2016 Vol. 34, No. 6
Display Method:
2016, 34(6): 1011-1020.
doi: 10.14027/j.cnki.cjxb.2016.06.001
Abstract:
The graptolitic shales of the Wufeng and Longmaxi Formations were widely deposited across the Ordovician and Silurian transition in South China. Based on the statistics of graptolite abundance from nearly 400 shale samples and total organic content (TOC) from nearly 100 shale samples in the Ordovician-Silurian boundary succession in Wuxi area of Chongqing, 23 shale samples have been further selected to determine the contribution of the graptolite abundance to overall TOC. The energy spectrum analysis showed the C and O contents in the graptolites are higher than those in the host of Wufeng and Longmaxi shales, and the TOC of the graptolite is apparently higher than that of the surrounding host, showing the graptolite might be one of the contributors of organic matter in the shale. However, the overall TOC in shales generally has a poor correlation with the graptolite abundance in shales, implying that the graptolite abundance in shales has not a great impact on the organic enrichment.
The graptolitic shales of the Wufeng and Longmaxi Formations were widely deposited across the Ordovician and Silurian transition in South China. Based on the statistics of graptolite abundance from nearly 400 shale samples and total organic content (TOC) from nearly 100 shale samples in the Ordovician-Silurian boundary succession in Wuxi area of Chongqing, 23 shale samples have been further selected to determine the contribution of the graptolite abundance to overall TOC. The energy spectrum analysis showed the C and O contents in the graptolites are higher than those in the host of Wufeng and Longmaxi shales, and the TOC of the graptolite is apparently higher than that of the surrounding host, showing the graptolite might be one of the contributors of organic matter in the shale. However, the overall TOC in shales generally has a poor correlation with the graptolite abundance in shales, implying that the graptolite abundance in shales has not a great impact on the organic enrichment.
2016, 34(6): 1021-1031.
doi: 10.14027/j.cnki.cjxb.2016.06.002
Abstract:
Two global positive carbon isotope excursions near the Middle to Late Ordovician transition-the Middle Darriwilian Inorganic Carbon Excursion(MDICE)and the Guttenberg Inorganic Carbon Excursion(GICE)——have been documented approximately in parallel with the major pulses of Great Ordovician Biodiversification Events(GOBE), great global sea level rises, geomagnetic reversals and significant variations of strontium, oxygen, sulfur isotopes in the ocean, indicating a possible causal link. Here, we reported the MDICE and GICE at Chenjiahe section in Yangtze area and compared them with their equivalents in Tarim Basin. Both the MDICE and GICE are found at the same stratigraphic level of rapid decrease of oceanic strontium isotope ratios in Yangtze Block and Tarim Basin, suggesting that the two carbon isotope excursions may be related to the enhanced hydrothermal activities at the middle ocean ridges, which could have increased releasing of essential nutrient elements such as iron into the seawater; this may have stimulated the biological blooms and increased oceanic primary productivity and organic burial, further inducing the positive carbon isotope excursions, i.e., the MDICE and GICE.
Two global positive carbon isotope excursions near the Middle to Late Ordovician transition-the Middle Darriwilian Inorganic Carbon Excursion(MDICE)and the Guttenberg Inorganic Carbon Excursion(GICE)——have been documented approximately in parallel with the major pulses of Great Ordovician Biodiversification Events(GOBE), great global sea level rises, geomagnetic reversals and significant variations of strontium, oxygen, sulfur isotopes in the ocean, indicating a possible causal link. Here, we reported the MDICE and GICE at Chenjiahe section in Yangtze area and compared them with their equivalents in Tarim Basin. Both the MDICE and GICE are found at the same stratigraphic level of rapid decrease of oceanic strontium isotope ratios in Yangtze Block and Tarim Basin, suggesting that the two carbon isotope excursions may be related to the enhanced hydrothermal activities at the middle ocean ridges, which could have increased releasing of essential nutrient elements such as iron into the seawater; this may have stimulated the biological blooms and increased oceanic primary productivity and organic burial, further inducing the positive carbon isotope excursions, i.e., the MDICE and GICE.
2016, 34(6): 1032-1043.
doi: 10.14027/j.cnki.cjxb.2016.06.003
Abstract:
The manganese ore deposit in Zunyi is one of the important types of manganese ore deposits in the Permian in China. The Nancha manganese ore deposit is a medium-scale subtle one found in the manganese ore zone of Zunyi area in recent years, and is the representative of the Zunyi-type manganese ore deposits. Trace element, rare earth element, and carbon isotope geochemical studies on manganese-bearing rock in Nancha manganese ore deposit show that samples predating Mn-ore deposition have V/(V+Ni) ratios between 0.6 and 0.65 (close to 0.60),and V/Cr ratios from 0.71 to 2.05 (avg. 1.34), as well as moderate Ce negative anomalies, indicating a dysoxic water condition under which they were deposited. The samples of Mn-ore deposits yield V/(V+Ni) ratios close to 0.45, and V/Cr ratios between 0.71 and 2.05, as well as weak Ce negative anomalies, pointing to an oxic to dysoxic condition. Those samples postdating the Mn-ore deposition have V/(V+Ni) ratios between 0.65 and 0.85 (avg. 0.76), and V/Cr ratios of > 4.18 mostly, as well as slightly Ce positive anomalies, suggesting an anoxic to dysoxic condition. The δEu values range mostly between 0.50 and 1.00, indicative of a weak influence of hydrothermal activity. Carbon isotope data reveal an obvious negative excursion across the Mn-bearing succession, reaching the nadir in the manganese ore horizon (-12.5‰ V-PDB), indicative of organic involvement likely associated with organic decaying. Therefore, the Nancha manganese ore deposit was initially precipitated as manganese (hydro-)oxides in the oxic water condition, which were reduced to Mn2+ and subsequently combined with CO32- to form the carbonate manganese ore deposit (MnCO3) below the sediment-water interface while the redox interface was gotten rising due to the sea-level rise (or transgression).
The manganese ore deposit in Zunyi is one of the important types of manganese ore deposits in the Permian in China. The Nancha manganese ore deposit is a medium-scale subtle one found in the manganese ore zone of Zunyi area in recent years, and is the representative of the Zunyi-type manganese ore deposits. Trace element, rare earth element, and carbon isotope geochemical studies on manganese-bearing rock in Nancha manganese ore deposit show that samples predating Mn-ore deposition have V/(V+Ni) ratios between 0.6 and 0.65 (close to 0.60),and V/Cr ratios from 0.71 to 2.05 (avg. 1.34), as well as moderate Ce negative anomalies, indicating a dysoxic water condition under which they were deposited. The samples of Mn-ore deposits yield V/(V+Ni) ratios close to 0.45, and V/Cr ratios between 0.71 and 2.05, as well as weak Ce negative anomalies, pointing to an oxic to dysoxic condition. Those samples postdating the Mn-ore deposition have V/(V+Ni) ratios between 0.65 and 0.85 (avg. 0.76), and V/Cr ratios of > 4.18 mostly, as well as slightly Ce positive anomalies, suggesting an anoxic to dysoxic condition. The δEu values range mostly between 0.50 and 1.00, indicative of a weak influence of hydrothermal activity. Carbon isotope data reveal an obvious negative excursion across the Mn-bearing succession, reaching the nadir in the manganese ore horizon (-12.5‰ V-PDB), indicative of organic involvement likely associated with organic decaying. Therefore, the Nancha manganese ore deposit was initially precipitated as manganese (hydro-)oxides in the oxic water condition, which were reduced to Mn2+ and subsequently combined with CO32- to form the carbonate manganese ore deposit (MnCO3) below the sediment-water interface while the redox interface was gotten rising due to the sea-level rise (or transgression).
2016, 34(6): 1044-1056.
doi: 10.14027/j.cnki.cjxb.2016.06.004
Abstract:
Barites are widely distributed in sedimentary records with various geological characteristics and formation processes. In general, sedimentary barites can be subdivided into marine (or biogenic), hydrothermal, diagenetic and cold seeps barites. The sedimentary environments, macro- and micro-occurrences, geochemical features (especially Sr and S isotopes) and corresponding geological implications of these four barite subtypes are controlled by the origin of barium- and sulfate-fluids (seawater, diagenetic porewater or hydrothermal fluids) and related interaction process (in seawater column, sediment column, sediment-water interface or hydrothermal system). In addition, this study further introduces the geological features of the Lower Cambrian barite-rich sediments in the Yangtze Block, South China, and summarizes the enrichment mechanisms having been proposed for these barite deposits and argues on their reconciliation and biases with geological features and processes. Based on the paleo-oceanic context during the Ediacaran-Cambrian transitional period, integrated sedimentological and geochemical researches together would provide better constrains on the origins of the Lower Cambrian barium-rich deposits in the Yangtze Block.
Barites are widely distributed in sedimentary records with various geological characteristics and formation processes. In general, sedimentary barites can be subdivided into marine (or biogenic), hydrothermal, diagenetic and cold seeps barites. The sedimentary environments, macro- and micro-occurrences, geochemical features (especially Sr and S isotopes) and corresponding geological implications of these four barite subtypes are controlled by the origin of barium- and sulfate-fluids (seawater, diagenetic porewater or hydrothermal fluids) and related interaction process (in seawater column, sediment column, sediment-water interface or hydrothermal system). In addition, this study further introduces the geological features of the Lower Cambrian barite-rich sediments in the Yangtze Block, South China, and summarizes the enrichment mechanisms having been proposed for these barite deposits and argues on their reconciliation and biases with geological features and processes. Based on the paleo-oceanic context during the Ediacaran-Cambrian transitional period, integrated sedimentological and geochemical researches together would provide better constrains on the origins of the Lower Cambrian barium-rich deposits in the Yangtze Block.
2016, 34(6): 1057-1067.
doi: 10.14027/j.cnki.cjxb.2016.06.005
Abstract:
Deeply buried (4 500 to 7 000 m) carbonate reservoirs in the Tazhong area, Tarim basin, NW China show obvious heterogeneity with porosity from zero in limestones to 27.8% in sour dolostones. However, origin of the porosity remains puzzled. Petrographic features, C, O isotopes were determined, and fluid inclusions were analyzed on diagenetic calcite and dolomite from Ordovician reservoirs to solve the puzzle. Ordovician carbonate reservoirs in the Tazhong area are controlled mainly by initial sedimentary environments and primary and near-surface diagenetic processes. However, vugs and pores generated from eogenetic and telogenetic meteoric dissolution were observed to have partially been destroyed due to subsequent compaction, filling and cementation. In some localities or wells (e.g. well ZG9 and TZ75), mesogenetic dissolution (e.g. thermochemical sulfate reduction, TSR) probably played an important role in pore production and reservoir quality improvement. The occurrence of TSR within Ordovician carbonate reservoirs are supported by TSR-originated calcite replacement of sulphate, and the association of sulfur species including acid gases (H2S), pyrite, anhydrite or barite and elemental sulfur with hydrocarbon and 12C-rich calcite with elevated homogenization temperatures. The TSR is observed to company with intensive dolomite dissolution, suggesting that TSR may have induced burial dissolution and thus probably increased the porosity of the sour dolostones reservoirs at least in some places. In contrast, no significant mesogenetic dissolution occurred in limestone reservoirs. The deeply buried sour dolostone reservoirs may therefore be potential exploration targets in Tarim basin.
Deeply buried (4 500 to 7 000 m) carbonate reservoirs in the Tazhong area, Tarim basin, NW China show obvious heterogeneity with porosity from zero in limestones to 27.8% in sour dolostones. However, origin of the porosity remains puzzled. Petrographic features, C, O isotopes were determined, and fluid inclusions were analyzed on diagenetic calcite and dolomite from Ordovician reservoirs to solve the puzzle. Ordovician carbonate reservoirs in the Tazhong area are controlled mainly by initial sedimentary environments and primary and near-surface diagenetic processes. However, vugs and pores generated from eogenetic and telogenetic meteoric dissolution were observed to have partially been destroyed due to subsequent compaction, filling and cementation. In some localities or wells (e.g. well ZG9 and TZ75), mesogenetic dissolution (e.g. thermochemical sulfate reduction, TSR) probably played an important role in pore production and reservoir quality improvement. The occurrence of TSR within Ordovician carbonate reservoirs are supported by TSR-originated calcite replacement of sulphate, and the association of sulfur species including acid gases (H2S), pyrite, anhydrite or barite and elemental sulfur with hydrocarbon and 12C-rich calcite with elevated homogenization temperatures. The TSR is observed to company with intensive dolomite dissolution, suggesting that TSR may have induced burial dissolution and thus probably increased the porosity of the sour dolostones reservoirs at least in some places. In contrast, no significant mesogenetic dissolution occurred in limestone reservoirs. The deeply buried sour dolostone reservoirs may therefore be potential exploration targets in Tarim basin.
2016, 34(6): 1068-1076.
doi: 10.14027/j.cnki.cjxb.2016.06.006
Abstract:
Peatlands contain a huge amount of carbon whose productivity will affect the global carbon cycle and even climate change. A number of productivity researches have been done on the Holocene peats, but few is dealing with the pre-quaternary due to a lack of precise dating method. In this paper, the geophysical logging signals were used to analyze the Milankovitch orbital cycles which were further used as a tool to date the "deep time" and to measure the carbon accumulation rates of the paleo-peatlands. The spectrum analysis has been conducted on the geophysical logging signals of a thick coal (No.6 seam) of the Early Cretaceous in the Jiergalangtu sag of the Erlian Basin, and the Milankovitch cycle parameters of 123 ka (eccentricity):38.1 ka (slope):22.1 ka (precession) have been obtained for this coal. These Milankovitch cycles were used as "measurement" to calculate the carbon accumulation rate and the net primary productivity (NPP) based on the carbon contents and coal rank of coal. The No.6 coal had a carbon accumulation rate of 35.1~38.9 g C/(m2·a) which corresponds to the carbon accumulation rate of 46.2~51.2 g C/(m2·a) and the net primary productivity (NPP) of 231~256 g C/(m2·a) for the Early Cretaceous peatlands. A comprehensive comparison with the productivity levels of the Holocene peatlands (NPP) of 150~250 g C/(m2·a) in the same latitude confirmed that the productivity level in the Early Cretaceous peatlands were controlled by paleo-temperature and concentration of carbon dioxide in the atmosphere. As the paleotemperature and concentration of carbon dioxide were closely related to the paleoclimates, these productivity values of the paleo-peatland would help us understand more about paleoclimates of "deep time".
Peatlands contain a huge amount of carbon whose productivity will affect the global carbon cycle and even climate change. A number of productivity researches have been done on the Holocene peats, but few is dealing with the pre-quaternary due to a lack of precise dating method. In this paper, the geophysical logging signals were used to analyze the Milankovitch orbital cycles which were further used as a tool to date the "deep time" and to measure the carbon accumulation rates of the paleo-peatlands. The spectrum analysis has been conducted on the geophysical logging signals of a thick coal (No.6 seam) of the Early Cretaceous in the Jiergalangtu sag of the Erlian Basin, and the Milankovitch cycle parameters of 123 ka (eccentricity):38.1 ka (slope):22.1 ka (precession) have been obtained for this coal. These Milankovitch cycles were used as "measurement" to calculate the carbon accumulation rate and the net primary productivity (NPP) based on the carbon contents and coal rank of coal. The No.6 coal had a carbon accumulation rate of 35.1~38.9 g C/(m2·a) which corresponds to the carbon accumulation rate of 46.2~51.2 g C/(m2·a) and the net primary productivity (NPP) of 231~256 g C/(m2·a) for the Early Cretaceous peatlands. A comprehensive comparison with the productivity levels of the Holocene peatlands (NPP) of 150~250 g C/(m2·a) in the same latitude confirmed that the productivity level in the Early Cretaceous peatlands were controlled by paleo-temperature and concentration of carbon dioxide in the atmosphere. As the paleotemperature and concentration of carbon dioxide were closely related to the paleoclimates, these productivity values of the paleo-peatland would help us understand more about paleoclimates of "deep time".
2016, 34(6): 1077-1091.
doi: 10.14027/j.cnki.cjxb.2016.06.007
Abstract:
The issue on sea-level changes across the Permian-Triassic boundary (PTB) has been disputed by the sedimentologists for a long time. It may also have relation with the largest mass extinction event during the transition of Permian-Triassic. However, it is not quite clear about the process and mechanism of the change of sea level in light of previous studies from local- and small-scale materials. The lack of reliable evidence from integrated perspectives would go against the identification of the process and duration of global sea-level variation. In this study, we systematically reviewed the literatures on the issue of sea-level changes during the transitions of Permian-Triassic, and summarized the main views including:(1) successive transgression, and (2) regression and following quick transgression. This study also compiled the development processes of these two different views, sedimentary features in diagnostic sections, the possible reasons of sea-level rise/fall, as well as the relationship between mass extinction and sea-level changes. Meanwhile, the causes of dispute on sea-level changes in the PTB were discussed preliminarily from available evidence. The aim of this study is to provide some clues to further recognize the process of sea-level changes during the PTB, and to provide substantial evidence to understand the background of global sea-level changes during the Permian-Triassic transition.
The issue on sea-level changes across the Permian-Triassic boundary (PTB) has been disputed by the sedimentologists for a long time. It may also have relation with the largest mass extinction event during the transition of Permian-Triassic. However, it is not quite clear about the process and mechanism of the change of sea level in light of previous studies from local- and small-scale materials. The lack of reliable evidence from integrated perspectives would go against the identification of the process and duration of global sea-level variation. In this study, we systematically reviewed the literatures on the issue of sea-level changes during the transitions of Permian-Triassic, and summarized the main views including:(1) successive transgression, and (2) regression and following quick transgression. This study also compiled the development processes of these two different views, sedimentary features in diagnostic sections, the possible reasons of sea-level rise/fall, as well as the relationship between mass extinction and sea-level changes. Meanwhile, the causes of dispute on sea-level changes in the PTB were discussed preliminarily from available evidence. The aim of this study is to provide some clues to further recognize the process of sea-level changes during the PTB, and to provide substantial evidence to understand the background of global sea-level changes during the Permian-Triassic transition.
2016, 34(6): 1092-1107.
doi: 10.14027/j.cnki.cjxb.2016.06.008
Abstract:
As the transition zone between terrestrial and marine environment, carbonate platform sediments record information both from ocean and land. Some geochemical research are carried on Cambrian carbonates and their acid-insoluble residua based on sedimentary facies analysis, focused on development of sedimentary environment, change of paleosalinity, sea level fluctuations, evolution of terrestrial chemical weathering intensity and climate change. Lithological and sedimentological research show that sedimentary facies of the Western Tarim Carbonate Platform in Cambrian was mainly restricted platform, restricted-evaporite platform or evaporite platform. Geochemical characteristics of carbonates is usually generated by sedimentation and reformed by diagenesis. The elemental composition and O isotope of our samples are respectively affected by sedimentary micro-facies and water-rock interaction, only Sr/Ba, Fe/Mn and C isotope of primary or penecontemporaneous dolomite can be used to indicate paleosalinity, offshore distance and other characteristics of sedimentary environment. Evolution of terrestrial chemical weathering intensity and climate change can be reflected by CIA(chemical index of alteration) of the carbonates' acid-insoluble residua. In Cambrian, restricted platform was developed in western Tarim when the RSL(relative sea level) is at high position, sedimentary environment was characterized by relatively low salinity, far offshore distance and weak biological activity, with moderate terrestrial chemical weathering and mild climate. On the contrary, when the RSL is relatively low, evaporite platform is developed and with sedimentary environment characterized by high salinity, near offshore distance and strong biological activity, the terrestrial chemical weathering is intense, indicating hot or possibly humid climate. The situation when restricted-evaporite platform developed is between the two forementioned. Relatively long-period evolution of the Western Tarim Carbonate Platform corresponding to facies' development may be controlled by global climate change and sea level fluctuations. Concretely, the evolution of marine sedimentary environment is mostly controlled by RSL change, and the change of terrestrial chemical weathering flux is mainly controlled by climate change. High consistency can be found among sedimentary facies sequences, evolution of marine sedimentary environment, change of terrestrial chemical weathering intensity, relative sea level change and climate change. Therefore, it represent a close ocean-land-climate coupling of the western Tarim Carbonate Platform in Cambrian.
As the transition zone between terrestrial and marine environment, carbonate platform sediments record information both from ocean and land. Some geochemical research are carried on Cambrian carbonates and their acid-insoluble residua based on sedimentary facies analysis, focused on development of sedimentary environment, change of paleosalinity, sea level fluctuations, evolution of terrestrial chemical weathering intensity and climate change. Lithological and sedimentological research show that sedimentary facies of the Western Tarim Carbonate Platform in Cambrian was mainly restricted platform, restricted-evaporite platform or evaporite platform. Geochemical characteristics of carbonates is usually generated by sedimentation and reformed by diagenesis. The elemental composition and O isotope of our samples are respectively affected by sedimentary micro-facies and water-rock interaction, only Sr/Ba, Fe/Mn and C isotope of primary or penecontemporaneous dolomite can be used to indicate paleosalinity, offshore distance and other characteristics of sedimentary environment. Evolution of terrestrial chemical weathering intensity and climate change can be reflected by CIA(chemical index of alteration) of the carbonates' acid-insoluble residua. In Cambrian, restricted platform was developed in western Tarim when the RSL(relative sea level) is at high position, sedimentary environment was characterized by relatively low salinity, far offshore distance and weak biological activity, with moderate terrestrial chemical weathering and mild climate. On the contrary, when the RSL is relatively low, evaporite platform is developed and with sedimentary environment characterized by high salinity, near offshore distance and strong biological activity, the terrestrial chemical weathering is intense, indicating hot or possibly humid climate. The situation when restricted-evaporite platform developed is between the two forementioned. Relatively long-period evolution of the Western Tarim Carbonate Platform corresponding to facies' development may be controlled by global climate change and sea level fluctuations. Concretely, the evolution of marine sedimentary environment is mostly controlled by RSL change, and the change of terrestrial chemical weathering flux is mainly controlled by climate change. High consistency can be found among sedimentary facies sequences, evolution of marine sedimentary environment, change of terrestrial chemical weathering intensity, relative sea level change and climate change. Therefore, it represent a close ocean-land-climate coupling of the western Tarim Carbonate Platform in Cambrian.
2016, 34(6): 1108-1119.
doi: 10.14027/j.cnki.cjxb.2016.06.009
Abstract:
With the maturity of theoretical systems of turbidity current and debris flow, gravity flow transformation has gradually drew more attention, and its related concept-hybrid event bed is also aroused at this time. The hybrid event bed is a depositional record of flow transformation from a single-period debris flow or turbidity current event, which is manifested by vertical depositional combination of various rheological characteristics. The sequence of a typical hybrid event bed contains five divisions:clean sand internal H1, banded internal H2, cohesive debrites internal H3, ripple-laminated internal H4 and massive mud internal H5, and obvious lithological interfacies are well identified in this bed. Hybrid event beds are well distributed in the coarse-grained deltas, the distal and lateral area of submarine fans and lobes, the transitional zone of channel-lobe and confined mini-basin margin with the vertical stacking thickness up to several meters. The recognition of hybrid event bed is extremely meaningful for further study on flow transformation of gravity flow and spatial rheological characteristics. Also, it promotes corresponding studies on the heterogeneity of hydrocarbon-bearing reservoirs and provides new thoughts for favorable deep-water reservoir sandbodies. The geophysics identification of hybrid bed and the flexible application of this new concept to the study on lacustrine gravity flow will be the next research direction.
With the maturity of theoretical systems of turbidity current and debris flow, gravity flow transformation has gradually drew more attention, and its related concept-hybrid event bed is also aroused at this time. The hybrid event bed is a depositional record of flow transformation from a single-period debris flow or turbidity current event, which is manifested by vertical depositional combination of various rheological characteristics. The sequence of a typical hybrid event bed contains five divisions:clean sand internal H1, banded internal H2, cohesive debrites internal H3, ripple-laminated internal H4 and massive mud internal H5, and obvious lithological interfacies are well identified in this bed. Hybrid event beds are well distributed in the coarse-grained deltas, the distal and lateral area of submarine fans and lobes, the transitional zone of channel-lobe and confined mini-basin margin with the vertical stacking thickness up to several meters. The recognition of hybrid event bed is extremely meaningful for further study on flow transformation of gravity flow and spatial rheological characteristics. Also, it promotes corresponding studies on the heterogeneity of hydrocarbon-bearing reservoirs and provides new thoughts for favorable deep-water reservoir sandbodies. The geophysics identification of hybrid bed and the flexible application of this new concept to the study on lacustrine gravity flow will be the next research direction.
2016, 34(6): 1120-1132.
doi: 10.14027/j.cnki.cjxb.2016.06.010
Abstract:
The later Permian-Triassic Nanpanjiang deep marine basin is located in the adjacent areas among Guangxi, Guizhou, and Yunnan, which developed based on the rift system during the later Permian. The space and the depth of the basin increased during the middle-Triassic and a set of deepwater flysch sediment was preserved in the basin. The environment of the basin was identified as foreland basin where there was a set of clastic and carbonate sediment in the northern part of the basin. The main study areas lie in the northern and middle part of the Nanpanjiang Basin(NPJB). Some kinds of flysch sedimentary structures can be used in the field work to get paleocurrent such as small oblique bedding, small climbing ripple bedding, convolute bedding, flute cast and so on. Based on the field measurement, stratum attitude correction and the rose diagrams drawing of paleocurrent, this article discusses the paleocurrent of the sediment during the Triassic time. 49 sets of paleocurrent data were exhibited here by which sedimentary provenances of NPJB can be constrained. During the middle Triassic time the sedimentary provenance of the southern part of NPJB(for example near Guangnan, Dixu, Bada, Funing) would be the Vietnam Block to the south of NPJB, the sedimentary provenance of the eastern part of NPJB(for example near Bama, Longchuan, Wangmo) would be the Jiangnan Block to the east, and the sedimentary provenance of the northern part of NPJB would be the inner Yangtze Platform to the north. The centre of subsidence is located at the areas south to Ceheng and north to Lucheng. Two palaeohigh belts were indentified between Longlin city and Xilin city, between Yangxu town and Boai town. The paleocurrent changed significantly during the late Triassic time at the northern part of the NPJB which was considered as a consequence of the tectonic fragment change.
The later Permian-Triassic Nanpanjiang deep marine basin is located in the adjacent areas among Guangxi, Guizhou, and Yunnan, which developed based on the rift system during the later Permian. The space and the depth of the basin increased during the middle-Triassic and a set of deepwater flysch sediment was preserved in the basin. The environment of the basin was identified as foreland basin where there was a set of clastic and carbonate sediment in the northern part of the basin. The main study areas lie in the northern and middle part of the Nanpanjiang Basin(NPJB). Some kinds of flysch sedimentary structures can be used in the field work to get paleocurrent such as small oblique bedding, small climbing ripple bedding, convolute bedding, flute cast and so on. Based on the field measurement, stratum attitude correction and the rose diagrams drawing of paleocurrent, this article discusses the paleocurrent of the sediment during the Triassic time. 49 sets of paleocurrent data were exhibited here by which sedimentary provenances of NPJB can be constrained. During the middle Triassic time the sedimentary provenance of the southern part of NPJB(for example near Guangnan, Dixu, Bada, Funing) would be the Vietnam Block to the south of NPJB, the sedimentary provenance of the eastern part of NPJB(for example near Bama, Longchuan, Wangmo) would be the Jiangnan Block to the east, and the sedimentary provenance of the northern part of NPJB would be the inner Yangtze Platform to the north. The centre of subsidence is located at the areas south to Ceheng and north to Lucheng. Two palaeohigh belts were indentified between Longlin city and Xilin city, between Yangxu town and Boai town. The paleocurrent changed significantly during the late Triassic time at the northern part of the NPJB which was considered as a consequence of the tectonic fragment change.
2016, 34(6): 1133-1146.
doi: 10.14027/j.cnki.cjxb.2016.06.011
Abstract:
The Upper Permian (Lopingian) Gequ Formation in the southern margin of the East Kunlun Mountains is composed of conglomerates, sandstones and calcareous mudstones of fan delta-sea carbonate plateau. It recorded the tectonic evolution of the East Kunlun orogenic belt during Late Hercynian-Early Indosinian. This paper studies the detrital modes and the compositions of major, trace and rare earth elements for sandstones of the Gequ Formation in Tandikejie area, north of Huashixia, and investigates the tectonic attributes and provenance types. Sandstone detrital modes show that the Gequ Formation consists of arkose and lithic arkose. The QtFL averages of sandstones are Qt 50.9%, F 36.8%, L 12.4%, feldspars are mainly K-feldspar, the composition of gravel and lithic is complex. Geochemistry analysis shows that average concentrations of SiO2, Al2O3, TiO2, TFe2O3, MgO, K2O and Na2O are 62.06%, 13.26%, 0.44%, 4.53%, 3.02%, 2.42% and 3.18%, respectively. Trace elements ratios such as Th/Sc, Th/U have high averages of 1.06, 7.71. The Gequ Formation sandstones have REE gross of 120.43×10-6. In the sandstones, LREE is relatively rich, the LREE/HREE ratio is 9.34, the (La/Yb)N ratio is 12, δEu is 0.96 and the anomaly of δEu is not obvious. According to the REE features, the Gequ Formation show similarities to the greywackes from continental island arc and affinity to the Caledonian subduction-collision arc type granites of the East Kunlun terrane. Based on the features and discriminant diagrams of clastic composition, major elements and trace elements, the provenance of the Gequ Formation sandstones came from the south microblock of East Kunlun, which was rifted from the East Kunlun terrane during Early Hercynian. The source rocks consisted of mainly granites and little sedimentary rocks, metamorphic rocks and acid-basic volcanic rocks, and the granites belong to the Caledonian continental island arc. Combined with regional geological background and previous basin studies, the Gequ Formation formed in back-bulge of foreland basin system.
The Upper Permian (Lopingian) Gequ Formation in the southern margin of the East Kunlun Mountains is composed of conglomerates, sandstones and calcareous mudstones of fan delta-sea carbonate plateau. It recorded the tectonic evolution of the East Kunlun orogenic belt during Late Hercynian-Early Indosinian. This paper studies the detrital modes and the compositions of major, trace and rare earth elements for sandstones of the Gequ Formation in Tandikejie area, north of Huashixia, and investigates the tectonic attributes and provenance types. Sandstone detrital modes show that the Gequ Formation consists of arkose and lithic arkose. The QtFL averages of sandstones are Qt 50.9%, F 36.8%, L 12.4%, feldspars are mainly K-feldspar, the composition of gravel and lithic is complex. Geochemistry analysis shows that average concentrations of SiO2, Al2O3, TiO2, TFe2O3, MgO, K2O and Na2O are 62.06%, 13.26%, 0.44%, 4.53%, 3.02%, 2.42% and 3.18%, respectively. Trace elements ratios such as Th/Sc, Th/U have high averages of 1.06, 7.71. The Gequ Formation sandstones have REE gross of 120.43×10-6. In the sandstones, LREE is relatively rich, the LREE/HREE ratio is 9.34, the (La/Yb)N ratio is 12, δEu is 0.96 and the anomaly of δEu is not obvious. According to the REE features, the Gequ Formation show similarities to the greywackes from continental island arc and affinity to the Caledonian subduction-collision arc type granites of the East Kunlun terrane. Based on the features and discriminant diagrams of clastic composition, major elements and trace elements, the provenance of the Gequ Formation sandstones came from the south microblock of East Kunlun, which was rifted from the East Kunlun terrane during Early Hercynian. The source rocks consisted of mainly granites and little sedimentary rocks, metamorphic rocks and acid-basic volcanic rocks, and the granites belong to the Caledonian continental island arc. Combined with regional geological background and previous basin studies, the Gequ Formation formed in back-bulge of foreland basin system.
2016, 34(6): 1147-1154.
doi: 10.14027/j.cnki.cjxb.2016.06.012
Abstract:
Junggar basin is one of the largest petroliferous basins in China, although a series of oil and gas fields had been found in the south of the basin, the oil-gas exploration in the fore mountain belt of Bogda Mountain did not make great breakthroughs. The reason may be associated with the few awareness of the evolution of the Bogda Mountain to control, restrain the evolution of the late peripheral sags and the hydrocarbon generation and the basin formation. The conservative fragmentary materials in sedimentary basins had recorded the lithosphere features of the orogenic belts at the margin of the South China block and kinetics characterization of basins during the sedimentary evolution. At the same time, as sedimentary heavy minerals were very stable and they had been participating in this long and complicated geological processes, which could provide the important information to the source rocks. Thus, in this text, based on the mineral petrology characteristics of heavy minerals, such as roundings, content changes, combination features and the different heavy mineral indexes, to study the uplift processes of Bogda Mountain in the period of Jurassic, which could provide strong evidence that Bogda Mountain uplifted in Toutunhe Formation of Middle Jurassic. Moreover, according to the features of heavy minerals, the tectonic evolution stages of Bogda Mountain during Jurassic period were divided into two parts:1) from early Jurassic to the late period of middle Jurassic, the tectonic evolution was relatively stable, and 2) from the late period of middle Jurassic to late Jurassic, tectonic uplifting was strong. In addition, combined with the previous research results such as tectono-thermochronology, U-Pb age and paleocurrent, we considered that the provenances of Bogda area were from Kalameili Montain during early Jurassic to the late period of middle Jurassic and Bogda Mountain during the late period of middle Jurassic to late Jurassic. And that, in the later period, the Bogda Mountain had been uplifted.
Junggar basin is one of the largest petroliferous basins in China, although a series of oil and gas fields had been found in the south of the basin, the oil-gas exploration in the fore mountain belt of Bogda Mountain did not make great breakthroughs. The reason may be associated with the few awareness of the evolution of the Bogda Mountain to control, restrain the evolution of the late peripheral sags and the hydrocarbon generation and the basin formation. The conservative fragmentary materials in sedimentary basins had recorded the lithosphere features of the orogenic belts at the margin of the South China block and kinetics characterization of basins during the sedimentary evolution. At the same time, as sedimentary heavy minerals were very stable and they had been participating in this long and complicated geological processes, which could provide the important information to the source rocks. Thus, in this text, based on the mineral petrology characteristics of heavy minerals, such as roundings, content changes, combination features and the different heavy mineral indexes, to study the uplift processes of Bogda Mountain in the period of Jurassic, which could provide strong evidence that Bogda Mountain uplifted in Toutunhe Formation of Middle Jurassic. Moreover, according to the features of heavy minerals, the tectonic evolution stages of Bogda Mountain during Jurassic period were divided into two parts:1) from early Jurassic to the late period of middle Jurassic, the tectonic evolution was relatively stable, and 2) from the late period of middle Jurassic to late Jurassic, tectonic uplifting was strong. In addition, combined with the previous research results such as tectono-thermochronology, U-Pb age and paleocurrent, we considered that the provenances of Bogda area were from Kalameili Montain during early Jurassic to the late period of middle Jurassic and Bogda Mountain during the late period of middle Jurassic to late Jurassic. And that, in the later period, the Bogda Mountain had been uplifted.
2016, 34(6): 1155-1164.
doi: 10.14027/j.cnki.cjxb.2016.06.013
Abstract:
The Saihantala Formation of Jiergalangtu depression deposited in basement subsidence deceleration-filling evolution stage. It was the product of the depresion in the early and middle stage of the lake's shrinking-stage. Its sequence stratigraphic units are parts of resgressive system tract. From bottom to top, it consists of shallow lacustrine facies, delta facies and meandering river facies. The extra-thick coal seam formed in the deep groove of the depression and symbiosed with a lot of thin layers of turbidity sandstone, its sedimentary environment should have been shallow lake and local deep lake.Traditional coal depositional model can hardly explain the cause of this extra-thick coal seam. Through the sedimentological study of gangue and the analysis of basin-fill sequence, a new model of extra-thick seam continental allochthonous genesis-"sub model of weak storms and underwater muddy and sandy gravity flow"-is established, abbreviated as Shengli basin sub model. The allochthonous coal may have deposited firstly in lake delta, and then transferred to shallow lake by slumping and turbidity, and after secondary differentiation, finally deposited as low ash coal seam.
The Saihantala Formation of Jiergalangtu depression deposited in basement subsidence deceleration-filling evolution stage. It was the product of the depresion in the early and middle stage of the lake's shrinking-stage. Its sequence stratigraphic units are parts of resgressive system tract. From bottom to top, it consists of shallow lacustrine facies, delta facies and meandering river facies. The extra-thick coal seam formed in the deep groove of the depression and symbiosed with a lot of thin layers of turbidity sandstone, its sedimentary environment should have been shallow lake and local deep lake.Traditional coal depositional model can hardly explain the cause of this extra-thick coal seam. Through the sedimentological study of gangue and the analysis of basin-fill sequence, a new model of extra-thick seam continental allochthonous genesis-"sub model of weak storms and underwater muddy and sandy gravity flow"-is established, abbreviated as Shengli basin sub model. The allochthonous coal may have deposited firstly in lake delta, and then transferred to shallow lake by slumping and turbidity, and after secondary differentiation, finally deposited as low ash coal seam.
2016, 34(6): 1165-1175.
doi: 10.14027/j.cnki.cjxb.2016.06.014
Abstract:
In this paper, a core (NT, 60.9 m in length) in the northern part of the Yangtze River Delta, from Nantong, Jiangsu province, were subjected to environmental magnetic analysis. In combination with analysis of lithology, particle size and diffuse reflectance spectroscopy (DRS), this paper discusses the magnetic properties of tidal deposits formed in early and late Holocene and its paleoenvironmental implications. Core NT can be divided into six depositional units, namely U1 to U6, from bottom to top, among which the lower part of U2 (49.9~44.8 m) and U6 (7.5~0.3 m) are interpreted to be tidal flat facies. They are characterized with lower S-ratios and higher hard isothermal remanent magnetization (HIRM) and SIRM/χ values, which indicates higher concentration and proportion of antiferromagntic minerals such as hematite and goethite. In combination with DRS, it is found that the enriched hematite and goethite occur in the upper part of U6, while only hematite is enriched in the lower part of U2. Such a difference in magnetic mineralogy is related to the sedimentary environments when these sediments are deposited. Sediments in U2 were formed during late stage of late Pleistocene to early Holocene and has been in subaerial condition for a long period, which favors hematite formation and preservation. With the rising sea-level during early Holocene, the salt marsh accreted vertically and eventually inundated, which does not favor the formation of goethite. In contrast, sediments in U6 were formed during the late Holocene. The oscillating redox condition favors the formation of goethite. Abundant maghemite and hematite were formed due to pedogenesis after land formation at a later stage. This study shows that sediments in salt marsh formed in different stages of the Holocene exhibits different magnetic properties. As a result, magnetic properties of sediments can provide information about the evolution of tidal flat, which has important implication for delta paleoenvironmental reconstruction.
In this paper, a core (NT, 60.9 m in length) in the northern part of the Yangtze River Delta, from Nantong, Jiangsu province, were subjected to environmental magnetic analysis. In combination with analysis of lithology, particle size and diffuse reflectance spectroscopy (DRS), this paper discusses the magnetic properties of tidal deposits formed in early and late Holocene and its paleoenvironmental implications. Core NT can be divided into six depositional units, namely U1 to U6, from bottom to top, among which the lower part of U2 (49.9~44.8 m) and U6 (7.5~0.3 m) are interpreted to be tidal flat facies. They are characterized with lower S-ratios and higher hard isothermal remanent magnetization (HIRM) and SIRM/χ values, which indicates higher concentration and proportion of antiferromagntic minerals such as hematite and goethite. In combination with DRS, it is found that the enriched hematite and goethite occur in the upper part of U6, while only hematite is enriched in the lower part of U2. Such a difference in magnetic mineralogy is related to the sedimentary environments when these sediments are deposited. Sediments in U2 were formed during late stage of late Pleistocene to early Holocene and has been in subaerial condition for a long period, which favors hematite formation and preservation. With the rising sea-level during early Holocene, the salt marsh accreted vertically and eventually inundated, which does not favor the formation of goethite. In contrast, sediments in U6 were formed during the late Holocene. The oscillating redox condition favors the formation of goethite. Abundant maghemite and hematite were formed due to pedogenesis after land formation at a later stage. This study shows that sediments in salt marsh formed in different stages of the Holocene exhibits different magnetic properties. As a result, magnetic properties of sediments can provide information about the evolution of tidal flat, which has important implication for delta paleoenvironmental reconstruction.
2016, 34(6): 1176-1186.
doi: 10.14027/j.cnki.cjxb.2016.06.015
Abstract:
The genesis and source of the Xiashu Loess has always been a hotspot of academic research. We have analyzed the grain size of quartz and it's surface microstructive of the Xiashu Loess in Zhoujiashan Nanjing. The results show that silt fraction of quartz grains(5~50 μm) accounts for absolute advantage. The content of the corase silt fraction of quartz grains(10~50 μm) occupies 65.4%. The content of <30 μm component occupies 62.98%, while the content of <20 μm component occupies 42.76%. There is an opposite changes of the content in section between clay fraction and coarse silt fraction. The Xiashu Loess in Zhoujiashan Nanjing is similar to typical Northern Loess in China with the particle size distribution and cumulative curves. Overall, it presents the characteristics of very fine skewness, poorly sorting, leptokurtic and asymmetrical bi-modal curve in quartz grain size parameters. Grade-standard deviation curves present the distribution of "twin peak". Two obvious peaks in standard deviation is nearly 7.962 1 μm and 39.905 2 μm. The scope of the grain size fraction, corresponding to the two peaks, present to 0.399 1~15.886 6 μm and 15.886 6~112.468 3 μm, respectively. The surface shapes of quartz grains are mainly sub-angular. Surface mechanical structures not only have the characteristics of eolian features such as rich dish-shaped pits, curve ridge, parallel joint surface, textured structure and so on, but also slightly show the underwater environment characteristic as conchoidal breakage fractures, underwater ground surface and V-shaped pits. Meanwhile, it is different to the surface microstructive between 5~30 μm component and 30~50 μm component. Finally, our analysis has found that the Xiashu Loess in Zhoujiashan Nanjing belongs to the typical eolian-formation debris. It is probably a high degree of mixture with multiple sources. Our study has an important theoretical significance to understand the area dust transport mechanism.
The genesis and source of the Xiashu Loess has always been a hotspot of academic research. We have analyzed the grain size of quartz and it's surface microstructive of the Xiashu Loess in Zhoujiashan Nanjing. The results show that silt fraction of quartz grains(5~50 μm) accounts for absolute advantage. The content of the corase silt fraction of quartz grains(10~50 μm) occupies 65.4%. The content of <30 μm component occupies 62.98%, while the content of <20 μm component occupies 42.76%. There is an opposite changes of the content in section between clay fraction and coarse silt fraction. The Xiashu Loess in Zhoujiashan Nanjing is similar to typical Northern Loess in China with the particle size distribution and cumulative curves. Overall, it presents the characteristics of very fine skewness, poorly sorting, leptokurtic and asymmetrical bi-modal curve in quartz grain size parameters. Grade-standard deviation curves present the distribution of "twin peak". Two obvious peaks in standard deviation is nearly 7.962 1 μm and 39.905 2 μm. The scope of the grain size fraction, corresponding to the two peaks, present to 0.399 1~15.886 6 μm and 15.886 6~112.468 3 μm, respectively. The surface shapes of quartz grains are mainly sub-angular. Surface mechanical structures not only have the characteristics of eolian features such as rich dish-shaped pits, curve ridge, parallel joint surface, textured structure and so on, but also slightly show the underwater environment characteristic as conchoidal breakage fractures, underwater ground surface and V-shaped pits. Meanwhile, it is different to the surface microstructive between 5~30 μm component and 30~50 μm component. Finally, our analysis has found that the Xiashu Loess in Zhoujiashan Nanjing belongs to the typical eolian-formation debris. It is probably a high degree of mixture with multiple sources. Our study has an important theoretical significance to understand the area dust transport mechanism.
2016, 34(6): 1187-1197.
doi: 10.14027/j.cnki.cjxb.2016.06.016
Abstract:
As one of the most important sedimentary facies for development of clastic rocks, prograding deltas are critical to petroleum exploration. Hence, it has important significances to reservoir prediction to strengthen researches on depositional model of prograding delta confluences area. Confluences of Dongying delta and Yong'an delta took place in the middle depositional stages of the third section in the Paleogene Shahejie Formation (Es3m) in Dongying Lake, Bohai Bay Basin. However, it has not received adequate attentions to issues of confluences patterns, and reservoir predication about the two delta systems. Based on core observations, loggings and seismic data, this presentation analyzed sedimentary characteristics of confluences deltas of Es3m in Dongying sag, discussed sedimentary stages and confluences process, and constructed a depositional model for prograding confluences deltas, for sake of providing reference for further exploration deployment and geological research. Results show that lake and prograding delta deposits were well developed and reservoir sandbodies were mainly deposited in underwater distributary channels, mouth bar secondary and scattered turbidites in the Es3m in Dongying Sag. It is considered that sedimentary scope of Dongying delta were possibly over estimated and extent of Yong'an Delta were probably underestimated. Depositions of the Es3m in Dongying Sag can be divided into 9 stages and their processes are differentiated to part-confluence and full-confluence stages. Subaqueous deltas confluences are suitable place for water flow convergence and loading of sediments. Superimposed sandbodies are favorable reservoirs with crucial significances for petroleum explorations in delta confluences area.
As one of the most important sedimentary facies for development of clastic rocks, prograding deltas are critical to petroleum exploration. Hence, it has important significances to reservoir prediction to strengthen researches on depositional model of prograding delta confluences area. Confluences of Dongying delta and Yong'an delta took place in the middle depositional stages of the third section in the Paleogene Shahejie Formation (Es3m) in Dongying Lake, Bohai Bay Basin. However, it has not received adequate attentions to issues of confluences patterns, and reservoir predication about the two delta systems. Based on core observations, loggings and seismic data, this presentation analyzed sedimentary characteristics of confluences deltas of Es3m in Dongying sag, discussed sedimentary stages and confluences process, and constructed a depositional model for prograding confluences deltas, for sake of providing reference for further exploration deployment and geological research. Results show that lake and prograding delta deposits were well developed and reservoir sandbodies were mainly deposited in underwater distributary channels, mouth bar secondary and scattered turbidites in the Es3m in Dongying Sag. It is considered that sedimentary scope of Dongying delta were possibly over estimated and extent of Yong'an Delta were probably underestimated. Depositions of the Es3m in Dongying Sag can be divided into 9 stages and their processes are differentiated to part-confluence and full-confluence stages. Subaqueous deltas confluences are suitable place for water flow convergence and loading of sediments. Superimposed sandbodies are favorable reservoirs with crucial significances for petroleum explorations in delta confluences area.
2016, 34(6): 1198-1207.
doi: 10.14027/j.cnki.cjxb.2016.06.017
Abstract:
The submarine fan reservoir in the north slope of Lingshui sag, Qiongdongnan basin are characterized by fine grain, unclear genesis of low permeability and unknown distribution of the "sweet spot". This paper analyzed the porosity evolution and diagenetic facies based on the rock thin section, scanning electron microscopy, mercury injection experiment, particle size and petrophysics data. Besides, the "sweet spot" was predicted from the aspect of diagenetic facies. The results showed that primary porosity and mould pore are the main pore type in the 2nd member of Meishan Formation reservoir. The target intervals was in the middle diagenesis A stage. Porosity evolution was discussed according to sedimentation factors and diagenesis as follows:Primary pore were controlled by depositional environment, which were decreased sharply by later mechanical compaction; Dissolution played a great role in porosity increasing. Middle compaction-feldspar dissolution, middle compaction-glauconite cementation, strong compaction-weak dissolution were identified in the study area. The "sweet spot" was distributed in the inner submarine fan which had strong hydrodynamic condition and developed middle compaction-feldspar dissolution.
The submarine fan reservoir in the north slope of Lingshui sag, Qiongdongnan basin are characterized by fine grain, unclear genesis of low permeability and unknown distribution of the "sweet spot". This paper analyzed the porosity evolution and diagenetic facies based on the rock thin section, scanning electron microscopy, mercury injection experiment, particle size and petrophysics data. Besides, the "sweet spot" was predicted from the aspect of diagenetic facies. The results showed that primary porosity and mould pore are the main pore type in the 2nd member of Meishan Formation reservoir. The target intervals was in the middle diagenesis A stage. Porosity evolution was discussed according to sedimentation factors and diagenesis as follows:Primary pore were controlled by depositional environment, which were decreased sharply by later mechanical compaction; Dissolution played a great role in porosity increasing. Middle compaction-feldspar dissolution, middle compaction-glauconite cementation, strong compaction-weak dissolution were identified in the study area. The "sweet spot" was distributed in the inner submarine fan which had strong hydrodynamic condition and developed middle compaction-feldspar dissolution.
2016, 34(6): 1208-1216.
doi: 10.14027/j.cnki.cjxb.2016.06.018
Abstract:
It is well known that shale possess abundant hydrocarbon resources and therefore attracted more and more in the recent years. It is the fact that there are only a few researches have been conducted as reservoir instead of source rocks blocks the exploration as well as development of the shale oil and gas. In this study, we look into the diagenetic processes of shale and evolution by heat simulation experiment conduction. The shale sample of which the Ro is 0.7%, from lower section of Es3 in Jiyang depression and composed of calcite, quartz, clay, organic matters and other minerals, was divided into four pieces. Different temperatures(150℃, 200℃, 250℃, 300℃) was set to modify a series of stage of the diagenetic evolution process. The solution from the experiments was detected for ions and organic acids. And the rock samples were observed under the SEM. The study shows that:①The content of organic acids increased with the rising temperature and it suggests that a relatively wide organic acid generated window which affects pore fluid features, exists in the period of organic matter thermal evolution. ②Even though feldspar and calcite are main soluble minerals in the sample, different dissolution process was observed both by the ion detection and by the SEM-observation. Feldspar is easier to be dissolved while the dissolution of calcite always goes after. The study also shows a narrow calcite dissolution window followed by its re-deposition happened during 200℃~250℃. ③The fine-grained quartz released from the clay mineral reaction smectite-illite transformation within the micropores of the shale precipitated as 1~3 μm sub-spherical discrete grains, short chains, and small clusters interpreted to be parts of larger interconnected microquartz networks and interlocking aggregates of several microquartz and authigenic clay (illite-smectite and illite)crystals. Shale formation can be seen as a closed system where various diagenesis are influencing each other to form a complex diagenesis system and result in more difficulties on diagenesis research.
It is well known that shale possess abundant hydrocarbon resources and therefore attracted more and more in the recent years. It is the fact that there are only a few researches have been conducted as reservoir instead of source rocks blocks the exploration as well as development of the shale oil and gas. In this study, we look into the diagenetic processes of shale and evolution by heat simulation experiment conduction. The shale sample of which the Ro is 0.7%, from lower section of Es3 in Jiyang depression and composed of calcite, quartz, clay, organic matters and other minerals, was divided into four pieces. Different temperatures(150℃, 200℃, 250℃, 300℃) was set to modify a series of stage of the diagenetic evolution process. The solution from the experiments was detected for ions and organic acids. And the rock samples were observed under the SEM. The study shows that:①The content of organic acids increased with the rising temperature and it suggests that a relatively wide organic acid generated window which affects pore fluid features, exists in the period of organic matter thermal evolution. ②Even though feldspar and calcite are main soluble minerals in the sample, different dissolution process was observed both by the ion detection and by the SEM-observation. Feldspar is easier to be dissolved while the dissolution of calcite always goes after. The study also shows a narrow calcite dissolution window followed by its re-deposition happened during 200℃~250℃. ③The fine-grained quartz released from the clay mineral reaction smectite-illite transformation within the micropores of the shale precipitated as 1~3 μm sub-spherical discrete grains, short chains, and small clusters interpreted to be parts of larger interconnected microquartz networks and interlocking aggregates of several microquartz and authigenic clay (illite-smectite and illite)crystals. Shale formation can be seen as a closed system where various diagenesis are influencing each other to form a complex diagenesis system and result in more difficulties on diagenesis research.
