2013 Vol. 31, No. 6
Display Method:
2013, 31(6): 939-953.
Abstract:
Qinling mountain and adjacent Ordos Basin constitute a mountain-basin coupling system. There is a close relation between Qinling uplifting and Ordos Basin forming. Indosinian, a key period of complicated Qingling orogeny, is characterized by the feature of polycyclic evolution. According to isotopic dating, Indosinian movement in Qingling area can be divided into three important stages, i.e., 230~238 Ma, 210~224 Ma and 198~206 Ma. Among them, the geological records in the middle stage are the most abundant. Geochronological correlation between orogenic belt and basin is difficult to be conducted, for it is difficult to study the age of sedimentary strata accurately. The deposition of tuff at the bottom of Ch7 oil bearing formation, an event layer, is characterized by wide spreading, isochronous and instantaneous. Abundant magmatic zircons are hosted in the tuff bed, and will act as a bridge on the isochronous correlation between Qingling orogenic belt and Ordos Basin. Based on U-Pb dating of zircons by the method of LA-ICP-MS collected from the tuff, the ages of tuff layers at the mid-upper and bottom of Ch7 oil bearing formation in Yanchang Formation are 221.8±2.0 Ma and 228.2±2.0 Ma, separately, respectively other depositional event ages are estimated further. It is put forward that the forming ages of uncomformities located at the bottom and top of Yanchang Formation are 237 Ma and 199.6 Ma, respectively, corresponding to the beginning or end of early and late stages of Indosinian tectonic events, and the age of the deepwater sandstone at mid-upper Ch7 and mid-lower Ch6 is formed during 215~224 Ma. Middle events, represented by tuff layer and mass gravity sand body, are identified in this study. The wide spreading tuff at the bottom of Ch7 oil-bearing formation and the thick deepwater sandstone, which is steadily distributed in depositional central of Ordos Basin, are the direct outcome of the middle event. Therefore, Indosinian movement resulted in two tectonic succession boundaries and two event deposits in Ordos Basin. In addition, eight coupling effects which were triggered by the middle event are uncovered in this paper. Some obvious transformations are revealed in sediment, petrology, geochemistry and biology. (1)The tuff layer at the bottom of Ch7 oil-bearing Formation is widely distributed in the west and southwest of Ordos Basin, covering more than 3×104 km2. (2)The landform altered from gentle slope and shallow-water to rapid and intense subsidence and wide spreading deep water. (3)Massive gravity sand body is distributed in the central of lacustrine, with some trace of tectonic event. (4)Asymmetry of basin become serious and the bottom shape is featured by western limb steep and the eastern limb gentle since Ch7 depositional period. (5)Compared with Ch10-Ch8 epoch, the basin central migrated counterclockwise since Ch7 epoch. (6)The sedimentary association developed from braided riverbraided river delta to alluvial fan-fan delta or alluvial fan-braided river-braided river-delta in the southwest and west of Ordos Basin. (7)Divided by the tuff layer at the bottom of Ch7 oil-bearing formation, there is a big gap in the content of quartz, feldspar, carbonate debris and chloritoid between Ch7-Ch1 sandstone and Ch10-Ch8 sandstone. (8)The sporopollen changed greatly. The sporopollen in Ch10-Ch8 strata is characterized by low diversity and fern spore stands dominant position. The sporopollen in Ch7-Ch1 mudstone is of high diversity and the content of gymnosperm pollen is banlance with fern spore. Therefore, comparison of Indosinian tectonic phases between Qinling orogenic zone and Ordos Basin shows a good agreement. However, process of mountain-basin coupling lasted long and is complicated, and further research is needed to be done.
Qinling mountain and adjacent Ordos Basin constitute a mountain-basin coupling system. There is a close relation between Qinling uplifting and Ordos Basin forming. Indosinian, a key period of complicated Qingling orogeny, is characterized by the feature of polycyclic evolution. According to isotopic dating, Indosinian movement in Qingling area can be divided into three important stages, i.e., 230~238 Ma, 210~224 Ma and 198~206 Ma. Among them, the geological records in the middle stage are the most abundant. Geochronological correlation between orogenic belt and basin is difficult to be conducted, for it is difficult to study the age of sedimentary strata accurately. The deposition of tuff at the bottom of Ch7 oil bearing formation, an event layer, is characterized by wide spreading, isochronous and instantaneous. Abundant magmatic zircons are hosted in the tuff bed, and will act as a bridge on the isochronous correlation between Qingling orogenic belt and Ordos Basin. Based on U-Pb dating of zircons by the method of LA-ICP-MS collected from the tuff, the ages of tuff layers at the mid-upper and bottom of Ch7 oil bearing formation in Yanchang Formation are 221.8±2.0 Ma and 228.2±2.0 Ma, separately, respectively other depositional event ages are estimated further. It is put forward that the forming ages of uncomformities located at the bottom and top of Yanchang Formation are 237 Ma and 199.6 Ma, respectively, corresponding to the beginning or end of early and late stages of Indosinian tectonic events, and the age of the deepwater sandstone at mid-upper Ch7 and mid-lower Ch6 is formed during 215~224 Ma. Middle events, represented by tuff layer and mass gravity sand body, are identified in this study. The wide spreading tuff at the bottom of Ch7 oil-bearing formation and the thick deepwater sandstone, which is steadily distributed in depositional central of Ordos Basin, are the direct outcome of the middle event. Therefore, Indosinian movement resulted in two tectonic succession boundaries and two event deposits in Ordos Basin. In addition, eight coupling effects which were triggered by the middle event are uncovered in this paper. Some obvious transformations are revealed in sediment, petrology, geochemistry and biology. (1)The tuff layer at the bottom of Ch7 oil-bearing Formation is widely distributed in the west and southwest of Ordos Basin, covering more than 3×104 km2. (2)The landform altered from gentle slope and shallow-water to rapid and intense subsidence and wide spreading deep water. (3)Massive gravity sand body is distributed in the central of lacustrine, with some trace of tectonic event. (4)Asymmetry of basin become serious and the bottom shape is featured by western limb steep and the eastern limb gentle since Ch7 depositional period. (5)Compared with Ch10-Ch8 epoch, the basin central migrated counterclockwise since Ch7 epoch. (6)The sedimentary association developed from braided riverbraided river delta to alluvial fan-fan delta or alluvial fan-braided river-braided river-delta in the southwest and west of Ordos Basin. (7)Divided by the tuff layer at the bottom of Ch7 oil-bearing formation, there is a big gap in the content of quartz, feldspar, carbonate debris and chloritoid between Ch7-Ch1 sandstone and Ch10-Ch8 sandstone. (8)The sporopollen changed greatly. The sporopollen in Ch10-Ch8 strata is characterized by low diversity and fern spore stands dominant position. The sporopollen in Ch7-Ch1 mudstone is of high diversity and the content of gymnosperm pollen is banlance with fern spore. Therefore, comparison of Indosinian tectonic phases between Qinling orogenic zone and Ordos Basin shows a good agreement. However, process of mountain-basin coupling lasted long and is complicated, and further research is needed to be done.
2013, 31(6): 965-979.
Abstract:
Carbonate rocks are widespread in China, and are important exploration targets for oil and gas. About carbonate facies and facies models, there still exist many problems to be solved, including chaotic nomination of facies, different names for the same environments, different meanings for the same name, incomplete facies models, obscure identification marks in such facies models and difficult application, and so on. In this paper, based on the author's experience of long term study on carbonate rocks and previous studies on modern and ancient carbonate environments, some carbonate facies are redefined, such as platforms, slopes and basins are classified into different types. Carbonate platforms are divided into islolated platform, rimmed platform and offshore platform. Rimmed platform is further divided into steep-slope rimmed platform and gentle-slope rimmed platform; offshore platform is further divided into steep-slope offshore platform and gentle-slope offshored platform. Slope is divided into gentle slope, steep slope and steep cliff. Basin is divided into shallow basin and deep basin. Origin and evolution sequence of platforms are analyzed, and platform evolution is divided into primary stage, early stage, middle stage and late stage. In different stages, platforms show different characteristics. Depositional models of different types of platforms and key characteristics of different facies are summarized.
Carbonate rocks are widespread in China, and are important exploration targets for oil and gas. About carbonate facies and facies models, there still exist many problems to be solved, including chaotic nomination of facies, different names for the same environments, different meanings for the same name, incomplete facies models, obscure identification marks in such facies models and difficult application, and so on. In this paper, based on the author's experience of long term study on carbonate rocks and previous studies on modern and ancient carbonate environments, some carbonate facies are redefined, such as platforms, slopes and basins are classified into different types. Carbonate platforms are divided into islolated platform, rimmed platform and offshore platform. Rimmed platform is further divided into steep-slope rimmed platform and gentle-slope rimmed platform; offshore platform is further divided into steep-slope offshore platform and gentle-slope offshored platform. Slope is divided into gentle slope, steep slope and steep cliff. Basin is divided into shallow basin and deep basin. Origin and evolution sequence of platforms are analyzed, and platform evolution is divided into primary stage, early stage, middle stage and late stage. In different stages, platforms show different characteristics. Depositional models of different types of platforms and key characteristics of different facies are summarized.
2013, 31(6): 994-1000.
Abstract:
A numerical model based on threedimensional incompressible Navier-Stokes equations and turbulence k-ε model for the simulation of turbidity currents is applied to study the flow and deposition of turbidity currents with constant inflows into different slope changes. Simulated results show some important characteristics about the flow of turbidity currents: the depth-averaged velocity of turbidity currents with constant inflows increases with bed slope; the higher the slope, the faster the thickness of currents increases in the downslope direction; on the nearly horizontal bed, velocity drops obviously while that from higher slope still keeps a relative higher velocity; also thickness of the currents increases almost at the same rate in the down stream direction, reflecting a slope-control on the water-entrainment of turbidity currents. As to deposition characteristics, the simulation shows that a critical slope exists for a given sediment: when the slope is lower, there are more deposition on slope than that on horizontal bed, the whole slope increases; while the slope is higher, there are erosion or less deposition on the slope with more deposition on downstream horizontal bed, thus resulting in a decrease in total slope. Understanding those flow and deposition characteristics of turbidity currents may assist us in well interpreting the in-situ profiles from outcrop or seismic survey and reconstructing the environment in which hydrocarbon reservoirs from.
A numerical model based on threedimensional incompressible Navier-Stokes equations and turbulence k-ε model for the simulation of turbidity currents is applied to study the flow and deposition of turbidity currents with constant inflows into different slope changes. Simulated results show some important characteristics about the flow of turbidity currents: the depth-averaged velocity of turbidity currents with constant inflows increases with bed slope; the higher the slope, the faster the thickness of currents increases in the downslope direction; on the nearly horizontal bed, velocity drops obviously while that from higher slope still keeps a relative higher velocity; also thickness of the currents increases almost at the same rate in the down stream direction, reflecting a slope-control on the water-entrainment of turbidity currents. As to deposition characteristics, the simulation shows that a critical slope exists for a given sediment: when the slope is lower, there are more deposition on slope than that on horizontal bed, the whole slope increases; while the slope is higher, there are erosion or less deposition on the slope with more deposition on downstream horizontal bed, thus resulting in a decrease in total slope. Understanding those flow and deposition characteristics of turbidity currents may assist us in well interpreting the in-situ profiles from outcrop or seismic survey and reconstructing the environment in which hydrocarbon reservoirs from.
2013, 31(6): 1008-1013.
Abstract:
Hummocky cross-stratification, as one of the marks of the identification of storm deposits, can reflect the sedimentary structures of turmoil best. The paper, based on the standing wave theory to explain the origin of hummocky cross-stratification, has proposed the view of hummocky cross-stratification forming in the node and the kinetic energy of formation of hummocky cross-stratification or standing wave is approximately constant.Through calculation,explained that the wavelength is longer,the wave height is shorter and the wavelength/wave height is increasing.Explained the variation of hummocky cross-stratification in sedimentary sequence of storm in JiaYuan group of Xu Zhou area,and verified the feasibility of the theory.This view is helpful to study the relationship between sedimentary sequence of storm and depth control.
Hummocky cross-stratification, as one of the marks of the identification of storm deposits, can reflect the sedimentary structures of turmoil best. The paper, based on the standing wave theory to explain the origin of hummocky cross-stratification, has proposed the view of hummocky cross-stratification forming in the node and the kinetic energy of formation of hummocky cross-stratification or standing wave is approximately constant.Through calculation,explained that the wavelength is longer,the wave height is shorter and the wavelength/wave height is increasing.Explained the variation of hummocky cross-stratification in sedimentary sequence of storm in JiaYuan group of Xu Zhou area,and verified the feasibility of the theory.This view is helpful to study the relationship between sedimentary sequence of storm and depth control.
2013, 31(6): 1022-1030.
Abstract:
Research on the Chongqing Yinkuangyakou bauxite deposit revealed that gallium is generally more than the lowest indicators of comprehensive utilization of industrial,gallium content of the bauxite deposits in the ore-bearing series are distributed, and gallium to Al2O3 weakly positive correlation. Sr/Ba ratio inferred continental sedimentation is main; the result which the sample Rb/K value is less than the standard marine sedimentary 0.006 reflected brackish transitional zone deposition to freshwater deposition; U/Th ratio range 0.1 to 0.73 and V/Cr ratio from 0.5 to 2.04, which can distinguish ore-bearing rock series are typical oxidizing environment; Seawater may influence ore-bearing rock series during deposition by the calculation of the ratio of Ni/Co found; Ga/Al ratio varied from 0.53 to 1.74, the mineralization medium pH changed magnitude smaller; containing pyrite from the ore-bearing rock mineral assemblage, kaolinite and other minerals can be inferred that the medium is acidic likely. Chondrite-normalized distribution patterns shows LREE enrichment and HREE losses, δCe <0.95 ( four samples )is negative anomalies, 0.95 <δCe <1.05 for normal samples 3, 19 positive anomalies,Eu shows negative anomalies; the overall aqueous media should mainly freshwater basic in oxidizing and acidic environment. The deposit is a continental deposit with the main freshwater to paralic environment.
Research on the Chongqing Yinkuangyakou bauxite deposit revealed that gallium is generally more than the lowest indicators of comprehensive utilization of industrial,gallium content of the bauxite deposits in the ore-bearing series are distributed, and gallium to Al2O3 weakly positive correlation. Sr/Ba ratio inferred continental sedimentation is main; the result which the sample Rb/K value is less than the standard marine sedimentary 0.006 reflected brackish transitional zone deposition to freshwater deposition; U/Th ratio range 0.1 to 0.73 and V/Cr ratio from 0.5 to 2.04, which can distinguish ore-bearing rock series are typical oxidizing environment; Seawater may influence ore-bearing rock series during deposition by the calculation of the ratio of Ni/Co found; Ga/Al ratio varied from 0.53 to 1.74, the mineralization medium pH changed magnitude smaller; containing pyrite from the ore-bearing rock mineral assemblage, kaolinite and other minerals can be inferred that the medium is acidic likely. Chondrite-normalized distribution patterns shows LREE enrichment and HREE losses, δCe <0.95 ( four samples )is negative anomalies, 0.95 <δCe <1.05 for normal samples 3, 19 positive anomalies,Eu shows negative anomalies; the overall aqueous media should mainly freshwater basic in oxidizing and acidic environment. The deposit is a continental deposit with the main freshwater to paralic environment.
2013, 31(6): 1041-1049.
Abstract:
This study aims to establish a high resolution paleomagnetic age scale of Borehole SZ04 (269.2 m in length) which was drilled from the western part of plain region on the south flank of the Yangtze River Delta. Combining with the absolute age and compared with the standard polarity column, the results show that the 269.2 m core consists of three polarity events including Brunhes, Matuyama and Gauss and three subpolarity events including Black, Jaramillo and Olduvai. The B/M and the M/G boundary are found at the depth of 100 m and 155 m, respectively; Clastic deposit at the bottom of Borehole SZ04 was formed at about 5.23 Ma. Analysis of the dating results indicates that obvious changes of the sediments magnetic susceptibility and lithostratigraphy characteristic are existed near each particular boundaries, which can be correlated with in a large region. Therefore, it is concluded that crust subsidence in this region was continuously occurred since Quaternary, accompanied with the subsidence center moving to the south and the crust subsidence activities were concentrated and intensified in three important time phase at about 2.58 Ma, 0.78 Ma and 0.125 Ma.
This study aims to establish a high resolution paleomagnetic age scale of Borehole SZ04 (269.2 m in length) which was drilled from the western part of plain region on the south flank of the Yangtze River Delta. Combining with the absolute age and compared with the standard polarity column, the results show that the 269.2 m core consists of three polarity events including Brunhes, Matuyama and Gauss and three subpolarity events including Black, Jaramillo and Olduvai. The B/M and the M/G boundary are found at the depth of 100 m and 155 m, respectively; Clastic deposit at the bottom of Borehole SZ04 was formed at about 5.23 Ma. Analysis of the dating results indicates that obvious changes of the sediments magnetic susceptibility and lithostratigraphy characteristic are existed near each particular boundaries, which can be correlated with in a large region. Therefore, it is concluded that crust subsidence in this region was continuously occurred since Quaternary, accompanied with the subsidence center moving to the south and the crust subsidence activities were concentrated and intensified in three important time phase at about 2.58 Ma, 0.78 Ma and 0.125 Ma.
2013, 31(6): 1059-1069.
Abstract:
Nanpu sag, located in Bohai Bay Basin, is a small rift lacustrine basin. In study areas, the sand distributions were effected by the fault activity in different levels and thus study of sequence stratigraphy and sedimentary should be guided by tectonic evolution as a principal axis. Through the analysis of faulting histories in different levels, the filling characteristics of sand body inside the basin can be explained. Combining 580 m core observation and 3D seismic data which covered the entire study area, sedimentary facies and fault evolution in offshore area of Nanpu Sag were defined. Periodic rifting activity in Nanpu sag could be classified into two periods from 31 Ma to 23.5 Ma, one is Shahejie Formation and the other is Donying Formation. Shahejie Formation can be divided into three sub-episodes which correspond with three third order sequences and only two sequences in Shahejie Formation would be discussed because of the overlying strata of study area were eroded in the course of the First member of Shahejie Formation and four third sub-episodes, which correspond to 4 third order sequences, were identified in Dongying Formation. Fan-delta and nearshore subaqueous fan were formed in the hanging wall of boundary fault, and the braided river delta deposits were developed in the gentle slope belt and the gravity flow deposits were found in deep lake and semideep lake area. In the same tectonic unit, steep region or gentle slope, for example, though the feature of sedimentary facies evolution is inheritance, vertical stages are obvious, by analyzing the filling sequences evolution sections. Active intensity of tectonic remains constant in each sub-episode, so vertical stages of sand bodies in the form of foreset and retrograde were controlled mainly by lake-level fluctuations which also have some impact on vertical stages between each sub-episode. After calculated and analyzed the fault activity velocity of Bogezhuang Fault, Gaoliu Fault and the faults in the transition zone coupled with the plans of sedimentary facies, to make clear the control of the fault to the deposition and filling, figured out the distributions of detrital material in catchment basin are strongly controlled by different level of faults which were classified into boundary fault and secondary fault. The activity of boundary fault with time-shared and segmentation control the migration and swing of fan delta deposit around steep slope through controlling the swing of transfer zone around the margin of basin. Some gravity flow deposits caused by earthquake or delta frontal instability occurred re-distribution along the transfer zones, which belong to secondary fault between the edge and inner of the basin. As the secondary fault movement is a multi-stage process, the inner transfer zones control the redistribution of autogenic deposits. All in all, the deposition and filling of basin were controlled by the fault evolution, activity intensity and tectonic styles and structural associations. The lake-level variation and climate exchange also play a very important role in determining the vertical stages in sub-episode. The research on fault activity in different levels and its impact for the depositional sand distribution can provide a new idea for the subsequent exploration.
Nanpu sag, located in Bohai Bay Basin, is a small rift lacustrine basin. In study areas, the sand distributions were effected by the fault activity in different levels and thus study of sequence stratigraphy and sedimentary should be guided by tectonic evolution as a principal axis. Through the analysis of faulting histories in different levels, the filling characteristics of sand body inside the basin can be explained. Combining 580 m core observation and 3D seismic data which covered the entire study area, sedimentary facies and fault evolution in offshore area of Nanpu Sag were defined. Periodic rifting activity in Nanpu sag could be classified into two periods from 31 Ma to 23.5 Ma, one is Shahejie Formation and the other is Donying Formation. Shahejie Formation can be divided into three sub-episodes which correspond with three third order sequences and only two sequences in Shahejie Formation would be discussed because of the overlying strata of study area were eroded in the course of the First member of Shahejie Formation and four third sub-episodes, which correspond to 4 third order sequences, were identified in Dongying Formation. Fan-delta and nearshore subaqueous fan were formed in the hanging wall of boundary fault, and the braided river delta deposits were developed in the gentle slope belt and the gravity flow deposits were found in deep lake and semideep lake area. In the same tectonic unit, steep region or gentle slope, for example, though the feature of sedimentary facies evolution is inheritance, vertical stages are obvious, by analyzing the filling sequences evolution sections. Active intensity of tectonic remains constant in each sub-episode, so vertical stages of sand bodies in the form of foreset and retrograde were controlled mainly by lake-level fluctuations which also have some impact on vertical stages between each sub-episode. After calculated and analyzed the fault activity velocity of Bogezhuang Fault, Gaoliu Fault and the faults in the transition zone coupled with the plans of sedimentary facies, to make clear the control of the fault to the deposition and filling, figured out the distributions of detrital material in catchment basin are strongly controlled by different level of faults which were classified into boundary fault and secondary fault. The activity of boundary fault with time-shared and segmentation control the migration and swing of fan delta deposit around steep slope through controlling the swing of transfer zone around the margin of basin. Some gravity flow deposits caused by earthquake or delta frontal instability occurred re-distribution along the transfer zones, which belong to secondary fault between the edge and inner of the basin. As the secondary fault movement is a multi-stage process, the inner transfer zones control the redistribution of autogenic deposits. All in all, the deposition and filling of basin were controlled by the fault evolution, activity intensity and tectonic styles and structural associations. The lake-level variation and climate exchange also play a very important role in determining the vertical stages in sub-episode. The research on fault activity in different levels and its impact for the depositional sand distribution can provide a new idea for the subsequent exploration.
2013, 31(6): 1070-1080.
Abstract:
Based on the analysis of seismic data, drilling data, drilling, paleontological data and well-seismic calibration, and combined with the characteristic of sedimentary sequence, tectonic evolution and climate periodic change in Chepaizi area, northwestern margin of Junggar Basin, the lower Cretaceous could be divided into 4 3rd order sequences under the guidance of high-resolution sequence stratigraphy analysis method. A sequence stratigraphic model for depression basin without slope break was established according to the gentle slope tectonic setting in Chepaizi area. In this model, the third-order sequence consisted of 2 system tracts, transgressive system tract (TST) and regressive system tract (RST). Coarse-grained fan delta front and fine-grained shore-shallow lacustrine was mainly developed in TST, and relatively coarse-grained shore-shallow lacustrine was developed in RST. The cyclicity feature of sediment evolution in the study area was obvious. Both the episodic movement and the ancient climate change of Lower Cretaceous play an important role during the sequence development.
Based on the analysis of seismic data, drilling data, drilling, paleontological data and well-seismic calibration, and combined with the characteristic of sedimentary sequence, tectonic evolution and climate periodic change in Chepaizi area, northwestern margin of Junggar Basin, the lower Cretaceous could be divided into 4 3rd order sequences under the guidance of high-resolution sequence stratigraphy analysis method. A sequence stratigraphic model for depression basin without slope break was established according to the gentle slope tectonic setting in Chepaizi area. In this model, the third-order sequence consisted of 2 system tracts, transgressive system tract (TST) and regressive system tract (RST). Coarse-grained fan delta front and fine-grained shore-shallow lacustrine was mainly developed in TST, and relatively coarse-grained shore-shallow lacustrine was developed in RST. The cyclicity feature of sediment evolution in the study area was obvious. Both the episodic movement and the ancient climate change of Lower Cretaceous play an important role during the sequence development.
2013, 31(6): 1088-1093.
Abstract:
As a key parameter in high-resolution sequence stratigraphy, the ratio of accommodation to sediment supply, named A/S for short, has been used to divide stratigrahpic base-level cycles. However, A/S has been classified into unity, increasing, decreasing and below zero, without any real data. According to the record of litho-facies and its thickness responded to the variation of A/S, this paper proposes an approach, named A/S interval quantization principle within special interval, to quantify the real data of A/S. Based on the former research, we found real sedimentary model, and set number on each litho-facies within the model (from bottom to top, ZYXWDCBA, 12345678, respectively). According the numbers' changing, they are classified two intervals, base-level rising (number bigger upward) and base-level falling (number smaller upward). In each interval, we define the ratio, number of sediment litho-face to number of bottom sediment litho-face, as A/S data, and every A/S data of litho-face is the same. The A/S data and its vertical changing has the same meanings with which in high-resolution sequence stratigraphy. Applying the approach, we quantify A/S data on classic braided-river sedimentary litho-faces. With two practices, we found the A/S data on the former research, and based on which to classify short-term base-level cycle. Comparing with the former research, the division of base-level based on the approach has ideal similarity. At the same time, the division is single and operation-simple, which can avoid the phenomenon that different base-level division in the same sediment.
As a key parameter in high-resolution sequence stratigraphy, the ratio of accommodation to sediment supply, named A/S for short, has been used to divide stratigrahpic base-level cycles. However, A/S has been classified into unity, increasing, decreasing and below zero, without any real data. According to the record of litho-facies and its thickness responded to the variation of A/S, this paper proposes an approach, named A/S interval quantization principle within special interval, to quantify the real data of A/S. Based on the former research, we found real sedimentary model, and set number on each litho-facies within the model (from bottom to top, ZYXWDCBA, 12345678, respectively). According the numbers' changing, they are classified two intervals, base-level rising (number bigger upward) and base-level falling (number smaller upward). In each interval, we define the ratio, number of sediment litho-face to number of bottom sediment litho-face, as A/S data, and every A/S data of litho-face is the same. The A/S data and its vertical changing has the same meanings with which in high-resolution sequence stratigraphy. Applying the approach, we quantify A/S data on classic braided-river sedimentary litho-faces. With two practices, we found the A/S data on the former research, and based on which to classify short-term base-level cycle. Comparing with the former research, the division of base-level based on the approach has ideal similarity. At the same time, the division is single and operation-simple, which can avoid the phenomenon that different base-level division in the same sediment.
2013, 31(6): 1105-1113.
Abstract:
There are gravity flow sediment in the third section, Shahejie Formation, Eocene in Shuangtaizi Structure Belt, Liaohe depression. Middle fan and outer fan are the main types of sedimentary facies. Growth fault and palaeogeomorphology co-controlled the deposition, and their distribution characteristics are depicted. Then, sedimentary facies controlling factors are studied. A sedimentary model that channel controlled distribution of sand, slope gradient controlled shape, and provenance controlled supplement of sediment is built up. Braided channel is controlled by growth fault and paleogeomorphology. Through the study of sedimentary facies, several results are concluded: in Shuangnan, as the slope of paleo-geomorphology is gentle, the transport distance of the braided channel sediments is long, the sinuosity is great, depositional differentiation is apparent, and the sediments characteristic is thin bed interbedding of sandstone and mudstone. However, in Shuangtaizi, as the slope of paleo-geomorphology is sharp, the transport distance of the braided channel sediments is short, the sinuosity is low, sedimentary differentiation is weak, and the sediments characteristic is interbedding of thick bed sandstone and thin bed mudstone. The differences of sedimentary mechanism between Shuangtaizi and Shuangnan make differences of the sedimentary facies distribution and sand body interbedding architectures in these two areas. Shuangtaizi has better sedimentary facies than Shuangnan, which is important to the reservoir quality.
There are gravity flow sediment in the third section, Shahejie Formation, Eocene in Shuangtaizi Structure Belt, Liaohe depression. Middle fan and outer fan are the main types of sedimentary facies. Growth fault and palaeogeomorphology co-controlled the deposition, and their distribution characteristics are depicted. Then, sedimentary facies controlling factors are studied. A sedimentary model that channel controlled distribution of sand, slope gradient controlled shape, and provenance controlled supplement of sediment is built up. Braided channel is controlled by growth fault and paleogeomorphology. Through the study of sedimentary facies, several results are concluded: in Shuangnan, as the slope of paleo-geomorphology is gentle, the transport distance of the braided channel sediments is long, the sinuosity is great, depositional differentiation is apparent, and the sediments characteristic is thin bed interbedding of sandstone and mudstone. However, in Shuangtaizi, as the slope of paleo-geomorphology is sharp, the transport distance of the braided channel sediments is short, the sinuosity is low, sedimentary differentiation is weak, and the sediments characteristic is interbedding of thick bed sandstone and thin bed mudstone. The differences of sedimentary mechanism between Shuangtaizi and Shuangnan make differences of the sedimentary facies distribution and sand body interbedding architectures in these two areas. Shuangtaizi has better sedimentary facies than Shuangnan, which is important to the reservoir quality.
2013, 31(6): 1122-1132.
Abstract:
Based on the analysis of TOC, trace elements of 3 typical Cambrian stratigraphic sections from platform-slope-basin in west Hunan-Hubei area. V/(V+Ni), U/Th, Ni/Co indicated Cambrian sediment turn from strong reducing environment to oxidized environment, and with a few oxidation-deoxidation sediment periodicity in slope zone. After normalized by NASC, δEu with positive anomaly and δCe with negative anomaly, and the abnormal degree showed a deeper-water from platform-slope-basin, as a whole regression after transgression in Cambrian. The environment of source rock in the bottom of Niutitang Formation was productive, strong reducing, and transgressive; the high TOC shale probably has relationship with reductive, nutritive elements-rich hydrothermal fluid flow, which upwelled along deep fracture during the transition from Sinian to Cambrian, and also with episodicity upwelling.
Based on the analysis of TOC, trace elements of 3 typical Cambrian stratigraphic sections from platform-slope-basin in west Hunan-Hubei area. V/(V+Ni), U/Th, Ni/Co indicated Cambrian sediment turn from strong reducing environment to oxidized environment, and with a few oxidation-deoxidation sediment periodicity in slope zone. After normalized by NASC, δEu with positive anomaly and δCe with negative anomaly, and the abnormal degree showed a deeper-water from platform-slope-basin, as a whole regression after transgression in Cambrian. The environment of source rock in the bottom of Niutitang Formation was productive, strong reducing, and transgressive; the high TOC shale probably has relationship with reductive, nutritive elements-rich hydrothermal fluid flow, which upwelled along deep fracture during the transition from Sinian to Cambrian, and also with episodicity upwelling.
Cretaceous Sedimentary System and Their Relationship with Danxia Landform in Xinjiang Basin, Jiangxi
2013, 31(6): 954-964.
Abstract:
By the depositional sequence, characteristics of petrology, paleo-ecology and landscape characteristics, this article discussed the cretaceous depositional system in Xinjiang Basin, Jiangxi. The author first discusses the relationship between the depositional system and Danxia landform. There are four kinds of depositional systems in Cretaceous of Xinjiang Basin: alluviation (proluvial), delta, lake, fan delta. Lower Cretaceous are of mainly semideep-deep lacustrine facies and fan delta sedimentary facies. In upper Cretaceous, the sedimentary facies distribution from south to north are flood alluvial facies, braided river, delta, beach-shallow lake, delta, braided river, flood alluvial facies. Further studied found that developed a large number of interconnected alluvial fan apron in the North and South margins of Xinjiang Basin, While the typical Danxia landforms are developed within a few places. The reason is not all of the alluvial fan can formed Danxia landform, the conditions of Danxia landform development is preserved much period superposition of the alluvial fan. According to the principle of sequence stratigraphy, must have certain space to make every alluvial fan product can be preserved. Through detailed field observation found that alluvial fan can develop deep valley only in the place of development of fracture. Deep valley can preserved alluvial fan to provide material basis of Danxia landforms. Because there is not enough space developed in Piedmont slope of the Multi stage alluvial fan, at long-term denudation area, is not easy to preserve, can not form the Danxia landforms, or Danxia landforms are small, scattered. In addition, Danxia landform development controlled by sedimentary subfacies and phase. Mainly for the continental basin filling homogeneity degree difference, difference between clastic granularity and cementation state of different sedimentary facies, resistant to weathering ability and ways is different. For example, the micro phase glutenite of main channel , braided stream in alluvial system conglomerate relatively hard, resistant to weathering and erosion capability. But sheetflood with relatively fine sediments such as sandstone, siltstone weathering resistant ability is weak, easily erosion by weathering and water. After the relatively weak interlayer difference weathering and erosion, mountain gravity unbalance, collapse along vertical joints, hard conglomerate, glutenite formed red cliffs, different modelling stone, or a similar strip protrusions or depressions, larger pits can be further developed into rock grooves or cave.The research results show that the Danxia landform of Xinjiang Basin spatial distribution and basin alluvial fan, braided river facies distribution has a good consistency, its developmental types obviously affected by sedimentary subfacies and facies.
By the depositional sequence, characteristics of petrology, paleo-ecology and landscape characteristics, this article discussed the cretaceous depositional system in Xinjiang Basin, Jiangxi. The author first discusses the relationship between the depositional system and Danxia landform. There are four kinds of depositional systems in Cretaceous of Xinjiang Basin: alluviation (proluvial), delta, lake, fan delta. Lower Cretaceous are of mainly semideep-deep lacustrine facies and fan delta sedimentary facies. In upper Cretaceous, the sedimentary facies distribution from south to north are flood alluvial facies, braided river, delta, beach-shallow lake, delta, braided river, flood alluvial facies. Further studied found that developed a large number of interconnected alluvial fan apron in the North and South margins of Xinjiang Basin, While the typical Danxia landforms are developed within a few places. The reason is not all of the alluvial fan can formed Danxia landform, the conditions of Danxia landform development is preserved much period superposition of the alluvial fan. According to the principle of sequence stratigraphy, must have certain space to make every alluvial fan product can be preserved. Through detailed field observation found that alluvial fan can develop deep valley only in the place of development of fracture. Deep valley can preserved alluvial fan to provide material basis of Danxia landforms. Because there is not enough space developed in Piedmont slope of the Multi stage alluvial fan, at long-term denudation area, is not easy to preserve, can not form the Danxia landforms, or Danxia landforms are small, scattered. In addition, Danxia landform development controlled by sedimentary subfacies and phase. Mainly for the continental basin filling homogeneity degree difference, difference between clastic granularity and cementation state of different sedimentary facies, resistant to weathering ability and ways is different. For example, the micro phase glutenite of main channel , braided stream in alluvial system conglomerate relatively hard, resistant to weathering and erosion capability. But sheetflood with relatively fine sediments such as sandstone, siltstone weathering resistant ability is weak, easily erosion by weathering and water. After the relatively weak interlayer difference weathering and erosion, mountain gravity unbalance, collapse along vertical joints, hard conglomerate, glutenite formed red cliffs, different modelling stone, or a similar strip protrusions or depressions, larger pits can be further developed into rock grooves or cave.The research results show that the Danxia landform of Xinjiang Basin spatial distribution and basin alluvial fan, braided river facies distribution has a good consistency, its developmental types obviously affected by sedimentary subfacies and facies.
2013, 31(6): 980-993.
Abstract:
Kuqa foreland basin is filled with three sets of conglomerate, which are Kalazha conglomerate at the top of Upper Jurassic, Yageliemu conglomerate at the bottom of Lower Cretaceous and Bashijiqike Formation at the top of Lower Cretaceous. Through the detailed description of regional distribution, petrological features, sephitic features, variation in thickness and comparison difference in depositional paleoenvironment between the three sets of conglomerate, conclude that these conglomerates have complex composition, low-compositional maturity and low-textual maturity. The characteristics of climate evolution which these conglomerates represent from early to late are arid, semi-arid →warm, moist→arid, hot. It reflects that these conglomerates are composed of three main sedimentary facies: alluvial fan, turbidite fan and seasonal braided river deposit. The relationship between conglomerate and tectonic activity indicates that the Kalazha conglomerate is the sign of tectonic activity during Late Jurassic. Yageliemu conglomerate is the result of over thrusting activities during the beginning of Early Cretaceous. And the conglomerate in Bashijiqike Formation is a sedimentary response to structural stillstand during the end of Early Cretaceous.
Kuqa foreland basin is filled with three sets of conglomerate, which are Kalazha conglomerate at the top of Upper Jurassic, Yageliemu conglomerate at the bottom of Lower Cretaceous and Bashijiqike Formation at the top of Lower Cretaceous. Through the detailed description of regional distribution, petrological features, sephitic features, variation in thickness and comparison difference in depositional paleoenvironment between the three sets of conglomerate, conclude that these conglomerates have complex composition, low-compositional maturity and low-textual maturity. The characteristics of climate evolution which these conglomerates represent from early to late are arid, semi-arid →warm, moist→arid, hot. It reflects that these conglomerates are composed of three main sedimentary facies: alluvial fan, turbidite fan and seasonal braided river deposit. The relationship between conglomerate and tectonic activity indicates that the Kalazha conglomerate is the sign of tectonic activity during Late Jurassic. Yageliemu conglomerate is the result of over thrusting activities during the beginning of Early Cretaceous. And the conglomerate in Bashijiqike Formation is a sedimentary response to structural stillstand during the end of Early Cretaceous.
2013, 31(6): 1001-1007.
Abstract:
The characteristics of the flow and deposition of turbidity currents in deep-sea is a focus of present research. A three-dimensional computational model based on Reynolds-averaged Navier-Stokes equation and buoyancy modified turbulence k-ε model is used to study the flow and deposition of turbidity currents in a sinuous submarine canyon with arc cross-section. The findings are: (1) subaqueous turbidity current generally increases its thickness on its way downstream due to the entrainment of environmental fluid and spills over the bank as soon as its thickness exceeds the height of the canyon, resulting in mass and momentum losses; (2) at channel bend apex, much current strips out due to centrifugal force; the largest local stripping occurs just downstream the outer bank of the bend apex, excess density of the stripped current reaches as much as 37.5% that of inflow; (3) the secondary flow at canyon bend apex is river-like, i.e. directed from outer bank to the inner bank near the bed for the arc-shaped channel simulated; (4) in the canyon simulated, deposition occurs around canyon center and downstream the inner bank of bend apex, while erosion occurs downstream the outer bank of bend apex. Those features may assist us in reconstructing the ancient environments in exploring the submarine hydrocarbon reservoirs by observing the turbidites.
The characteristics of the flow and deposition of turbidity currents in deep-sea is a focus of present research. A three-dimensional computational model based on Reynolds-averaged Navier-Stokes equation and buoyancy modified turbulence k-ε model is used to study the flow and deposition of turbidity currents in a sinuous submarine canyon with arc cross-section. The findings are: (1) subaqueous turbidity current generally increases its thickness on its way downstream due to the entrainment of environmental fluid and spills over the bank as soon as its thickness exceeds the height of the canyon, resulting in mass and momentum losses; (2) at channel bend apex, much current strips out due to centrifugal force; the largest local stripping occurs just downstream the outer bank of the bend apex, excess density of the stripped current reaches as much as 37.5% that of inflow; (3) the secondary flow at canyon bend apex is river-like, i.e. directed from outer bank to the inner bank near the bed for the arc-shaped channel simulated; (4) in the canyon simulated, deposition occurs around canyon center and downstream the inner bank of bend apex, while erosion occurs downstream the outer bank of bend apex. Those features may assist us in reconstructing the ancient environments in exploring the submarine hydrocarbon reservoirs by observing the turbidites.
2013, 31(6): 1014-1021.
Abstract:
PH, conductivity, dissolved oxygen and concentration of HCO3-, Ca2+ , as well as other anion and cation, was monitored by certain space to explain the evolution of stream water chemistry along the flow path of Baishuwan Spring downstream in Nanchuan, Chongqing, China. After surfacing, stream water chemistry was changed regularly by CO2 outgassing, water became increasingly supersaturated with calcium carbonate and the obviously precipitation occurred. The result shows that, concentration of HCO3-, Ca2+, conductivity(EC) and CO2 partial pressure declined along the flow path, caused by CO2 outgassing, while pH value and saturation index of common carbonate minerals increased. The concentration gradient between atmosphere and water is the main factor affecting the degassing rate, while the creek drainage gradient also has a certain influence. Extent of degassing at the spring vent is decisive factors controlling the carbonate deposition along the flow path. The small flow during dry season, a great degree of degassing, high level of Ca2+ concentration, and the hydraulic disturbance which accelerates CO2 outgassing, as well as the physical adsorption of litter and other substances in the creek drainage, factors above all play active role in deposition of calcium carbonate.
PH, conductivity, dissolved oxygen and concentration of HCO3-, Ca2+ , as well as other anion and cation, was monitored by certain space to explain the evolution of stream water chemistry along the flow path of Baishuwan Spring downstream in Nanchuan, Chongqing, China. After surfacing, stream water chemistry was changed regularly by CO2 outgassing, water became increasingly supersaturated with calcium carbonate and the obviously precipitation occurred. The result shows that, concentration of HCO3-, Ca2+, conductivity(EC) and CO2 partial pressure declined along the flow path, caused by CO2 outgassing, while pH value and saturation index of common carbonate minerals increased. The concentration gradient between atmosphere and water is the main factor affecting the degassing rate, while the creek drainage gradient also has a certain influence. Extent of degassing at the spring vent is decisive factors controlling the carbonate deposition along the flow path. The small flow during dry season, a great degree of degassing, high level of Ca2+ concentration, and the hydraulic disturbance which accelerates CO2 outgassing, as well as the physical adsorption of litter and other substances in the creek drainage, factors above all play active role in deposition of calcium carbonate.
2013, 31(6): 1031-1040.
Abstract:
There are a series of depositing travertine domes and salt springs in South Bank of Dogai Coring of Tibet. With results of chemical composition of springs, we found that these springs have a high K concentration and belong tolixiviation brine. Thus, determining the source of K is a very important question. The research on travertine will help us resolve this Problem. Travertine in this area were composed of autochthonous travertine and clastic travertine,and have a high K ,Fe and light REE concentration. REE distribution patterns of different springs have the same trend and show that mineral substance of springs water come from the same stratigraphic position. With a REE comparison of travertine and major strata, we confirm that travertine and Suowa Formation have obvious genetic relationship. This result is consistent with correlation analysis for travertine and Suowa Formation. Combined paleographic and paleoclimatic data, we think that Suowa Formation has an exploration potential of potash. In addition, δD, δ18O and δ13C of salt springs and travertine indicate that H2O of springs come from atmospheric precipitation and CO2 of travertine has a characteristic of lithosphere deep source. Also, travertine in this area is thermogene travertine.
There are a series of depositing travertine domes and salt springs in South Bank of Dogai Coring of Tibet. With results of chemical composition of springs, we found that these springs have a high K concentration and belong tolixiviation brine. Thus, determining the source of K is a very important question. The research on travertine will help us resolve this Problem. Travertine in this area were composed of autochthonous travertine and clastic travertine,and have a high K ,Fe and light REE concentration. REE distribution patterns of different springs have the same trend and show that mineral substance of springs water come from the same stratigraphic position. With a REE comparison of travertine and major strata, we confirm that travertine and Suowa Formation have obvious genetic relationship. This result is consistent with correlation analysis for travertine and Suowa Formation. Combined paleographic and paleoclimatic data, we think that Suowa Formation has an exploration potential of potash. In addition, δD, δ18O and δ13C of salt springs and travertine indicate that H2O of springs come from atmospheric precipitation and CO2 of travertine has a characteristic of lithosphere deep source. Also, travertine in this area is thermogene travertine.
2013, 31(6): 1050-1058.
Abstract:
A 100-m-long sediment core (ZK1) from the modern Huanghe Delta (Bohai Sea) were analyzed to document the stratigraphy and sea-level changes since the Late Quaternary. Accelerator mass spectrometry 14C dating and analyses of benthic foraminifera, ostracods, and sedimentary characteristics were analyzed for Core ZK1. Seven depositional units (DU1 to DU7 in descending order) were identified and interpreted as follows: DU 7 corresponds to terrestrial facies in MIS 4; DU 6 and DU 4, to alternating terrestrial and marine facies in MIS 3; DU 3, to terrestrial facies in MIS 2; DU 2, to Holocene marine facies; and DU 1, to the modern Huanghe Delta sediments deposited since 1855. By correlation with other well-studied cores in the nearby area, three transgressive layers of Core ZK1 were in agreement with Bohai and Xianxian transgressions in MIS3, and Huanghua transgressions in MIS1. These sedimentary facies of Core ZK1 reflect several sea-level fluctuations since MIS4, which played a key role in controlling the sedimentary environments in the study area.
A 100-m-long sediment core (ZK1) from the modern Huanghe Delta (Bohai Sea) were analyzed to document the stratigraphy and sea-level changes since the Late Quaternary. Accelerator mass spectrometry 14C dating and analyses of benthic foraminifera, ostracods, and sedimentary characteristics were analyzed for Core ZK1. Seven depositional units (DU1 to DU7 in descending order) were identified and interpreted as follows: DU 7 corresponds to terrestrial facies in MIS 4; DU 6 and DU 4, to alternating terrestrial and marine facies in MIS 3; DU 3, to terrestrial facies in MIS 2; DU 2, to Holocene marine facies; and DU 1, to the modern Huanghe Delta sediments deposited since 1855. By correlation with other well-studied cores in the nearby area, three transgressive layers of Core ZK1 were in agreement with Bohai and Xianxian transgressions in MIS3, and Huanghua transgressions in MIS1. These sedimentary facies of Core ZK1 reflect several sea-level fluctuations since MIS4, which played a key role in controlling the sedimentary environments in the study area.
2013, 31(6): 1081-1087.
Abstract:
On the basis of previous studies on the sequence stratigraphic framework of Zhujiang—HanJiang Formtation in the shelf break zone in southeast Panyu natural gas area, Pearl River Mouth Basin, and comprehensively using well drilling, logging and seismic data and sequence stratigraphic principles, the characteristics of sedimentary sequence for SQhj2 of the middle segment of Hanjiang Formation was studied.It was divided into lowstand system tract, transgressive system tract and highstand system tract, and the lowstand system tract can be recognized as two stages（two fourth order cycles）—the early and late stage lowstand system tract. The sequence structure and depositional system tract has the feature of four-layer architecture. From up to down, the SQhj2 can be divided into transgressive system tract ,highstand system tract, the early and late stage lowstand system tract in the seismic section. On the basis of the constitutive characteristics of the sequence structure and depositional system tract was demonstrated, SQhj2 sedimentary sequence model was established. In this model, under the sequence boundary of SB13.8, the late highstand system tract of SQhj1 developed the falling stage system tract. And above the SB13.8,the sequence of SQhj2 developed the early and late stage lowstand system tract under the shelf break. The favorable zones of the study area were predicted, and the sand body of lowstand system tract controlled by the paleo uplift and the shelf break is the favorable reservoir sand body and the distribution area of the lithologic and stratigraphic trap.
On the basis of previous studies on the sequence stratigraphic framework of Zhujiang—HanJiang Formtation in the shelf break zone in southeast Panyu natural gas area, Pearl River Mouth Basin, and comprehensively using well drilling, logging and seismic data and sequence stratigraphic principles, the characteristics of sedimentary sequence for SQhj2 of the middle segment of Hanjiang Formation was studied.It was divided into lowstand system tract, transgressive system tract and highstand system tract, and the lowstand system tract can be recognized as two stages（two fourth order cycles）—the early and late stage lowstand system tract. The sequence structure and depositional system tract has the feature of four-layer architecture. From up to down, the SQhj2 can be divided into transgressive system tract ,highstand system tract, the early and late stage lowstand system tract in the seismic section. On the basis of the constitutive characteristics of the sequence structure and depositional system tract was demonstrated, SQhj2 sedimentary sequence model was established. In this model, under the sequence boundary of SB13.8, the late highstand system tract of SQhj1 developed the falling stage system tract. And above the SB13.8,the sequence of SQhj2 developed the early and late stage lowstand system tract under the shelf break. The favorable zones of the study area were predicted, and the sand body of lowstand system tract controlled by the paleo uplift and the shelf break is the favorable reservoir sand body and the distribution area of the lithologic and stratigraphic trap.
2013, 31(6): 1094-1104.
Abstract:
Coarse sediments of nearshore subaqueous fan or fan delta were mainly developed in the third member or the forth member of Shahejie Formation in steep slope zones of different depressions in Jiyang sag, such as nearshore subaqueous fan in the north of Dongying depression (Li 88 well region) and Chezhen depression (Che 66 well region), delta in the north of Huimin depression (Jishan Sand Body), and fan delta in the north of Zhanhua depression (Yi 170 well region). But their sedimentary types and compositions were different. Great amounts of data from cores and reservoir analysis demonstrated that the reservoir of Shahejie Fm. had undergone a series of diagenesis, such as compaction, cementation, dissolution and replacement in burial diagenetic evolution, resulted in the low porosity and permeability reservoirs. Although it showed the similarity of the burial depth (mostly 2 000~3 000 m) and diagenesis evolution stages (the middle diagenetic phase) of Shahejie Fm. in Jiyang sag, differences of reservoir quality in these steep slopes of different depressions still existed. These kinds of differences were caused by sedimentary condition and diagenetic evolution differences. Under the same burial depth and diagenetic evolution stages, dissolution process had played a significant role in improving reservoir quality (the porosity up to 20% and the permeability up to 60×10-3 μm2). The comprehensive research results of reservoir controlling factors and characteristics indicated that, the favorable reservoirs of Shahejie Fm. in the steep slope of Jiyang sag developed in the depth about 2200m in Dongying, Chezhen and Huiming depressions, and the depth of 2 900 m in Zhanhua depressions. The channel sandbodies originated from delta and nearshore subaqueous fan, which were rich in dissolution pores, would be the favorable exploration targets in the future.
Coarse sediments of nearshore subaqueous fan or fan delta were mainly developed in the third member or the forth member of Shahejie Formation in steep slope zones of different depressions in Jiyang sag, such as nearshore subaqueous fan in the north of Dongying depression (Li 88 well region) and Chezhen depression (Che 66 well region), delta in the north of Huimin depression (Jishan Sand Body), and fan delta in the north of Zhanhua depression (Yi 170 well region). But their sedimentary types and compositions were different. Great amounts of data from cores and reservoir analysis demonstrated that the reservoir of Shahejie Fm. had undergone a series of diagenesis, such as compaction, cementation, dissolution and replacement in burial diagenetic evolution, resulted in the low porosity and permeability reservoirs. Although it showed the similarity of the burial depth (mostly 2 000~3 000 m) and diagenesis evolution stages (the middle diagenetic phase) of Shahejie Fm. in Jiyang sag, differences of reservoir quality in these steep slopes of different depressions still existed. These kinds of differences were caused by sedimentary condition and diagenetic evolution differences. Under the same burial depth and diagenetic evolution stages, dissolution process had played a significant role in improving reservoir quality (the porosity up to 20% and the permeability up to 60×10-3 μm2). The comprehensive research results of reservoir controlling factors and characteristics indicated that, the favorable reservoirs of Shahejie Fm. in the steep slope of Jiyang sag developed in the depth about 2200m in Dongying, Chezhen and Huiming depressions, and the depth of 2 900 m in Zhanhua depressions. The channel sandbodies originated from delta and nearshore subaqueous fan, which were rich in dissolution pores, would be the favorable exploration targets in the future.
2013, 31(6): 1114-1121.
Abstract:
Central canyon is located in Qiongdongnan Basin deep water area of the northern South China Sea, and is key areas in oil and gas exploration. So far, canyon about the microfacies, causes and sandbody distribution rule are still in dispute. Therefore, based on the new drilled well, high-resolution 3-D data, we carried out a series of work, such as technical analysis for the rock and mineral characteristics, particle size analysis, sedimentary structures, paleontological features, well logging facies, and using the RMS amplitude attribute, a variety of slicing technology, etc. The results show that the canyon is the deeper downcutting and scours to the older strata eastwards within the Huang Liu group (T40 ~ T30). The three genetic facies are included in the Central canyon channel system: muddy channel, point bar, and levee complex. Integration of tectonic setting, ancient landforms and planar deposition facies superimposed map indicates that point bar developed in the bend of the canyon paletopography and interpreted to be associated to continuous lateral migration during channel evolution, resulting in the deposition of lateral accretion packages in the inner side of the channel and erosion at the outer side of the channel. Characteristics of lithology and log in the well drilling through the Central canyon contain sets of sand bodies, named point bar in this paper, and thin mudstones. Point bar can form sizable reservoir elements as much as 8~20.5 km2 in the central canyon.
Central canyon is located in Qiongdongnan Basin deep water area of the northern South China Sea, and is key areas in oil and gas exploration. So far, canyon about the microfacies, causes and sandbody distribution rule are still in dispute. Therefore, based on the new drilled well, high-resolution 3-D data, we carried out a series of work, such as technical analysis for the rock and mineral characteristics, particle size analysis, sedimentary structures, paleontological features, well logging facies, and using the RMS amplitude attribute, a variety of slicing technology, etc. The results show that the canyon is the deeper downcutting and scours to the older strata eastwards within the Huang Liu group (T40 ~ T30). The three genetic facies are included in the Central canyon channel system: muddy channel, point bar, and levee complex. Integration of tectonic setting, ancient landforms and planar deposition facies superimposed map indicates that point bar developed in the bend of the canyon paletopography and interpreted to be associated to continuous lateral migration during channel evolution, resulting in the deposition of lateral accretion packages in the inner side of the channel and erosion at the outer side of the channel. Characteristics of lithology and log in the well drilling through the Central canyon contain sets of sand bodies, named point bar in this paper, and thin mudstones. Point bar can form sizable reservoir elements as much as 8~20.5 km2 in the central canyon.
