized by isolated fault segmentation (pre-existing structures) →"soft connection"→"hard connection", meanwhile, there are typical relay structures at the transition site of Hongxi fault.
