2017 Vol. 35, No. 6
Display Method:
2017, 35(6): 1087-1096.
doi: 10.14027/j.cnki.cjxb.2017.06.001
Abstract:
The Santanghu area is an intracontinental starved lacustrine rift basin from later Carboniferous to the middle Permian, and is mainly composed of interlaminated carbonate rocks and tuffaceous shale with little intervals of pyroclastic and hydrothermal exhalative rocks. This paper focuses on one special interval type which mainly contains of dolomite and smectite, and research for its forming mechanism on the basis of petrology, mineralogy and geochemistry. The simple mineral composition and euhedral crystal with partly embayed boundaries suggest an igneous origin. The rock is thin-bedded without inner stratified structure, indicating fast and mixed deposition processes from a density flow. Aggregates formed by tiny minerals may be caused by accretionary lapilli formed in clastic flow with high density and high temperature. Finally, features of geochemistry show a mainly mantle-derived origin with mixed crustal material. Comprehensively, this type of rock is deposited from subaqueous high-density pyroclastic flow fed by carbonatite eruptions, and altered by contemporaneous or later hydrothermal fluid.
The Santanghu area is an intracontinental starved lacustrine rift basin from later Carboniferous to the middle Permian, and is mainly composed of interlaminated carbonate rocks and tuffaceous shale with little intervals of pyroclastic and hydrothermal exhalative rocks. This paper focuses on one special interval type which mainly contains of dolomite and smectite, and research for its forming mechanism on the basis of petrology, mineralogy and geochemistry. The simple mineral composition and euhedral crystal with partly embayed boundaries suggest an igneous origin. The rock is thin-bedded without inner stratified structure, indicating fast and mixed deposition processes from a density flow. Aggregates formed by tiny minerals may be caused by accretionary lapilli formed in clastic flow with high density and high temperature. Finally, features of geochemistry show a mainly mantle-derived origin with mixed crustal material. Comprehensively, this type of rock is deposited from subaqueous high-density pyroclastic flow fed by carbonatite eruptions, and altered by contemporaneous or later hydrothermal fluid.
2017, 35(6): 1097-1109.
doi: 10.14027/j.cnki.cjxb.2017.06.002
Abstract:
The 11th international conference on fluvial sedimentology was held in University of Calgary, Canada, from 17 to 21 July 2017. As a pageant of international fluvial sedimentology, once four years, scholars who came from North America, European, Australia and Asia attended the conference. A series of academic topics were presented and discussed in different technical programs. More reports and sessions focus the following fields:1)River dynamics and change, including linking modern river processes to the ancient record, beyond overbank-complex dynamics of channel-floodplain systems, perspectives on river dynamics and change, and reconstructing river channel migration:Next generation forensics for plane evolution patterns, and turbulence, grain interactions, and sedimentation in alluvial and bedrock rivers. 2)Rivers on the edge, including where the river meets the sea:morphodynamics and sedimentology in systems with combined fluvial and tidal currents, transitions in flow, morphology and stratigraphy along river-fed margins, and dryland fluvial and alluvial systems, fluvial-aeolian interaction, and pre-vegetation, non-vegetated, or ‘normal’ rivers, processes and deposits. 3)Fluvial stratigraphy and subsurface resources, from source to sink sedimentological and stratigraphic analysis, braided or meandering are fluvial facies models useful, and types of rivers preserved in the stratigraphic record. 4)Managing fluvial landscapes, including the climate changing, mud and vegetation of floodplain influence on the discharge and models of fluvial, and the evolution of alluvial island and meandering channel, and the role of biostabilized sediments in fluvial environments. Based on the data of 11th International Conference on fluvial sedimentology, we considered the quantitative research of evolution progress of fluvial, the physical simulation and numerical simulation of fluvial sedimentology, reconstructing the point bar and calculate the date of facies model, and using the detrital zircons as a next dating tool in source to sink sedimentological and stratigraphic analysis, in which some will still be important research and development fields of international fluvial sedimentology.
The 11th international conference on fluvial sedimentology was held in University of Calgary, Canada, from 17 to 21 July 2017. As a pageant of international fluvial sedimentology, once four years, scholars who came from North America, European, Australia and Asia attended the conference. A series of academic topics were presented and discussed in different technical programs. More reports and sessions focus the following fields:1)River dynamics and change, including linking modern river processes to the ancient record, beyond overbank-complex dynamics of channel-floodplain systems, perspectives on river dynamics and change, and reconstructing river channel migration:Next generation forensics for plane evolution patterns, and turbulence, grain interactions, and sedimentation in alluvial and bedrock rivers. 2)Rivers on the edge, including where the river meets the sea:morphodynamics and sedimentology in systems with combined fluvial and tidal currents, transitions in flow, morphology and stratigraphy along river-fed margins, and dryland fluvial and alluvial systems, fluvial-aeolian interaction, and pre-vegetation, non-vegetated, or ‘normal’ rivers, processes and deposits. 3)Fluvial stratigraphy and subsurface resources, from source to sink sedimentological and stratigraphic analysis, braided or meandering are fluvial facies models useful, and types of rivers preserved in the stratigraphic record. 4)Managing fluvial landscapes, including the climate changing, mud and vegetation of floodplain influence on the discharge and models of fluvial, and the evolution of alluvial island and meandering channel, and the role of biostabilized sediments in fluvial environments. Based on the data of 11th International Conference on fluvial sedimentology, we considered the quantitative research of evolution progress of fluvial, the physical simulation and numerical simulation of fluvial sedimentology, reconstructing the point bar and calculate the date of facies model, and using the detrital zircons as a next dating tool in source to sink sedimentological and stratigraphic analysis, in which some will still be important research and development fields of international fluvial sedimentology.
2017, 35(6): 1110-1120.
doi: 10.14027/j.cnki.cjxb.2017.06.003
Abstract:
The characteristics of siliciclastic-carbonate mixed sedimentary environment still remains unknown, resulting in poor understanding of distribution of mixed rock. In this study, the sedimentary environments and environmental parameters of Carboniferous in Bamai area, Tarim Basin are deeply studied, using observation of thin sections, measurement of minerals composition, and elements composition. The mixed rocks were deposited, carbonate restricted platform and open platform. The concentrations of Ti, Rb, K, Al are used to divide the degrees of mixed sedimentation into four levels due to their good relationship with the degree of mixing. The salinity was reflected by Na content and Na/Ca. The depth of water was reflected by Mn/Fe and Sr content. The redox condition was reflected by V/(V+Ni). And, the paleoclimate was analyzed from Ti/Al and Mg/Sr. The result of geochemical indices shows the mixed sedimentation beyond Ⅱ level occurred at humid climate, while there was no obvious mixing at arid climate. Meanwhile, most mixed sedimentation accompanied by sea level fall. On the open platform, there was only I level mixed sedimentation, while Ⅲ-IV level mixed sedimentation developed on the barrier coast and restricted platform. The mixed sedimentation in each depositional environment can record the change of sea level and paleoclimate.
The characteristics of siliciclastic-carbonate mixed sedimentary environment still remains unknown, resulting in poor understanding of distribution of mixed rock. In this study, the sedimentary environments and environmental parameters of Carboniferous in Bamai area, Tarim Basin are deeply studied, using observation of thin sections, measurement of minerals composition, and elements composition. The mixed rocks were deposited, carbonate restricted platform and open platform. The concentrations of Ti, Rb, K, Al are used to divide the degrees of mixed sedimentation into four levels due to their good relationship with the degree of mixing. The salinity was reflected by Na content and Na/Ca. The depth of water was reflected by Mn/Fe and Sr content. The redox condition was reflected by V/(V+Ni). And, the paleoclimate was analyzed from Ti/Al and Mg/Sr. The result of geochemical indices shows the mixed sedimentation beyond Ⅱ level occurred at humid climate, while there was no obvious mixing at arid climate. Meanwhile, most mixed sedimentation accompanied by sea level fall. On the open platform, there was only I level mixed sedimentation, while Ⅲ-IV level mixed sedimentation developed on the barrier coast and restricted platform. The mixed sedimentation in each depositional environment can record the change of sea level and paleoclimate.
2017, 35(6): 1121-1132.
doi: 10.14027/j.cnki.cjxb.2017.06.004
Abstract:
We have firstly reported the presence of eight kinds of microbially induced sedimentary structures (MISSs) or sedimentary surface textures, including growth ridges, growth postulas, curved desiccation cracks, spindle-shaped cracks, "Manchuriophycus" structures, dendritic desiccation cracks, polygonal desiccation cracks and desiccation cracks from the terrestrial upper Permian Sunjiagou Formation and lower Triassic Liujiagou Formation in Jiyuan western Henan. Large U ridges, oriented sand quartz, mica grains and thin clayey laminae arranged parallel to bedding plane are the main features visible under the microscope. A series of evidence indicate that the Jiyuan MISSs are of biogenic origin. Compared with MISSs of the Mesoproterozoic Yunmengshan Formation in Lushan, the Mesoproterozoic Changchougou Formation in Licheng, Lower Triassic Liujiagou Formation in Yiyang and Liulin, we concluded that microbially induced sedimentary structures has special taphonomic characteristics and was controlled by the end-Permian mass extinction, sedimentary environments and climate factor in Jiyuan. MISSs of Jiyuan stands for terrestrial ecosystems following the end-Permian mass extinction with rich microbial community, scarce metazoan, poor plant, hot weather and serious soil erosion.
We have firstly reported the presence of eight kinds of microbially induced sedimentary structures (MISSs) or sedimentary surface textures, including growth ridges, growth postulas, curved desiccation cracks, spindle-shaped cracks, "Manchuriophycus" structures, dendritic desiccation cracks, polygonal desiccation cracks and desiccation cracks from the terrestrial upper Permian Sunjiagou Formation and lower Triassic Liujiagou Formation in Jiyuan western Henan. Large U ridges, oriented sand quartz, mica grains and thin clayey laminae arranged parallel to bedding plane are the main features visible under the microscope. A series of evidence indicate that the Jiyuan MISSs are of biogenic origin. Compared with MISSs of the Mesoproterozoic Yunmengshan Formation in Lushan, the Mesoproterozoic Changchougou Formation in Licheng, Lower Triassic Liujiagou Formation in Yiyang and Liulin, we concluded that microbially induced sedimentary structures has special taphonomic characteristics and was controlled by the end-Permian mass extinction, sedimentary environments and climate factor in Jiyuan. MISSs of Jiyuan stands for terrestrial ecosystems following the end-Permian mass extinction with rich microbial community, scarce metazoan, poor plant, hot weather and serious soil erosion.
2017, 35(6): 1133-1143.
doi: 10.14027/j.cnki.cjxb.2017.06.005
Abstract:
In the present study, coastal dune deposits are analyzed to derive the information on historical storm events. Paleotempestology investigations were carried out for the southeastern part of Hainan Island. The storm deposits identified are interbedded within the aeolian coastal dune profiles on the Jianling coast. They are characterized by coarse-grained overwash deposits during the extreme storm events, as revealed on the basis of detailed stratigraphic division, grain size and magnetic susceptibility analyses. The age of the storms events was determined using the 14C and OSL dating methods, in combination with historical documents. When a storm surge hits the coast, the coastal dune may be overtopped or breached, and a low-lying dune associated with a large, flat terrain at the backshore is suitable for trapping the storm sediment to form a thick-bedded, sandy washover deposit. The Stockdon empirical equation was used to calculate the overwash height, indicating that the storm record at the Jianling site represents the product formed by several storms, with their return periods being 100 to 200 years. The result obtained implies that the coastal dune here contain important information on the intensity and frequency of occurrence of the South China Sea typhoons.
In the present study, coastal dune deposits are analyzed to derive the information on historical storm events. Paleotempestology investigations were carried out for the southeastern part of Hainan Island. The storm deposits identified are interbedded within the aeolian coastal dune profiles on the Jianling coast. They are characterized by coarse-grained overwash deposits during the extreme storm events, as revealed on the basis of detailed stratigraphic division, grain size and magnetic susceptibility analyses. The age of the storms events was determined using the 14C and OSL dating methods, in combination with historical documents. When a storm surge hits the coast, the coastal dune may be overtopped or breached, and a low-lying dune associated with a large, flat terrain at the backshore is suitable for trapping the storm sediment to form a thick-bedded, sandy washover deposit. The Stockdon empirical equation was used to calculate the overwash height, indicating that the storm record at the Jianling site represents the product formed by several storms, with their return periods being 100 to 200 years. The result obtained implies that the coastal dune here contain important information on the intensity and frequency of occurrence of the South China Sea typhoons.
2017, 35(6): 1144-1157.
doi: 10.14027/j.cnki.cjxb.2017.06.006
Abstract:
The manganese deposits are mainly distributed in Southwestern Guangxi area, which was regarded as one of the most predominant ore types in this area. However, the Triassic stratigraphic frameworks of manganese deposit in the southwestern Guangxi area is rarely discussed. The spectral analysis and filter methods can be adopted to divide cyclic sequence hierarchy and discuss depositional mechanism, and the cumulative residual curves from average amplitude variations of good logs are introduced and demonstrated as a valid graphical method to define depositional regime transformation and check boundary surfaces of cyclic sequences. The cumulative residual curves results show the positive half waves and negative half waves of cumulative residual curves are, respectively, corresponds to upward-deepening and upward-shallowing sedimentary successions in low frequency cyclic sequences in a well interval. Transform points of positive half waves and negative half waves are calibrated to boundary surface depth of cyclic sequences. The GR log data from Well 0302 of Southwestern Guangxi Area as a case example, cumulative residual curves are calculated and constructed on well log data. The low and high frequency cyclic sequences are distinguished and its procedure and methods are illustrated in detail. The significance and interpretation of amplitudes and wavelength changes of sedimentary cycles are discussed in this paper. The Beisi Formation of the Lower Triassic can be divided into four forth-order sequences, and the manganese ore deposit developed in the regression cycle. The origin model of manganese ore can be divided in three stages:1) Sea-level fall-the oxidizing manganese is formation; 2) Sea-level rise-the oxidizing manganese is transformed in manganese carbonate; 3) The maximum flooding surface-a little manganese carbonate is formed. The investigation provides a new effective approach to build the correlating framework of high-resolution sequence in Southwestern Guangxi Area.
The manganese deposits are mainly distributed in Southwestern Guangxi area, which was regarded as one of the most predominant ore types in this area. However, the Triassic stratigraphic frameworks of manganese deposit in the southwestern Guangxi area is rarely discussed. The spectral analysis and filter methods can be adopted to divide cyclic sequence hierarchy and discuss depositional mechanism, and the cumulative residual curves from average amplitude variations of good logs are introduced and demonstrated as a valid graphical method to define depositional regime transformation and check boundary surfaces of cyclic sequences. The cumulative residual curves results show the positive half waves and negative half waves of cumulative residual curves are, respectively, corresponds to upward-deepening and upward-shallowing sedimentary successions in low frequency cyclic sequences in a well interval. Transform points of positive half waves and negative half waves are calibrated to boundary surface depth of cyclic sequences. The GR log data from Well 0302 of Southwestern Guangxi Area as a case example, cumulative residual curves are calculated and constructed on well log data. The low and high frequency cyclic sequences are distinguished and its procedure and methods are illustrated in detail. The significance and interpretation of amplitudes and wavelength changes of sedimentary cycles are discussed in this paper. The Beisi Formation of the Lower Triassic can be divided into four forth-order sequences, and the manganese ore deposit developed in the regression cycle. The origin model of manganese ore can be divided in three stages:1) Sea-level fall-the oxidizing manganese is formation; 2) Sea-level rise-the oxidizing manganese is transformed in manganese carbonate; 3) The maximum flooding surface-a little manganese carbonate is formed. The investigation provides a new effective approach to build the correlating framework of high-resolution sequence in Southwestern Guangxi Area.
2017, 35(6): 1158-1165.
doi: 10.14027/j.cnki.cjxb.2017.06.007
Abstract:
Analysis of a sediment core from Wulungu Lake of Xinjiang was carried out by using environmental proxy of grain-size. Combining with 210Pb and 137Cs dating, the characteristics and environmental significance of sensitive grain-size components of Wulungu Lake sediments were studied in Wulungu Lake region. The results showed that the sediment core mainly consisted of clay and fine-silty, however, grain-size displayed a sudden shift before and after 1970 AD:the coarse particle fraction (>16 μm) was significantly increased. The grain size characteristics of the sediments also changed significantly during 1830-1842 AD and in about 1910 AD. The analysis of grain-size frequency distribution curves of the sediment core indicated that the transportation medium or transporting force had changed significantly during corresponding periods. Based on this result, environmentally sensitive grain-size component C2 (7-25 μm) was extracted by the variations of the grain-size standard deviation. Based on correlation analysis between sensitive grain-size component and meteorological data, the environmental significance of sensitive grain-size component C2 was explicated. The results indicated that the content of sensitive grain-size component C2 was related to the regional spring and summer average temperature and winter snowfall, and reflected the intensity of the snow meltwater into the lake. The significant increase of the content of component C2 during 1830~1842 AD and in about 1910 AD thus reflect the increased water inflow and higher lake level. The significant change of grain size characteristics of the sediments during 1960s-70s was related to human activity.
Analysis of a sediment core from Wulungu Lake of Xinjiang was carried out by using environmental proxy of grain-size. Combining with 210Pb and 137Cs dating, the characteristics and environmental significance of sensitive grain-size components of Wulungu Lake sediments were studied in Wulungu Lake region. The results showed that the sediment core mainly consisted of clay and fine-silty, however, grain-size displayed a sudden shift before and after 1970 AD:the coarse particle fraction (>16 μm) was significantly increased. The grain size characteristics of the sediments also changed significantly during 1830-1842 AD and in about 1910 AD. The analysis of grain-size frequency distribution curves of the sediment core indicated that the transportation medium or transporting force had changed significantly during corresponding periods. Based on this result, environmentally sensitive grain-size component C2 (7-25 μm) was extracted by the variations of the grain-size standard deviation. Based on correlation analysis between sensitive grain-size component and meteorological data, the environmental significance of sensitive grain-size component C2 was explicated. The results indicated that the content of sensitive grain-size component C2 was related to the regional spring and summer average temperature and winter snowfall, and reflected the intensity of the snow meltwater into the lake. The significant increase of the content of component C2 during 1830~1842 AD and in about 1910 AD thus reflect the increased water inflow and higher lake level. The significant change of grain size characteristics of the sediments during 1960s-70s was related to human activity.
2017, 35(6): 1166-1176.
doi: 10.14027/j.cnki.cjxb.2017.06.008
Abstract:
The Standard Microfacies (SMF) Types are virtual categories that summarize microfacies with identical criteria. SMF 1 to SMF 26 are divided following the order of the facies zones in the rimmed carbonate platform going from the basin to the subaerial exposure areas, and the plates of the SMF Types, as well as the model of the SMF Types distributed in facies zones are developed by Flügel. Based on that, the SMF Types of the Ordovician carbonate in the Yubei area were studied. Nine of the SMF Types have been recognized in total, which always occur in certain assemblages. The assemblages are SMF 15-C, SMF 16-NON-LAMINATED and SMF 17 in the Penglaiba-lower Yingshan Formations (O1p-O1-2ylower), SMF 16-NON-LAMINATED, SMF 17 and SMF 23 in the upper Yingshan-Yijianfang Formations (O1-2yupper-O2yj), SMF 6 and SMF 12-CRIN, as well as SMF 1-BURROWED in the Qiaerbake Formation (O3q), SMF 11 and SMF 9, as well as SMF 15-C, SMF 16-NON-LAMINATED and SMF 17 in the Lianglitage Formation (O3l). Additionally, the characteristics of the log responses were analyzed for the assemblages of SMF Types, whose spatial distributions were outlined by comparison of the gamma log curves along the well-tie sections. The originally depositional environments were recovered for the Ordovician formations according to assemblages of the SMF Types and their spatial distribution. The study results indicated that the Ordovician had experienced the evolution of four depositional environments in the Yubei area, that is, open marine (O1p-O1-2ylower), restricted marine (O1-2yupper-O2yj), slope-deep shelf (O3q) and platform margin-open marine (O3l) in sequence.
The Standard Microfacies (SMF) Types are virtual categories that summarize microfacies with identical criteria. SMF 1 to SMF 26 are divided following the order of the facies zones in the rimmed carbonate platform going from the basin to the subaerial exposure areas, and the plates of the SMF Types, as well as the model of the SMF Types distributed in facies zones are developed by Flügel. Based on that, the SMF Types of the Ordovician carbonate in the Yubei area were studied. Nine of the SMF Types have been recognized in total, which always occur in certain assemblages. The assemblages are SMF 15-C, SMF 16-NON-LAMINATED and SMF 17 in the Penglaiba-lower Yingshan Formations (O1p-O1-2ylower), SMF 16-NON-LAMINATED, SMF 17 and SMF 23 in the upper Yingshan-Yijianfang Formations (O1-2yupper-O2yj), SMF 6 and SMF 12-CRIN, as well as SMF 1-BURROWED in the Qiaerbake Formation (O3q), SMF 11 and SMF 9, as well as SMF 15-C, SMF 16-NON-LAMINATED and SMF 17 in the Lianglitage Formation (O3l). Additionally, the characteristics of the log responses were analyzed for the assemblages of SMF Types, whose spatial distributions were outlined by comparison of the gamma log curves along the well-tie sections. The originally depositional environments were recovered for the Ordovician formations according to assemblages of the SMF Types and their spatial distribution. The study results indicated that the Ordovician had experienced the evolution of four depositional environments in the Yubei area, that is, open marine (O1p-O1-2ylower), restricted marine (O1-2yupper-O2yj), slope-deep shelf (O3q) and platform margin-open marine (O3l) in sequence.
2017, 35(6): 1177-1185.
doi: 10.14027/j.cnki.cjxb.2017.06.009
Abstract:
The organic reef in the Carboniferous System along the northeast margin of Qaidam Basin was reported in this paper, and the organic reef development characteristics and regional distribution were descripted. Based on field research and indoor microscopic analysis, combining core observation and description, using geochemistry and petrology method, summarizing the biological, stratum and petrology feature of organic reef in Carboniferous, northeast margin of Qaidam Basin. The article analyzed the main output layer and scale of the organic reef, discussed the palaeoenvironment and petroleum geological significance in northeast margin of Qaidam Basin. The results showed that research area's Reef-building organism is mainly composed by Tetracoralla and also include some Tabulata, the morphology of coral reef is very abundant, such as pyramidal-shape or plate-shape solitary coral, tubular, fasciculate and cellular colonial coral. Reef-inserted organisms were mainly Brachiopod and crinoid. Coral reef is punctiform or discontinuous banded in stratums, three kinds of types are identified by coral reef developing laws and distributional characteristics:clusters of vertical tubular coral, clusters of horizontal extension tubular coral and clusters of the top downward sloping tubular coral. According to biological content in rock, organic reef can be classified to coral skeletons limestone, coral grain limestone, biological granular limestone, containing biological granular limestone and micrite. In Early Carboniferous epoch in northeast margin of Qaidam Basin, the sedimentary environment is mainly carbonate platform while Late Carboniferous epoch it became tidal flat environments which was a transitional zone between marine and continent. Organic reef in the study area is mainly located in the third or fourth section in Huaitoutala Formation of Lower Carboniferous. It developed good source rock and thick layer of oil sands, showing strong ability of hydrocarbon generation and oil migration process.
The organic reef in the Carboniferous System along the northeast margin of Qaidam Basin was reported in this paper, and the organic reef development characteristics and regional distribution were descripted. Based on field research and indoor microscopic analysis, combining core observation and description, using geochemistry and petrology method, summarizing the biological, stratum and petrology feature of organic reef in Carboniferous, northeast margin of Qaidam Basin. The article analyzed the main output layer and scale of the organic reef, discussed the palaeoenvironment and petroleum geological significance in northeast margin of Qaidam Basin. The results showed that research area's Reef-building organism is mainly composed by Tetracoralla and also include some Tabulata, the morphology of coral reef is very abundant, such as pyramidal-shape or plate-shape solitary coral, tubular, fasciculate and cellular colonial coral. Reef-inserted organisms were mainly Brachiopod and crinoid. Coral reef is punctiform or discontinuous banded in stratums, three kinds of types are identified by coral reef developing laws and distributional characteristics:clusters of vertical tubular coral, clusters of horizontal extension tubular coral and clusters of the top downward sloping tubular coral. According to biological content in rock, organic reef can be classified to coral skeletons limestone, coral grain limestone, biological granular limestone, containing biological granular limestone and micrite. In Early Carboniferous epoch in northeast margin of Qaidam Basin, the sedimentary environment is mainly carbonate platform while Late Carboniferous epoch it became tidal flat environments which was a transitional zone between marine and continent. Organic reef in the study area is mainly located in the third or fourth section in Huaitoutala Formation of Lower Carboniferous. It developed good source rock and thick layer of oil sands, showing strong ability of hydrocarbon generation and oil migration process.
2017, 35(6): 1186-1196.
doi: 10.14027/j.cnki.cjxb.2017.06.010
Abstract:
Sandstone intrusions are a common class of soft-sediment deformation. They are formed by the forceful intrusion of fluidization sand into overlying sealing sequence during early stages of burial. Based on 3-D high-resolution seismic data and logging data, we utilize methods of seismic reflection configuration analysis and coherence cube slice to illustrate geometry and induced mechanism of sandstone intrusions. Results indicated that sand intrusions appear V-shaped or W-shaped high amplitude anomalies in seismic sections; conical bodies are 1-2 km on the plane and up to hundreds of meters high; fluid emplacement and polygonal fault systems inducing cap-rock fracture are the key factors for overpressure of depositional sand body and fluidization of sand. After injection, sandstone intrusions may serve as high-permeability fluid flow passage for a long term and has great significance for vertical migration of fluid. More importantly, sandstone intrusions may serve as favorable reservoirs. So it has a great guiding significance to evaluation of cap-rock sealing capacity and hydrocarbon exploration.
Sandstone intrusions are a common class of soft-sediment deformation. They are formed by the forceful intrusion of fluidization sand into overlying sealing sequence during early stages of burial. Based on 3-D high-resolution seismic data and logging data, we utilize methods of seismic reflection configuration analysis and coherence cube slice to illustrate geometry and induced mechanism of sandstone intrusions. Results indicated that sand intrusions appear V-shaped or W-shaped high amplitude anomalies in seismic sections; conical bodies are 1-2 km on the plane and up to hundreds of meters high; fluid emplacement and polygonal fault systems inducing cap-rock fracture are the key factors for overpressure of depositional sand body and fluidization of sand. After injection, sandstone intrusions may serve as high-permeability fluid flow passage for a long term and has great significance for vertical migration of fluid. More importantly, sandstone intrusions may serve as favorable reservoirs. So it has a great guiding significance to evaluation of cap-rock sealing capacity and hydrocarbon exploration.
2017, 35(6): 1197-1204.
doi: 10.14027/j.cnki.cjxb.2017.06.011
Abstract:
Submarine channels as the main reservoir of deep-water oil and gas is an important goal of deep-water oil and gas exploration in passive continental margin basin. The multi-periodic tectonic activities of the salt structures result in being not clear about the distribution law of channel sand body in the Lower Congo Basin. The research on interactions between submarine channels and salt structures contributes to predict the distribution of channel sand body. In salt structures and submarine channels widely developed area of Lower Congo Basin, based on three-dimensional seismic data, the interactions between salt structures and submarine channels are analyzed and build the interaction model of salt structures related to submarine channels is established. Six submarine channels-salt structures interactions can be defined, respectively, as confinement, diversion, blocking, corrosion, deflection, and erosion. The interactions between channels and salt structures may be dictated by the timing of salt structural activities related to the channel development and the erosional power of the channels. Salt structures which predate the channel development and the weak erosional power of the flows within the submarine channels cause channels to take a moderate confinement or diversion. When the erosional power of the flows is strong enough, submarine channels can continue to incise across the salt structures. The large-scale salt structures can block the submarine channels causing reflection of turbidity alone the submarine channel, and lobes develop. Activities of the salt structures which are consistent with channels development may cause deflection. Overlying submarine channels which predate salt structures may be eroded.
Submarine channels as the main reservoir of deep-water oil and gas is an important goal of deep-water oil and gas exploration in passive continental margin basin. The multi-periodic tectonic activities of the salt structures result in being not clear about the distribution law of channel sand body in the Lower Congo Basin. The research on interactions between submarine channels and salt structures contributes to predict the distribution of channel sand body. In salt structures and submarine channels widely developed area of Lower Congo Basin, based on three-dimensional seismic data, the interactions between salt structures and submarine channels are analyzed and build the interaction model of salt structures related to submarine channels is established. Six submarine channels-salt structures interactions can be defined, respectively, as confinement, diversion, blocking, corrosion, deflection, and erosion. The interactions between channels and salt structures may be dictated by the timing of salt structural activities related to the channel development and the erosional power of the channels. Salt structures which predate the channel development and the weak erosional power of the flows within the submarine channels cause channels to take a moderate confinement or diversion. When the erosional power of the flows is strong enough, submarine channels can continue to incise across the salt structures. The large-scale salt structures can block the submarine channels causing reflection of turbidity alone the submarine channel, and lobes develop. Activities of the salt structures which are consistent with channels development may cause deflection. Overlying submarine channels which predate salt structures may be eroded.
2017, 35(6): 1205-1216.
doi: 10.14027/j.cnki.cjxb.2017.06.012
Abstract:
Because the strontium isotope is not easy to be fractionated and can be compared with the time, the strontium isotope can be used as an effective index of fluid tracing. Oxygen isotopes can reflect the temperature, fluid and other factors, and carbon isotopes can reflect the organic matter, so they can be used as the strontium isotope supplement. The time and possibility of opening of in different parts of the fault can be judged by using fluid tracing diagram. In this paper, we take the example of faults around the anticlinal belt Jiao Shi Ba and make use of strontium, carbon and oxygen isotopes in the veins to study the vertical sealing of faults. The evaluation results show that the strata under the Silurian strata are communication in this area and there is a period of strontium-rich fluid from deep crust. But protected by decollement from mudstone in the Silurian strata, the period of strontium rich fluid cannot migration to upper strata through faults. This area was at last through two times of tectonic movement in the late period. Aiming at Silurian Longmaxi shale gas reservoir, different faults have obvious differences. From the plane of view, the vertical sealing of faults in the middle of Fangdoushan fault zone, and the south of Daershan fault zone, the south of Wujiang fault zone is bad. The vertical sealing of faults in the north of Wujinag fault zone, the south of Tiantaichang fault zone is medium. The vertical sealing of faults in the north of Fangdoushan fault zone, the south of Fangdoushan fault zone, and the north of Tiantaichang fault zone is good.
Because the strontium isotope is not easy to be fractionated and can be compared with the time, the strontium isotope can be used as an effective index of fluid tracing. Oxygen isotopes can reflect the temperature, fluid and other factors, and carbon isotopes can reflect the organic matter, so they can be used as the strontium isotope supplement. The time and possibility of opening of in different parts of the fault can be judged by using fluid tracing diagram. In this paper, we take the example of faults around the anticlinal belt Jiao Shi Ba and make use of strontium, carbon and oxygen isotopes in the veins to study the vertical sealing of faults. The evaluation results show that the strata under the Silurian strata are communication in this area and there is a period of strontium-rich fluid from deep crust. But protected by decollement from mudstone in the Silurian strata, the period of strontium rich fluid cannot migration to upper strata through faults. This area was at last through two times of tectonic movement in the late period. Aiming at Silurian Longmaxi shale gas reservoir, different faults have obvious differences. From the plane of view, the vertical sealing of faults in the middle of Fangdoushan fault zone, and the south of Daershan fault zone, the south of Wujiang fault zone is bad. The vertical sealing of faults in the north of Wujinag fault zone, the south of Tiantaichang fault zone is medium. The vertical sealing of faults in the north of Fangdoushan fault zone, the south of Fangdoushan fault zone, and the north of Tiantaichang fault zone is good.
2017, 35(6): 1217-1224.
doi: 10.14027/j.cnki.cjxb.2017.06.013
Abstract:
Using the data of cores and thin sections, based on the classification of Ma541 reservoir pore types in the study area and through the pore description of thin sections, the image analysis of casting thin sections and other methods, this paper gives a detailed classification of gypsum-model pore filling types and makes an elaboration of filling process. The study shows that Ma541 reservoir developed the following 4 pore types as dissolved pore (anhydrite-model pore and other solution pores), intercrystalline pore, intercrystalline solution pores and microcrack in the study area. According to the analysis to the carbon-oxygen isotopic characteristics of different fillings in the anhydrite-model pore, the fillings are mainly composed of dolomite, calcite and anhydrite, the fillings of partial filling anhydrite-model pore are mainly composed of dolomite silts, dolomite silts + quartz, dolomite silts + ankerite and the fillings of all filling anhydrite-model pore are mainly composed of dolomite silts + calcite, dolomite silts + quartz + calcite and dolomite silts + anhydrite. The comprehensive analysis reveals that the anhydrite-model pore is formed by the preservation of crystal outline after the dissolution of gypsum and other easily soluble crystals. Filling process in the anhydrite-model pore can be divided into the following several stages. Firstly, the anhydrite-model pore is filled with dolomite silts and dark-gray calcite in the naked weathering period. Then, the anhydrite-model pore is filled with authigenic quartz, white sparry calcite, ankerite and anhydrite.
Using the data of cores and thin sections, based on the classification of Ma541 reservoir pore types in the study area and through the pore description of thin sections, the image analysis of casting thin sections and other methods, this paper gives a detailed classification of gypsum-model pore filling types and makes an elaboration of filling process. The study shows that Ma541 reservoir developed the following 4 pore types as dissolved pore (anhydrite-model pore and other solution pores), intercrystalline pore, intercrystalline solution pores and microcrack in the study area. According to the analysis to the carbon-oxygen isotopic characteristics of different fillings in the anhydrite-model pore, the fillings are mainly composed of dolomite, calcite and anhydrite, the fillings of partial filling anhydrite-model pore are mainly composed of dolomite silts, dolomite silts + quartz, dolomite silts + ankerite and the fillings of all filling anhydrite-model pore are mainly composed of dolomite silts + calcite, dolomite silts + quartz + calcite and dolomite silts + anhydrite. The comprehensive analysis reveals that the anhydrite-model pore is formed by the preservation of crystal outline after the dissolution of gypsum and other easily soluble crystals. Filling process in the anhydrite-model pore can be divided into the following several stages. Firstly, the anhydrite-model pore is filled with dolomite silts and dark-gray calcite in the naked weathering period. Then, the anhydrite-model pore is filled with authigenic quartz, white sparry calcite, ankerite and anhydrite.
2017, 35(6): 1225-1240.
doi: 10.14027/j.cnki.cjxb.2017.06.014
Abstract:
Based on the analysis of core facies, logging facies, seismic facies and analysis assay data, with the field practice induction of glutenite sedimentary,this paper draw conclusions that:Fan-fan delta glutenite sedimentary system under the control of contemporaneous reverse thrust show the progradation deposition on the whole in P3w. Indicating the phase-sequence characteristics called "Alluvial fan toe (channel flow)-Alluvial fan middle/Fan delta plain (braided stream)-Fan delta front(distributary belt)-former fan delta/shallow lake (be mixed up with subaqueous fan)".with the development of such five typical glutenite sedimentary microfacies types as channel flow, debris flow/sandy debris flow, braided channel, underwater distributary channel, sectoral waterway. The cumulative effect of contemporaneous reverse fault belt continuous uplifting and denudation, make the sedimentary of fan toe in alluvial fan thinning, with more and more obvious trend of contemporaneous reverse fault controlling the sedimentary facies differentiation. Shale content is the key control factors of glutenite reservoir quality under the extrusion background. The diagenetic compaction cut hole effect in poor mud glutenite reservoir is weak, with the higher residual intergranular pore development and the higher development level of crush seam in coarse particles communicating intergranular pore, the reservoir quality of poor mud glutenite is best. Based on combination of reservoir space,the favorable reservoir facies belt can be divided into two types:primary intergranular pore-crush seam development zones and primary intergranular pore-secondary dissolution pore development zones. The former mainly distributed in the fault zone-upper slope belt near structural high position, the latter mainly distributed in middle-lower slope belt.
Based on the analysis of core facies, logging facies, seismic facies and analysis assay data, with the field practice induction of glutenite sedimentary,this paper draw conclusions that:Fan-fan delta glutenite sedimentary system under the control of contemporaneous reverse thrust show the progradation deposition on the whole in P3w. Indicating the phase-sequence characteristics called "Alluvial fan toe (channel flow)-Alluvial fan middle/Fan delta plain (braided stream)-Fan delta front(distributary belt)-former fan delta/shallow lake (be mixed up with subaqueous fan)".with the development of such five typical glutenite sedimentary microfacies types as channel flow, debris flow/sandy debris flow, braided channel, underwater distributary channel, sectoral waterway. The cumulative effect of contemporaneous reverse fault belt continuous uplifting and denudation, make the sedimentary of fan toe in alluvial fan thinning, with more and more obvious trend of contemporaneous reverse fault controlling the sedimentary facies differentiation. Shale content is the key control factors of glutenite reservoir quality under the extrusion background. The diagenetic compaction cut hole effect in poor mud glutenite reservoir is weak, with the higher residual intergranular pore development and the higher development level of crush seam in coarse particles communicating intergranular pore, the reservoir quality of poor mud glutenite is best. Based on combination of reservoir space,the favorable reservoir facies belt can be divided into two types:primary intergranular pore-crush seam development zones and primary intergranular pore-secondary dissolution pore development zones. The former mainly distributed in the fault zone-upper slope belt near structural high position, the latter mainly distributed in middle-lower slope belt.
2017, 35(6): 1241-1253.
doi: 10.14027/j.cnki.cjxb.2017.06.015
Abstract:
Based on the microscopic description of core, macroscopic observation, 3D seismic data interpretation and previous research results, this paper studied the sedimentary characteristics, patterns and influencing factors of the gravity flow in Paleogene of Nanpu sag. Research results show that:Slump rock, Sandy debris flow, Turbidity flow is the mainly types of gravity flow deposit in Nanpu sag. Among them,the development degree of sandy debris flow is the highest. Cumulative thickness of single well drilling is 220 m, single layer thickness is up to 30 m. Cumulative grain-size distribution curve largely present two stages, C-M diagram is parallel to the QR segment,this Shows the origin of the deposited non-traction flow; Turbidity flow develops positive grading. Single layer thickness is less than 1 m but it has characteristic of multiple stage development. Incomplete BaoMa sequence can be seen in it and Tc Period is easier to see but Td Period is rare. Turbidity flow is commonly found in the outer and upper parts of sandy debris flow deposit; the size of slump rock particle is smaller, crumpled structure and convolute bedding are extremely developed, the development degree of slump rock is higher in structure 4. Shaleitian, Matouying and other uplifts, active volcano, fault activity and earthquake in Paleogene, deep water environment of Dongying Formation and Shahejie Formation, as well as slope break zone provide the conditions for gravity flow deposition. Finally, considering the various factors we establish gravity flow sedimentation model of fan delta-short steep slope type (structure 1,4) and Braided River Delta-long ramp type(structure 2,3) for Nanpu sag, and then this paper analyzes different deposition rules of them.
Based on the microscopic description of core, macroscopic observation, 3D seismic data interpretation and previous research results, this paper studied the sedimentary characteristics, patterns and influencing factors of the gravity flow in Paleogene of Nanpu sag. Research results show that:Slump rock, Sandy debris flow, Turbidity flow is the mainly types of gravity flow deposit in Nanpu sag. Among them,the development degree of sandy debris flow is the highest. Cumulative thickness of single well drilling is 220 m, single layer thickness is up to 30 m. Cumulative grain-size distribution curve largely present two stages, C-M diagram is parallel to the QR segment,this Shows the origin of the deposited non-traction flow; Turbidity flow develops positive grading. Single layer thickness is less than 1 m but it has characteristic of multiple stage development. Incomplete BaoMa sequence can be seen in it and Tc Period is easier to see but Td Period is rare. Turbidity flow is commonly found in the outer and upper parts of sandy debris flow deposit; the size of slump rock particle is smaller, crumpled structure and convolute bedding are extremely developed, the development degree of slump rock is higher in structure 4. Shaleitian, Matouying and other uplifts, active volcano, fault activity and earthquake in Paleogene, deep water environment of Dongying Formation and Shahejie Formation, as well as slope break zone provide the conditions for gravity flow deposition. Finally, considering the various factors we establish gravity flow sedimentation model of fan delta-short steep slope type (structure 1,4) and Braided River Delta-long ramp type(structure 2,3) for Nanpu sag, and then this paper analyzes different deposition rules of them.
2017, 35(6): 1254-1264.
doi: 10.14027/j.cnki.cjxb.2017.06.016
Abstract:
Over 500 kerogens as well selected saturate and aromatic fractions and n-alkanes from various age source rocks in the Sichuan basin were analyzed using MS and GC-ir-MS for δ13C ratios, to characterize the age-trend in organic carbon isotopic composition in marine and terrestrial sediments and their thermal evolution during over-mature stage. Moreover, different kind of marine and terrestrial source rocks with respect to their biological organic sources were distinguished using carbon isotopes in combination with other analytical data. The results indicate the kerogens from marine sediments in Sinian Dengying to middle Triassic Leikoupo Formations in this basin show a trend toward isotopically heavy values with decreasing age, possibly due to biological evolution. Whereas, a reversal isotopic-age trend for the terrigenous organic carbon is observed in upper Triassic Xujiahe to middle Jurassic Qingfoyan Formations and is considered to be dependent of biological source and sedimentary environment. The organic inputs of marine and terrestrial source rocks cannot be differentiated using the carbon isotopic ratios of kerogen, however, it can be distinguished by δ13C values of saturated and aromatic fractions and CV values. The marine and lacustrine source rocks with different facies are of obviously varying δ13C values of kerogens, thus the isotopic ratio, combined with additional relate-source data, can be acted as an indicator for their organic source. Coal and mudstone in coal-bearing strata is not distinguishable for their kerogen carbon isotopes, but has different profiles of n-alkane isotopes with more negative values in mudstone related to coal. The marine (type-Ⅱ)and terrigenous (type-Ⅲ) kerogens both continuously become isotopically enriched in 13C by 1‰~2‰ with maturation during high-over maturity. The negatively sloping curve of carbon isotope for individual n-alkanes from coaly source rock at mature stage is transferred into a flat one at high maturity. These variations in carbon isotope compositions are helpful for oil & gas-rock correlation and hydrocarbon source identification.
Over 500 kerogens as well selected saturate and aromatic fractions and n-alkanes from various age source rocks in the Sichuan basin were analyzed using MS and GC-ir-MS for δ13C ratios, to characterize the age-trend in organic carbon isotopic composition in marine and terrestrial sediments and their thermal evolution during over-mature stage. Moreover, different kind of marine and terrestrial source rocks with respect to their biological organic sources were distinguished using carbon isotopes in combination with other analytical data. The results indicate the kerogens from marine sediments in Sinian Dengying to middle Triassic Leikoupo Formations in this basin show a trend toward isotopically heavy values with decreasing age, possibly due to biological evolution. Whereas, a reversal isotopic-age trend for the terrigenous organic carbon is observed in upper Triassic Xujiahe to middle Jurassic Qingfoyan Formations and is considered to be dependent of biological source and sedimentary environment. The organic inputs of marine and terrestrial source rocks cannot be differentiated using the carbon isotopic ratios of kerogen, however, it can be distinguished by δ13C values of saturated and aromatic fractions and CV values. The marine and lacustrine source rocks with different facies are of obviously varying δ13C values of kerogens, thus the isotopic ratio, combined with additional relate-source data, can be acted as an indicator for their organic source. Coal and mudstone in coal-bearing strata is not distinguishable for their kerogen carbon isotopes, but has different profiles of n-alkane isotopes with more negative values in mudstone related to coal. The marine (type-Ⅱ)and terrigenous (type-Ⅲ) kerogens both continuously become isotopically enriched in 13C by 1‰~2‰ with maturation during high-over maturity. The negatively sloping curve of carbon isotope for individual n-alkanes from coaly source rock at mature stage is transferred into a flat one at high maturity. These variations in carbon isotope compositions are helpful for oil & gas-rock correlation and hydrocarbon source identification.
2017, 35(6): 1265-1273.
doi: 10.14027/j.cnki.cjxb.2017.06.017
Abstract:
The trace elements of sedimentary rocks have a high sensitivity on hydrological changes of sedimentary environment, so the trace elements can be used as an effective method on the study of paleoclimate and paleoenvironment during deposition period. The Zhifang Formation in Ordos Basin is a new series of strata of Triassic with oil & gas seeps, the ancient climate and ancient water environment have great significance in restoring the ancient sedimentary framework and geography of that period and hydrocarbon accumulation. In this paper, the trace element of the profile and 21 shale and siltstone core sample of the middle Triassic Zhifang Formation in Ordos Basin have been determined by means of ICP-MS, and trace elements of strontium (Sr), ba (Ba), thorium (Th), uranium (U), vanadium (V), nickel (Ni), cobalt (Co) were selected as the discriminant mark, and combining sedimentology and sporopollen analysis, the sedimentary environment and ancient climate characteristics of Ordos Basin were discussed. The results show that by Li, Sr, Ni, Ga content and the ratio of Sr/Ba indicating the sedimentary environment was continental fresh-brackish water. The ratio of U/Th is from 0.09 to 0.38, δU is from 0.43 to 1.07, the ratio of V/(V+Ni)is from 0.69 to 0.89, the ratio of V/Cr is from 0.87 to 5.57, the ratio of Ni/Co is from 1.21 to 2.93, which indicate the oxidation-weak reduction environment. Combining sedimentology mark and quantitative calculation of Co elements, the average water depth of Zhifang Formation is less than 30 m, and the large catchment lake has not yet formed. The ratio of Sr/Cu is from 0.85 to 16.7, most Sr/Cu ratio is less than 10, and combining with the sporopollen analysis, which show that the dry climate of Heshanggou Formation was translated into warm climate of Zhifang Formation.
The trace elements of sedimentary rocks have a high sensitivity on hydrological changes of sedimentary environment, so the trace elements can be used as an effective method on the study of paleoclimate and paleoenvironment during deposition period. The Zhifang Formation in Ordos Basin is a new series of strata of Triassic with oil & gas seeps, the ancient climate and ancient water environment have great significance in restoring the ancient sedimentary framework and geography of that period and hydrocarbon accumulation. In this paper, the trace element of the profile and 21 shale and siltstone core sample of the middle Triassic Zhifang Formation in Ordos Basin have been determined by means of ICP-MS, and trace elements of strontium (Sr), ba (Ba), thorium (Th), uranium (U), vanadium (V), nickel (Ni), cobalt (Co) were selected as the discriminant mark, and combining sedimentology and sporopollen analysis, the sedimentary environment and ancient climate characteristics of Ordos Basin were discussed. The results show that by Li, Sr, Ni, Ga content and the ratio of Sr/Ba indicating the sedimentary environment was continental fresh-brackish water. The ratio of U/Th is from 0.09 to 0.38, δU is from 0.43 to 1.07, the ratio of V/(V+Ni)is from 0.69 to 0.89, the ratio of V/Cr is from 0.87 to 5.57, the ratio of Ni/Co is from 1.21 to 2.93, which indicate the oxidation-weak reduction environment. Combining sedimentology mark and quantitative calculation of Co elements, the average water depth of Zhifang Formation is less than 30 m, and the large catchment lake has not yet formed. The ratio of Sr/Cu is from 0.85 to 16.7, most Sr/Cu ratio is less than 10, and combining with the sporopollen analysis, which show that the dry climate of Heshanggou Formation was translated into warm climate of Zhifang Formation.
2017, 35(6): 1274-1283.
doi: 10.14027/j.cnki.cjxb.2017.06.018
Abstract:
Thermophilic microbiology has achieved rapid progress in the past 20 to 30 years and about 70 genera (140 species) of thermophilic bacteria have been found. The optimum growth temperature range for these bacteria is generally above 60℃ or 80℃, and the maximum temperature is 110℃~113℃. Anaerobic microorganisms, including a variety of bacteria like decomposition microorganisms, hydrogenogens and methanogens, are widely distributed from low temperature to high temperature in both shallow and deep deposits. They can be distributed in the deep water or on the surface of rock. The temperature at which these species live is close to the main temperature of oil formation (60℃~100℃).
Microorganisms are unicellular organisms, which have small individuals and simple structures. Each of their cells can directly feel the environmental stimuli when the environment changes. Then, they are more capable of adaptation and easier to generate genetic variations. A hypersaline environment of high temperature, high pressure is suitable for the thermophilic bacteria. The large number discoveries about the thermophilic bacterium provide a solid theoretical basis for understanding the origin of life and the formation of the oil and gas reservoirs. The conversion of sedimentary organic matter into petroleum is related to the process of degradation of macromolecular organic matter (molecular weight can reach tens of thousands to hundreds of thousands) into middle and low molecular compounds and the process of elimination of oxygen-containing (and other heteroatoms-containing) groups. These processes are mainly carried out by the microorganisms. Carbon is the core atom that constitutes life. Microorganisms need to draw the carbon source from the organic matter to form the cellular material, such as cell wall, cell membrane, cytoplasm, and cell nucleus. Macromolecular organic matter can be absorbed by microorganisms when they are gradually broken down into simple organic matter, such as dipeptides from the decomposition of protein and simple sugars from the hydrolysis of carbohydrates. Anaerobic microorganisms will constantly obtain carbons and can help to turn the organic matter into simple compounds gradually. Anaerobic respiration of microorganisms leads to a reduction of the oxygen-containing compounds, forming the compounds that are more reduced than the original ones. As the final electron acceptor material in the anaerobic respiration of sediments, the organic matter containing groups such as hydroxyl, carboxyl, etc. then form the hydrocarbons by elimination of the oxygen-containing groups.
Thermophilic microbiology has achieved rapid progress in the past 20 to 30 years and about 70 genera (140 species) of thermophilic bacteria have been found. The optimum growth temperature range for these bacteria is generally above 60℃ or 80℃, and the maximum temperature is 110℃~113℃. Anaerobic microorganisms, including a variety of bacteria like decomposition microorganisms, hydrogenogens and methanogens, are widely distributed from low temperature to high temperature in both shallow and deep deposits. They can be distributed in the deep water or on the surface of rock. The temperature at which these species live is close to the main temperature of oil formation (60℃~100℃).
Microorganisms are unicellular organisms, which have small individuals and simple structures. Each of their cells can directly feel the environmental stimuli when the environment changes. Then, they are more capable of adaptation and easier to generate genetic variations. A hypersaline environment of high temperature, high pressure is suitable for the thermophilic bacteria. The large number discoveries about the thermophilic bacterium provide a solid theoretical basis for understanding the origin of life and the formation of the oil and gas reservoirs. The conversion of sedimentary organic matter into petroleum is related to the process of degradation of macromolecular organic matter (molecular weight can reach tens of thousands to hundreds of thousands) into middle and low molecular compounds and the process of elimination of oxygen-containing (and other heteroatoms-containing) groups. These processes are mainly carried out by the microorganisms. Carbon is the core atom that constitutes life. Microorganisms need to draw the carbon source from the organic matter to form the cellular material, such as cell wall, cell membrane, cytoplasm, and cell nucleus. Macromolecular organic matter can be absorbed by microorganisms when they are gradually broken down into simple organic matter, such as dipeptides from the decomposition of protein and simple sugars from the hydrolysis of carbohydrates. Anaerobic microorganisms will constantly obtain carbons and can help to turn the organic matter into simple compounds gradually. Anaerobic respiration of microorganisms leads to a reduction of the oxygen-containing compounds, forming the compounds that are more reduced than the original ones. As the final electron acceptor material in the anaerobic respiration of sediments, the organic matter containing groups such as hydroxyl, carboxyl, etc. then form the hydrocarbons by elimination of the oxygen-containing groups.
2017, 35(6): 1284-1292.
doi: 10.14027/j.cnki.cjxb.2017.06.019
Abstract:
Senegal Basin is the largest passive margin basin with salt in western Africa, but it has limited petroleum exploration activities. Only non-commercial petroleum and heavy oil have been discovered before 2010. However, some oil exploration breakthroughs have been made in offshore area in recent five years. The paper analyzed the oils and source biomarkers as well as source rocks rock hydrocarbon potential. The results show that Aptian-Albian and Cenomanian-Turonian source rocks exist in offshore area. The former is characterized by light δ13Corg and lower Sulfur content. The maturity is at oil window or more. The latter is typical of heavy δ13Corg and medium sulfur content. The maturity is at oil window or low. Oil-source correlation indicates that F-1 Albian oil was generated from Aptian-Albian source rocks and F-1 Turonian oil from Cenomanian-Turonian source rocks. While the S-1 Albian oil shows mix sources characteristics.
Senegal Basin is the largest passive margin basin with salt in western Africa, but it has limited petroleum exploration activities. Only non-commercial petroleum and heavy oil have been discovered before 2010. However, some oil exploration breakthroughs have been made in offshore area in recent five years. The paper analyzed the oils and source biomarkers as well as source rocks rock hydrocarbon potential. The results show that Aptian-Albian and Cenomanian-Turonian source rocks exist in offshore area. The former is characterized by light δ13Corg and lower Sulfur content. The maturity is at oil window or more. The latter is typical of heavy δ13Corg and medium sulfur content. The maturity is at oil window or low. Oil-source correlation indicates that F-1 Albian oil was generated from Aptian-Albian source rocks and F-1 Turonian oil from Cenomanian-Turonian source rocks. While the S-1 Albian oil shows mix sources characteristics.
2017, 35(6): 1293-1316.
doi: 10.14027/j.cnki.cjxb.2017.06.020
Abstract:
Sedimentary geochemistry is an important content and tool of sedimentary study, playing an essential role in understanding the evolution of Earth surface system and related resource-environment effects. With the increasing investments in scientific and technological researches, and the laboratory platform construction and technological advance in geochemical analysis, the studies of sedimentary geochemistry in China have stepped into a period of rapid development and gained increasing academic influences in the world. However, to narrow the gap with international leading countries and/or academic communities, sedimentary geochemistry studies in China should persistently aim to more high-quality outcomes and innovations, particularly in aspects of analytical technologies, methods and basic theories. Therefore, the Chinese sedimentological community should strengthen the overall planning and strategic arrangement for the development of sedimentary geochemistry:1) in term of tactics, strive for development and innovation in geochemical theory, method and technology; enhance high-resolution geochronological constraints on sedimentary and diagenetic process; promote the ability of accurate extraction and quantitative modeling for geochemical data; 2) in term of strategy, explore the evolution and distribution of geochemical proxies in greater geological space and time scale; intensify the applications of sedimentary geochemistry on critical scientific issues, such as the co-evolution of geological environment and life at critical transitions in Earth's history, and the formation and evolution of sedimentary ore deposits and fossil fuels. In this context, sedimentary geochemical studies in China are expected to further improve the academic achievement and influence in the world, realizing leapfrog development.
Sedimentary geochemistry is an important content and tool of sedimentary study, playing an essential role in understanding the evolution of Earth surface system and related resource-environment effects. With the increasing investments in scientific and technological researches, and the laboratory platform construction and technological advance in geochemical analysis, the studies of sedimentary geochemistry in China have stepped into a period of rapid development and gained increasing academic influences in the world. However, to narrow the gap with international leading countries and/or academic communities, sedimentary geochemistry studies in China should persistently aim to more high-quality outcomes and innovations, particularly in aspects of analytical technologies, methods and basic theories. Therefore, the Chinese sedimentological community should strengthen the overall planning and strategic arrangement for the development of sedimentary geochemistry:1) in term of tactics, strive for development and innovation in geochemical theory, method and technology; enhance high-resolution geochronological constraints on sedimentary and diagenetic process; promote the ability of accurate extraction and quantitative modeling for geochemical data; 2) in term of strategy, explore the evolution and distribution of geochemical proxies in greater geological space and time scale; intensify the applications of sedimentary geochemistry on critical scientific issues, such as the co-evolution of geological environment and life at critical transitions in Earth's history, and the formation and evolution of sedimentary ore deposits and fossil fuels. In this context, sedimentary geochemical studies in China are expected to further improve the academic achievement and influence in the world, realizing leapfrog development.
