2015 Vol. 40, No. 5
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2015, 40(5): 763-776.
doi: 10.3799/dqkx.2015.063
Abstract:
Based on the lithological association and sedimentary environments, the clastic stratal succession around the Taketai plateau in western Junggar is named as a new lithostratigraphic unit—Taketai Formation, which was previously assigned to the Early Carboniferous Hebukehe Formation. Taketai Formation can be subdivided into two members; the lower part is made up of volcanoclastic rocks intercalated with volcanic rocks, while the upper part is characterized by normal clastic rocks, volcanoclastic rocks and calcareous clastic rocks with a few limestones, volcanic rocks and thin coal seams. The Taketai Formation overlies the Wenlock Shaerbuer Formation in angular unconformity and its top is covered with Quaternary deposits. According to conodonts and other fossils preserved in the formation, Taketai Formation is considered to be the Late Devonian. It is formed from the littoral-neritic sea to swamp in a regression background. The same time-different stratum units of the Taketai Formation include the Zhulumute and Hongguleleng formations in adjacent regions, and it was caused by the Late Devonian marine transgression and regression from west to east in the study area.
Based on the lithological association and sedimentary environments, the clastic stratal succession around the Taketai plateau in western Junggar is named as a new lithostratigraphic unit—Taketai Formation, which was previously assigned to the Early Carboniferous Hebukehe Formation. Taketai Formation can be subdivided into two members; the lower part is made up of volcanoclastic rocks intercalated with volcanic rocks, while the upper part is characterized by normal clastic rocks, volcanoclastic rocks and calcareous clastic rocks with a few limestones, volcanic rocks and thin coal seams. The Taketai Formation overlies the Wenlock Shaerbuer Formation in angular unconformity and its top is covered with Quaternary deposits. According to conodonts and other fossils preserved in the formation, Taketai Formation is considered to be the Late Devonian. It is formed from the littoral-neritic sea to swamp in a regression background. The same time-different stratum units of the Taketai Formation include the Zhulumute and Hongguleleng formations in adjacent regions, and it was caused by the Late Devonian marine transgression and regression from west to east in the study area.
2015, 40(5): 777-796.
doi: 10.3799/dqkx.2015.064
Abstract:
Understanding of the formation and occurrence of intermediate-basic dyke swarms can facilitate future studies on the magmatic evolution and tectonic settings. The Xiaerpu and Xiaoxihu intermediate-basic dyke swarms in West Junggar are principally composed of dioritic porphyrite, with minor diabase. LA-ICP-MS zircon U-Pb dating results indicate that the Xiaerpu dyke swarm is emplaced with age of 308.6±5.5 Ma. It is concluded that these dykes are the products of magmatism in Late Carboniferous based on the geological relationship between the dykes and host granitic rocks, and previous chronological studies. The dykes are characterized by high Mg#(> 40), high MgO(> 3%) and Al2O3(> 16%), belonging to calc-alkaline rocks and metaluminous rocks (with A/CNK approximately at 0.9 and A/NK > 2). The rocks have lower total REE (most are concentrated in 40×10-6-60 ×10-6), with enriched LREE and slightly positive Eu anomalies ((La/Yb)N=3.03-11.32, δEu=1.00-1.20). All samples are highly depleted in (Nb, Ta, Ti and Th), and enriched in (Sr, Ba, K and Rb). Meanwhile, the high contents of Sr (> 500×10-6), low contents of Y and Yb, high values of Sr/Y ratios (36.98-95.74), indicate the rocks (except sample XEP01, XEP02 and XXH06) are analogous to Mg-enriched adakitic rocks. Dykes have depleted Sr-Nd isotopic composition ((87Sr/86Sr)i=0.703 58-0.703 80, εNd(t)=5.76-6.34). Geochemical and isotopic compositions indicate that depleted-mantle components and materials related to subduction have prominent significance in the origin source of these dykes. Combined with the district geological evolution history and previous studies, we propose that West Junggar was under a post-collisional regime in Late Carboniferous. Due to the melting of remnant subducted oceanic slab, the slab melts interacted with the mantle materials to varying extent during ascent, and then accompanied fractional crystallization of clinopyroxene that generated the Mg-enriched adakitic rocks in Xiaerpu and Xiaoxihu intermediate-basic dyke swarms; and fractional crystallization of clinopyroxene of depleted-mantle materials metasomatised by slab melts can account for the formation of the diabase in Xiaerpu dyke swarm and the amphibolic diorite in Xiaoxihu dyke swarm. The emplacement of large-scale intermediate-basic dyke swarms further show that West Junggar was under a post-collisional extensional environment in Late Carboniferous.
Understanding of the formation and occurrence of intermediate-basic dyke swarms can facilitate future studies on the magmatic evolution and tectonic settings. The Xiaerpu and Xiaoxihu intermediate-basic dyke swarms in West Junggar are principally composed of dioritic porphyrite, with minor diabase. LA-ICP-MS zircon U-Pb dating results indicate that the Xiaerpu dyke swarm is emplaced with age of 308.6±5.5 Ma. It is concluded that these dykes are the products of magmatism in Late Carboniferous based on the geological relationship between the dykes and host granitic rocks, and previous chronological studies. The dykes are characterized by high Mg#(> 40), high MgO(> 3%) and Al2O3(> 16%), belonging to calc-alkaline rocks and metaluminous rocks (with A/CNK approximately at 0.9 and A/NK > 2). The rocks have lower total REE (most are concentrated in 40×10-6-60 ×10-6), with enriched LREE and slightly positive Eu anomalies ((La/Yb)N=3.03-11.32, δEu=1.00-1.20). All samples are highly depleted in (Nb, Ta, Ti and Th), and enriched in (Sr, Ba, K and Rb). Meanwhile, the high contents of Sr (> 500×10-6), low contents of Y and Yb, high values of Sr/Y ratios (36.98-95.74), indicate the rocks (except sample XEP01, XEP02 and XXH06) are analogous to Mg-enriched adakitic rocks. Dykes have depleted Sr-Nd isotopic composition ((87Sr/86Sr)i=0.703 58-0.703 80, εNd(t)=5.76-6.34). Geochemical and isotopic compositions indicate that depleted-mantle components and materials related to subduction have prominent significance in the origin source of these dykes. Combined with the district geological evolution history and previous studies, we propose that West Junggar was under a post-collisional regime in Late Carboniferous. Due to the melting of remnant subducted oceanic slab, the slab melts interacted with the mantle materials to varying extent during ascent, and then accompanied fractional crystallization of clinopyroxene that generated the Mg-enriched adakitic rocks in Xiaerpu and Xiaoxihu intermediate-basic dyke swarms; and fractional crystallization of clinopyroxene of depleted-mantle materials metasomatised by slab melts can account for the formation of the diabase in Xiaerpu dyke swarm and the amphibolic diorite in Xiaoxihu dyke swarm. The emplacement of large-scale intermediate-basic dyke swarms further show that West Junggar was under a post-collisional extensional environment in Late Carboniferous.
2015, 40(5): 797-809.
doi: 10.3799/dqkx.2015.065
Abstract:
To provide new evidences for the stratigraphic division of Devonian and Carboniferous as well as paleoenvironmental reconstruction of western Junggar, Xinjiang, NW China. The biostratigraphic data of Devonian-Carboniferous boundary (D-C) has been explored in this study by field sampling and laboratory analysis in western Junggar. 12 ostracod species (including 1 new species) from the Devonian-Carboniferous in the Emuha section of western Junggar are first described and presented. It is found that they belong to 9 genera, including Cavellina sublatiovata, C.cf. obesa, C. sp., Glyptopleura sp., Healdianella renalata, H. sp., Bairdiocypris vafra, Bairdia sp., Rectobairdia sp., Fabalicypris sp., Youngiella calvata, Coelonella xizhunensis sp. nov.. The stratigraphical distribution of ostracods in the Emuha section suggests that the Hongguleleng Formation should be Late Devonian to the Early Carboniferous in age. In terms of paleoecology, the retrieved ostracods indicate an off-shore environment during intermittent periods of volcanic activities in volcanic arc zone.
To provide new evidences for the stratigraphic division of Devonian and Carboniferous as well as paleoenvironmental reconstruction of western Junggar, Xinjiang, NW China. The biostratigraphic data of Devonian-Carboniferous boundary (D-C) has been explored in this study by field sampling and laboratory analysis in western Junggar. 12 ostracod species (including 1 new species) from the Devonian-Carboniferous in the Emuha section of western Junggar are first described and presented. It is found that they belong to 9 genera, including Cavellina sublatiovata, C.cf. obesa, C. sp., Glyptopleura sp., Healdianella renalata, H. sp., Bairdiocypris vafra, Bairdia sp., Rectobairdia sp., Fabalicypris sp., Youngiella calvata, Coelonella xizhunensis sp. nov.. The stratigraphical distribution of ostracods in the Emuha section suggests that the Hongguleleng Formation should be Late Devonian to the Early Carboniferous in age. In terms of paleoecology, the retrieved ostracods indicate an off-shore environment during intermittent periods of volcanic activities in volcanic arc zone.
Geochronological, Geochemical and Petrogenesis of Bieluagaxi Granodioritic Pluton in Western Junggar
2015, 40(5): 810-823.
doi: 10.3799/dqkx.2015.066
Abstract:
For a better understanding of the petrogenesis and tectonic environment of the acidic intrusive rocks in Western Junggar, a study is carried out on Bieluagaxi granodioritic pluton located in the Central part of West Junggar. Its petrogenesis, magma source, tectonics setting based on petrography, zircon LA-ICP-MS U-Pb ages, whole-rock major and trace elements, and Sr-Nd isotopic compositions are discussed in detail. LA-ICP-MS U-Pb zircon data of the granodiorite give weighted ages of 318.7±3.3 Ma. Bieluagaxi granodiorite is calc-alkaline suite with high MgO(Mg#=49-59), Ni and Cr contents. Bieluagaxi granodiorite is strongly enriched in large ion lithophile elements (LILEs, e.g. K, Rb, Sr and Ba), but it displays depletion of high field strength elements (HFSEs, e.g. Nb, Ta and Ti). In terms of Sr-Nd isotopic compositions, granodiorite has low initial 87Sr/86Sr ratios (0.704 297-0.704 399) and high positive εNd(t) (5.8-6.5). Therefore, we suggest that the early Late Carboniferous Bieluagaxi granodioritic pluton has been generated in a subduction setting, the mantle wedge began to partially melt due to the upward fluid from the dehydration of subducting oceanic slab, resulting in the asthenospheric mafic magma underplating the lower crust. Then, the lower juvenile basaltic crust derived from the depleted mantle underwent partial melting to generate the I type granites of the Bieluagaxi granodioritic pluton.
For a better understanding of the petrogenesis and tectonic environment of the acidic intrusive rocks in Western Junggar, a study is carried out on Bieluagaxi granodioritic pluton located in the Central part of West Junggar. Its petrogenesis, magma source, tectonics setting based on petrography, zircon LA-ICP-MS U-Pb ages, whole-rock major and trace elements, and Sr-Nd isotopic compositions are discussed in detail. LA-ICP-MS U-Pb zircon data of the granodiorite give weighted ages of 318.7±3.3 Ma. Bieluagaxi granodiorite is calc-alkaline suite with high MgO(Mg#=49-59), Ni and Cr contents. Bieluagaxi granodiorite is strongly enriched in large ion lithophile elements (LILEs, e.g. K, Rb, Sr and Ba), but it displays depletion of high field strength elements (HFSEs, e.g. Nb, Ta and Ti). In terms of Sr-Nd isotopic compositions, granodiorite has low initial 87Sr/86Sr ratios (0.704 297-0.704 399) and high positive εNd(t) (5.8-6.5). Therefore, we suggest that the early Late Carboniferous Bieluagaxi granodioritic pluton has been generated in a subduction setting, the mantle wedge began to partially melt due to the upward fluid from the dehydration of subducting oceanic slab, resulting in the asthenospheric mafic magma underplating the lower crust. Then, the lower juvenile basaltic crust derived from the depleted mantle underwent partial melting to generate the I type granites of the Bieluagaxi granodioritic pluton.
2015, 40(5): 824-839.
doi: 10.3799/dqkx.2015.067
Abstract:
The Taihua Group, exposed in the southernmost terminal Trans-North China Orogen (TNCO), is important for deciphering the mysterious evolution processes of the southern margin of the North China Craton during Proterozoic, and determination of the collision time of the eastern and western blocks of the North China Craton. Petrological study on three kinds of migmatites formed by anatexis from the Taihua Group in Xiaoqinling area, West Henan, indicates that the transformation of migmatites caused by anatexis is uneven, which is obviously limited by the composition of protolith, structure of rocks and other properties. LA-ICP-MS U-Pb dating of the anatexis zircons shows that the protolith crystallized in the Paleoproterozoic and the anatexis occurred at about 1.8 Ga. The migmatites and contemporaneous mafic dike swarms and A-type granite in the study area were generated in a post-orogenic, extensional environment following continent-continent collision at 1.85 Ga between the eastern and western blocks of the North China Craton.
The Taihua Group, exposed in the southernmost terminal Trans-North China Orogen (TNCO), is important for deciphering the mysterious evolution processes of the southern margin of the North China Craton during Proterozoic, and determination of the collision time of the eastern and western blocks of the North China Craton. Petrological study on three kinds of migmatites formed by anatexis from the Taihua Group in Xiaoqinling area, West Henan, indicates that the transformation of migmatites caused by anatexis is uneven, which is obviously limited by the composition of protolith, structure of rocks and other properties. LA-ICP-MS U-Pb dating of the anatexis zircons shows that the protolith crystallized in the Paleoproterozoic and the anatexis occurred at about 1.8 Ga. The migmatites and contemporaneous mafic dike swarms and A-type granite in the study area were generated in a post-orogenic, extensional environment following continent-continent collision at 1.85 Ga between the eastern and western blocks of the North China Craton.
2015, 40(5): 840-850.
doi: 10.3799/dqkx.2015.068
Abstract:
Migrated sequence stratigraphic architecture represents a special type in continental lacustrine rift basin. However, its characteristics and main controlling factors are unclear yet. Lower Wenchang Formation (PSQ1-PSQ4) is mainly distributed at south of Huizhou depression, while upper Wenchang Formation (PSQ5-PSQ7) is distributed at northern part. It is found in this study that sequences in Wenchang Formation migrate from southeast to northwest across Huizhou depression. Migration of sequence is generally caused by different stages of episodic tectonic activity. In rifted stage IA, tectonic activities of southern depression strengthen largely and sequences configuration show as Type T, which mostly develops lower Wenchang Formation. However, as for rifted stage IB, northern tectonic activities become stronger, which results in migration of depocenter and subsidence center from north to south. And sequences configuration show as Type H which mainly develops upper Wenchang Formation. Moreover, migration of sequence stratigraphic unit generates multi-block along the direction of migration and also a combination of multi-stage oil and gas reservoirs, which are all of great potential for exploration.
Migrated sequence stratigraphic architecture represents a special type in continental lacustrine rift basin. However, its characteristics and main controlling factors are unclear yet. Lower Wenchang Formation (PSQ1-PSQ4) is mainly distributed at south of Huizhou depression, while upper Wenchang Formation (PSQ5-PSQ7) is distributed at northern part. It is found in this study that sequences in Wenchang Formation migrate from southeast to northwest across Huizhou depression. Migration of sequence is generally caused by different stages of episodic tectonic activity. In rifted stage IA, tectonic activities of southern depression strengthen largely and sequences configuration show as Type T, which mostly develops lower Wenchang Formation. However, as for rifted stage IB, northern tectonic activities become stronger, which results in migration of depocenter and subsidence center from north to south. And sequences configuration show as Type H which mainly develops upper Wenchang Formation. Moreover, migration of sequence stratigraphic unit generates multi-block along the direction of migration and also a combination of multi-stage oil and gas reservoirs, which are all of great potential for exploration.
2015, 40(5): 851-862.
doi: 10.3799/dqkx.2015.069
Abstract:
To better understand the sedimentary characteristics of the cone-in-cone structure in the outcrop areas, and to explore the causes of the formation and the environmental issues of the cone-in-cone structure, we employ methods such as outcrop measure, polished thin section observation, X-ray diffraction analysis, cathode-ray luminescence, electronic scanning in this study. It is discovered that cone-in-cone structure develops radially around the calcareous concretions, with conical apex pointing straight to the concretion center; the major mineral composition of cone-in-cone structure is fibrous low magnesium calcite, with fibrous calcite crystals being cone-shaped nest, with wavy extinction which appears uniform red-brown under cathodoluminescence microscopy without diagenetic ribbon with trace element fractionation and precipitation. The developing scale of cone-in-cone concretions is in the control of primary sedimentary environment obviously. It is considered that the growth of cone-in-cone concretions has distinct stages; the original sedimentary environment should be shallow lake sedimentary environment with about 5-30 m depth and relatively higher energy. It is concluded that the formation of cone-in-cone structure is a result of synsedimentary biological deposition, cementation and later overburden static pressure.
To better understand the sedimentary characteristics of the cone-in-cone structure in the outcrop areas, and to explore the causes of the formation and the environmental issues of the cone-in-cone structure, we employ methods such as outcrop measure, polished thin section observation, X-ray diffraction analysis, cathode-ray luminescence, electronic scanning in this study. It is discovered that cone-in-cone structure develops radially around the calcareous concretions, with conical apex pointing straight to the concretion center; the major mineral composition of cone-in-cone structure is fibrous low magnesium calcite, with fibrous calcite crystals being cone-shaped nest, with wavy extinction which appears uniform red-brown under cathodoluminescence microscopy without diagenetic ribbon with trace element fractionation and precipitation. The developing scale of cone-in-cone concretions is in the control of primary sedimentary environment obviously. It is considered that the growth of cone-in-cone concretions has distinct stages; the original sedimentary environment should be shallow lake sedimentary environment with about 5-30 m depth and relatively higher energy. It is concluded that the formation of cone-in-cone structure is a result of synsedimentary biological deposition, cementation and later overburden static pressure.
2015, 40(5): 863-869.
doi: 10.3799/dqkx.2015.070
Abstract:
Abundant information about paleo-environment, paleo-climate and paleolithic culture can be obtained from the red earth in southern China. However, the vermicular paleosol is proposed to be incapable of interpretating the original information about the past climate and envrionment changes owing to the intensive pedogenesis in the tropical-subtropical area. Therefore, previous studies on bio-climatic approaches including pollen, spore fossils and phytoliths are also believed to be not suitable for such kind of stratigraphy. Despite that some studies show the microbial molecular fossils are useful in the paleo-environment reconstruction, but their implications in red earth need to be further explored and confirmed. It is necessary to introduce some new methods to extract the detailed biological information in the red earth. In this study, we collected red earth samples from the Xuancheng section, Anhui Province in the Middle-Lower Reaches of the Yangtze River, which is well-dated and sensitive to climate change. Microbial lipids in the red earth are extracted by employing alkaline hydrolysis combined with the field survey and the laboratory investigation. The characteristics of the microbial lipids, especially glycerol dialkyl glycerol tetraethers (GDGTs) are investigated. The distributions of GDGTs from the Xuancheng profile show that all GDGT-derived proxies in the lower part of profile fluctuates frequently, whereas they are relatively stable in the upper part, which indicates that the paleo-environment changed frequently during the early period of this profile but the later soil environment was relatively stable. The CBT-inferred soil pH ranges from 7.0 to 8.0, indicating that the soil parent material likely comes from the arid areas in northwestern China or alternatively from the dry river sediments in the Middle-Lower Reaches of the Yangtze River. The low BIT values suggest that it was very dry at 130 ka BP in the Xuancheng region.
Abundant information about paleo-environment, paleo-climate and paleolithic culture can be obtained from the red earth in southern China. However, the vermicular paleosol is proposed to be incapable of interpretating the original information about the past climate and envrionment changes owing to the intensive pedogenesis in the tropical-subtropical area. Therefore, previous studies on bio-climatic approaches including pollen, spore fossils and phytoliths are also believed to be not suitable for such kind of stratigraphy. Despite that some studies show the microbial molecular fossils are useful in the paleo-environment reconstruction, but their implications in red earth need to be further explored and confirmed. It is necessary to introduce some new methods to extract the detailed biological information in the red earth. In this study, we collected red earth samples from the Xuancheng section, Anhui Province in the Middle-Lower Reaches of the Yangtze River, which is well-dated and sensitive to climate change. Microbial lipids in the red earth are extracted by employing alkaline hydrolysis combined with the field survey and the laboratory investigation. The characteristics of the microbial lipids, especially glycerol dialkyl glycerol tetraethers (GDGTs) are investigated. The distributions of GDGTs from the Xuancheng profile show that all GDGT-derived proxies in the lower part of profile fluctuates frequently, whereas they are relatively stable in the upper part, which indicates that the paleo-environment changed frequently during the early period of this profile but the later soil environment was relatively stable. The CBT-inferred soil pH ranges from 7.0 to 8.0, indicating that the soil parent material likely comes from the arid areas in northwestern China or alternatively from the dry river sediments in the Middle-Lower Reaches of the Yangtze River. The low BIT values suggest that it was very dry at 130 ka BP in the Xuancheng region.
2015, 40(5): 870-880.
doi: 10.3799/dqkx.2015.071
Abstract:
The environment and climate information during the Holocene is indispensable data for the global climate modeling and forecasting. Scenarios of regional vegetation and climate changes around the Celebes Sea during the Holocene are explored based on the alynological and oxygen isotope records of core MD98-2178 (3.6200°N, 118.7000°E; 1 984 m water depth) from the northwest Celebes Sea in this study. Sea-level changes are discussed since the marine pollen record of core MD98-2178 is considered as an indicator. The sharp decline in concentration of all pollen groups during the Early Holocene, ~10-7 ka BP, indicates a sea-level rise. All pollen groups at 7-4 ka BP suggest sustaining of a high sea-level. The marine pollen record after 4 ka BP shows a slight fall of sea-level. The significant increase in pollen percentage of the tropical montane forest during the Middle Holocene, 5-4 ka BP, suggests a much cold condition along the Celebes Sea at the time. It is suggested that precipitation along the Celebes Sea has been affected by variations of land-ocean distribution and solar activities. It is implied by fluctuation in fern spores record that precipitation was at a high level during the Early Holocene, but lowered after the Middle Holocene, which is in a similar pattern as indicated by the Indonesian stalagmite records.
The environment and climate information during the Holocene is indispensable data for the global climate modeling and forecasting. Scenarios of regional vegetation and climate changes around the Celebes Sea during the Holocene are explored based on the alynological and oxygen isotope records of core MD98-2178 (3.6200°N, 118.7000°E; 1 984 m water depth) from the northwest Celebes Sea in this study. Sea-level changes are discussed since the marine pollen record of core MD98-2178 is considered as an indicator. The sharp decline in concentration of all pollen groups during the Early Holocene, ~10-7 ka BP, indicates a sea-level rise. All pollen groups at 7-4 ka BP suggest sustaining of a high sea-level. The marine pollen record after 4 ka BP shows a slight fall of sea-level. The significant increase in pollen percentage of the tropical montane forest during the Middle Holocene, 5-4 ka BP, suggests a much cold condition along the Celebes Sea at the time. It is suggested that precipitation along the Celebes Sea has been affected by variations of land-ocean distribution and solar activities. It is implied by fluctuation in fern spores record that precipitation was at a high level during the Early Holocene, but lowered after the Middle Holocene, which is in a similar pattern as indicated by the Indonesian stalagmite records.
2015, 40(5): 881-889.
doi: 10.3799/dqkx.2015.072
Abstract:
Planktonic foraminifera Globigerinoides ruber (G. ruber) shell weight of sediment samples from South China Sea (SCS) located in the South China Sea and MD06-3052 located in the western Pacific are tested using size-normalized shell weight method and traditional shell weight method. In comparison with traditional shell weight method, SCS data indicate that the size-normalized shell weight method for G. ruber can significantly reduce the influence of test size on foraminifera shell weight in the study area. Comparing the variation curves of CO2 concentration (pCO2) recorded in Vostok ice core, MD06-3052 G. ruber data show that size-normalized shell weight can indicate the change of sea surface water [CO32-] more effectively. The size-normalized shell weight method provides a reliable and rapid proxy for the weight analyses in the paleoceanographic study, and a potential proxy in studying the influence of surface sea water in global carbon cycle since Late Pleistocene.
Planktonic foraminifera Globigerinoides ruber (G. ruber) shell weight of sediment samples from South China Sea (SCS) located in the South China Sea and MD06-3052 located in the western Pacific are tested using size-normalized shell weight method and traditional shell weight method. In comparison with traditional shell weight method, SCS data indicate that the size-normalized shell weight method for G. ruber can significantly reduce the influence of test size on foraminifera shell weight in the study area. Comparing the variation curves of CO2 concentration (pCO2) recorded in Vostok ice core, MD06-3052 G. ruber data show that size-normalized shell weight can indicate the change of sea surface water [CO32-] more effectively. The size-normalized shell weight method provides a reliable and rapid proxy for the weight analyses in the paleoceanographic study, and a potential proxy in studying the influence of surface sea water in global carbon cycle since Late Pleistocene.
2015, 40(5): 890-899.
doi: 10.3799/dqkx.2015.073
Abstract:
The Yingdong oilfield, western Qaidam basin, is an important petroleum exploration front in the basin. However, the distribution of oil-gas-water is complex due to the complex structures and the pervasive faulting in the reservoirs and the petroleum accumulation process is still to be probed in detail. The petroleum accumulation process in the area was investigated by using an integrated grain fluorescence, fluid inclusion and organic geochemical analyses in this study. The results show follows: (1) There were two episodes of oil charge in N21-N22, as reflected by three types of hydrocarbon inclusions, occurred in around 12 Ma and 5 Ma, respectively. (2) The current oil accumulations in the oilfield derived from upward migration of palaeo-oil reservoirs in the depth are from the same sources. (3) The QGF index which is larger than 2 and the development of yellow fluorescent hydrocarbon inclusions with low mature crude oil indicate that there existed crude oil with low maturity recharge in the early stage. Such crude oil came from the same low mature oil source and there is no high mature oil in the source. The decreasing of light component with increasing buried depth indicates that the blue fluorescent hydrocarbon inclusions and gas hydrocarbon inclusions resulted from the late tectonic activity and the fault adjusted upward migration degassing channel system. The Yingdong oilfield has great exploration potential because of the inheritance structural development and the occurrence of two episodes of hydrocarbon accumulations.
The Yingdong oilfield, western Qaidam basin, is an important petroleum exploration front in the basin. However, the distribution of oil-gas-water is complex due to the complex structures and the pervasive faulting in the reservoirs and the petroleum accumulation process is still to be probed in detail. The petroleum accumulation process in the area was investigated by using an integrated grain fluorescence, fluid inclusion and organic geochemical analyses in this study. The results show follows: (1) There were two episodes of oil charge in N21-N22, as reflected by three types of hydrocarbon inclusions, occurred in around 12 Ma and 5 Ma, respectively. (2) The current oil accumulations in the oilfield derived from upward migration of palaeo-oil reservoirs in the depth are from the same sources. (3) The QGF index which is larger than 2 and the development of yellow fluorescent hydrocarbon inclusions with low mature crude oil indicate that there existed crude oil with low maturity recharge in the early stage. Such crude oil came from the same low mature oil source and there is no high mature oil in the source. The decreasing of light component with increasing buried depth indicates that the blue fluorescent hydrocarbon inclusions and gas hydrocarbon inclusions resulted from the late tectonic activity and the fault adjusted upward migration degassing channel system. The Yingdong oilfield has great exploration potential because of the inheritance structural development and the occurrence of two episodes of hydrocarbon accumulations.
2015, 40(5): 900-908.
doi: 10.3799/dqkx.2015.074
Abstract:
In order to explore the developmental process of carbonate platform in the South China Sea (SCS) and its control factors, the organic molecular compound index method were described in this study. The branched isoprenoid tetraether (BIT) index is the ratio between the branched glycerol dialkyl glycerol tetraethers (bGDGTs) from terrigenous supply and isoprenoid GDGTs (iGDGTs) from marine crenarchaeol comprising the majority of denominator, which serves as a proxy for provenance discrimination of the organic matter and related sedimentary environments in paleoenvironmental research. The BIT curve of well Xike-1 is characterized by a unique "high-low-high" feature up section, indicating the effects of sea-level variations and carbonate platform development since Middle Miocene in the SCS. Strata with reef-beach facies were developed within carbonate platforms of Xisha Islands influenced by decrease in global as well as regional sea-level during the Late Miocene, with increased BIT values due to plenty of precipitation. Between Late Miocene and Pliocene when sea-level was higher, carbonate platforms were better formed in shallow marine environment with low BIT values. Carbonate platforms of Xisha Islands were periodically exposed in Quaternary as a result of sea-level decline over glacial cycles, leading to the second increase in BIT. Our results demonstrate that carbonate platforms of Xisha Islands have been affected by regional sea-level variations, reflecting a coupling effect on the SCS by global sea-level fluctuations and regional tectonic subductions.
In order to explore the developmental process of carbonate platform in the South China Sea (SCS) and its control factors, the organic molecular compound index method were described in this study. The branched isoprenoid tetraether (BIT) index is the ratio between the branched glycerol dialkyl glycerol tetraethers (bGDGTs) from terrigenous supply and isoprenoid GDGTs (iGDGTs) from marine crenarchaeol comprising the majority of denominator, which serves as a proxy for provenance discrimination of the organic matter and related sedimentary environments in paleoenvironmental research. The BIT curve of well Xike-1 is characterized by a unique "high-low-high" feature up section, indicating the effects of sea-level variations and carbonate platform development since Middle Miocene in the SCS. Strata with reef-beach facies were developed within carbonate platforms of Xisha Islands influenced by decrease in global as well as regional sea-level during the Late Miocene, with increased BIT values due to plenty of precipitation. Between Late Miocene and Pliocene when sea-level was higher, carbonate platforms were better formed in shallow marine environment with low BIT values. Carbonate platforms of Xisha Islands were periodically exposed in Quaternary as a result of sea-level decline over glacial cycles, leading to the second increase in BIT. Our results demonstrate that carbonate platforms of Xisha Islands have been affected by regional sea-level variations, reflecting a coupling effect on the SCS by global sea-level fluctuations and regional tectonic subductions.
2015, 40(5): 909-917.
doi: 10.3799/dqkx.2015.075
Abstract:
Hydrocarbon generation simulation experiment (pyrolysis) is important for studying petroleum generation mechanisms and quantitatively estimating hydrocarbon generation potential of source rocks. The simulation experiment results not only depend on the temperature, pressure and duration, but also on the pore fluid, source rock compaction. In this paper, marine black mudstone with low maturity from the Permian Dalong Formation (P2d) is used for hydrocarbon generation simulations with two types of high-pressure liquid water and low-pressure water steam. The results show that the high-pressure liquid water can increase the organic matter petroleum generation potential greatly, enhancing oil generation and retarding the transformation from oil to gas, suggesting important influence of geological factors such as high-pressure liquid water, fluid pressure and pore space on the hydrocarbon generation of the source rocks. The increase of the petroleum generation potential is due to the fact that the physicochemistry reaction of the kerogen is greatly enhanced at the presence of the near-critical properties water. It is concluded that the water in the pore space of the source rocks is of the high-pressure and low-temperature liquid water in the subsurface temperature (100-200 ℃) and pressure (30-120 MPa) conditions, which has the properties of near-critical water. Therefore, the hydrocarbon generation simulation experiment (pyrolysis) with high-pressure liquid water is more close to the actual geological conditions than that of the low pressure water steam and could be used to estimate hydrocarbon generation potential of source rock more effectively.
Hydrocarbon generation simulation experiment (pyrolysis) is important for studying petroleum generation mechanisms and quantitatively estimating hydrocarbon generation potential of source rocks. The simulation experiment results not only depend on the temperature, pressure and duration, but also on the pore fluid, source rock compaction. In this paper, marine black mudstone with low maturity from the Permian Dalong Formation (P2d) is used for hydrocarbon generation simulations with two types of high-pressure liquid water and low-pressure water steam. The results show that the high-pressure liquid water can increase the organic matter petroleum generation potential greatly, enhancing oil generation and retarding the transformation from oil to gas, suggesting important influence of geological factors such as high-pressure liquid water, fluid pressure and pore space on the hydrocarbon generation of the source rocks. The increase of the petroleum generation potential is due to the fact that the physicochemistry reaction of the kerogen is greatly enhanced at the presence of the near-critical properties water. It is concluded that the water in the pore space of the source rocks is of the high-pressure and low-temperature liquid water in the subsurface temperature (100-200 ℃) and pressure (30-120 MPa) conditions, which has the properties of near-critical water. Therefore, the hydrocarbon generation simulation experiment (pyrolysis) with high-pressure liquid water is more close to the actual geological conditions than that of the low pressure water steam and could be used to estimate hydrocarbon generation potential of source rock more effectively.
2015, 40(5): 918-924.
doi: 10.3799/dqkx.2015.076
Abstract:
Non-Darcian flow is likely to occur in the region near a pumping well because of high velocities, while flow becomes Darcian again in the region far away from the pumping well as the velocity decreases. To describe these characteristics, a two-region non-Darcian flow model toward a partially penetrating well is developed in this study. The flow in the region near the pumping well is assumed to be non-Darcian which can be described by the Izbash equation. The flow in the region far away from the pumping well was assumed to be Darcian as well as the vertical flow due to the low velocities. A linearization procedure associated with the Laplace transform and finite cosine transform is used to work out such two-region non-Darcian flow model. The characteristics of the drawdowns under such flow conditions are examined. It is concluded that: (1) the drawdown in the non-Darcian flow region is the same as that of the fully non-Darcian flow model at early times, and it is the same at that of the fully Darcian flow model and larger than that of the fully non-Darcian flow model at late times. (2) the drawdown in the Darcian flow region is larger than that of the fully Darcian flow model and smaller than that of the full non-Darcian flow model at early times; (3) the drawdown-distance behavior indicates that the drawdown in the non-Darcian flow region increases as the power index n in the Izbash equation increases, while the value of n has a little effect on the drawdown in the Darcian flow region. The results of this study will be of great theoretical significance for the aquifer parameters estimation with the pumping test data in a partially penetrating well.
Non-Darcian flow is likely to occur in the region near a pumping well because of high velocities, while flow becomes Darcian again in the region far away from the pumping well as the velocity decreases. To describe these characteristics, a two-region non-Darcian flow model toward a partially penetrating well is developed in this study. The flow in the region near the pumping well is assumed to be non-Darcian which can be described by the Izbash equation. The flow in the region far away from the pumping well was assumed to be Darcian as well as the vertical flow due to the low velocities. A linearization procedure associated with the Laplace transform and finite cosine transform is used to work out such two-region non-Darcian flow model. The characteristics of the drawdowns under such flow conditions are examined. It is concluded that: (1) the drawdown in the non-Darcian flow region is the same as that of the fully non-Darcian flow model at early times, and it is the same at that of the fully Darcian flow model and larger than that of the fully non-Darcian flow model at late times. (2) the drawdown in the Darcian flow region is larger than that of the fully Darcian flow model and smaller than that of the full non-Darcian flow model at early times; (3) the drawdown-distance behavior indicates that the drawdown in the non-Darcian flow region increases as the power index n in the Izbash equation increases, while the value of n has a little effect on the drawdown in the Darcian flow region. The results of this study will be of great theoretical significance for the aquifer parameters estimation with the pumping test data in a partially penetrating well.
2015, 40(5): 925-932.
doi: 10.3799/dqkx.2015.077
Abstract:
It is necessary to take into account the dip angle effects on accurate estimation of hydrogeological parameters in the sloping confined aquifer. To explore how the dip angle influences the test response, a new slug test model is developed in this study by using theoretical and filed data analysis. For test well, it is found that when the aquifer hydraulic conductivity is relatively low, a larger dip angle causes a faster recovery of the non-oscillatory test response; when the aquifer hydraulic conductivity is relatively high, a larger dip angle causes an increase of amplitude of the oscillatory test response. The dip angle effect is more pronounced for a larger storage coefficient, being less sensitive to the change of transmissivity. An empirical relationship is developed for the limiting dip angle as a function of the dimensionless storage coefficient. The function can be used to predict whether the estimate of hydrogeological parameters would be influenced by the dip angle. The effect can be neglected if the dip angle is less than the upper limit. However, it cannot be neglected if the dip angle is larger than the upper limit, otherwise, it can result in an overestimate of transmissivity and an underestimate of the storage coefficient.
It is necessary to take into account the dip angle effects on accurate estimation of hydrogeological parameters in the sloping confined aquifer. To explore how the dip angle influences the test response, a new slug test model is developed in this study by using theoretical and filed data analysis. For test well, it is found that when the aquifer hydraulic conductivity is relatively low, a larger dip angle causes a faster recovery of the non-oscillatory test response; when the aquifer hydraulic conductivity is relatively high, a larger dip angle causes an increase of amplitude of the oscillatory test response. The dip angle effect is more pronounced for a larger storage coefficient, being less sensitive to the change of transmissivity. An empirical relationship is developed for the limiting dip angle as a function of the dimensionless storage coefficient. The function can be used to predict whether the estimate of hydrogeological parameters would be influenced by the dip angle. The effect can be neglected if the dip angle is less than the upper limit. However, it cannot be neglected if the dip angle is larger than the upper limit, otherwise, it can result in an overestimate of transmissivity and an underestimate of the storage coefficient.
2015, 40(5): 933-940.
doi: 10.3799/dqkx.2015.078
Abstract:
The chlorobenzene (CB) desorption characteristics on clay matrix at room temperature condition were investigated to examine the CB's migration under a low concentration of ethanol. To find out if the CB polluted the soil (clay) of the Chemical Factory at Wuhan, Hubei Province, China, three series of experiments were performed in this study. The first is the best leaching filtering condition. The second is the verification of the result of the best leaching condition and the third is testing the desorption kinetics of CB on clay. The results show that the solution to soil ratio (mL/g) was 25∶1 and ethanol concentration of 10% had the best leaching condition at 2 h at the room temperature. Moreover, the extraction rate of the chlorobenzene in soil was 90% under the best leaching condition. It was found that all desorption isotherm data of CB in clay could be best described with Freundlich equations. Using a low concentration of ethanol to restore the CB polluted clay is practicable. It can prevent secondary pollution while retaining the soil function as well.
The chlorobenzene (CB) desorption characteristics on clay matrix at room temperature condition were investigated to examine the CB's migration under a low concentration of ethanol. To find out if the CB polluted the soil (clay) of the Chemical Factory at Wuhan, Hubei Province, China, three series of experiments were performed in this study. The first is the best leaching filtering condition. The second is the verification of the result of the best leaching condition and the third is testing the desorption kinetics of CB on clay. The results show that the solution to soil ratio (mL/g) was 25∶1 and ethanol concentration of 10% had the best leaching condition at 2 h at the room temperature. Moreover, the extraction rate of the chlorobenzene in soil was 90% under the best leaching condition. It was found that all desorption isotherm data of CB in clay could be best described with Freundlich equations. Using a low concentration of ethanol to restore the CB polluted clay is practicable. It can prevent secondary pollution while retaining the soil function as well.
