2018 Vol. 36, No. 2
Display Method:
2018, 36(2): 215-231.
doi: 10.14027/j.issn.1000-0550.2018.001
Abstract:
The basic geological parameters, including total organic carbon conten (TOC) and type, thermal evolution of organic matter(Ro) thickness of hydrocarbon source rocks, mineral composition and content, reservoir characteristics, which all controlled by sedimentary facies, are the main elements to evaluate the enrichment of shale gas in regional geology survey stage. On the basis of the detailed study of sedimentary facies, by mapping the lithofacies palaeogeography, distribution of the fine-grained sedimentary rocks which are rich in organic matter can be figured out. So, the lithofacies paleogeography controls the developmental characteristics of the shale gas. Using the basic geological parameters, the shale gas favorable areas in southern Sichuan Basin and its peripheral region were preliminarily evaluated. The black rocks of shallow shelf facies in Longmaxi Formation of Silurian, as long as being up into middle diagenetic stage, would be able to be shale gas reservoirs in southern Sichuan Basin and its periphery. On the basis of our previous study, through analyzing the shale gas geologic feature of Longmaxi Formation in southern Sichuan Basin and its periphery, the point of view is further demonstrated, that the study of sedimentary facies or lithofacies palaeogeography is the key and foundation of shale gas geology survey and evaluation.
The basic geological parameters, including total organic carbon conten (TOC) and type, thermal evolution of organic matter(Ro) thickness of hydrocarbon source rocks, mineral composition and content, reservoir characteristics, which all controlled by sedimentary facies, are the main elements to evaluate the enrichment of shale gas in regional geology survey stage. On the basis of the detailed study of sedimentary facies, by mapping the lithofacies palaeogeography, distribution of the fine-grained sedimentary rocks which are rich in organic matter can be figured out. So, the lithofacies paleogeography controls the developmental characteristics of the shale gas. Using the basic geological parameters, the shale gas favorable areas in southern Sichuan Basin and its peripheral region were preliminarily evaluated. The black rocks of shallow shelf facies in Longmaxi Formation of Silurian, as long as being up into middle diagenetic stage, would be able to be shale gas reservoirs in southern Sichuan Basin and its periphery. On the basis of our previous study, through analyzing the shale gas geologic feature of Longmaxi Formation in southern Sichuan Basin and its periphery, the point of view is further demonstrated, that the study of sedimentary facies or lithofacies palaeogeography is the key and foundation of shale gas geology survey and evaluation.
2018, 36(2): 232-242.
doi: 10.14027/j.issn.1000-0550.2018.090
Abstract:
Oncoids occur in Sinian Dengying Formation in Ziyang Maliu region of Sichuan Basin. Using the field geological survey, the polarizing microscope and field emission scanning electron microscopy (SEM) to study oncoids of morphology, structure, sedimentary environment and the main control factors, the result is as follows:oncoids are developed in the middle and upper of the four section of the Dengying Formation, they can be divided into four categories:TypeⅠnormal oncoid, Type Ⅱnormal compound oncoid, Type Ⅲ thin skin oncoid, Type Ⅳ thin skin compound oncoid, and given priority to with Type Ⅰ. Oncoids of morphology are given priority to with spherical, and few ellipsoid, bar and irregular shape of oncoids. The conditions of the forming of oncoids are sufficient material basis in Sinian Dengying Formation, appropriate middle-high energy hydrodynamic conditions and the injection of low terrigenous clastic material. Research shows that the sedimentary environment of the oncoids in the middle and upper of the four section of the Dengying Formation is in a medium-high energy shallow gentle slope belt.
Oncoids occur in Sinian Dengying Formation in Ziyang Maliu region of Sichuan Basin. Using the field geological survey, the polarizing microscope and field emission scanning electron microscopy (SEM) to study oncoids of morphology, structure, sedimentary environment and the main control factors, the result is as follows:oncoids are developed in the middle and upper of the four section of the Dengying Formation, they can be divided into four categories:TypeⅠnormal oncoid, Type Ⅱnormal compound oncoid, Type Ⅲ thin skin oncoid, Type Ⅳ thin skin compound oncoid, and given priority to with Type Ⅰ. Oncoids of morphology are given priority to with spherical, and few ellipsoid, bar and irregular shape of oncoids. The conditions of the forming of oncoids are sufficient material basis in Sinian Dengying Formation, appropriate middle-high energy hydrodynamic conditions and the injection of low terrigenous clastic material. Research shows that the sedimentary environment of the oncoids in the middle and upper of the four section of the Dengying Formation is in a medium-high energy shallow gentle slope belt.
2018, 36(2): 243-256.
doi: 10.14027/j.issn.1000-0550.2018.032
Abstract:
Based on detailed study on the macroscopic and microscopic sedimentary features of the Shipu Group in the Xiangshan, 19 lithofacies were recognized (including 14 detrital rock lithofacies and 5 carbonate lithofacies). According to the sedimentary interpretations of lithofacies, sedimentary structures, and microfacies associations, we recognized three major facies for the Shipu Group (i.e., fan delta, tidal flat, and the offshore-shallow sea). Based on the unconformity and sedimentary trend mutants identified in the Shipu section, 5 intact T-R sequences and 1 poor-preserved T-R sequence which only contains the regressive systems tract were suggested in the Shipu section, and the regional change of relative sea level was established by the superposition mode of systems tract and types of facies. The results indicated that the third-order changes of the relative sea level in the Shipu area is characterized by persistent transgression during the period from the Aptian to the Albian, but the forth-order changes of relative sea level fluctuate frequently. The changes of relative sea level in the Shipu section largely coincided with the changes of eustatic sea level during Aptian-Albian. However, the relative sea level elevated during the time of 119-116 Ma and 104-100 Ma which deviated from the eustatic sea level. Considering the intense volcanic activity in these periods, we suggested that the changes of the relative sea level in the Shipu section were controlled by the eustatic sea level and regional tectonic activity.
Based on detailed study on the macroscopic and microscopic sedimentary features of the Shipu Group in the Xiangshan, 19 lithofacies were recognized (including 14 detrital rock lithofacies and 5 carbonate lithofacies). According to the sedimentary interpretations of lithofacies, sedimentary structures, and microfacies associations, we recognized three major facies for the Shipu Group (i.e., fan delta, tidal flat, and the offshore-shallow sea). Based on the unconformity and sedimentary trend mutants identified in the Shipu section, 5 intact T-R sequences and 1 poor-preserved T-R sequence which only contains the regressive systems tract were suggested in the Shipu section, and the regional change of relative sea level was established by the superposition mode of systems tract and types of facies. The results indicated that the third-order changes of the relative sea level in the Shipu area is characterized by persistent transgression during the period from the Aptian to the Albian, but the forth-order changes of relative sea level fluctuate frequently. The changes of relative sea level in the Shipu section largely coincided with the changes of eustatic sea level during Aptian-Albian. However, the relative sea level elevated during the time of 119-116 Ma and 104-100 Ma which deviated from the eustatic sea level. Considering the intense volcanic activity in these periods, we suggested that the changes of the relative sea level in the Shipu section were controlled by the eustatic sea level and regional tectonic activity.
2018, 36(2): 257-266.
doi: 10.14027/j.issn.1000-0550.2018.024
Abstract:
Brown-yellow marl and grey-green mudstone of Linxiang Formation above nodular limestone develops upwards successively in Chengkou, Chongqing. Grey-green mudstone changes into dark silica mudstone of Wufeng Formation-Longmaxi Formation gradually. Changes from deep to shallow, then to deep of water depth are unraveled. Much anoxic and less oxic in redox condition upwards the Yanmai profile from Linxiang Formation to Wufeng Formation-Longmaxi Formation in general is indicated with the help of element geochemical analysis. A weak enhanced oxidation exists in the middle-upper portion of Linxiang Formation, implying structural uplift of Yichang movement. Higher paleoproductivity are seen in Guanyinqiao member and Layer 5 of Linxiang Formation, which are much oxic relatively, corresponding to the ascending current and the sea-level falling at that time, which are caused by the global gradual cooling down climate. The tectonic setting of Linxiang Formation-Longmaxi Formation inclines to an active continental arc environment. Less terrigenous constituent and more volcanic clastic component upwards Yanmai profile is indicated. The silica mudstone of Wufeng Formation and Longmaxi Formation shows apparent geochemical characteristics of hot water deposition, which may be influenced by deep hydrothermal activity.
Brown-yellow marl and grey-green mudstone of Linxiang Formation above nodular limestone develops upwards successively in Chengkou, Chongqing. Grey-green mudstone changes into dark silica mudstone of Wufeng Formation-Longmaxi Formation gradually. Changes from deep to shallow, then to deep of water depth are unraveled. Much anoxic and less oxic in redox condition upwards the Yanmai profile from Linxiang Formation to Wufeng Formation-Longmaxi Formation in general is indicated with the help of element geochemical analysis. A weak enhanced oxidation exists in the middle-upper portion of Linxiang Formation, implying structural uplift of Yichang movement. Higher paleoproductivity are seen in Guanyinqiao member and Layer 5 of Linxiang Formation, which are much oxic relatively, corresponding to the ascending current and the sea-level falling at that time, which are caused by the global gradual cooling down climate. The tectonic setting of Linxiang Formation-Longmaxi Formation inclines to an active continental arc environment. Less terrigenous constituent and more volcanic clastic component upwards Yanmai profile is indicated. The silica mudstone of Wufeng Formation and Longmaxi Formation shows apparent geochemical characteristics of hot water deposition, which may be influenced by deep hydrothermal activity.
2018, 36(2): 267-279.
doi: 10.14027/j.issn.1000-0550.2018.028
Abstract:
The largest mass extinction event in the Phanerozoic took place at the end of Permian. The cause of this biological crisis is still remaining controversial. This work uses the carbon isotope, major and minor elements across the Permian-Triassic boundary at the Dongling section in the Xiushui city of the Jiangxi Province to study the relationship between the global carbon cycle perturbation and consistent provenance changes and the mass extinction. The results show that the carbonate carbon isotope profile displays stepwise negative excursion. The magnitudes of first and secondary stepwise are 2‰ and 2.5‰, respectively, with a total magnitude of 4.5‰. In the process of stepwise negative excursion of carbon isotope,the provenance of silicate composition in the carbonate rock changes from mafic igneous rocks to island arc intermediate-acid igneous rocks. The later probably concern with the volcanic eruption of Southern China Island. According to negative excursion of carbon isotope has the same time with the change of provenance and ash layer, conjecture it may relate to South China island arc volcanism and volcanism eruption of Siberian large igneous provinces. Large-scale volcanism eruption released or triggered carbon dioxides and methane. These greenhouse gases and the global regression probably are the main causes for this stepwise carbon isotopic excursion across the Permian-Triassic boundary. The deteriorated environments resulted from the volcanism, e.g., global warming, marine anoxia, marine acidification, large sediment influx resulted from vegetation deterioration, lead to the increased pressure of organism existence and thus the mass extinction.
The largest mass extinction event in the Phanerozoic took place at the end of Permian. The cause of this biological crisis is still remaining controversial. This work uses the carbon isotope, major and minor elements across the Permian-Triassic boundary at the Dongling section in the Xiushui city of the Jiangxi Province to study the relationship between the global carbon cycle perturbation and consistent provenance changes and the mass extinction. The results show that the carbonate carbon isotope profile displays stepwise negative excursion. The magnitudes of first and secondary stepwise are 2‰ and 2.5‰, respectively, with a total magnitude of 4.5‰. In the process of stepwise negative excursion of carbon isotope,the provenance of silicate composition in the carbonate rock changes from mafic igneous rocks to island arc intermediate-acid igneous rocks. The later probably concern with the volcanic eruption of Southern China Island. According to negative excursion of carbon isotope has the same time with the change of provenance and ash layer, conjecture it may relate to South China island arc volcanism and volcanism eruption of Siberian large igneous provinces. Large-scale volcanism eruption released or triggered carbon dioxides and methane. These greenhouse gases and the global regression probably are the main causes for this stepwise carbon isotopic excursion across the Permian-Triassic boundary. The deteriorated environments resulted from the volcanism, e.g., global warming, marine anoxia, marine acidification, large sediment influx resulted from vegetation deterioration, lead to the increased pressure of organism existence and thus the mass extinction.
2018, 36(2): 280-290.
doi: 10.14027/j.issn.1000-0550.2018.025
Abstract:
Through detailed field geological survey, various soft-sediment deformation structures are found in Huangqikou Formation in Changcheng System of the middle part of Helan Mountain, including liquefied sand dykes(veins), liquefied hydraulic fracture structures and liquefied breccias, load structures, ball-and-pillow structures, beaded structures, convolution lamination (liquefied curled deformation structures) and step microfaults. Relatively higher compositional maturity and lower texture maturity of quartz sandstones are observed under microscope. Sandstone grains are mostly subround-round, with various sizes. Muddy sediments mix with clastic particles, or intersperse in sandstones in irregular vein-like form. Micro thrust faults are found cutting laminae under microscope. The sedimentary environment of Huangqikou Formation is identified as littoral-neritic sea by analyses of environment and observation of sedimentary structures (such as ridged ripples, small cross-bedding, horizontal bedding and mud cracks). Soft-sediment deformation structures in Huangqikou Formation are most likely formed by seismic events, not gravitational load. Four seismic event layers are identified in middle-low part of the first member of Huangqikou Formation. We speculate that at early stage of deposition of Huangqikou Formation, crustal movement was relatively active, then gradually tended to a stable state, appearance of seismites may be related to tectonic setting of extension-rifting of Helan aulacogen.
Through detailed field geological survey, various soft-sediment deformation structures are found in Huangqikou Formation in Changcheng System of the middle part of Helan Mountain, including liquefied sand dykes(veins), liquefied hydraulic fracture structures and liquefied breccias, load structures, ball-and-pillow structures, beaded structures, convolution lamination (liquefied curled deformation structures) and step microfaults. Relatively higher compositional maturity and lower texture maturity of quartz sandstones are observed under microscope. Sandstone grains are mostly subround-round, with various sizes. Muddy sediments mix with clastic particles, or intersperse in sandstones in irregular vein-like form. Micro thrust faults are found cutting laminae under microscope. The sedimentary environment of Huangqikou Formation is identified as littoral-neritic sea by analyses of environment and observation of sedimentary structures (such as ridged ripples, small cross-bedding, horizontal bedding and mud cracks). Soft-sediment deformation structures in Huangqikou Formation are most likely formed by seismic events, not gravitational load. Four seismic event layers are identified in middle-low part of the first member of Huangqikou Formation. We speculate that at early stage of deposition of Huangqikou Formation, crustal movement was relatively active, then gradually tended to a stable state, appearance of seismites may be related to tectonic setting of extension-rifting of Helan aulacogen.
2018, 36(2): 291-301.
doi: 10.14027/j.issn.1000-0550.2018.003
Abstract:
Better understanding of the late Paleozoic sedimentary sequences in Baoshan block were obtained by detailed field measurement, borehole logging combined with sequence stratigraphic and facies studies as well as carbon and oxygen isotopic analysis of the lower Carboniferous Xiangshan Formation and lower Permian Dingjiazhai Formation at the Xiyi area, northern Baoshan Block. Three lithologic units were recognized in the Lower Carboniferous Xiangshan Formation, which are in ascending order represent lower slope, upper slope and carbonate platform depositional settings, respectively. The Lower Permian Dingjiazhai Formation was interpreted to be glacial-marine deposits according to distinctive pebbly calcareous moraine diamictite and local development of dropstones. The δ13CPDB profile demonstrates a gradual increasing trend up section in the Lower Carboniferous Xiangshan Formation, indicating a relatively stable sedimentary environment possible due to a steady increase of organic carbon burial. Combined with previous paleomagnetic results, biotic correlation and tectonic studies, it is presumed that the Baoshan Block was in a stable setting as a part of the northern Gondwana. However, the δ13CPDB values drop dramatically on the cessation of the pebbly moraine carbonate which represents the ending of glacial period, and correspond well with the first temperature rise event as well as massive basalt eruption in the early Permian. The above collectively indicate that the Baoshan Block was separated from the northeast Gondwana and started to drift northwards in the early Permian. The present study not only sheds light on the paleoceanic, paleogeographic and paleoclimatic significance of the Paleozoic Submasu Block, but also provides new carbon isotope chemostratigraphy for the contemporary sedimentary sequences.
Better understanding of the late Paleozoic sedimentary sequences in Baoshan block were obtained by detailed field measurement, borehole logging combined with sequence stratigraphic and facies studies as well as carbon and oxygen isotopic analysis of the lower Carboniferous Xiangshan Formation and lower Permian Dingjiazhai Formation at the Xiyi area, northern Baoshan Block. Three lithologic units were recognized in the Lower Carboniferous Xiangshan Formation, which are in ascending order represent lower slope, upper slope and carbonate platform depositional settings, respectively. The Lower Permian Dingjiazhai Formation was interpreted to be glacial-marine deposits according to distinctive pebbly calcareous moraine diamictite and local development of dropstones. The δ13CPDB profile demonstrates a gradual increasing trend up section in the Lower Carboniferous Xiangshan Formation, indicating a relatively stable sedimentary environment possible due to a steady increase of organic carbon burial. Combined with previous paleomagnetic results, biotic correlation and tectonic studies, it is presumed that the Baoshan Block was in a stable setting as a part of the northern Gondwana. However, the δ13CPDB values drop dramatically on the cessation of the pebbly moraine carbonate which represents the ending of glacial period, and correspond well with the first temperature rise event as well as massive basalt eruption in the early Permian. The above collectively indicate that the Baoshan Block was separated from the northeast Gondwana and started to drift northwards in the early Permian. The present study not only sheds light on the paleoceanic, paleogeographic and paleoclimatic significance of the Paleozoic Submasu Block, but also provides new carbon isotope chemostratigraphy for the contemporary sedimentary sequences.
2018, 36(2): 302-309.
doi: 10.14027/j.issn.1000-0550.2018.040
Abstract:
Bauxite deposit in Wuzhengdao of Qianbei, which is the biggest bauxite deposit of China, is sedimentary type bauxite, which is affected by facies and change of sea level. Based on analysis of lithology and geochemistry of bauxite-bearing rock series in the study area, the bauxite is formed in shore lake and shallow lake. So the bauxite is deposited in fresh water. The chlorite rock and bauxite rock are deposited in fan delta and tidal flat facies. The hydrodynamic condition determines types and grade of bauxite. Grain bauxite is formed in strong hydrodynamic condition, soil type bauxite is formed in weak hydrodynamic condition. The chlorite rock and bauxite rock are deposited during rise of sea level, and bauxite is deposited during drop of sea level. The span of drop period is much greater than rise period, which explains why forming of bauxite is a long weathering progress. Up to three cycles can be identified during deposit of bauxite-bearing rock series, and the three cycles are consistent with corresponding period deposit of carbonate rock and clastic rock in adjacent area.
Bauxite deposit in Wuzhengdao of Qianbei, which is the biggest bauxite deposit of China, is sedimentary type bauxite, which is affected by facies and change of sea level. Based on analysis of lithology and geochemistry of bauxite-bearing rock series in the study area, the bauxite is formed in shore lake and shallow lake. So the bauxite is deposited in fresh water. The chlorite rock and bauxite rock are deposited in fan delta and tidal flat facies. The hydrodynamic condition determines types and grade of bauxite. Grain bauxite is formed in strong hydrodynamic condition, soil type bauxite is formed in weak hydrodynamic condition. The chlorite rock and bauxite rock are deposited during rise of sea level, and bauxite is deposited during drop of sea level. The span of drop period is much greater than rise period, which explains why forming of bauxite is a long weathering progress. Up to three cycles can be identified during deposit of bauxite-bearing rock series, and the three cycles are consistent with corresponding period deposit of carbonate rock and clastic rock in adjacent area.
2018, 36(2): 310-318.
doi: 10.14027/j.issn.1000-0550.2018.035
Abstract:
The content and distribution of Dahu swamp Core granularity extracted from Mastersizer 2000 were analyzed based on standard deviation change. Three environmental sensitive grain-size components:0.6-7.1 μm (C1), 20-44.8 μm (C2) and 89.3-447.7 μm (C3) of its sediments at the depth of 348 cm were identified by the mathematical method of grain-size classes and standard deviation values. Combined with the distribution characteristic of sediment and the results of radiocarbon dating, we select C2 as an index to establish a sequence of 16 000 years of climate change in the Dahu swamp Core. During the period of 16.0-11.5 ka B.P., sensitive component of the overall content is low, the climate and environment of the studied area was relatively dry. During the period of 11.5-6.0 ka B.P., sensitive component of the overall content is low and the climate is wet. During the period of 6.0-3.8 ka B.P., the climate became dry, and sensitive grain-size group content increased. From 3.8 ka B.P. to now, the content of sensitive particle fraction is generally low. Considering the anthropogenic interference factors, this paper does not discuss in detail. The study found that the climate was very unstable through reconstructing the paleoclimate of Dahu lake-swamp area since the Late Glacial. In addition, we can draw a conclusion that climate change of Dahu lake-swamp is global by contrast to the GISP2 ice core climate records and D4 stalagmite in Dongge cave. And we find that the climate change in the study area may be related to solar activity.
The content and distribution of Dahu swamp Core granularity extracted from Mastersizer 2000 were analyzed based on standard deviation change. Three environmental sensitive grain-size components:0.6-7.1 μm (C1), 20-44.8 μm (C2) and 89.3-447.7 μm (C3) of its sediments at the depth of 348 cm were identified by the mathematical method of grain-size classes and standard deviation values. Combined with the distribution characteristic of sediment and the results of radiocarbon dating, we select C2 as an index to establish a sequence of 16 000 years of climate change in the Dahu swamp Core. During the period of 16.0-11.5 ka B.P., sensitive component of the overall content is low, the climate and environment of the studied area was relatively dry. During the period of 11.5-6.0 ka B.P., sensitive component of the overall content is low and the climate is wet. During the period of 6.0-3.8 ka B.P., the climate became dry, and sensitive grain-size group content increased. From 3.8 ka B.P. to now, the content of sensitive particle fraction is generally low. Considering the anthropogenic interference factors, this paper does not discuss in detail. The study found that the climate was very unstable through reconstructing the paleoclimate of Dahu lake-swamp area since the Late Glacial. In addition, we can draw a conclusion that climate change of Dahu lake-swamp is global by contrast to the GISP2 ice core climate records and D4 stalagmite in Dongge cave. And we find that the climate change in the study area may be related to solar activity.
2018, 36(2): 319-332.
doi: 10.14027/j.issn.1000-0550.2018.037
Abstract:
The Ordovician-Silurian transition was an interval which revealed major changes in the Earth's biotic, climatic, and environmental systems, triggering the Hirnantian glaciation and end-Ordovician mass extinctions. The paleo-ocean environment experienced intense shift and exerted a crucial impact on the global cycles of carbon, molybdenum and sulfur during O-S transition. In addition, the weakness of continental weathering reduced 187Os and 87Sr flux, resulting in positive δ187Os and δ87Sr excursions. This first ice age, since the late Neoproterozoic, was the culmination of a cooling trend that had begun in the early or middle Ordovician, and was linked to some combination of reduced volcanic arc outgassing, enhanced silicate weathering, increased organic carbon burial and so on. There exist many problems about the genesis of Hirnantian glaciation, such as lacking in individual biostratigraphy which can control the carbonate platform in shallow water and mudstone in deep water simultaneously, as well as the high-precision analysis based on geochemical proxies and isochronous stratigraphic correlation. Meanwhile diagenesis, weathering and tectonic-thermal events also exerted an important impact on reconstruction of Hirnantian glaciation, resulting in inaccurate interpretation.
The Ordovician-Silurian transition was an interval which revealed major changes in the Earth's biotic, climatic, and environmental systems, triggering the Hirnantian glaciation and end-Ordovician mass extinctions. The paleo-ocean environment experienced intense shift and exerted a crucial impact on the global cycles of carbon, molybdenum and sulfur during O-S transition. In addition, the weakness of continental weathering reduced 187Os and 87Sr flux, resulting in positive δ187Os and δ87Sr excursions. This first ice age, since the late Neoproterozoic, was the culmination of a cooling trend that had begun in the early or middle Ordovician, and was linked to some combination of reduced volcanic arc outgassing, enhanced silicate weathering, increased organic carbon burial and so on. There exist many problems about the genesis of Hirnantian glaciation, such as lacking in individual biostratigraphy which can control the carbonate platform in shallow water and mudstone in deep water simultaneously, as well as the high-precision analysis based on geochemical proxies and isochronous stratigraphic correlation. Meanwhile diagenesis, weathering and tectonic-thermal events also exerted an important impact on reconstruction of Hirnantian glaciation, resulting in inaccurate interpretation.
2018, 36(2): 333-342.
doi: 10.14027/j.issn.1000-0550.2018.043
Abstract:
Loess is one of the most detailed terrestrial widespread high resolution archives of climate and environment change, the study of the loess-paleosol sequences in Pamir allows one to assess the changes in the environment and pedogenesis over the interglacial and glacial epoch of the Quaternary period. However, deciphering such amount information requires multi-proxy to investigate the temporal process of aeolian dust and paleoclimate, which is important for understanding the forcing mechanisms of past climate in Pamir region and also for predicting the future regional climate changes under the global warming background. Soil color, one of the sensitive proxies for paleoclimate, has been widely used as an indicator of chemical and biological properties as well as the soil-forming process in the loess study. In view of above analysis, combined with magnetic susceptibility, calcium carbonate and organic matter proxies, this paper measured the chromatic proxies to investigate the spatial and temporal variations of soil color and their major controlling factors at the Pamir loess section dominated by westerlies. The results show that the introduction of chroma could compensate for defects in paleoclimate reconstruction when magnetic susceptibility cannot record the process of climate change and soil development well. In the process of loess accumulation, lightness L*, to a large extent, was dominated by color components a* and b*, furthermore, may be correlated to the substance that affect color component a*,b*. Redness a* and yellowness b* were controlled by the similar climatic factors and might process the consistent color material because of their relatively high correlation. Largely influenced by the categories and contents of iron oxide and correspond well with magnetic susceptibility, Redness a* could indirectly reflect the climate change and pedogenic environment in this region.The relationship between chromatic proxies and magnetic susceptibility indicate that magnetic susceptibility and a* show a positive correlation, for L* it is a negative one; this is due to the fact that their dominating matter is different. Only the combination between chromatic proxies and other climatic proxies, could we reconstruct a reasonable and reliable process of climate change in the Pamir region.
Loess is one of the most detailed terrestrial widespread high resolution archives of climate and environment change, the study of the loess-paleosol sequences in Pamir allows one to assess the changes in the environment and pedogenesis over the interglacial and glacial epoch of the Quaternary period. However, deciphering such amount information requires multi-proxy to investigate the temporal process of aeolian dust and paleoclimate, which is important for understanding the forcing mechanisms of past climate in Pamir region and also for predicting the future regional climate changes under the global warming background. Soil color, one of the sensitive proxies for paleoclimate, has been widely used as an indicator of chemical and biological properties as well as the soil-forming process in the loess study. In view of above analysis, combined with magnetic susceptibility, calcium carbonate and organic matter proxies, this paper measured the chromatic proxies to investigate the spatial and temporal variations of soil color and their major controlling factors at the Pamir loess section dominated by westerlies. The results show that the introduction of chroma could compensate for defects in paleoclimate reconstruction when magnetic susceptibility cannot record the process of climate change and soil development well. In the process of loess accumulation, lightness L*, to a large extent, was dominated by color components a* and b*, furthermore, may be correlated to the substance that affect color component a*,b*. Redness a* and yellowness b* were controlled by the similar climatic factors and might process the consistent color material because of their relatively high correlation. Largely influenced by the categories and contents of iron oxide and correspond well with magnetic susceptibility, Redness a* could indirectly reflect the climate change and pedogenic environment in this region.The relationship between chromatic proxies and magnetic susceptibility indicate that magnetic susceptibility and a* show a positive correlation, for L* it is a negative one; this is due to the fact that their dominating matter is different. Only the combination between chromatic proxies and other climatic proxies, could we reconstruct a reasonable and reliable process of climate change in the Pamir region.
2018, 36(2): 343-353.
doi: 10.14027/j.issn.1000-0550.2018.026
Abstract:
In the southern part of the Tengger Desert, the last glacial dissolution stratum of its Tumen profile consists of three layers of dune sand, two layers of lacustrine sediments, two layers of paleosol and five layers of sand loess. Through the chronological study of the sedimentary facies and testing of the main elements, the results define the stratum attributes to the last glacial dissolution stratum; once all the CIAs calculated, the order of CIA index appears as sand dune > loess > paleosoil > lacustrine sediments from the largest to the smallest. By contrast, it is found that the weathering intensity (climatic environment) of all the sedimentary facies indicated by CIA is in contradiction with the research conclusion that the granularity indicates the climate change in this period. With a deep study and discussion of the contradiction phenomenon, the following conclusions are obtained:1) The sedimentary material of the paleosol, lacustrine sediments and loess may originate from the Loess Plateau, on the southeast side of the soil door section. The provenance of sand dune is strongly influenced by the dune sand from the Tengger Desert in the north. The differences of the chemical elements of sedimentary facies make the comparison between the CIA index of different sedimentary facies congenitally deficient. 2) The low-lying topography where the soil door section locates at will produce water-catching effect, so that the migratory elements such as calcium, sodium, potassium and others will migrate with the precipitation of water to the surface of the sedimentary facies and the CIA indexes of different sedimentary facies are influenced to be too small to reflect the true weathering intensity. 3) The application of CIA indexes as a surrogate indicator of palaeoclimate change shall comprehensively consider the sedimentary facies provenance differences and the effect of the sedimentary environment; hence, the CIA index has limited application in indicating the paleoclimatic change.
In the southern part of the Tengger Desert, the last glacial dissolution stratum of its Tumen profile consists of three layers of dune sand, two layers of lacustrine sediments, two layers of paleosol and five layers of sand loess. Through the chronological study of the sedimentary facies and testing of the main elements, the results define the stratum attributes to the last glacial dissolution stratum; once all the CIAs calculated, the order of CIA index appears as sand dune > loess > paleosoil > lacustrine sediments from the largest to the smallest. By contrast, it is found that the weathering intensity (climatic environment) of all the sedimentary facies indicated by CIA is in contradiction with the research conclusion that the granularity indicates the climate change in this period. With a deep study and discussion of the contradiction phenomenon, the following conclusions are obtained:1) The sedimentary material of the paleosol, lacustrine sediments and loess may originate from the Loess Plateau, on the southeast side of the soil door section. The provenance of sand dune is strongly influenced by the dune sand from the Tengger Desert in the north. The differences of the chemical elements of sedimentary facies make the comparison between the CIA index of different sedimentary facies congenitally deficient. 2) The low-lying topography where the soil door section locates at will produce water-catching effect, so that the migratory elements such as calcium, sodium, potassium and others will migrate with the precipitation of water to the surface of the sedimentary facies and the CIA indexes of different sedimentary facies are influenced to be too small to reflect the true weathering intensity. 3) The application of CIA indexes as a surrogate indicator of palaeoclimate change shall comprehensively consider the sedimentary facies provenance differences and the effect of the sedimentary environment; hence, the CIA index has limited application in indicating the paleoclimatic change.
2018, 36(2): 354-365.
doi: 10.14027/j.issn.1000-0550.2018.030
Abstract:
The reservoir characteristics and diagenesis of the Triassic Baikouquan Formation in the Mabei area, Junggar Basin, were studied based on data from core, thin sections, scanning electron microscopy, well logging and mud logging. The results show that the sediments of this area are mainly sandy conglomerate, unequal grain conglomerate, conglomerate sandstone and fine sandstone, and the structural maturity and compositional maturity of reservoir are generally low. The reservoirs mainly experienced compaction, cementation and dissolution, and the muddy matrix has a great influence on diagenesis and pore evolution. Based on the petrological characteristics, diagenesis and the influence of muddy on the reservoir characteristics, the division of diagenetic facies of the study area is established, which include six parts:high maturity and strong dissolution facies, high maturity and moderately cemented dissolution facies, high maturity and strong compaction-weak dissolution facies, high maturity and strong cementation facies, low maturity and strong compaction facies, and low matureity and strong cementation facies. The different diagenetic facies reflect different depositional environments and diagenesis, which is related with pore type and physical properties of reservoir. Every kind of diagenetic facies has different characteristics of diagenetic sequence, pore evolution pattern, and profile and plane distribution characteristics, which could provide the basic knowledge for the prediction for high-quality reservoir.
The reservoir characteristics and diagenesis of the Triassic Baikouquan Formation in the Mabei area, Junggar Basin, were studied based on data from core, thin sections, scanning electron microscopy, well logging and mud logging. The results show that the sediments of this area are mainly sandy conglomerate, unequal grain conglomerate, conglomerate sandstone and fine sandstone, and the structural maturity and compositional maturity of reservoir are generally low. The reservoirs mainly experienced compaction, cementation and dissolution, and the muddy matrix has a great influence on diagenesis and pore evolution. Based on the petrological characteristics, diagenesis and the influence of muddy on the reservoir characteristics, the division of diagenetic facies of the study area is established, which include six parts:high maturity and strong dissolution facies, high maturity and moderately cemented dissolution facies, high maturity and strong compaction-weak dissolution facies, high maturity and strong cementation facies, low maturity and strong compaction facies, and low matureity and strong cementation facies. The different diagenetic facies reflect different depositional environments and diagenesis, which is related with pore type and physical properties of reservoir. Every kind of diagenetic facies has different characteristics of diagenetic sequence, pore evolution pattern, and profile and plane distribution characteristics, which could provide the basic knowledge for the prediction for high-quality reservoir.
2018, 36(2): 366-375.
doi: 10.14027/j.issn.1000-0550.2018.023
Abstract:
Taking modern deposition as a guide, this paper uses cores, logging geology and seismic geology technology to study the types of sand body on the meander-belt boundary and internal structure characteristics of complex meander belt. The typical feature of complicated meander belt is that the proportion of abandoned channel sand body was between 65%~95% on both sides of the boundary in the meander belt, and this ratio is greater than 85% in the concave side. Through the comparative analysis of the forward model, logging geology section and waveform and amplitude of seismic reflection axis after frequency division, the modes of boundary contact and superposition between point bars was summed up in this study i.e. meander belt:main body of point bar-initial point bar-early river edge, the beginning of point bar-the abandoned channel, the beginning of point bar-the beginning of point bar, abandoned channel-abandoned channel, abandoned channel -the beginning of point bar, the end of the river-point bar, etc. And then, the internal structure model of meander belt was established based on the contact and superposition architectures between point bars.
Taking modern deposition as a guide, this paper uses cores, logging geology and seismic geology technology to study the types of sand body on the meander-belt boundary and internal structure characteristics of complex meander belt. The typical feature of complicated meander belt is that the proportion of abandoned channel sand body was between 65%~95% on both sides of the boundary in the meander belt, and this ratio is greater than 85% in the concave side. Through the comparative analysis of the forward model, logging geology section and waveform and amplitude of seismic reflection axis after frequency division, the modes of boundary contact and superposition between point bars was summed up in this study i.e. meander belt:main body of point bar-initial point bar-early river edge, the beginning of point bar-the abandoned channel, the beginning of point bar-the beginning of point bar, abandoned channel-abandoned channel, abandoned channel -the beginning of point bar, the end of the river-point bar, etc. And then, the internal structure model of meander belt was established based on the contact and superposition architectures between point bars.
2018, 36(2): 376-389.
doi: 10.14027/j.issn.1000-0550.2018.027
Abstract:
In order to unify the classification scheme of gravity flow in Dongying depression and further improve the depositional model of delta and gravity flow system in rifted lacustrine basin, this paper selected the delta and gravity flow sand bodies in the Mid-E2s3 of Niuzhuang sag as research object, then used seismic data, well logs and core observation to analyze the sedimentary characteristics, genetic mechanism, distributions and depositional model of deltaic and gravity flow sand bodies within the framework of sequence stratigraphy. The results show that the Mid-E2s3 of Niuzhuang sag can be divided into one T-R sequence, viz one lacustrine transgressive system tract and one regressive system tract. The T-R sequence can be further divided into 6 parasequence sets which correspond to 6 cycles of deltaic sand bodies. The gravity flow sand bodies were widely distributed in regressive system tract, viz parasequence set 5 to parasequence set 1 while the distribution was limited in transgressive system tract. Four types of gravity flow were recognized:slide, slump, debris flow and turbidity current. Slide deposits showed a zonal distribution near delta front sand bodies. Slump and debris flow deposits distributed farther on the slope or near the slope point. Sheet-like turbidites were distributed in the deep part of the sag. Deltaic progradation rate was up to 200 m/104 a. During the E2s3 period, the fault activity rate was significantly enhanced. The structural slope break zone developed along the direction of provenance. Sporopollen assemblage was dominated by subtropical plants. The value of δ13CPDB and δ18OPDB showed a pronounced negative excursion. All these phenomena reveal that, the high speed deltaic progradation rate, structural slope break zone and fracture movement, warm and humid paleoclimate condition controlled the generation and distribution of delta and gravity flow sand bodies in the study area during the Mid-E2s3 period.
In order to unify the classification scheme of gravity flow in Dongying depression and further improve the depositional model of delta and gravity flow system in rifted lacustrine basin, this paper selected the delta and gravity flow sand bodies in the Mid-E2s3 of Niuzhuang sag as research object, then used seismic data, well logs and core observation to analyze the sedimentary characteristics, genetic mechanism, distributions and depositional model of deltaic and gravity flow sand bodies within the framework of sequence stratigraphy. The results show that the Mid-E2s3 of Niuzhuang sag can be divided into one T-R sequence, viz one lacustrine transgressive system tract and one regressive system tract. The T-R sequence can be further divided into 6 parasequence sets which correspond to 6 cycles of deltaic sand bodies. The gravity flow sand bodies were widely distributed in regressive system tract, viz parasequence set 5 to parasequence set 1 while the distribution was limited in transgressive system tract. Four types of gravity flow were recognized:slide, slump, debris flow and turbidity current. Slide deposits showed a zonal distribution near delta front sand bodies. Slump and debris flow deposits distributed farther on the slope or near the slope point. Sheet-like turbidites were distributed in the deep part of the sag. Deltaic progradation rate was up to 200 m/104 a. During the E2s3 period, the fault activity rate was significantly enhanced. The structural slope break zone developed along the direction of provenance. Sporopollen assemblage was dominated by subtropical plants. The value of δ13CPDB and δ18OPDB showed a pronounced negative excursion. All these phenomena reveal that, the high speed deltaic progradation rate, structural slope break zone and fracture movement, warm and humid paleoclimate condition controlled the generation and distribution of delta and gravity flow sand bodies in the study area during the Mid-E2s3 period.
2018, 36(2): 390-400.
doi: 10.14027/j.issn.1000-0550.2018.036
Abstract:
Nowadays, petroleum geologists have paid more attention to the Forced Regressive Systems Tract (FRST) for the development of effective reservoir rocks therein, however, studies focused on potential source rocks of FRST are rare. In this paper, a combination of lithology, well logging and geochemical analysis data of Termit Basin (Niger) was used to investigate the types, well logging identification and geochemical characteristics of source rocks in FRST. Furthermore, the development of different source rocks have been preliminarily analyzed on the basis of the total organic carbon (TOC) prediction model established by an improved ΔlogR method. Results indicate that 4 types of source rocks occur in FRST:coal/coaly mudstone, shoreface mudstone, deltaic mudstone and offshore mudstone. Offshore source rocks vertically distribute in the bottom sections of FRST, and the shoreface source rocks widely occurred in FRST while the thin coal/coaly mudstone existed associating with coastal marsh and deltaic environment. Shoreface mudstones are classified as good to excellent source rocks with type Ⅱ2 kerogen and high TOC content; the deltaic mudstones consist of poor to good source rocks with higher heterogeneity than others, while the offshore source rocks are poor due to the dominance of Type Ⅲ kerogen. In this study, a TOC prediction model was established with the value of ΔlogR acquired from a plot of lgR versus Δt. TOC prediction curves from the model of different wells in Termit Basin indicate that most of FRST source rocks in different tectonic blocks have a good to excellent hydrocarbon potential, mainly consist of shoreface source rocks with larger cumulative thickness and higher hydrocarbon potential than others. Based on the evolution progress and the examples of Termit Basin, we can draw the conclusion that excellent source rocks could be occurred in the FRST, and the shoreface mudstones might be their main types of source rocks.
Nowadays, petroleum geologists have paid more attention to the Forced Regressive Systems Tract (FRST) for the development of effective reservoir rocks therein, however, studies focused on potential source rocks of FRST are rare. In this paper, a combination of lithology, well logging and geochemical analysis data of Termit Basin (Niger) was used to investigate the types, well logging identification and geochemical characteristics of source rocks in FRST. Furthermore, the development of different source rocks have been preliminarily analyzed on the basis of the total organic carbon (TOC) prediction model established by an improved ΔlogR method. Results indicate that 4 types of source rocks occur in FRST:coal/coaly mudstone, shoreface mudstone, deltaic mudstone and offshore mudstone. Offshore source rocks vertically distribute in the bottom sections of FRST, and the shoreface source rocks widely occurred in FRST while the thin coal/coaly mudstone existed associating with coastal marsh and deltaic environment. Shoreface mudstones are classified as good to excellent source rocks with type Ⅱ2 kerogen and high TOC content; the deltaic mudstones consist of poor to good source rocks with higher heterogeneity than others, while the offshore source rocks are poor due to the dominance of Type Ⅲ kerogen. In this study, a TOC prediction model was established with the value of ΔlogR acquired from a plot of lgR versus Δt. TOC prediction curves from the model of different wells in Termit Basin indicate that most of FRST source rocks in different tectonic blocks have a good to excellent hydrocarbon potential, mainly consist of shoreface source rocks with larger cumulative thickness and higher hydrocarbon potential than others. Based on the evolution progress and the examples of Termit Basin, we can draw the conclusion that excellent source rocks could be occurred in the FRST, and the shoreface mudstones might be their main types of source rocks.
2018, 36(2): 401-414.
doi: 10.14027/j.issn.1000-0550.2018.029
Abstract:
The Chang 8 oil member of the Upper Triassic Yanchang Formation in Zhenjing area in the southern Ordos basin is typically a tight sandstone reservoir. Based on the analysis of cast thin sections, cathode-luminescence thin sections, fluorescence thin sections, SEM, XRD and fluid inclusions test etc., the reservoir characters, diagenesis and hydrocarbon emplacement and its phases are studied, the quantitative study on porosity evolution is conducted as well as porosity evolution is recovered with the coupling of diagenesis and hydrocarbon accumulation. These analyses indicate the sandstones are mostly feldspathic litharenites and lithic arkoses with low composition and textural maturity. The reservoir mainly develops carbonate cement, silica cement and authigenic clay minerals. It mainly develops intergranular dissolution pores and residual original intergranular pores. The reservoir is in the middle diagenetic stage B and develops intensive mechanical compaction and cementation but weak dissolution. Mechanical compaction and cementation play an important role in reducing reservoir porosity, resulting in decreases of porosity by 22.2% and 14.6%, respectively. Dissolution and replacement add 22.2% and 14.6% in porosity, respectively. During the early and middle oil emplacement phases, the reservoir is in good properties, while in late oil emplacement phase, the reservoir is in the densification stage. The coupling relationship between reservoir densification history and hydrocarbon emplacement is "densification after hydrocarbon accumulation".
The Chang 8 oil member of the Upper Triassic Yanchang Formation in Zhenjing area in the southern Ordos basin is typically a tight sandstone reservoir. Based on the analysis of cast thin sections, cathode-luminescence thin sections, fluorescence thin sections, SEM, XRD and fluid inclusions test etc., the reservoir characters, diagenesis and hydrocarbon emplacement and its phases are studied, the quantitative study on porosity evolution is conducted as well as porosity evolution is recovered with the coupling of diagenesis and hydrocarbon accumulation. These analyses indicate the sandstones are mostly feldspathic litharenites and lithic arkoses with low composition and textural maturity. The reservoir mainly develops carbonate cement, silica cement and authigenic clay minerals. It mainly develops intergranular dissolution pores and residual original intergranular pores. The reservoir is in the middle diagenetic stage B and develops intensive mechanical compaction and cementation but weak dissolution. Mechanical compaction and cementation play an important role in reducing reservoir porosity, resulting in decreases of porosity by 22.2% and 14.6%, respectively. Dissolution and replacement add 22.2% and 14.6% in porosity, respectively. During the early and middle oil emplacement phases, the reservoir is in good properties, while in late oil emplacement phase, the reservoir is in the densification stage. The coupling relationship between reservoir densification history and hydrocarbon emplacement is "densification after hydrocarbon accumulation".
2018, 36(2): 415-426.
doi: 10.14027/j.issn.1000-0550.2018.034
Abstract:
Geochemical characteristics of mudstones contain a large amount of geological information, which are widely used in the analysis of provenance and sedimentary environments. The Permo-Carboniferous mudstones from the Jiaozuo Coalfield of Henan Province, northern China, were analyzed by means of X-ray fluorescence spectrometer and ICP-MS, and the major elements, trace elements, rare earth elements(REE) and minerals were determined. The provenance, source area weathering and paleoenvironmental characteristics are discussed. Argillaceous rocks were predominantly derived from post-Archean felsic igneous rocks based on the high values of Al2O3/TiO2, low values of Cr/Zr,K2O/Al2O3 and plots of Zr-TiO2,Th/Co-La/Sc,Ni-Cr and (Gd/Yb)N-Eu/Eu*. The values of CIA were underestimated because of potassium metasomatism of the argillaceous source area reflected by Al2O3-CaO*+Na2O-K2O diagrams and high clay mineral composition. Palaeo-weathering indices(CIW ratios) and Al2O3-CaO*-Na2O diagrams suggest that the source rocks were subjected to an extreme chemical weathering. Trace element composition characteristics (Sr/Ba, B/Ga) indicate that from the Benxi Formation to the early Taiyuan Formation, the sedimentary environment is marine facies, from the mid Taiyuan Formation to the early Shanxi Formation, the sedimentary environment is marine-continental transitional facies, from the mid Shanxi Formation to the Shangshihezi Formation, and the sedimentary environment is continental facies.
Geochemical characteristics of mudstones contain a large amount of geological information, which are widely used in the analysis of provenance and sedimentary environments. The Permo-Carboniferous mudstones from the Jiaozuo Coalfield of Henan Province, northern China, were analyzed by means of X-ray fluorescence spectrometer and ICP-MS, and the major elements, trace elements, rare earth elements(REE) and minerals were determined. The provenance, source area weathering and paleoenvironmental characteristics are discussed. Argillaceous rocks were predominantly derived from post-Archean felsic igneous rocks based on the high values of Al2O3/TiO2, low values of Cr/Zr,K2O/Al2O3 and plots of Zr-TiO2,Th/Co-La/Sc,Ni-Cr and (Gd/Yb)N-Eu/Eu*. The values of CIA were underestimated because of potassium metasomatism of the argillaceous source area reflected by Al2O3-CaO*+Na2O-K2O diagrams and high clay mineral composition. Palaeo-weathering indices(CIW ratios) and Al2O3-CaO*-Na2O diagrams suggest that the source rocks were subjected to an extreme chemical weathering. Trace element composition characteristics (Sr/Ba, B/Ga) indicate that from the Benxi Formation to the early Taiyuan Formation, the sedimentary environment is marine facies, from the mid Taiyuan Formation to the early Shanxi Formation, the sedimentary environment is marine-continental transitional facies, from the mid Shanxi Formation to the Shangshihezi Formation, and the sedimentary environment is continental facies.
