2017 Vol. 42, No. 2
Display Method:
PDF 229KB
2017, 42(2): 161-172.
doi: 10.3799/dqkx.2017.013
Abstract:
The study on the influence of sedimentary environments on the altered clay mineralogy facilitates accurate stratigraphical correlation using volcanic ashes as marked beds. However, the relationships among the stacking ordering, illite layer contents, parent magma and environmental condition are still poorly known. A case study on altered vocalnic materials near the Permian-Triassic boundary in the Xinmin section, Guizhou province was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), geochemical analysis, and oxygen isotope analysis methods. Results show that all the four volcanic ash layers contain two phases of mixed-layered illite/smectite (I/S) with R3 structure and varied layer contents, and clay mineral aggregates were found having replaced the volcaniclastic particles or have grown on the surfaces of volcaniclastic particles. It can be inferred that clay minerals formed in sedimentary to early diagenesis periods since the materials preserve argillaceous texture when clay minerals were produced. The number of Fe3+ atoms are 0.16 and 0.17 respectively in the samples XM-5-1 and XM-5-2, and 0.14 in both samples XM-5-3 and XM-5-4, indicating that parent magmas of the latter ones were more of meta acid compared with the former two. It is indicative of more intense alteration of the latter two volcanic ash layers, together with the apparent Eu negative anomaly and less K2O contents. Oxygen isotopic composition of the volcanic ashes ranges narrowly from 17.3‰ to 18.1‰, consistent with the equilibrium value between smectite and ocean water at 25 ℃, suggesting that chemical composition of the Xinmin clay minerals is related to conditions of submarine diagenesis alteration since the clay mineralogy of different volcanic ash layer depends on its parent magma and degree of diagenesis alteration.
The study on the influence of sedimentary environments on the altered clay mineralogy facilitates accurate stratigraphical correlation using volcanic ashes as marked beds. However, the relationships among the stacking ordering, illite layer contents, parent magma and environmental condition are still poorly known. A case study on altered vocalnic materials near the Permian-Triassic boundary in the Xinmin section, Guizhou province was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), geochemical analysis, and oxygen isotope analysis methods. Results show that all the four volcanic ash layers contain two phases of mixed-layered illite/smectite (I/S) with R3 structure and varied layer contents, and clay mineral aggregates were found having replaced the volcaniclastic particles or have grown on the surfaces of volcaniclastic particles. It can be inferred that clay minerals formed in sedimentary to early diagenesis periods since the materials preserve argillaceous texture when clay minerals were produced. The number of Fe3+ atoms are 0.16 and 0.17 respectively in the samples XM-5-1 and XM-5-2, and 0.14 in both samples XM-5-3 and XM-5-4, indicating that parent magmas of the latter ones were more of meta acid compared with the former two. It is indicative of more intense alteration of the latter two volcanic ash layers, together with the apparent Eu negative anomaly and less K2O contents. Oxygen isotopic composition of the volcanic ashes ranges narrowly from 17.3‰ to 18.1‰, consistent with the equilibrium value between smectite and ocean water at 25 ℃, suggesting that chemical composition of the Xinmin clay minerals is related to conditions of submarine diagenesis alteration since the clay mineralogy of different volcanic ash layer depends on its parent magma and degree of diagenesis alteration.
2017, 42(2): 173-190.
doi: 10.3799/dqkx.2017.014
Abstract:
The fine chronological constraints and the determination of tectonic setting of the Early Neoproterozoic magmatic rocks in the Pingshui area are important breakthroughs for the Neoproterozoic evolution mechanism in South China. This paper presents a synthesis of zircon U-Pb geochronological, whole rock elementaland Sr-Nd isotopic geochemistry study on the Taohong diorite from Pingshui region along the Eastern Jiangnan Orogen. Two representative samples yielded weighed mean 206Pb/238U ages of 913±2 Ma and 898±2 Ma, respectively, representing the crystallization ages of the dioritic pluton. In the case of loss on ignition free, the dioritic samples are characterized by SiO2 of 58.33%-63.36%, Al2O3 of 15.76%-17.42%, Na2O of 2.62%-3.12%, K2O of 0.53%-1.53% and A/CNK of 0.84-0.92, classified as low to medium-K metaluminous series. Their chondrite-normalized rare earth elements (REEs) patterns exhibit a right-sloping tendency with more enriched light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs) ((La/Yb)N=4.65-6.09) and slightly Eu abnormality (δEu=0.82-1.01). On the primitive mantle-normalized multi-elements patterns, these samples have strong enrichment in large iron lithophile elements (LILEs) (Rb, Ba, K and Sr) and depletion in high field-strength elements (HFSEs) with marked negative Nb, Ta and Ti, similar to those of typical arc magmatites. The samples show low (87Sr/86Sr)i of 0.703 060-0.703 076 ratio and high positive εNd(t) of +6.58 to +6.76 values. It is inferred that the formation of the rocks is attributed to the partial melting of the mantle wedge peridotite, which was modified by the subducted slab-derived fluid and melt during the southeastwards subduction of ancient oceanic crust between the Yangtze and Cathaysia Block. In conjunction with previous studies, it is proposed that the Shuangxiwu Group along Eastern Jiangnan Orogen resulted from suturing of the Yangtze and Cathaysia Block, and is not related to Grenvillian Orogen in petrogenesis.
The fine chronological constraints and the determination of tectonic setting of the Early Neoproterozoic magmatic rocks in the Pingshui area are important breakthroughs for the Neoproterozoic evolution mechanism in South China. This paper presents a synthesis of zircon U-Pb geochronological, whole rock elementaland Sr-Nd isotopic geochemistry study on the Taohong diorite from Pingshui region along the Eastern Jiangnan Orogen. Two representative samples yielded weighed mean 206Pb/238U ages of 913±2 Ma and 898±2 Ma, respectively, representing the crystallization ages of the dioritic pluton. In the case of loss on ignition free, the dioritic samples are characterized by SiO2 of 58.33%-63.36%, Al2O3 of 15.76%-17.42%, Na2O of 2.62%-3.12%, K2O of 0.53%-1.53% and A/CNK of 0.84-0.92, classified as low to medium-K metaluminous series. Their chondrite-normalized rare earth elements (REEs) patterns exhibit a right-sloping tendency with more enriched light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs) ((La/Yb)N=4.65-6.09) and slightly Eu abnormality (δEu=0.82-1.01). On the primitive mantle-normalized multi-elements patterns, these samples have strong enrichment in large iron lithophile elements (LILEs) (Rb, Ba, K and Sr) and depletion in high field-strength elements (HFSEs) with marked negative Nb, Ta and Ti, similar to those of typical arc magmatites. The samples show low (87Sr/86Sr)i of 0.703 060-0.703 076 ratio and high positive εNd(t) of +6.58 to +6.76 values. It is inferred that the formation of the rocks is attributed to the partial melting of the mantle wedge peridotite, which was modified by the subducted slab-derived fluid and melt during the southeastwards subduction of ancient oceanic crust between the Yangtze and Cathaysia Block. In conjunction with previous studies, it is proposed that the Shuangxiwu Group along Eastern Jiangnan Orogen resulted from suturing of the Yangtze and Cathaysia Block, and is not related to Grenvillian Orogen in petrogenesis.
2017, 42(2): 191-206.
doi: 10.3799/dqkx.2017.015
Abstract:
The multiple Mesozoic and Mesozoic igneous rocks in the well drilling in the North Yellow Sea basin confirm the multi-stage tectonic activity experienced by the Mesozoic has been accompanied by the development of multi-stage igneous rocks. A petrology study is carried out on magnetic susceptibility, density, main elements, ICP-MS trace elements and rare earth elements of the volcanics of X1 and X2 well of North Yellow Sea basin in this paper. Results show that tephrite and trachy basalt of Pre-Mesozoic in X1 well of North Yellow Sea basin is weaker magnetic ((131.5-138.5)(4π×10-6). Dacite in the lower part of X2 and dacite containing breccia in the upper part is weak magnetic ((27.5-82.5)(4π×10-6)) and rocks of medium density. The tephrite of X1 belongs to the high potassium calcalkaline series and the trachy basalt is the calcalkaline series. These two kinds of volcanics are characterized by higher ΣREE (108.11×10-6 to 208.02×10-6), enriched LREE (LREE/HREE=4.04-6.91) and weak anomalies with δEu (0.99-1.18). And the two layers of volcanic in X2 are both characterized by lower ΣREE, enriched LREE and weak anomalies with δEu. The rare elements are characterized by enriched Ba, U and Sr and depleted Nb and Ta. The ratios of (Rb/Sr)N, (La/Nb)N and (Ba/Nb)N are all higher than those of the original mantle, which indicates that the magma derived from the crust melting. It is concluded that the volcanics of North Yellow Sea basin in Pre-Mesozoic formed in the plate tectonic setting the ones in Mesozoic probably formed in the back-arc extension of plate subduction.
The multiple Mesozoic and Mesozoic igneous rocks in the well drilling in the North Yellow Sea basin confirm the multi-stage tectonic activity experienced by the Mesozoic has been accompanied by the development of multi-stage igneous rocks. A petrology study is carried out on magnetic susceptibility, density, main elements, ICP-MS trace elements and rare earth elements of the volcanics of X1 and X2 well of North Yellow Sea basin in this paper. Results show that tephrite and trachy basalt of Pre-Mesozoic in X1 well of North Yellow Sea basin is weaker magnetic ((131.5-138.5)(4π×10-6). Dacite in the lower part of X2 and dacite containing breccia in the upper part is weak magnetic ((27.5-82.5)(4π×10-6)) and rocks of medium density. The tephrite of X1 belongs to the high potassium calcalkaline series and the trachy basalt is the calcalkaline series. These two kinds of volcanics are characterized by higher ΣREE (108.11×10-6 to 208.02×10-6), enriched LREE (LREE/HREE=4.04-6.91) and weak anomalies with δEu (0.99-1.18). And the two layers of volcanic in X2 are both characterized by lower ΣREE, enriched LREE and weak anomalies with δEu. The rare elements are characterized by enriched Ba, U and Sr and depleted Nb and Ta. The ratios of (Rb/Sr)N, (La/Nb)N and (Ba/Nb)N are all higher than those of the original mantle, which indicates that the magma derived from the crust melting. It is concluded that the volcanics of North Yellow Sea basin in Pre-Mesozoic formed in the plate tectonic setting the ones in Mesozoic probably formed in the back-arc extension of plate subduction.
2017, 42(2): 207-222.
doi: 10.3799/dqkx.2017.016
Abstract:
The source of the Mid-Late Triassic adakitic rocks remains controversial in the eastern Hebei-western Liaoning Province in recent years, and there is a lack of petrogenesis studies on the Baizhangzi granitic rocks within this NE-striking uplift. Zircon U-Pb and Hf isotope data, whole rock major and trace element and Sr, Nd isotope data are presented for the Baizhangzi graniticintrusive rocks in this paper.Zircon U-Pb datingyields a weighted mean age of 233±3 Ma. The granitic rocks are featured with the high contentof MgO and Mg#, and low content of Cr, Co, Ni. The granitic intrusive rocks are enriched in large-ion lithophile elements, depleted in high-field-strength elements (e.g. Nb, Ta, Ti, P), and display strong positive Pb, Th anomalies and negative Nb, Ta, Ti, P anomalies. Rare earth elements (REE) display right-dipping chondrite-normalized REE patterns, indicating significant fractionation between light REE and heavy REE. The initial 87Sr/86Sr ratios and εNd(t) values vary from 0.704 45 to 0.705 24 and -7.3 to -1.7, respectively. The εHf(t) values of zircons vary from -13.4 to -5.9. It is concluded that the Baizhangzi granitic rocks were derived from partial melting of mafic lower continental crust of the NCC. The high Sr/Y, low Y and negative Nb-Ta anomalies are intrinsic characteristics of the lower continental crust. The Baizhangzi granitic rocks have decoupled Nb-Ta characteristics similar to the Archean-Paleoproterozoic TTG suites, which indicates that the Archean-Paleoproterozoic TTG rocks might have been involved in the magma source. The nonradiogenic Sr, scattered Nd-Hf isotopic compositions and low compatible trace element contents also suggest that the granitic rocks were derived from modified lower continental crust. The mafic lower continental crust has experienced modification by basaltic underplating during the Early Mesozoic, which led to formation of some juvenile crust materials. At the same time, melts produced by melting of the lower continental crust induced by basaltic underplating experienced fractional crystallization of plagioclase to some extent and intruded into the supercrust.
The source of the Mid-Late Triassic adakitic rocks remains controversial in the eastern Hebei-western Liaoning Province in recent years, and there is a lack of petrogenesis studies on the Baizhangzi granitic rocks within this NE-striking uplift. Zircon U-Pb and Hf isotope data, whole rock major and trace element and Sr, Nd isotope data are presented for the Baizhangzi graniticintrusive rocks in this paper.Zircon U-Pb datingyields a weighted mean age of 233±3 Ma. The granitic rocks are featured with the high contentof MgO and Mg#, and low content of Cr, Co, Ni. The granitic intrusive rocks are enriched in large-ion lithophile elements, depleted in high-field-strength elements (e.g. Nb, Ta, Ti, P), and display strong positive Pb, Th anomalies and negative Nb, Ta, Ti, P anomalies. Rare earth elements (REE) display right-dipping chondrite-normalized REE patterns, indicating significant fractionation between light REE and heavy REE. The initial 87Sr/86Sr ratios and εNd(t) values vary from 0.704 45 to 0.705 24 and -7.3 to -1.7, respectively. The εHf(t) values of zircons vary from -13.4 to -5.9. It is concluded that the Baizhangzi granitic rocks were derived from partial melting of mafic lower continental crust of the NCC. The high Sr/Y, low Y and negative Nb-Ta anomalies are intrinsic characteristics of the lower continental crust. The Baizhangzi granitic rocks have decoupled Nb-Ta characteristics similar to the Archean-Paleoproterozoic TTG suites, which indicates that the Archean-Paleoproterozoic TTG rocks might have been involved in the magma source. The nonradiogenic Sr, scattered Nd-Hf isotopic compositions and low compatible trace element contents also suggest that the granitic rocks were derived from modified lower continental crust. The mafic lower continental crust has experienced modification by basaltic underplating during the Early Mesozoic, which led to formation of some juvenile crust materials. At the same time, melts produced by melting of the lower continental crust induced by basaltic underplating experienced fractional crystallization of plagioclase to some extent and intruded into the supercrust.
2017, 42(2): 223-239.
doi: 10.3799/dqkx.2017.017
Abstract:
In spite of much research focused on thermal evolution history-tectonic activity of the Ailao Shan-Red River fault zone (ASRR) during Late Oligocene-Early Miocene, its thermal reconstruction is limited. Moreover, the related thermal disturbance factors are often ignored and the measured ages (cooling ages) are generally irrationally recognized as the timing of tectonic events in the existing studies. Combined with the pressure-temperature-depth paths (P-T-D) and paleogeomorphology reconstruction, the T-t paths of the ASRR are constructed to explore the genesis of T-t paths and the evolutionary characteristics of the fault zone systematically. The cooling process of the metamorphic massif can be divided into two phases: for Day Nui Con Voi is 32-30 Ma and 26-24 Ma, while for the Ailao Shan is 32-22 Ma and 22-20 Ma. In the first phase, the rapid cooling may have been caused by the strata denudation or tectonic denudation, followed by the more rapid cooling of the second phase, in which the intensity weakening of the fault has been more dominant, compared with the denudation and other factors. With the clockwise rotation and extrusion of the Indochina terrane relative to the South China block, the sinistral tensile transformation zone in the south propagated northwards. Additionally, the spatial differences in the tectonic activities induced the varied cooling processes for the southeastern and northwestern part. In phase Ⅰ, the tectonic uplift in the southeastern part presented earlier and stronger than the northwestern one, with the northwestward propagation and weakening of the sinistral tensile transformation. So the cooling process of the southeastern part was much earlier and more rapid, compared with the northwestern process. In phase Ⅱ, the activity of the ASRR which acted as the boundary of the plate extrusion became weak northwards, along with a new period of Tibet uplift in early Miocene. Then the change stimulated another rapid cooling process, showing the northwestward decreasing trend.
In spite of much research focused on thermal evolution history-tectonic activity of the Ailao Shan-Red River fault zone (ASRR) during Late Oligocene-Early Miocene, its thermal reconstruction is limited. Moreover, the related thermal disturbance factors are often ignored and the measured ages (cooling ages) are generally irrationally recognized as the timing of tectonic events in the existing studies. Combined with the pressure-temperature-depth paths (P-T-D) and paleogeomorphology reconstruction, the T-t paths of the ASRR are constructed to explore the genesis of T-t paths and the evolutionary characteristics of the fault zone systematically. The cooling process of the metamorphic massif can be divided into two phases: for Day Nui Con Voi is 32-30 Ma and 26-24 Ma, while for the Ailao Shan is 32-22 Ma and 22-20 Ma. In the first phase, the rapid cooling may have been caused by the strata denudation or tectonic denudation, followed by the more rapid cooling of the second phase, in which the intensity weakening of the fault has been more dominant, compared with the denudation and other factors. With the clockwise rotation and extrusion of the Indochina terrane relative to the South China block, the sinistral tensile transformation zone in the south propagated northwards. Additionally, the spatial differences in the tectonic activities induced the varied cooling processes for the southeastern and northwestern part. In phase Ⅰ, the tectonic uplift in the southeastern part presented earlier and stronger than the northwestern one, with the northwestward propagation and weakening of the sinistral tensile transformation. So the cooling process of the southeastern part was much earlier and more rapid, compared with the northwestern process. In phase Ⅱ, the activity of the ASRR which acted as the boundary of the plate extrusion became weak northwards, along with a new period of Tibet uplift in early Miocene. Then the change stimulated another rapid cooling process, showing the northwestward decreasing trend.
2017, 42(2): 240-257.
doi: 10.3799/dqkx.2017.018
Abstract:
The Nima basin in the Bangong suture zone documented the geological information of the evolution of Tibetan Plateau, which helps to restore the tecto-paleogeography and provide the sedimentological evidences of uplift of the Plateau. However, the study of the NiuBao Formation of Paleogene strata in the north depression of the basin is still relatively weak. The provenance and tectonic evolution of Niubao Formation were analyzed by the methods of petrology, zircon U-Pb chronology and heavy minerals in this study. It is found that the north of Nima basin evolved into a depression controlled by collision and extrusion accompanied by the shortening of the crust and the activation of tectonic movements from Early Cretaceous to Paleogene, the north of Nima basin evolved into an depocenter controlled by tectonism. The Niubao Formation in the north depression is a bidirectional source. The source of north sediments primarily originated from the granites and acid magmatic rocks dominated by Early Cretaceous granitic rocks, while the source of south sediments were primarily sedimentary rocks, and basic or ultra-basic rocks. The detrital zircons of U-Pb ages have 5 peaks, namely 105-134 Ma, 500-550 Ma, 700-900 Ma, 1 700-2 100 Ma and near 2 500 Ma, and 105-134 Ma is believed to be responses to the subduction of the Bangong-Nujiang oceanic crust and volcanic activity in surrounding terrances. It is further confirmed that the Niubao Formation is derived from the north and south terranes of the northern depression. Palaeogeographic characteristics are determined by the extrusion and thrusting deformation. Sedimentary processes and sources are closely related to the uplift, erosion and magmatic activities in the Nima basin.
The Nima basin in the Bangong suture zone documented the geological information of the evolution of Tibetan Plateau, which helps to restore the tecto-paleogeography and provide the sedimentological evidences of uplift of the Plateau. However, the study of the NiuBao Formation of Paleogene strata in the north depression of the basin is still relatively weak. The provenance and tectonic evolution of Niubao Formation were analyzed by the methods of petrology, zircon U-Pb chronology and heavy minerals in this study. It is found that the north of Nima basin evolved into a depression controlled by collision and extrusion accompanied by the shortening of the crust and the activation of tectonic movements from Early Cretaceous to Paleogene, the north of Nima basin evolved into an depocenter controlled by tectonism. The Niubao Formation in the north depression is a bidirectional source. The source of north sediments primarily originated from the granites and acid magmatic rocks dominated by Early Cretaceous granitic rocks, while the source of south sediments were primarily sedimentary rocks, and basic or ultra-basic rocks. The detrital zircons of U-Pb ages have 5 peaks, namely 105-134 Ma, 500-550 Ma, 700-900 Ma, 1 700-2 100 Ma and near 2 500 Ma, and 105-134 Ma is believed to be responses to the subduction of the Bangong-Nujiang oceanic crust and volcanic activity in surrounding terrances. It is further confirmed that the Niubao Formation is derived from the north and south terranes of the northern depression. Palaeogeographic characteristics are determined by the extrusion and thrusting deformation. Sedimentary processes and sources are closely related to the uplift, erosion and magmatic activities in the Nima basin.
2017, 42(2): 258-272.
doi: 10.3799/dqkx.2017.019
Abstract:
The Lower Cretaceous source rocks in Anan sag of Erlian basin develop a set of lacustrine fine-grained dolomitic rocks, composed of dolomitic mudstone, dolomitic tuffite, and dolomitic sandstone, which are rich in tight oil. But its petrological characteristics and origin of dolomite are still unclear.Analysis of core observation, thin section, Scanning Electron Microscope (SEM), and geochemical data show the dolomitic rocks mainly include: (1) The subhedral, micritic-powder crystalline dolomite distributing in laminated and star structure dolomitic mudstone and dolomitic tuffite; (2) The euhedral, powder-fine crystalline dolomite distributed massive dolomitic tuffite and dolomitic sandstone. Their mechanisms of dolomitization are different: (1) The subhedral, micritic-powder crystalline dolomite with higher δ13CPDB values (av. 5.4‰), higher δ18CPDB (av. -13‰), and lower fluid inclusion homogenization temperature (50-75 ℃), is dominated by early diagenetic dolomitization associated with methanogenesis. The source of Mg2+ is mainly from alteration of tuffaceous materials. (2) The euhedral, powder-fine crystalline dolomite is characteristic of bigger and finer crystals, lower δ13CPDB values (0.2‰-0.7‰), lower δ18OPDB (av. -19.4‰), and higher fluid inclusion homogenization temperature (about 119 ℃). It is dominated by burial dolomitizationand affected by the controls of methanogenesis anddegradation of organic matter.The source of Mg2+ is mainly from transformation of clay minerals and deep fluid.
The Lower Cretaceous source rocks in Anan sag of Erlian basin develop a set of lacustrine fine-grained dolomitic rocks, composed of dolomitic mudstone, dolomitic tuffite, and dolomitic sandstone, which are rich in tight oil. But its petrological characteristics and origin of dolomite are still unclear.Analysis of core observation, thin section, Scanning Electron Microscope (SEM), and geochemical data show the dolomitic rocks mainly include: (1) The subhedral, micritic-powder crystalline dolomite distributing in laminated and star structure dolomitic mudstone and dolomitic tuffite; (2) The euhedral, powder-fine crystalline dolomite distributed massive dolomitic tuffite and dolomitic sandstone. Their mechanisms of dolomitization are different: (1) The subhedral, micritic-powder crystalline dolomite with higher δ13CPDB values (av. 5.4‰), higher δ18CPDB (av. -13‰), and lower fluid inclusion homogenization temperature (50-75 ℃), is dominated by early diagenetic dolomitization associated with methanogenesis. The source of Mg2+ is mainly from alteration of tuffaceous materials. (2) The euhedral, powder-fine crystalline dolomite is characteristic of bigger and finer crystals, lower δ13CPDB values (0.2‰-0.7‰), lower δ18OPDB (av. -19.4‰), and higher fluid inclusion homogenization temperature (about 119 ℃). It is dominated by burial dolomitizationand affected by the controls of methanogenesis anddegradation of organic matter.The source of Mg2+ is mainly from transformation of clay minerals and deep fluid.
2017, 42(2): 273-285.
doi: 10.3799/dqkx.2017.020
Abstract:
As an important reservoir type in deepwater environment, turbidite channel and studies on its architecture are important t for efficient development of an oil field. In order to clearly understand the reservoir architecture of M oilfield, a semi-quantitative to quantitative study on turbidite channel depositional architecture patterns was conducted by analyses of seismic stratigraphy, seismic sedimentology and sedimentary petrography of the middle to lower slope at M oilfield, West Africa, and the sedimentary evolution was analyzed on the basis of core, outcrop, logging and seismic data. Results show that in the study area, stages 3 to 5 are single channel, complex channel, and channel system respectively. Single channel sinuosity is negatively correlated with slope, and internal grain size becomes increasingly fine and thickness decreases from bottom to top and from the axis to the edge. The migration type of a single channel within one complex channel can be divided into lateral migration and along paleocurrent migration horizontally, and lateral stack, echelon stack, and swing stack in section view. O73 channel system comprises of a semi-confining type and a non-confining type. Horizontally, there is semi-confining channel system close to the source while non-confining one far away from it. In terms of vertical evolution, it is most typically displayed within non-confining channel system, which shows decreasing undercutting and more lateral accretion, larger sinuosity and smaller channel sand body from the bottom up. Comprehensive analyses indicate that controlling factors of M oilfield turbidite sedimentary model and its evolution are paleotography slope and source supply.
As an important reservoir type in deepwater environment, turbidite channel and studies on its architecture are important t for efficient development of an oil field. In order to clearly understand the reservoir architecture of M oilfield, a semi-quantitative to quantitative study on turbidite channel depositional architecture patterns was conducted by analyses of seismic stratigraphy, seismic sedimentology and sedimentary petrography of the middle to lower slope at M oilfield, West Africa, and the sedimentary evolution was analyzed on the basis of core, outcrop, logging and seismic data. Results show that in the study area, stages 3 to 5 are single channel, complex channel, and channel system respectively. Single channel sinuosity is negatively correlated with slope, and internal grain size becomes increasingly fine and thickness decreases from bottom to top and from the axis to the edge. The migration type of a single channel within one complex channel can be divided into lateral migration and along paleocurrent migration horizontally, and lateral stack, echelon stack, and swing stack in section view. O73 channel system comprises of a semi-confining type and a non-confining type. Horizontally, there is semi-confining channel system close to the source while non-confining one far away from it. In terms of vertical evolution, it is most typically displayed within non-confining channel system, which shows decreasing undercutting and more lateral accretion, larger sinuosity and smaller channel sand body from the bottom up. Comprehensive analyses indicate that controlling factors of M oilfield turbidite sedimentary model and its evolution are paleotography slope and source supply.
2017, 42(2): 286-297.
doi: 10.3799/dqkx.2017.021
Abstract:
Rehai, located in the Tengchong volcanic region of Yunnan Province, is a typical magma-heated hydrothermal system in mainland China. Taking Rehai as the study area, the thioarsenic species in hot springs were quantitatively determined for the first time and their geochemical geneses were identified. The sulfide-rich geothermal water samples were collected and immediately treated via rapid freezing technique in-situ and then detertnine the arsenic species in the lab, which is superior to the traditional methods of pretreatment and measurement of aqueous arsenic. The traditional acidification treatment of arsenic-bearing, sulfide-rich water sample inevitably results in the precipitation of tri-thioarsenate as the form of amorphous S-As compounds. Furthermore, the common use of anion-exchange column is not capable of fully collecting thioarsenic species and separating them from arsenate in-situ. Under the control of magmatic fluid input and intense fluid-rock interactions at high reservoir temperatures, the neutral to slightly alkaline hot springs discharged from the Rehai hydrothermal system are rich in sulfide and arsenic, facilitating the formation of thioarsenic species. Mono-thioarsenate, di-thioarsenate and tri-thioarsenate were detected in the Rehai hot springs with ratios to total arsenic up to 26.7%, 43.3% and 33.7%, respectively. In two sub-hydrothermal areas of Rehai, i.e. the Liuhuangtang area and the Zaotanghe area, the hot springs are distributed along the main N-S stretching faults and the secondary E-W stretching faults, respectively, and therefore the geothermal waters went through different cooling processes (adiabatic cooling and mixing with shallow cold groundwaters, respectively) prior to their discharge to the surface. Thus the hot springs from Liuhuangtang have relatively higher concentrations of sulfide and arsenic as well as various thioarsenic species.
Rehai, located in the Tengchong volcanic region of Yunnan Province, is a typical magma-heated hydrothermal system in mainland China. Taking Rehai as the study area, the thioarsenic species in hot springs were quantitatively determined for the first time and their geochemical geneses were identified. The sulfide-rich geothermal water samples were collected and immediately treated via rapid freezing technique in-situ and then detertnine the arsenic species in the lab, which is superior to the traditional methods of pretreatment and measurement of aqueous arsenic. The traditional acidification treatment of arsenic-bearing, sulfide-rich water sample inevitably results in the precipitation of tri-thioarsenate as the form of amorphous S-As compounds. Furthermore, the common use of anion-exchange column is not capable of fully collecting thioarsenic species and separating them from arsenate in-situ. Under the control of magmatic fluid input and intense fluid-rock interactions at high reservoir temperatures, the neutral to slightly alkaline hot springs discharged from the Rehai hydrothermal system are rich in sulfide and arsenic, facilitating the formation of thioarsenic species. Mono-thioarsenate, di-thioarsenate and tri-thioarsenate were detected in the Rehai hot springs with ratios to total arsenic up to 26.7%, 43.3% and 33.7%, respectively. In two sub-hydrothermal areas of Rehai, i.e. the Liuhuangtang area and the Zaotanghe area, the hot springs are distributed along the main N-S stretching faults and the secondary E-W stretching faults, respectively, and therefore the geothermal waters went through different cooling processes (adiabatic cooling and mixing with shallow cold groundwaters, respectively) prior to their discharge to the surface. Thus the hot springs from Liuhuangtang have relatively higher concentrations of sulfide and arsenic as well as various thioarsenic species.
2017, 42(2): 298-306.
doi: 10.3799/dqkx.2017.022
Abstract:
Under arid and semi-arid climate, high iodine concentration in groundwater of the Datong basin, has been a serious threat to the safety of drinking water for the residents. Sediments composition and rare earth elements (REE) were studied on the 300 m core samples from iodine-affected area of the Datong basin. Results show that the groundwater system in the study area is alkalescent (pH: 7.18~9.64) partial reductive environment, and sediments show the slightly negative anomalies of Ce and Eu. The content of iodine in sediments is 0~1.78×10-6. The content of ΣREE are high and the ΣLREE/ΣHREE ratios are 2.79~4.14, which means samples are enriched in LREE and depleted in HREE. There is a negative relationship between the concentrations of ΣREE and iodine. Although the reductive dissolution of the iron oxide / hydroxide mineral can result in the release of them, strong absorption of iodine by the low crystallinity minerals produced by sedimentary organic matter makes the iodine content in sediments higher. In slightly weak alkaline environment, the process of REE re-adsorption might attributed to the enrichment of LREE in sediments. The relationship between iodine contents and redox sensitive components (TOC, U, V and [Eu]N show that the redox conditions and organic matter content in groundwater system are important factors that affect the concentration of iodine.
Under arid and semi-arid climate, high iodine concentration in groundwater of the Datong basin, has been a serious threat to the safety of drinking water for the residents. Sediments composition and rare earth elements (REE) were studied on the 300 m core samples from iodine-affected area of the Datong basin. Results show that the groundwater system in the study area is alkalescent (pH: 7.18~9.64) partial reductive environment, and sediments show the slightly negative anomalies of Ce and Eu. The content of iodine in sediments is 0~1.78×10-6. The content of ΣREE are high and the ΣLREE/ΣHREE ratios are 2.79~4.14, which means samples are enriched in LREE and depleted in HREE. There is a negative relationship between the concentrations of ΣREE and iodine. Although the reductive dissolution of the iron oxide / hydroxide mineral can result in the release of them, strong absorption of iodine by the low crystallinity minerals produced by sedimentary organic matter makes the iodine content in sediments higher. In slightly weak alkaline environment, the process of REE re-adsorption might attributed to the enrichment of LREE in sediments. The relationship between iodine contents and redox sensitive components (TOC, U, V and [Eu]N show that the redox conditions and organic matter content in groundwater system are important factors that affect the concentration of iodine.
2017, 42(2): 307-314.
doi: 10.3799/dqkx.2017.023
Abstract:
Characterization of the spatial distributions of aquifer heterogeneity is the premise of accurately simulating groundwater flow and contaminant migration. Based on the laboratory sandbox test of a synthetic heterogeneous aquifer, hydraulic tomography and kriging are used to characterize hydraulic conductivity (K) of the heterogeneous aquifer in this study. The results show that:(1) Compared with kriging, hydraulic tomography can get higher precision to characterize the K field and predict groundwater flow process of the heterogeneous aquifer; (2) in the pumping tests of hydraulic tomography, increasing the number of pumping tests can effectively improve accuracy of inversion of hydraulic tomography, however, after reaching a certain degree, increasing the number of pumping test can not significantly improve the effect of the parameter inversion. Subsequently, it is necessary to further research the appropriate number of pumping tests of hydraulic tomography for further optimizing pumping wells.
Characterization of the spatial distributions of aquifer heterogeneity is the premise of accurately simulating groundwater flow and contaminant migration. Based on the laboratory sandbox test of a synthetic heterogeneous aquifer, hydraulic tomography and kriging are used to characterize hydraulic conductivity (K) of the heterogeneous aquifer in this study. The results show that:(1) Compared with kriging, hydraulic tomography can get higher precision to characterize the K field and predict groundwater flow process of the heterogeneous aquifer; (2) in the pumping tests of hydraulic tomography, increasing the number of pumping tests can effectively improve accuracy of inversion of hydraulic tomography, however, after reaching a certain degree, increasing the number of pumping test can not significantly improve the effect of the parameter inversion. Subsequently, it is necessary to further research the appropriate number of pumping tests of hydraulic tomography for further optimizing pumping wells.
