2014 Vol. 32, No. 6
Display Method:
2014, 32(6): 997-1006.
Abstract:
The Mesozoic and Cenozoic basin of Lanping attracts more and more attention because of its accumulation of large amounts of metal deposits. This paper take Paleogene infilling sequence in the basin as the research object, adopt clastic composition, geochemical means to study the evolution of Lanping Paleogene basin, to further explore the relationship between Paleogene each evolution stage and mineralization in Lanping Basin, for the next step prospecting direction. The results show that Lanping Basin occur deformation due to the slow uplift of the Yangtze continent in Paleocene- Early Eocene(E1-E21), thus formed nearly north and south trending long and narrow type extrusion depression basin, on the whole the basin formed East steep and west slope, shallow in the east and deep in the west, sediment grain size coarsening upward gradually, showed the water upward shallowing and lake gradually atrophy.Because of the stage of the extrusion depression, it's relatively stable. Lanping Basin both east and west sides of orogenic belt to the basin hinterland strong thrust propagation because of the Himalayan movement in Late Eocene- Oligocene(E22-E3), formed pattern of the wedge nappe and sedimentary basin to further narrow, most areas of extrusion fold and with some degree of difference uplift, caused only residual sedimentary record intermontane basin in the north of Lanping Basin, the southern and central part of basin is mostly uplift and develop into denudation area. Most area of Lanping Basin inversion mountain, only in the nappe front residual intermontane basin, basin filling by molasse conglomerate of Baoxiangsi Formation and Jinsichang Formation in the Eocene-Oligocene, this period is Lanping Basin bidirectional thrust nappe most intensely active period. On the results of previous studies on the Lanping Basin metallogenic rule discovery that ore-forming and tectonic-sedimentary evolution of Lanping Basin with good coupled. Basin sedimentary rocks-hosted base metal deposit ore emplacement is closely related to the internal deformation of the basin, which controlled by Indian - Asian continental collision and extrusion, Yangtze paleocontinent and Yunnan-Tibet ancient mosaic and collision. According to the basin Paleogene infilling sequence characteristics and substance accumulation rules, thinking that the Paleogene Lanping Basin under the compressional tectonic background, forming the ore-control structures are extruded and depression - fold structure, mass region extrusion strike-slip structure. These structural deformation can be ore structures, can also be a guide ore structure. The Paleogene tectonic and sedimentary evolution of the Lanping Basin can be further divided into two stages: The first stage is squeeze-depression of the Paleocene - early Eocene, the second stage is the extrusion strike-slip stage of late Eocene-Oligocene.In the early stage of the extrusion and depression(65~41 Ma), formed vein Cu deposit and Fulongchang vein Cu-Ag-Pb-Zn (48~49 Ma) deposit of the Lanping Basin western depression fold nappe belt. Ore was only intermittent veinlike due to the space constraints of ore. In the late extrusion strike-slip stage (40~26 Ma), the edge of the basin to the side basin hinterland produce nappe movement and one side along the boundary fault strike slip movement. Formed large-scale east and west nappe. When the nappe advance to the deposition of gypsum salt built, gravity pressure and density inversion makes salt diapir rise form the dome structure, Thus formed Hexi-Sanshan Pb-Zn (-Ag-Sr) deposits and Jinding super large Pb-Zn (-34 Ma) deposits of the Lanping Basin Eastern thrust nappe belt.
The Mesozoic and Cenozoic basin of Lanping attracts more and more attention because of its accumulation of large amounts of metal deposits. This paper take Paleogene infilling sequence in the basin as the research object, adopt clastic composition, geochemical means to study the evolution of Lanping Paleogene basin, to further explore the relationship between Paleogene each evolution stage and mineralization in Lanping Basin, for the next step prospecting direction. The results show that Lanping Basin occur deformation due to the slow uplift of the Yangtze continent in Paleocene- Early Eocene(E1-E21), thus formed nearly north and south trending long and narrow type extrusion depression basin, on the whole the basin formed East steep and west slope, shallow in the east and deep in the west, sediment grain size coarsening upward gradually, showed the water upward shallowing and lake gradually atrophy.Because of the stage of the extrusion depression, it's relatively stable. Lanping Basin both east and west sides of orogenic belt to the basin hinterland strong thrust propagation because of the Himalayan movement in Late Eocene- Oligocene(E22-E3), formed pattern of the wedge nappe and sedimentary basin to further narrow, most areas of extrusion fold and with some degree of difference uplift, caused only residual sedimentary record intermontane basin in the north of Lanping Basin, the southern and central part of basin is mostly uplift and develop into denudation area. Most area of Lanping Basin inversion mountain, only in the nappe front residual intermontane basin, basin filling by molasse conglomerate of Baoxiangsi Formation and Jinsichang Formation in the Eocene-Oligocene, this period is Lanping Basin bidirectional thrust nappe most intensely active period. On the results of previous studies on the Lanping Basin metallogenic rule discovery that ore-forming and tectonic-sedimentary evolution of Lanping Basin with good coupled. Basin sedimentary rocks-hosted base metal deposit ore emplacement is closely related to the internal deformation of the basin, which controlled by Indian - Asian continental collision and extrusion, Yangtze paleocontinent and Yunnan-Tibet ancient mosaic and collision. According to the basin Paleogene infilling sequence characteristics and substance accumulation rules, thinking that the Paleogene Lanping Basin under the compressional tectonic background, forming the ore-control structures are extruded and depression - fold structure, mass region extrusion strike-slip structure. These structural deformation can be ore structures, can also be a guide ore structure. The Paleogene tectonic and sedimentary evolution of the Lanping Basin can be further divided into two stages: The first stage is squeeze-depression of the Paleocene - early Eocene, the second stage is the extrusion strike-slip stage of late Eocene-Oligocene.In the early stage of the extrusion and depression(65~41 Ma), formed vein Cu deposit and Fulongchang vein Cu-Ag-Pb-Zn (48~49 Ma) deposit of the Lanping Basin western depression fold nappe belt. Ore was only intermittent veinlike due to the space constraints of ore. In the late extrusion strike-slip stage (40~26 Ma), the edge of the basin to the side basin hinterland produce nappe movement and one side along the boundary fault strike slip movement. Formed large-scale east and west nappe. When the nappe advance to the deposition of gypsum salt built, gravity pressure and density inversion makes salt diapir rise form the dome structure, Thus formed Hexi-Sanshan Pb-Zn (-Ag-Sr) deposits and Jinding super large Pb-Zn (-34 Ma) deposits of the Lanping Basin Eastern thrust nappe belt.
2014, 32(6): 1007-1015.
Abstract:
The Upper Cretaceous Qiupa Formation in Tantou Basin of the western Henan province is a set of terrestrial clastic deposits. The lithology is mainly made up of thick-bedded or massive red brown silty mudstone in which intercalated beds are instability of graded bedding or massive gravel, sandy gravel or sandstone. Abundant ichnofossils were found in the strata, including Palaeophycus tubularis, Beaconites autarcticus, Planolites ichnosp.1, Planolites ichnosp.2, Scoyenia gracilis, Skolithos ichnosp., and Rhizoliths. According to the outcrop characteristics of these ichnofossils and the sedimentary features of their surrounding rocks, the Beaconites-Scoyenia ichnoassemblage and Palaeophycus-Rhizoliths ichnoassemblage were established and their sedimentary environmental models were proposed. The Beaconites-Scoyenia ichnoassemblage which is consisted of Beaconites antarcticus, Scoyenia gracilis, Planolites ichnosp.2 and Skolithos ichnosp represents the shore and shallow lacustrine sedimentary environments. The Palaeophycus-Rhizoliths ichnoassemblage which is consisted of Palaeophycus tubularis, Planolites ichnosp.1, Beaconites antarcticus and Rhizoliths represents the lacustrine fan-delta plain to fan-delta front sedimentary environments. Based on the comprehensive analysis of the lithology, sedimentary structures, sedimentary sequences and ichnofossil assemblages of the strata, 5 types of depositional sequences are differentiated and the Qiupa Formation is explained to have formed sequentially from the alluvial fan to lacustrine fan delta and then to shore and shallow lake environments.. In addition, the evolution of sedimentary environments represented in the formation is discussed. The research results not only may enrich the ichnofossil database of terrestrial basins in China and offer new data to complete further continental ichnofacies mode, but also offer scientific evidence to explain the palaeobios survival and preserved palaeoenvironments in Tantou basins of western Henan.
The Upper Cretaceous Qiupa Formation in Tantou Basin of the western Henan province is a set of terrestrial clastic deposits. The lithology is mainly made up of thick-bedded or massive red brown silty mudstone in which intercalated beds are instability of graded bedding or massive gravel, sandy gravel or sandstone. Abundant ichnofossils were found in the strata, including Palaeophycus tubularis, Beaconites autarcticus, Planolites ichnosp.1, Planolites ichnosp.2, Scoyenia gracilis, Skolithos ichnosp., and Rhizoliths. According to the outcrop characteristics of these ichnofossils and the sedimentary features of their surrounding rocks, the Beaconites-Scoyenia ichnoassemblage and Palaeophycus-Rhizoliths ichnoassemblage were established and their sedimentary environmental models were proposed. The Beaconites-Scoyenia ichnoassemblage which is consisted of Beaconites antarcticus, Scoyenia gracilis, Planolites ichnosp.2 and Skolithos ichnosp represents the shore and shallow lacustrine sedimentary environments. The Palaeophycus-Rhizoliths ichnoassemblage which is consisted of Palaeophycus tubularis, Planolites ichnosp.1, Beaconites antarcticus and Rhizoliths represents the lacustrine fan-delta plain to fan-delta front sedimentary environments. Based on the comprehensive analysis of the lithology, sedimentary structures, sedimentary sequences and ichnofossil assemblages of the strata, 5 types of depositional sequences are differentiated and the Qiupa Formation is explained to have formed sequentially from the alluvial fan to lacustrine fan delta and then to shore and shallow lake environments.. In addition, the evolution of sedimentary environments represented in the formation is discussed. The research results not only may enrich the ichnofossil database of terrestrial basins in China and offer new data to complete further continental ichnofacies mode, but also offer scientific evidence to explain the palaeobios survival and preserved palaeoenvironments in Tantou basins of western Henan.
2014, 32(6): 1016-1025.
Abstract:
The deep lacustrine mudrock are the important source rock as well as self-stored reservoirs. The exploration of unconventional resources has been a hot topic at present. Being the main target of tight oil and shale oil, it's characteristics and formation mechanism have been paid great attention. Chang 7 member of Yanchang Formation, which is deposited in the late Triassic, is the main source rock of Ordos Basin.
A classification scheme based on the constituents and texture is proposed. The research of the lacustrine mudstone of Chang 7 member indicates that the deep lacustrine mudstone comprises at least 5 lithofacies: massive mudstone, graded laminated mudstone, wavy laminated shale, even laminated shale, and block-like laminated shale. These mudstone facies assemble two categories on the basis of self-generating characteristics, i.e. allogenous mudrock, including massive mudstone, graded laminated mudstone; autogenic mudrock, including wavy laminated shale, even laminated shale, block-like shale.
This classification is associated with sedimentary environment. Shallow lake which is influenced by delta is dominated by massive mudstone; shallow-semi shallow lake being influenced by lake currents and waves is mainly deposited with wavy laminated shale; deep quite lake is associated with even laminated shale; deep lake depression is dominated by graded mudstone; block-like shale mainly appears in the period of volcano eruption.
However, the mudstone lithology is changing with the evolution of the lake and thus one interval has different types of mudrock. The lithology can be changed within centimeters. We can conclude in this way that the mudrock interval is highly heterogeneous, which makes our prediction much more difficult. As a whole, graded mudstone is the interval of tight oil and the block-like shale is the main source rock and contains shale oil.
The deep lacustrine mudrock are the important source rock as well as self-stored reservoirs. The exploration of unconventional resources has been a hot topic at present. Being the main target of tight oil and shale oil, it's characteristics and formation mechanism have been paid great attention. Chang 7 member of Yanchang Formation, which is deposited in the late Triassic, is the main source rock of Ordos Basin.
A classification scheme based on the constituents and texture is proposed. The research of the lacustrine mudstone of Chang 7 member indicates that the deep lacustrine mudstone comprises at least 5 lithofacies: massive mudstone, graded laminated mudstone, wavy laminated shale, even laminated shale, and block-like laminated shale. These mudstone facies assemble two categories on the basis of self-generating characteristics, i.e. allogenous mudrock, including massive mudstone, graded laminated mudstone; autogenic mudrock, including wavy laminated shale, even laminated shale, block-like shale.
This classification is associated with sedimentary environment. Shallow lake which is influenced by delta is dominated by massive mudstone; shallow-semi shallow lake being influenced by lake currents and waves is mainly deposited with wavy laminated shale; deep quite lake is associated with even laminated shale; deep lake depression is dominated by graded mudstone; block-like shale mainly appears in the period of volcano eruption.
However, the mudstone lithology is changing with the evolution of the lake and thus one interval has different types of mudrock. The lithology can be changed within centimeters. We can conclude in this way that the mudrock interval is highly heterogeneous, which makes our prediction much more difficult. As a whole, graded mudstone is the interval of tight oil and the block-like shale is the main source rock and contains shale oil.
2014, 32(6): 1026-1034.
Abstract:
With the further exploration and production of hydrocarbon resources, objective and detailed anatomy for internal architecture of reservoir bodies is becoming the necessary approach to improve the efficiency of development. Outcrop based sedimentary section plays an irreplaceable role in building geological model of underground reservoir. Taking the Yan'an Formation developed in Yan'an area of the Ordos Basin as an example, the internal architecture of a subaqueous sedimentary succession in lacustrine deltaic environment was anatomized, employing the research thoughts of sedimentology and architecture elements. According to this study, 9 lithotypes, 3 kinds of litho associations are identified in Peizhuang section. Furthermore, 6 kinds of sedimentary architecture elements such as prodelta, sheet sandstone, distal sandstone, mouth bar, subaqueous distributary channel, subaqueous distributary bay are identified as a result. Five hierarchy bounding surfaces are also recognized in the subaqueous distributary channel succession. It's suggested that not only subaqueous distributary channel, but also mouth bar, distal bar, sheet bar and so on are developed in delta front of so-called shallow-water delta. Generally, there is an upward coarsening succession in the studied section, while the progressive architecture of delta front is difficult to be recognized in outcrop scale. In consideration of the controversy about shallow-water delta, we suggest that enhancing outcrop-based study and particular physical modeling should be the key solutions.
With the further exploration and production of hydrocarbon resources, objective and detailed anatomy for internal architecture of reservoir bodies is becoming the necessary approach to improve the efficiency of development. Outcrop based sedimentary section plays an irreplaceable role in building geological model of underground reservoir. Taking the Yan'an Formation developed in Yan'an area of the Ordos Basin as an example, the internal architecture of a subaqueous sedimentary succession in lacustrine deltaic environment was anatomized, employing the research thoughts of sedimentology and architecture elements. According to this study, 9 lithotypes, 3 kinds of litho associations are identified in Peizhuang section. Furthermore, 6 kinds of sedimentary architecture elements such as prodelta, sheet sandstone, distal sandstone, mouth bar, subaqueous distributary channel, subaqueous distributary bay are identified as a result. Five hierarchy bounding surfaces are also recognized in the subaqueous distributary channel succession. It's suggested that not only subaqueous distributary channel, but also mouth bar, distal bar, sheet bar and so on are developed in delta front of so-called shallow-water delta. Generally, there is an upward coarsening succession in the studied section, while the progressive architecture of delta front is difficult to be recognized in outcrop scale. In consideration of the controversy about shallow-water delta, we suggest that enhancing outcrop-based study and particular physical modeling should be the key solutions.
2014, 32(6): 1035-1045.
Abstract:
Observations from outcrop, thin sections and geochemical analyses of limestone samples collected from Middle Permian Qixia Formation at Jinlingxiang section in Shizhu, Chongqing City, make it possible to reveal characteristics of geochemistry and paleoenvironment. The 10 samples have low contents in SiO2 (<5%), MgO(<2.5%), low ratios of Mn/Sr(<0.1), Fe/Sr(<1), high contents in Sr(average: 1 751×10-6), δ18OPDB(>-10‰), meanwhile, SiO2 are strong positive correlated with MgO, which imply that samples have not experienced intense dolomitization and silicification implying no alteration on the chemical nature during diagenetic processes. Thus, they could be used as reliable objects to reconstruct paleoenvironment. Samples are usually high in CaO (average:53.81%) content, low in Na2O(average: 0.051%), Al2O3(average: 0.17%), TiO2(average: 0.012%)contents, which indicate stable marine paleoenvironment barely with terrigenous input. Low ratios of MgO/CaO(average:0.026), high ratios of 100×(MgO/Al2O3) (average:1241), Sr/Ba(average:286) integrated with 1 000×(Sr/Ca) (average:4.54) hint that Qixia Formation deposited in continental shelf (far shore) under humid climate. Geochemical indices for palaeoredox conditions, for example, U/Al, V/Al, Mo/Al, Cr/Al, Co/Al, V/(V+Ni) and U/Th, conform that the carbonate successions in the study area were accumulated in a dysaerobic-anaerobic environment. Terrestrial elements Σ(Al2O3+TiO2) contents decrease gradually, seawater depth indices: ratios of Sr/Ba and 1 000×(Sr/Ca) increase steadily from bottom to top, which reflect the coast were further away, terrigenous supply reduced gradually and sea level continued rising during deposition.
Observations from outcrop, thin sections and geochemical analyses of limestone samples collected from Middle Permian Qixia Formation at Jinlingxiang section in Shizhu, Chongqing City, make it possible to reveal characteristics of geochemistry and paleoenvironment. The 10 samples have low contents in SiO2 (<5%), MgO(<2.5%), low ratios of Mn/Sr(<0.1), Fe/Sr(<1), high contents in Sr(average: 1 751×10-6), δ18OPDB(>-10‰), meanwhile, SiO2 are strong positive correlated with MgO, which imply that samples have not experienced intense dolomitization and silicification implying no alteration on the chemical nature during diagenetic processes. Thus, they could be used as reliable objects to reconstruct paleoenvironment. Samples are usually high in CaO (average:53.81%) content, low in Na2O(average: 0.051%), Al2O3(average: 0.17%), TiO2(average: 0.012%)contents, which indicate stable marine paleoenvironment barely with terrigenous input. Low ratios of MgO/CaO(average:0.026), high ratios of 100×(MgO/Al2O3) (average:1241), Sr/Ba(average:286) integrated with 1 000×(Sr/Ca) (average:4.54) hint that Qixia Formation deposited in continental shelf (far shore) under humid climate. Geochemical indices for palaeoredox conditions, for example, U/Al, V/Al, Mo/Al, Cr/Al, Co/Al, V/(V+Ni) and U/Th, conform that the carbonate successions in the study area were accumulated in a dysaerobic-anaerobic environment. Terrestrial elements Σ(Al2O3+TiO2) contents decrease gradually, seawater depth indices: ratios of Sr/Ba and 1 000×(Sr/Ca) increase steadily from bottom to top, which reflect the coast were further away, terrigenous supply reduced gradually and sea level continued rising during deposition.
2014, 32(6): 1046-1051.
Abstract:
The organic carbon and nitrogen isotopes in marine sediments provide a lot of information about marine paleoenvironmental and carbon and nitrogen cycles. However, different pretreatment methods have different impacts on the accuracy of the results of organic carbon and nitrogen isotope. This paper analyzed the factors affecting the pretreatment process on the basis of a great many condition tests. (1) Acid treatment Containers Material: The organic carbon and nitrogen isotope values of acid treatment with polypropylene and glass centrifugal tubes make no difference. (2) Drying methods: The sample δ13C will be fractionationed for the escape of light carbon and volatile components caused by heat-drying. The sample δ15N will be fractionationed caused by the fresh and acid-treated samples heat-dried. (3) The drive acid method and wash acid times: Dissolved organic carbon and nitrogen will be loss caused by washing, resulting in δ13C and δ15N values more partial than the true ones. Meanwhile, steaming acid can not get rid of chloride ions effectively. The effect of acid wash times on δ13C is very small, but it will result in δ15N partial. In short, using of freeze-drying, the choice of PP centrifugal tube as the main acid treatment washing and drying vessels, with good reproducibility, get more satisfactory and accurate test δ13C and δ15N values.
The organic carbon and nitrogen isotopes in marine sediments provide a lot of information about marine paleoenvironmental and carbon and nitrogen cycles. However, different pretreatment methods have different impacts on the accuracy of the results of organic carbon and nitrogen isotope. This paper analyzed the factors affecting the pretreatment process on the basis of a great many condition tests. (1) Acid treatment Containers Material: The organic carbon and nitrogen isotope values of acid treatment with polypropylene and glass centrifugal tubes make no difference. (2) Drying methods: The sample δ13C will be fractionationed for the escape of light carbon and volatile components caused by heat-drying. The sample δ15N will be fractionationed caused by the fresh and acid-treated samples heat-dried. (3) The drive acid method and wash acid times: Dissolved organic carbon and nitrogen will be loss caused by washing, resulting in δ13C and δ15N values more partial than the true ones. Meanwhile, steaming acid can not get rid of chloride ions effectively. The effect of acid wash times on δ13C is very small, but it will result in δ15N partial. In short, using of freeze-drying, the choice of PP centrifugal tube as the main acid treatment washing and drying vessels, with good reproducibility, get more satisfactory and accurate test δ13C and δ15N values.
2014, 32(6): 1052-1059.
Abstract:
As one of the most common authigenic minerals in continental margin sediments, pyrite has been proved as an important indicator of sedimentary environment, early diagenesis and gas hydrates. So far, the identification and handpicking under binocular microscope and the analysis of Chromium reduction sulfur (CRS) are the two most commonly used methods for the analysis of authigenic pyrite in marine sediments, however there is yet rare study made for comparisons of those two methods. In this paper, both methods are employed to the shallow sediments of Site 4B, northern continental slope of the South China Sea for comparison in authigenic pyrite analysis. The results show that 1) the pyrite contents and their sulfur isotopic values obtained by both methods exhibit great synchronicity in the major variations; 2) the discrepancies between two methods are limited to a certain small range with little changes throughout the sampled interval. Therefore, both methods can inform us of the major changes of pyrite contents and their sulfur isotopic values in the studied sediments. However, both methods have their advantages and disadvantages. While theoretically, CRS seems more scientific and accurate, observation and recognition under the binocular microscope are much easier operated and more economical and practical. We suggest that it might be a better choice to combine both methods in the practice of analyzing authigenic pyrite in marine sediments, which means that the binocular microscope for the overall variation of pyrite concentration and CRS for more precise and versatile analysis within the critical intervals with major changes.
As one of the most common authigenic minerals in continental margin sediments, pyrite has been proved as an important indicator of sedimentary environment, early diagenesis and gas hydrates. So far, the identification and handpicking under binocular microscope and the analysis of Chromium reduction sulfur (CRS) are the two most commonly used methods for the analysis of authigenic pyrite in marine sediments, however there is yet rare study made for comparisons of those two methods. In this paper, both methods are employed to the shallow sediments of Site 4B, northern continental slope of the South China Sea for comparison in authigenic pyrite analysis. The results show that 1) the pyrite contents and their sulfur isotopic values obtained by both methods exhibit great synchronicity in the major variations; 2) the discrepancies between two methods are limited to a certain small range with little changes throughout the sampled interval. Therefore, both methods can inform us of the major changes of pyrite contents and their sulfur isotopic values in the studied sediments. However, both methods have their advantages and disadvantages. While theoretically, CRS seems more scientific and accurate, observation and recognition under the binocular microscope are much easier operated and more economical and practical. We suggest that it might be a better choice to combine both methods in the practice of analyzing authigenic pyrite in marine sediments, which means that the binocular microscope for the overall variation of pyrite concentration and CRS for more precise and versatile analysis within the critical intervals with major changes.
2014, 32(6): 1060-1071.
Abstract:
Through the restructuring of the Kuche river section of Lower Cretaceous-Paleogene Kumugeliemu group sedimentary outcrop observation, analysis of sandstone lithology combination, sedimentary structure, gravel characteristics and sedimentary environment, combined with the sedimentary features of seasonal river in Tianshan north and south. It is an important depositional system that the seasonal rivers and seasonal river delta developed under arid climatic conditions in Cretaceous of Kuche depression. The seasonal river sedimentary characteristics of the lower Cretaceous Bashijiqike Formation and the extensive development is very similar, both typical fluvial facies sedimentary rhythm sand body is widespread, the river bottom mud gravel and detritus thick massive large-scale cross bedding sandstone, but also show a high-energy fine sandstones and silty sandstone, with higher structural maturity and lower compositional maturity. On this basis, the establishment of the Kuche river section of Lower Cretaceous Basi Group restructuring of sedimentary facies model. In Baxigai Formation sedimentary period, development area wide shallow lakes larger in Kuche depression, the development of seasonal rivers into the lakes formed seasonal rivers Delta. In Bashijiqike Formation sedimentary period, a number of small lakes emergence in front of the ancient Tianshan Mountains, ancient Tianshan Piedmont seasonal braided river and a large number of multiple seasonal small braided delta were deposited.
Through the restructuring of the Kuche river section of Lower Cretaceous-Paleogene Kumugeliemu group sedimentary outcrop observation, analysis of sandstone lithology combination, sedimentary structure, gravel characteristics and sedimentary environment, combined with the sedimentary features of seasonal river in Tianshan north and south. It is an important depositional system that the seasonal rivers and seasonal river delta developed under arid climatic conditions in Cretaceous of Kuche depression. The seasonal river sedimentary characteristics of the lower Cretaceous Bashijiqike Formation and the extensive development is very similar, both typical fluvial facies sedimentary rhythm sand body is widespread, the river bottom mud gravel and detritus thick massive large-scale cross bedding sandstone, but also show a high-energy fine sandstones and silty sandstone, with higher structural maturity and lower compositional maturity. On this basis, the establishment of the Kuche river section of Lower Cretaceous Basi Group restructuring of sedimentary facies model. In Baxigai Formation sedimentary period, development area wide shallow lakes larger in Kuche depression, the development of seasonal rivers into the lakes formed seasonal rivers Delta. In Bashijiqike Formation sedimentary period, a number of small lakes emergence in front of the ancient Tianshan Mountains, ancient Tianshan Piedmont seasonal braided river and a large number of multiple seasonal small braided delta were deposited.
2014, 32(6): 1072-1082.
Abstract:
Although the marine sediments bacteria play an important role in marine environment, a comprehensive view of community characteristics is still lacking, to understand the characteristics of microbial community structure in gas hydrate potential region and to evaluate how bacterial community structure response to gas hydrate, we used PCR-based technology: terminal restriction fragment length polymorphism(T-RFLP) and denaturing gradient gel electrophoresis (DGGE), combine environment parameters such as sediment grain size, total organic carbon(TOC), deposition rate and sediment age to research the diversity of bacterial communities and structure in sediments from the adjacent region of Jiulong Methane Reef 973-4 in the northern South China Sea, and we divided the 973-4 core into three parts in the base of environmental parameters: surface layer, contain 20 cm, 192 cm, 236 cm, 326 cm, 382 cm; middle layer, contain 552 cm, 592 cm, 716 cm, 796 cm; and deep layer, contain 862 cm, 1 082 cm, 1 196 cm.
The environment parameters show that the total organic carbon content decrease from surface to deep, and the content was between 0.20% to 1.83%, mostly greater than 0.5%, it can provide source for the formation of gas hydrate; the average sediment grain is between 6 μm to 8 μm; the age of the bottom of 973-4 core is 43 431 a, reveal to oxygen isotopic Ⅲ period, and the average deposition rate of this core was 34.6 cm·ka-1, meet the deposition rate of natural gas hydrate formation conditions.
The result of T-RFLP show that there were much higher values of richness, Shannon-wiener index and evenness index in surface layer sediments and deep layer than the middle layer, but 716 cm was higher than other depths sediments in middle layer by the analysis of terminal restriction fragment(T-RFs). The Shannon-wiener index in some depth was lower than 2.0, show the low diversity of microbial. The three parameters have the same trend. Three parameters increased initially then reduced from deep layer to 716 cm, and the trend from 716 cm to surface layer was decrease and then increase. Though clustering result on the terminal restriction fragments(T-RFs) areas and denaturing gradient gel electrophoresis patterns shows that: the surface sediments 20 cm to 192 cm have higher similarity, the value is 52%, 236 cm were similar to 1 196, the similarity is 76%, 382 cm to 1 082 cm similarity is 38%, besides have similarity with 326 cm, 552 cm, 796 cm; the different depths in middle layer have similarity, simultaneously 716 cm and 862 cm were higher similar, this is connection with the methane level in middle layer, and methane can affect the community composition of microbial. Middle layer located in oxygen isotopicⅡ period, the template is cool, it led to the sea levels drop and made the change of the methane, and the change of methane concentration lead to great difference of microbial community structure in middle with surface and deep layers. The deep sediments microbial community has higher similarity with the surface layer because of the methane concentration was lower than middle layer and the similar total organic carbon content. Through clustering analysis and sediment environment parameters indicated that the vertical distribution of bacterial was coincided with the sediment total organic carbon content, grain size and methane concentration. And the difference of microbial community structure related to the geologic conditions for example depth, the change of sediment properties, methane concentration.
Through compare T-RFLP chromatogram to Mica3 database and sequencing the DGGE bands to analysis the diversity of the sediments and the result showed that:Proteobacteria were the dominant phylum, and α-,γ-,δ-Proteobacteria were the main class within Proteobacteria, other bacteria include Actionmycetes, Firmicutes and Chloroflexi. The dominate bacteria in surface layer is δ-Proteobacteria, most of microbial were related to the hydrothermal vent of deep sea sediments, and δ-Proteobacteria have related with sulfur cycle, indicated that sulfide metabolism especially the sulfate reduction was important process; in middle layer α-Proteobacteria, δ-Proteobacteria were the dominant bacteria and almost related to the deep-sea methane seep and pacific deep-sea sediment, suggest that sulfate reduction and methane oxidation were the main process in middle layer; α-Proteobacteria was dominated in deep layer, we conclude that methane oxidation was the main process, indicating that our deep-sea sampling might be influence by the gas hydrate. In addition, methane oxidizing bacteria such as Methanotrophs and Sulfate-reducing bacteria occur in middle layer where has higher methane concentration areas, and the bacterial were related to the bacterial retrieved from sulfide chimneys, hydrothermal vent environment and areas where has confirm existing gas hydrate, indicated that the microbial community structure in core 973-4 have relation with gas hydrate decomposition and release, suggest that this zone maybe exist gas hydrate. Our data suggest that other bacteria are also involved in methane oxidation in these environments, and combine with the environment parameters we conclude that this zone exist gas hydrate, and conclusion the sulfate reduction methane oxidation transform zone located in the depths of 500 cm to 900 cm.
Although the marine sediments bacteria play an important role in marine environment, a comprehensive view of community characteristics is still lacking, to understand the characteristics of microbial community structure in gas hydrate potential region and to evaluate how bacterial community structure response to gas hydrate, we used PCR-based technology: terminal restriction fragment length polymorphism(T-RFLP) and denaturing gradient gel electrophoresis (DGGE), combine environment parameters such as sediment grain size, total organic carbon(TOC), deposition rate and sediment age to research the diversity of bacterial communities and structure in sediments from the adjacent region of Jiulong Methane Reef 973-4 in the northern South China Sea, and we divided the 973-4 core into three parts in the base of environmental parameters: surface layer, contain 20 cm, 192 cm, 236 cm, 326 cm, 382 cm; middle layer, contain 552 cm, 592 cm, 716 cm, 796 cm; and deep layer, contain 862 cm, 1 082 cm, 1 196 cm.
The environment parameters show that the total organic carbon content decrease from surface to deep, and the content was between 0.20% to 1.83%, mostly greater than 0.5%, it can provide source for the formation of gas hydrate; the average sediment grain is between 6 μm to 8 μm; the age of the bottom of 973-4 core is 43 431 a, reveal to oxygen isotopic Ⅲ period, and the average deposition rate of this core was 34.6 cm·ka-1, meet the deposition rate of natural gas hydrate formation conditions.
The result of T-RFLP show that there were much higher values of richness, Shannon-wiener index and evenness index in surface layer sediments and deep layer than the middle layer, but 716 cm was higher than other depths sediments in middle layer by the analysis of terminal restriction fragment(T-RFs). The Shannon-wiener index in some depth was lower than 2.0, show the low diversity of microbial. The three parameters have the same trend. Three parameters increased initially then reduced from deep layer to 716 cm, and the trend from 716 cm to surface layer was decrease and then increase. Though clustering result on the terminal restriction fragments(T-RFs) areas and denaturing gradient gel electrophoresis patterns shows that: the surface sediments 20 cm to 192 cm have higher similarity, the value is 52%, 236 cm were similar to 1 196, the similarity is 76%, 382 cm to 1 082 cm similarity is 38%, besides have similarity with 326 cm, 552 cm, 796 cm; the different depths in middle layer have similarity, simultaneously 716 cm and 862 cm were higher similar, this is connection with the methane level in middle layer, and methane can affect the community composition of microbial. Middle layer located in oxygen isotopicⅡ period, the template is cool, it led to the sea levels drop and made the change of the methane, and the change of methane concentration lead to great difference of microbial community structure in middle with surface and deep layers. The deep sediments microbial community has higher similarity with the surface layer because of the methane concentration was lower than middle layer and the similar total organic carbon content. Through clustering analysis and sediment environment parameters indicated that the vertical distribution of bacterial was coincided with the sediment total organic carbon content, grain size and methane concentration. And the difference of microbial community structure related to the geologic conditions for example depth, the change of sediment properties, methane concentration.
Through compare T-RFLP chromatogram to Mica3 database and sequencing the DGGE bands to analysis the diversity of the sediments and the result showed that:Proteobacteria were the dominant phylum, and α-,γ-,δ-Proteobacteria were the main class within Proteobacteria, other bacteria include Actionmycetes, Firmicutes and Chloroflexi. The dominate bacteria in surface layer is δ-Proteobacteria, most of microbial were related to the hydrothermal vent of deep sea sediments, and δ-Proteobacteria have related with sulfur cycle, indicated that sulfide metabolism especially the sulfate reduction was important process; in middle layer α-Proteobacteria, δ-Proteobacteria were the dominant bacteria and almost related to the deep-sea methane seep and pacific deep-sea sediment, suggest that sulfate reduction and methane oxidation were the main process in middle layer; α-Proteobacteria was dominated in deep layer, we conclude that methane oxidation was the main process, indicating that our deep-sea sampling might be influence by the gas hydrate. In addition, methane oxidizing bacteria such as Methanotrophs and Sulfate-reducing bacteria occur in middle layer where has higher methane concentration areas, and the bacterial were related to the bacterial retrieved from sulfide chimneys, hydrothermal vent environment and areas where has confirm existing gas hydrate, indicated that the microbial community structure in core 973-4 have relation with gas hydrate decomposition and release, suggest that this zone maybe exist gas hydrate. Our data suggest that other bacteria are also involved in methane oxidation in these environments, and combine with the environment parameters we conclude that this zone exist gas hydrate, and conclusion the sulfate reduction methane oxidation transform zone located in the depths of 500 cm to 900 cm.
2014, 32(6): 1083-1088.
Abstract:
To understand the pollution characteristics of nitrogen and phosphorus in surface sediment of the Eastern byas of Lake Taihu (Gonghu Bay, Guangfu Bay and Yuyang Bay) and its relationship with the growth of aquatic macrophytes, contents of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) of surface sediments were determined based on the investigation of surface sediment in eastern bays of Lake Taihu with aquatic macrophytes. The effects of aquatic macrophytes on pollution characteristics of TN, TP and TOC in surface sediments were analyzed, and pollution assessment for surface sediments was made. The results showed that the contents of TN, TP and TOC in growing area of aquatic macrophytes were significantly lower than that of the contrasted open water area, and the growth of aquatic plants has significant effect on TN, TP and TOC contents in surface sediments. Correlation analysis showed that TOC and TN were significantly correlated (R2=0.832 8), but with less significant correlation to TP (R2=0.166 5), reflecting TOC could become an important source of nitrogen in the deposition process of lake sediments, but less impact on the phosphorus. By evaluation pollution situation with organic index and organic nitrogen, the average organic index of Gonghu Bay, Guangfu Bay and Yuyang Bay were 0.142 7, 0.228 6, and 0.208 6, respectively. However, the average number of organic nitrogen was on the Ⅲ and Ⅳ level, which showed that nitrogen pollution of sediment is more serious. The investigation suggested that the control and reduction of nitrogen in surface sediment of the contrasted open water area are of important significance to the prevention and control of lake eutrophication.
To understand the pollution characteristics of nitrogen and phosphorus in surface sediment of the Eastern byas of Lake Taihu (Gonghu Bay, Guangfu Bay and Yuyang Bay) and its relationship with the growth of aquatic macrophytes, contents of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) of surface sediments were determined based on the investigation of surface sediment in eastern bays of Lake Taihu with aquatic macrophytes. The effects of aquatic macrophytes on pollution characteristics of TN, TP and TOC in surface sediments were analyzed, and pollution assessment for surface sediments was made. The results showed that the contents of TN, TP and TOC in growing area of aquatic macrophytes were significantly lower than that of the contrasted open water area, and the growth of aquatic plants has significant effect on TN, TP and TOC contents in surface sediments. Correlation analysis showed that TOC and TN were significantly correlated (R2=0.832 8), but with less significant correlation to TP (R2=0.166 5), reflecting TOC could become an important source of nitrogen in the deposition process of lake sediments, but less impact on the phosphorus. By evaluation pollution situation with organic index and organic nitrogen, the average organic index of Gonghu Bay, Guangfu Bay and Yuyang Bay were 0.142 7, 0.228 6, and 0.208 6, respectively. However, the average number of organic nitrogen was on the Ⅲ and Ⅳ level, which showed that nitrogen pollution of sediment is more serious. The investigation suggested that the control and reduction of nitrogen in surface sediment of the contrasted open water area are of important significance to the prevention and control of lake eutrophication.
2014, 32(6): 1089-1099.
Abstract:
Sediment core and high-resolution subbottom profiles from the western Taiwan Shoal were analyzed to research stratigraphic sequence, paleo-environmental development of the Shoal. According to the analyses of sedimentary characteristics, grain-sizes and AMS 14C dating, three marine strata and two terrestrial strata were recovered in the core, which were confidently correlated with seismic units in the profiles. The bottom marine strata (DU6) were mainly composed of intertidal and subtidal deposits and were formed in the Marine Isotope Stage (MIS) 5.1; the middle marine strata (DU4) mainly consisted of littoral and intertidal deposits and were formed in the MIS 3; the top marine strata (DU2 and DU1) were transgressive sands and tidal sands in the last deglaciation, respectively. The two terrestrial strata (DU5 and DU3) were incised valley filling deposits, and were formed in the MIS 4 and MIS 2, respectively. Transgressive medium - coarse sands (DU2) constructed the base of sand waves. The main body of sand waves (DU1), which had been formed since the high sea-level stage in Holocene, mainly consisted of medium - coarse sands and gravelly medium - coarse sands, with stable grain-size and good sorting on the top. Grain-size frequency distribution curves of sand waves have a modal number of -1 to 3 Φ; probability cumulative curves are two-segment pattern generally, with leap composition more than 80% and suspension composition less than 20%.Correlative analysis shows that there is a positive correlative between mean grain-size and sorting coefficient of tidal sand deposits (DU1), indicating that the stronger tidal current scouring the coarser grain-size and the better sorting is the sandy deposits.
Sediment core and high-resolution subbottom profiles from the western Taiwan Shoal were analyzed to research stratigraphic sequence, paleo-environmental development of the Shoal. According to the analyses of sedimentary characteristics, grain-sizes and AMS 14C dating, three marine strata and two terrestrial strata were recovered in the core, which were confidently correlated with seismic units in the profiles. The bottom marine strata (DU6) were mainly composed of intertidal and subtidal deposits and were formed in the Marine Isotope Stage (MIS) 5.1; the middle marine strata (DU4) mainly consisted of littoral and intertidal deposits and were formed in the MIS 3; the top marine strata (DU2 and DU1) were transgressive sands and tidal sands in the last deglaciation, respectively. The two terrestrial strata (DU5 and DU3) were incised valley filling deposits, and were formed in the MIS 4 and MIS 2, respectively. Transgressive medium - coarse sands (DU2) constructed the base of sand waves. The main body of sand waves (DU1), which had been formed since the high sea-level stage in Holocene, mainly consisted of medium - coarse sands and gravelly medium - coarse sands, with stable grain-size and good sorting on the top. Grain-size frequency distribution curves of sand waves have a modal number of -1 to 3 Φ; probability cumulative curves are two-segment pattern generally, with leap composition more than 80% and suspension composition less than 20%.Correlative analysis shows that there is a positive correlative between mean grain-size and sorting coefficient of tidal sand deposits (DU1), indicating that the stronger tidal current scouring the coarser grain-size and the better sorting is the sandy deposits.
2014, 32(6): 1100-1112.
Abstract:
Field investigation was carried out from Xunyang to Yunxian along the upper Hanjiang River valley, typical palaeoflood slackwater deposit interbedded in loess-like sediments were found in the profile of XTZ, NGK and JJTZ, which indicate these bedded slackwater deposits recorded the information of palaeoflood events. Systematic sampling for optical dating was carried out on these profiles. The Post-IR OSL single aliquot regeneration (SAR) protocol was used to determine equivalent and 14 OSL ages were obtained. The results show that there were two stage extreme palaeofloods occurred 9.5~8.5 ka B.P. and 3.2~2.8 ka B.P, respectively. According to the analysis of grain-size distribution and magnetic susceptibility, the relationship between Holocene palaeoflood events and climate change was established. The transitional loess (Lt) was dated to 11 500~8 500 a B.P. It has recorded the climatic shift from cold and moist to amelioration during the Early Holocene and dust storm activity gradually decreased. The Luvisol (S0) was dated 8 500~ 3 100 a B.P. It has recorded the warm-humid climate during the mid-Holocene Climatic Optimum. This is a period with more intensified pedogenesis. The loess (L0) was dated to 3 100 a B.P. that has recorded the climate decline during the Late Holocene and dust storms were obviously intensified to form modern loess. Environment records from all over the world revealed the temperature rising, relative precipitation increasing and climatic fluctuation during the period of 9.5~8.5 ka, which lead to abrupt climate events occured frequently such as cooling, flood and drought; during the period of 3.2~2.8 ka, that is a turning period from the Middle Holocene to the Late Holocene, climate changing to aridity, climate change intensively, atmosphere instability and precipitation variability. Therefore, climate changing and transformation were the main reason of frequent flood occurence. The climatic Hydrography event recorded during 9.5~8.5 ka and 3.2~2.8 ka represents the concrete manifestation of the hydrological system to global climate change. The regional responses of the hydrological system. It is significant to understand the regional responses of the hydrological system to global climate change.
Field investigation was carried out from Xunyang to Yunxian along the upper Hanjiang River valley, typical palaeoflood slackwater deposit interbedded in loess-like sediments were found in the profile of XTZ, NGK and JJTZ, which indicate these bedded slackwater deposits recorded the information of palaeoflood events. Systematic sampling for optical dating was carried out on these profiles. The Post-IR OSL single aliquot regeneration (SAR) protocol was used to determine equivalent and 14 OSL ages were obtained. The results show that there were two stage extreme palaeofloods occurred 9.5~8.5 ka B.P. and 3.2~2.8 ka B.P, respectively. According to the analysis of grain-size distribution and magnetic susceptibility, the relationship between Holocene palaeoflood events and climate change was established. The transitional loess (Lt) was dated to 11 500~8 500 a B.P. It has recorded the climatic shift from cold and moist to amelioration during the Early Holocene and dust storm activity gradually decreased. The Luvisol (S0) was dated 8 500~ 3 100 a B.P. It has recorded the warm-humid climate during the mid-Holocene Climatic Optimum. This is a period with more intensified pedogenesis. The loess (L0) was dated to 3 100 a B.P. that has recorded the climate decline during the Late Holocene and dust storms were obviously intensified to form modern loess. Environment records from all over the world revealed the temperature rising, relative precipitation increasing and climatic fluctuation during the period of 9.5~8.5 ka, which lead to abrupt climate events occured frequently such as cooling, flood and drought; during the period of 3.2~2.8 ka, that is a turning period from the Middle Holocene to the Late Holocene, climate changing to aridity, climate change intensively, atmosphere instability and precipitation variability. Therefore, climate changing and transformation were the main reason of frequent flood occurence. The climatic Hydrography event recorded during 9.5~8.5 ka and 3.2~2.8 ka represents the concrete manifestation of the hydrological system to global climate change. The regional responses of the hydrological system. It is significant to understand the regional responses of the hydrological system to global climate change.
2014, 32(6): 1113-1122.
Abstract:
Based on the theory of sequence stratigraphy and analysis of seismic data, logging, cores and outcrop information, the sequence stratigraphy framework of Cretaceous in the central Tabei Uplift is established. The Kapushaliang Group as a second-order sequence, is divided into five third-order sequences. Each third-order sequence consists of lowstand system tract, transgression system tract and highstand system tract. Braided river, meandering delta and laucstrine facies are recognized within the sequence. The distribution of sedimentary systems are analysed with the tectonic evolution of the foreland basin. Halahatang area is located in back-bulge zone of the Kuqa depression foreland basin. The structural evolution of foreland basin of Kuqa depression in Cretaceous has its phases, which controls the characteristics of depositional palaeogeography development in the depression in different stages. The sand bodied of lowstand system tract and highstand system tract of SQ1, SQ2 and SQ5 are favorable explore targets and the meandering delta front in the middle of the study area are also favorable zones.
Based on the theory of sequence stratigraphy and analysis of seismic data, logging, cores and outcrop information, the sequence stratigraphy framework of Cretaceous in the central Tabei Uplift is established. The Kapushaliang Group as a second-order sequence, is divided into five third-order sequences. Each third-order sequence consists of lowstand system tract, transgression system tract and highstand system tract. Braided river, meandering delta and laucstrine facies are recognized within the sequence. The distribution of sedimentary systems are analysed with the tectonic evolution of the foreland basin. Halahatang area is located in back-bulge zone of the Kuqa depression foreland basin. The structural evolution of foreland basin of Kuqa depression in Cretaceous has its phases, which controls the characteristics of depositional palaeogeography development in the depression in different stages. The sand bodied of lowstand system tract and highstand system tract of SQ1, SQ2 and SQ5 are favorable explore targets and the meandering delta front in the middle of the study area are also favorable zones.
2014, 32(6): 1123-1131.
Abstract:
The Oriente basin of Ecuador has produced a substantial amount of oil over the past years. The Cretaceous is the main exploration target in the northeastern block of Oriente Basin in Ecuador. But now in the study area, there are certain differences on the understanding of the sequence development number, the position of the sequence boundary and the sequence composition among different scholars. The classification projects of sequence stratigraphy haven't been systematically recognized. It greatly restricts any further exploration of hydrocarbons. Therefore, it has great theoretic and practical significance to carry out thorough researches on sequence stratigraphy of Cretaceous in northeastern block. Based on the comprehensive analysis of core, well logging and seismic data, sequence boundaries of the Cretaceous in northeastern block of Oriente Basin are identified according to seismic reflection terminal, the stacking patterns of sequence as well as changes of lithology and isochronous stratigraphic framework of the Cretaceous including Hollin and Napo Formation is established. Hollin and Napo Formations are divided into one second order sequence (KSS1), six third order sequences (KSQ1-KSQ6), sixteen fourth order sequences and thirty-four fifth order sequences. The KSQ1-KSQ5 has complete system tract composition which develops SMST, TST and HST system tract. The KSQ6 only develops SMST system tract. According to synthetic records for calibration of the seismic profile and combining with drilling and logging sequence stratigraphic division, seismic as well as drilling and logging data consistency of sequence stratigraphic division of Cretaceous in the study area has been implemented.
In the sequence division of Cretaceous in the northeastern block of Oriente Basin, the characteristics of sequence boundary recognition at all levels are obvious. Second order sequence boundaries correspond to typical seismic profile unconformity truncation feature. Third order sequence boundaries include partly onlap, truncation and downlap seismic reflection termination. Drilling profile are all lithological abrupt change surface, showed the abrupt change surface in the well logging due to the sediments from the shallow water to the deep water. The lowstand of fourth order sequence are shelf marginal systems tracts. It is difficult to identify fourth order sequence boundaries in seismic line, but it is easy to identify in well logging. The key element to identify interfaces is to determine the first flooding surface and the maximum flooding surface. Mainly based on the change of parasequence group staked style in well logging, showed the conversion interface of aggradation-retrogradation-progradation. Fifth order sequence boundaries correspond to the main flooding surface. The identification of interfaces are depending on the thickness of the formation development, the overlay style, the well logging response characteristics and the basic upward shoaling succession cycle of the relative sea level.
Typical mixed clastic and carbonate gentle dipping slope sequence stratigraphy development mode has been identified in the study area. Cretaceous as a relatively complete second order sequence, experienced a complete sedimentary cycle that the relatively down-up-down sea level. Also, the third order sequence has apparent transgression-regression cycle which responds to sedimentary environment that undergo multi-period transitions from tidal flat to restricted platform, to inner shelf subaqueous shoal and to outer shelf mudstone. Then the sea level drops, meanwhile the sedimentary environment evolves into inner shelf limestone bank and restricted platform. Establishment of isochronous stratigraphic framework of the Cretaceous will provide scientific basis for predicting the distribution of favorable sand body in the northeast block, Oriente Basin.
The Oriente basin of Ecuador has produced a substantial amount of oil over the past years. The Cretaceous is the main exploration target in the northeastern block of Oriente Basin in Ecuador. But now in the study area, there are certain differences on the understanding of the sequence development number, the position of the sequence boundary and the sequence composition among different scholars. The classification projects of sequence stratigraphy haven't been systematically recognized. It greatly restricts any further exploration of hydrocarbons. Therefore, it has great theoretic and practical significance to carry out thorough researches on sequence stratigraphy of Cretaceous in northeastern block. Based on the comprehensive analysis of core, well logging and seismic data, sequence boundaries of the Cretaceous in northeastern block of Oriente Basin are identified according to seismic reflection terminal, the stacking patterns of sequence as well as changes of lithology and isochronous stratigraphic framework of the Cretaceous including Hollin and Napo Formation is established. Hollin and Napo Formations are divided into one second order sequence (KSS1), six third order sequences (KSQ1-KSQ6), sixteen fourth order sequences and thirty-four fifth order sequences. The KSQ1-KSQ5 has complete system tract composition which develops SMST, TST and HST system tract. The KSQ6 only develops SMST system tract. According to synthetic records for calibration of the seismic profile and combining with drilling and logging sequence stratigraphic division, seismic as well as drilling and logging data consistency of sequence stratigraphic division of Cretaceous in the study area has been implemented.
In the sequence division of Cretaceous in the northeastern block of Oriente Basin, the characteristics of sequence boundary recognition at all levels are obvious. Second order sequence boundaries correspond to typical seismic profile unconformity truncation feature. Third order sequence boundaries include partly onlap, truncation and downlap seismic reflection termination. Drilling profile are all lithological abrupt change surface, showed the abrupt change surface in the well logging due to the sediments from the shallow water to the deep water. The lowstand of fourth order sequence are shelf marginal systems tracts. It is difficult to identify fourth order sequence boundaries in seismic line, but it is easy to identify in well logging. The key element to identify interfaces is to determine the first flooding surface and the maximum flooding surface. Mainly based on the change of parasequence group staked style in well logging, showed the conversion interface of aggradation-retrogradation-progradation. Fifth order sequence boundaries correspond to the main flooding surface. The identification of interfaces are depending on the thickness of the formation development, the overlay style, the well logging response characteristics and the basic upward shoaling succession cycle of the relative sea level.
Typical mixed clastic and carbonate gentle dipping slope sequence stratigraphy development mode has been identified in the study area. Cretaceous as a relatively complete second order sequence, experienced a complete sedimentary cycle that the relatively down-up-down sea level. Also, the third order sequence has apparent transgression-regression cycle which responds to sedimentary environment that undergo multi-period transitions from tidal flat to restricted platform, to inner shelf subaqueous shoal and to outer shelf mudstone. Then the sea level drops, meanwhile the sedimentary environment evolves into inner shelf limestone bank and restricted platform. Establishment of isochronous stratigraphic framework of the Cretaceous will provide scientific basis for predicting the distribution of favorable sand body in the northeast block, Oriente Basin.
2014, 32(6): 1132-1139.
Abstract:
Paleocene to Eocene-age Wilcox Group which is deeply buried and distributed extensively is the significant oil-bearing reservoir in the deep waters of the northern Gulf of Mexico Basin. The different recognition of Wilcox sedimentary facies existed. In this article, by means of observing cores, analyzing sections and well logging data, we studied on the sedimentary environment and characteristics of the Wilcox group. The result shows that Wilcox group in the deep waters of the northern Gulf of Mexico pertained to deepwater basin-floor fan deposits. The sandstone is very fine to fine-grained arkostic and lithic sandstones. And, we analyzed the provenance of Wilcox and discussed the effect of salt related mini-basin controlling the deposition in deepwater setting. Based on this study, we propose a model for Wilcox deposition, in which the lower slope is defined as channel and there is deepwater fan in basin floor.
Paleocene to Eocene-age Wilcox Group which is deeply buried and distributed extensively is the significant oil-bearing reservoir in the deep waters of the northern Gulf of Mexico Basin. The different recognition of Wilcox sedimentary facies existed. In this article, by means of observing cores, analyzing sections and well logging data, we studied on the sedimentary environment and characteristics of the Wilcox group. The result shows that Wilcox group in the deep waters of the northern Gulf of Mexico pertained to deepwater basin-floor fan deposits. The sandstone is very fine to fine-grained arkostic and lithic sandstones. And, we analyzed the provenance of Wilcox and discussed the effect of salt related mini-basin controlling the deposition in deepwater setting. Based on this study, we propose a model for Wilcox deposition, in which the lower slope is defined as channel and there is deepwater fan in basin floor.
2014, 32(6): 1140-1152.
Abstract:
Submarine leveed-channel complexes on the continental slope in OML130 area of West Africa have been anatomized with high-resolution seismic data near the present seabed. Seismic reflection features for each sedimentary elements of the submarine gravity-flow induced leveed-channel complex has been analyzed and summarized. The geometric outlines and the interior infill characteristics have been introduced in detail. Seismic reflections for single channel have the V-shaped cross-sectional motifs with relatively high amplitudes and low continuities at the lower interval, which indicate the relatively coarse-grained sediments, whilst for the upper part of a channel, seismic reflections have the motifs indicating fine-grained sediments with moderate amplitudes and great continuities and the sinuous ribbon plan form. With the analysis on features of cutting and filling, three stacking patterns of channels in the leveed-channel complexes have been summarized. It is concluded that each later channel develops independently from at most cases the earlier channels in terms of the process compared with the sinuous meandering channels in fluvial systems. So, it leads to the three stacking patterns occurred in the different parts of this submarine leveed-channel system. A depositional model for the continental slope leveed-channel complex in West Africa is envisioned based on the analysis of the controlling factors with the data from near-seabed seismic as well as the deeper hydrocarbon-producing intervals. It is likely that the leveed-channel complexes can be occurred simultaneously with the depositional lobate-fan complexes side by side or alternatively downslope with each other. Near seabed high-resolution seismic data help us gain a much more insight than ever into the characteristics of the deep-water depositional systems and build the more rational and applicable models, which will enhance the related studies more successfully.
Submarine leveed-channel complexes on the continental slope in OML130 area of West Africa have been anatomized with high-resolution seismic data near the present seabed. Seismic reflection features for each sedimentary elements of the submarine gravity-flow induced leveed-channel complex has been analyzed and summarized. The geometric outlines and the interior infill characteristics have been introduced in detail. Seismic reflections for single channel have the V-shaped cross-sectional motifs with relatively high amplitudes and low continuities at the lower interval, which indicate the relatively coarse-grained sediments, whilst for the upper part of a channel, seismic reflections have the motifs indicating fine-grained sediments with moderate amplitudes and great continuities and the sinuous ribbon plan form. With the analysis on features of cutting and filling, three stacking patterns of channels in the leveed-channel complexes have been summarized. It is concluded that each later channel develops independently from at most cases the earlier channels in terms of the process compared with the sinuous meandering channels in fluvial systems. So, it leads to the three stacking patterns occurred in the different parts of this submarine leveed-channel system. A depositional model for the continental slope leveed-channel complex in West Africa is envisioned based on the analysis of the controlling factors with the data from near-seabed seismic as well as the deeper hydrocarbon-producing intervals. It is likely that the leveed-channel complexes can be occurred simultaneously with the depositional lobate-fan complexes side by side or alternatively downslope with each other. Near seabed high-resolution seismic data help us gain a much more insight than ever into the characteristics of the deep-water depositional systems and build the more rational and applicable models, which will enhance the related studies more successfully.
2014, 32(6): 1153-1161.
Abstract:
The Quantou-Nenjiang Formations of Songliao Basin belong to the depression period, developed large fluvial facies in Quantou Formation, but developed large lacustrine-delta deposition in Qingshankou, Yaojia and Nenjiang Formations. The reservoir strata are mainly point bar sand body, progradational and retrogradational delta sand body and the gravity flow sand body of lacustrine facies. The traditional work of exploration just focused on 2D seismic data by point-line research method, so there may be some mistakes in understanding spatial form, the interior structure and the distribution of the sand bodies. By the enlargement of the cover area and the improvement of the acquisition accuracy in 3D seismic works, the Seismic Sedimentology is widespread used in North Songliao Basin. With fine depicting of the geologic bodies, we found that the progradational delta has the typical bird foot shape controlled by the high angle fluvial facies, narrow in the delta front, but wide in the delta plain, without underwater distributary channels developed. The retrogradational delta has the weeping willow shape controlled by the low angle laucustrine facies, wide in the delta front, but narrow in the delta plain, developed the underwater distributary channels. And we found large slump fan and turbidite fan in Qingshankou Formation and group 2-3 of Nenjiang Formation. Also, we found large turbidite channel in Yaojia Formation and group 1 of Nenjiang Formation. This study will cover the shortage of the traditional research techniques and refresh the new field of the exploration in North Songliao Basin.
The Quantou-Nenjiang Formations of Songliao Basin belong to the depression period, developed large fluvial facies in Quantou Formation, but developed large lacustrine-delta deposition in Qingshankou, Yaojia and Nenjiang Formations. The reservoir strata are mainly point bar sand body, progradational and retrogradational delta sand body and the gravity flow sand body of lacustrine facies. The traditional work of exploration just focused on 2D seismic data by point-line research method, so there may be some mistakes in understanding spatial form, the interior structure and the distribution of the sand bodies. By the enlargement of the cover area and the improvement of the acquisition accuracy in 3D seismic works, the Seismic Sedimentology is widespread used in North Songliao Basin. With fine depicting of the geologic bodies, we found that the progradational delta has the typical bird foot shape controlled by the high angle fluvial facies, narrow in the delta front, but wide in the delta plain, without underwater distributary channels developed. The retrogradational delta has the weeping willow shape controlled by the low angle laucustrine facies, wide in the delta front, but narrow in the delta plain, developed the underwater distributary channels. And we found large slump fan and turbidite fan in Qingshankou Formation and group 2-3 of Nenjiang Formation. Also, we found large turbidite channel in Yaojia Formation and group 1 of Nenjiang Formation. This study will cover the shortage of the traditional research techniques and refresh the new field of the exploration in North Songliao Basin.
2014, 32(6): 1162-1170.
Abstract:
Based on the drilling and seismic data in Baiyun Depression, development and evolution of sedimentary facies are comprehensively analyzed in the Wenchang and Enping Formation, Baiyun Depression of Pearl River Mouth Basin. Through the limited well data, three sedimentary facies, delta facies, fan-delta facies and lacustrine facies, are identified in Baiyun Depression; Logging curve of delta facies shows an inverse cycle, but subset normal cycle in some parts; Logging curve(gamma-ray) of fan-delta curve shows an inverse cycle and subset normal cycle overall; Lacustrine facies mainly are mudstone deposition, partly mingled with sand bar or carbonate beach bar. Nine types of seismic facies are identified in Baiyun Dpression. The research shows that the continuinous subsidence of the basin causes the long time of the deep lacustrine facies development and the formation of the thick-layer resource rock. Influenced by lower Panyu Uplift, a delta facies developed in the northern gentle slope in Baiyun Depression, fan-delta facies developed from southwestern to southern abrupt slope. And the development of partial delta facies has a succession.
Based on the drilling and seismic data in Baiyun Depression, development and evolution of sedimentary facies are comprehensively analyzed in the Wenchang and Enping Formation, Baiyun Depression of Pearl River Mouth Basin. Through the limited well data, three sedimentary facies, delta facies, fan-delta facies and lacustrine facies, are identified in Baiyun Depression; Logging curve of delta facies shows an inverse cycle, but subset normal cycle in some parts; Logging curve(gamma-ray) of fan-delta curve shows an inverse cycle and subset normal cycle overall; Lacustrine facies mainly are mudstone deposition, partly mingled with sand bar or carbonate beach bar. Nine types of seismic facies are identified in Baiyun Dpression. The research shows that the continuinous subsidence of the basin causes the long time of the deep lacustrine facies development and the formation of the thick-layer resource rock. Influenced by lower Panyu Uplift, a delta facies developed in the northern gentle slope in Baiyun Depression, fan-delta facies developed from southwestern to southern abrupt slope. And the development of partial delta facies has a succession.
2014, 32(6): 1171-1180.
Abstract:
The petroleum exploration of Junggar Basin shows that a mass of high quality reservoirs developed in Triassic Baikouquan Formation of Mabei region, while the genesis of high quality reservoir still needs further research. The characteristics of reservoir petrology, physical property, sedimentary environment and diagenesis indicate that reservoir of Triassic Baikouquan Formation in Mabei area is mainly composed of coarse clastic glutenite. The fine grained clastic sandstone reservoirs less developed, reservoirs average porosity is mainly between 7% and 9%, and average permeability is 0.9×10-3μm2 and 1.4×10-3μm2; Fan-delta front subaqueous distributary channel and fan-delta plain distributary channel are favorable reservoirs which are affected by structural slop-break zone, due to long time water washing, Fan-delta front subaqueous distributary channel glutenite reservoir property is best and then Fan-delta plain distributary channel sand body. Compaction causes higher argillaceous matrix glutenite reservoir property irreversibly decrease, proper eogenetic cement provide the supported grain skeleton, which can resist compaction effect on reservoir physical properties, but late diagenesis lots of cement can block the pore and bad to reservoirs. Whereas the dissolution of feldspar particles and zeolite cement has positive significance on the improvement of the reservoir property.
The petroleum exploration of Junggar Basin shows that a mass of high quality reservoirs developed in Triassic Baikouquan Formation of Mabei region, while the genesis of high quality reservoir still needs further research. The characteristics of reservoir petrology, physical property, sedimentary environment and diagenesis indicate that reservoir of Triassic Baikouquan Formation in Mabei area is mainly composed of coarse clastic glutenite. The fine grained clastic sandstone reservoirs less developed, reservoirs average porosity is mainly between 7% and 9%, and average permeability is 0.9×10-3μm2 and 1.4×10-3μm2; Fan-delta front subaqueous distributary channel and fan-delta plain distributary channel are favorable reservoirs which are affected by structural slop-break zone, due to long time water washing, Fan-delta front subaqueous distributary channel glutenite reservoir property is best and then Fan-delta plain distributary channel sand body. Compaction causes higher argillaceous matrix glutenite reservoir property irreversibly decrease, proper eogenetic cement provide the supported grain skeleton, which can resist compaction effect on reservoir physical properties, but late diagenesis lots of cement can block the pore and bad to reservoirs. Whereas the dissolution of feldspar particles and zeolite cement has positive significance on the improvement of the reservoir property.
2014, 32(6): 1181-1187.
Abstract:
In recent years, the analysis on core samples from the middle-shallow source rocks in Qijia-Gulong Depression of Songliao Basin are getting more and more, it's necessary to re-evaluate the hydrocarbon-generation amount of the middle-shallow source rocks. The geochemical characteristics of core samples from the middle-shallow source rocks in Qijia-Gulong Depression were collected and analyzed. The hydrocarbon generated transformation ratio with depth of the middle-shallow source rocks in Qijia-Gulong Depression was calculated using the chemical kinetics method, which is based on the high temperature thermal simulation of low maturity source rock samples. Then the hydrocarbon-generation amount was evaluated quantitatively. The results show that: the middle-shallow source rocks in Qijia-Gulong Depression of Songliao Basin are extremely rich in organic matter. The organic matter types of them are good. And the thermal evolution stage of them is from immature to mature. The hydrocarbon generation threshold depth of the middle-shallow source rocks is about 1 500 m, and the depth of beginning to quickly generate hydrocarbon is about 1 750 m. The middle-shallow source rocks of the first member of Qingshankou formation (K1qn1), the second and third member of Qingshankou formation (K1qn2+3) and the first member of Nenjiang formation (K1n1) are mainly generated oil associated with a small amount of gas. The amounts of oil generated from them are 195.95×108 t, 241.79×108 t and 134.77×108 t. The amounts of gas generated from them are 36.89×1011 m3, 17.64×1011 m3 and 4.02×1011 m3, respectively. The oil and gas resource are (28.63~57.25) ×108 t and (0.29~0.59) ×1011 m3 in middle-shallow strata of Qijia-Gulong depression in Songliao Basin.
In recent years, the analysis on core samples from the middle-shallow source rocks in Qijia-Gulong Depression of Songliao Basin are getting more and more, it's necessary to re-evaluate the hydrocarbon-generation amount of the middle-shallow source rocks. The geochemical characteristics of core samples from the middle-shallow source rocks in Qijia-Gulong Depression were collected and analyzed. The hydrocarbon generated transformation ratio with depth of the middle-shallow source rocks in Qijia-Gulong Depression was calculated using the chemical kinetics method, which is based on the high temperature thermal simulation of low maturity source rock samples. Then the hydrocarbon-generation amount was evaluated quantitatively. The results show that: the middle-shallow source rocks in Qijia-Gulong Depression of Songliao Basin are extremely rich in organic matter. The organic matter types of them are good. And the thermal evolution stage of them is from immature to mature. The hydrocarbon generation threshold depth of the middle-shallow source rocks is about 1 500 m, and the depth of beginning to quickly generate hydrocarbon is about 1 750 m. The middle-shallow source rocks of the first member of Qingshankou formation (K1qn1), the second and third member of Qingshankou formation (K1qn2+3) and the first member of Nenjiang formation (K1n1) are mainly generated oil associated with a small amount of gas. The amounts of oil generated from them are 195.95×108 t, 241.79×108 t and 134.77×108 t. The amounts of gas generated from them are 36.89×1011 m3, 17.64×1011 m3 and 4.02×1011 m3, respectively. The oil and gas resource are (28.63~57.25) ×108 t and (0.29~0.59) ×1011 m3 in middle-shallow strata of Qijia-Gulong depression in Songliao Basin.
2014, 32(6): 1188-1200.
Abstract:
The North Carnarvon basin is Australia's most important oil and gas basin, also one of main gas- rich basins in the world. In Triassic, North Carnarvon basin belongs to pericratonic depression and the strata are hugely thick and widely distributed. Mandatory regression occurred in northwest shelf of Australia in Late middle Triassic, causing the transformation of Triassic sedimentary framework, North Carnarvon basin, and the depositional environment of North Carnarvon basin from offshore turn into the transition facies, thus two distinct strata-Locker shale and Mungaroo group deposited in North Carnarvon basin. In this article, paleogeographic setting of Locker shale and Mungaroo group and characteristics of associated source rock and organic maceral are elaborated under macro-micro scales, and organic-inorganic aspects.
On a macro level, Mungaroo group is dominated by large-scale delta interbedded distributary channel sandstones and dark mudstones. The mudstone in proximal delta plain is thin, of which terrigenous organic matter content is high and TOC content can be up to 1.59%, besides, thin coal seams just developed locally. The mudstone in remote delta plain is thick, of which terrigenous organic matter content is high and TOC content is highest and can be up to 4.11%, besides, thin coal seams developed widely. The mudstone in delta front is thick, of which terrigenous organic matter content is low and TOC content can be up to 1.05%. Locker Shale is composed of major shallow sea depositional association and small-scale delta. The source rock in open shallow sea subfacies is the thick, what's more, prodelta, offshore and open shallow sea subfacies TOC content is much lower, and three sub-phases average TOC is 1.16%.
On a micro level, sedimentary facies of Mungaroo group from the proximal plain facies-distal plain facies-front subfacies liptinite content gradually increased, with that vitrinite first increased and then decreased, but inertinite first decreased and then increased. As Locker Shale, by the prodelta to neritic facies liptinite increased, with that both vitrinite and inertinite reduced.
The distribution of source rocks and organic maceral is closely related to special paleogeographic and monsoon flood paleoclimate setting of the southern margin of Thethys. The distal delta plain of Mungaroo group is the most favorable environment for the development of source rock. Lithofacies palaeogeographic framework and Sedimentary evolution regularity in Trassic of North Carnarvon Basin reflect the sedimentary characteristics which is dominated by paroxysmal water under the effect of greenhouse climate, providing a new train of thought for oil and gas resource evaluation in a similar geological setting.
The North Carnarvon basin is Australia's most important oil and gas basin, also one of main gas- rich basins in the world. In Triassic, North Carnarvon basin belongs to pericratonic depression and the strata are hugely thick and widely distributed. Mandatory regression occurred in northwest shelf of Australia in Late middle Triassic, causing the transformation of Triassic sedimentary framework, North Carnarvon basin, and the depositional environment of North Carnarvon basin from offshore turn into the transition facies, thus two distinct strata-Locker shale and Mungaroo group deposited in North Carnarvon basin. In this article, paleogeographic setting of Locker shale and Mungaroo group and characteristics of associated source rock and organic maceral are elaborated under macro-micro scales, and organic-inorganic aspects.
On a macro level, Mungaroo group is dominated by large-scale delta interbedded distributary channel sandstones and dark mudstones. The mudstone in proximal delta plain is thin, of which terrigenous organic matter content is high and TOC content can be up to 1.59%, besides, thin coal seams just developed locally. The mudstone in remote delta plain is thick, of which terrigenous organic matter content is high and TOC content is highest and can be up to 4.11%, besides, thin coal seams developed widely. The mudstone in delta front is thick, of which terrigenous organic matter content is low and TOC content can be up to 1.05%. Locker Shale is composed of major shallow sea depositional association and small-scale delta. The source rock in open shallow sea subfacies is the thick, what's more, prodelta, offshore and open shallow sea subfacies TOC content is much lower, and three sub-phases average TOC is 1.16%.
On a micro level, sedimentary facies of Mungaroo group from the proximal plain facies-distal plain facies-front subfacies liptinite content gradually increased, with that vitrinite first increased and then decreased, but inertinite first decreased and then increased. As Locker Shale, by the prodelta to neritic facies liptinite increased, with that both vitrinite and inertinite reduced.
The distribution of source rocks and organic maceral is closely related to special paleogeographic and monsoon flood paleoclimate setting of the southern margin of Thethys. The distal delta plain of Mungaroo group is the most favorable environment for the development of source rock. Lithofacies palaeogeographic framework and Sedimentary evolution regularity in Trassic of North Carnarvon Basin reflect the sedimentary characteristics which is dominated by paroxysmal water under the effect of greenhouse climate, providing a new train of thought for oil and gas resource evaluation in a similar geological setting.
