According to the data of the mineral assemblages, the sediment layers with authigenic glauconite were found in the X<sub>1</sub> core collected from the northeast of the Beibu Gulf. Pliocene sediment layer...According to the data of the mineral assemblages, the sediment layers with authigenic glauconite were found in the X<sub>1</sub> core collected from the northeast of the Beibu Gulf. Pliocene sediment layer containing a lot of foraminifera shows a shallow sea facies. Its thickness is larger than 30 m and is located at the depth below 59 m of the core.展开更多
This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists o...This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.展开更多
Celadonite and glauconite are comparable in terms of physical,chemical and mineralogical characteristics.Formation of both these minerals requires slightly oxygen-depleted conditions in a semiconfined micro-environmen...Celadonite and glauconite are comparable in terms of physical,chemical and mineralogical characteristics.Formation of both these minerals requires slightly oxygen-depleted conditions in a semiconfined micro-environment,facilitating the uptake of Fe into the structure.Although glauconite is ubiquitous in marine deposits,celadonite forms in both marine and non-marine environments,more commonly by altering intermediate to mafic rocks.A review of data across the geological column shows that both these minerals are more common in the Mesozoic and Cenozoic,which may be related to extensive volcanism.The composition of celadonite and glauconite is highly variable and is controlled by the availability of cations within the pore water micro-environment.The major element composition of celadonite overlaps with that of evolved to highly evolved glauconite to a large extent.Existing data and representative samples of celadonite and glauconite reveal subtle differences in X-ray diffraction parameters and Fourier transform infrared(FTIR)spectra.Celadonite shows sharper basal and hkl reflections than glauconite.It characteristically exhibits distinct 111-021,003-022,023 and 130-131,and 060 reflections at less than 1.51A,indicating a betterordered crystallographic structure than glauconite.The FTIR spectra of celadonite and glauconite show similar absorption bands although Si-O bending,Si-O stretching and OH-stretching bands are sharper and well resolved in celadonite than that of glauconite.For palaeoenvironmental interpretations,it is,therefore,necessary to examine the subtle differences in X-ray diffraction parameters and FTIR spectra to confirm the identification of these two minerals.The composition of celadonite relates closely to the host rock and depositional environment.The celadonite associated with mafic rock shows relatively high Fe,Mg and low Al contents.In contrast,those associated with felsic to intermediate composition rocks show slightly higher contents of Al and lower content of Fe,Mg.The mineral chemistry of celadonite varies from marine to continental settings.Marine celadonite contains higher Fe,Mg and lesser Al than their non-marine counterpart.Celadonite with relatively higher Al may show slightly lower interlayer K than Fe and Mg-rich celadonite for charge balancing.展开更多
Drill cuttings,though rarely used,are crucial subsurface samples to understand petrographic properties affecting reservoir quality.Unlike core material,cuttings are continuously available along the wellbore and can be...Drill cuttings,though rarely used,are crucial subsurface samples to understand petrographic properties affecting reservoir quality.Unlike core material,cuttings are continuously available along the wellbore and can be used during drilling to monitor progress.Therefore,cuttings may allow a semi-quantitative,statistical calibration of rock properties from the subsurface,but they are often underutilized.Although fracture and vein orientations cannot be reconstructed from drill cuttings,the presence of veins and their internal textures(open,partially sealed or sealed) in specific formation sections and depths can be identified and analyzed using e.g.,transmitted light microscopy and cathodoluminescence to supplement characterization at the well site and subsequently assess production behavior.Borehole gamma ray logs in combination with handheld portable X-ray fluorescence(pXRF) analyses on cleaned and dried drill cuttings can be used to further improve the depth accuracy of the cutting samples and to geochemically fingerprint the samples,based on the Si/Al ratio,as a proxy for sandstone-rich and mudrock-rich sections of the well.In this study,eighty-three sandstone cutting samples from two wells,covering~400 m of stratigraphy targeting the Paleocene-Eocene Greifenstein Fm.equivalent(Glauconite Sandstone,GLS) in the Vienna Basin(Austria),were studied.They also cover parts of three different reservoir sections(1.to 3.GLS).The Flysch play in the Vienna Basin hosts several sand stone-mud rock interbeds and is composed of several nappes,forming complex reservoir compartments.The glauconite contents vary between different sections of the GLS,where the highest is observed in the 3.GLS.The sandstones are predominantly cemented by ferroan calcite,resulting in low optical porosity(<5 %)in both wells,with only individually elevated porosity,related to partially dissolved K-feldspar grains.A paragenetic sequence solely based on cuttings further highlights that reservoir quality in the studied section is independent of sandstone compaction,but is related to lower optical porosity in finer-grained sa ndstones and higher carbonate vein cement conte nts.Furthermo re,productive intervals are related to lower Fe+Mg contents.The understanding of reservoir properties,diagenesis,and their influence on fluid flow is crucial for successful exploration and reduction of uncertainty in reservoir production and development.The diagenetic variations from cuttings and the geochemical fingerprint by pXRF are linked to reservoir quality and production performance of individual well perforations.This approach can provide additional information on reservoir quality where core material is unavailable.展开更多
Small shelly fossils(SSFs)have long been recognized as important to the studies of both metazoan evolution and the onset of biomineralization during the Cambrian radiation.The marked decline in the occurrence,diversit...Small shelly fossils(SSFs)have long been recognized as important to the studies of both metazoan evolution and the onset of biomineralization during the Cambrian radiation.The marked decline in the occurrence,diversity and abundance of SSFs in the middle to late Cambrian,when compared with the early Cambrian,has often been regarded as a result of the closure of a phosphatization window.Despite this,there have been numerous and consistent reports of SSFs from the middle Cambrian and younger deposits.To identify possible factors influencing SSF preservation,five microfacies including bioclastic limestone,flat-pebble conglomerates with bioclasts,hummocky cross-stratified grainstone with bioclasts,bioclastic grainstone in hardgrounds and glauconite bioclastic wackstone-packstone,from Cambrian Series 2 to Miaolingian in North China are compared to assess how differences in lithology impact the preservation potential of SSFs.Our results,based on 35,161 SSF specimens from deposits across six sections,suggest that there are still abundant and diverse SSFs in the middle Cambrian of North China preserved in ways not exclusively reliant on the presence of phosphate and that SSF preservation can be linked to the differences in microfacies in the early to middle Cambrian of North China.展开更多
Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow in...Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow into the ocean, especially in deltaic environments with high hydrodynamic conditions. At the same time, sandstone sequences with grain-coating chlorites also tend to have relatively high glauconite and pyrite content. EPMA composition analysis shows that glauconites with ‘‘high Al and low Fe’’ content indicate slightly to semi-saline marine environments with weak alkaline and weakly reducing conditions. By analyzing the chlorite-containing sandstone bodies of the southern Sichuan Xujiahe Formation, this study found that chlorite was mainly distributed in sedimentary microfacies, including underwater distributary channels, distributary channels, shallow lake sandstone dams, and mouth bars. Chlorite had a tendency to form in the upper parts of sandstone bodies with signs of increased base level, representing the influence of marine（lacustrine）transgression. This is believed to be influenced by megamonsoons in the Middle and Upper Yangtze Region during the Late Triassic Epoch. During periods of abundant precipitation, river discharges increased and more Fe particulates flowed into the ocean（lake）. In the meantime,increases or decreases in lake level were only affected byprecipitation for short periods of time. The sedimentary environment shifted from weakly oxidizing to weak alkaline, weakly reducing conditions as sea level increased, and Fe-rich minerals as authigenic chlorite and glauconite began to form and deposit.展开更多
Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and ...Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the Mn O content in siderite decreases, but FeOand Mg O content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains,which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The KO content of glauconite is low or absent, indicating its short formation time.展开更多
The objective of this work is to study the efficiency of some surface modified phyllosilicate minerals （bentonite and glauconite） in the removal of dyes from textile waste water. It is found that complete dye remova...The objective of this work is to study the efficiency of some surface modified phyllosilicate minerals （bentonite and glauconite） in the removal of dyes from textile waste water. It is found that complete dye removal was achieved by using 10-25g modified glauconite from solutions having a dye concentration of 10-50 mg/L. Adsorption data were modeled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. Adsorption capacities and optimum adsorption isotherms were predicted by linear regression method. The analysis of experimental isotherms showed that Langmuir isotherm reasonably fit the experimental data in the studied concentration range for the adsorption of dye onto glauconite mineral surface where Freundlich isotherm fit the experimental data for the adsorption of dve onto bentonite mineral surface.展开更多
Although Paleogene warm climatic intervals have received considerable attention for atmospheric and oceanographic changes,the authigenic mineralization associated with these time spans remains overlooked.An extensive ...Although Paleogene warm climatic intervals have received considerable attention for atmospheric and oceanographic changes,the authigenic mineralization associated with these time spans remains overlooked.An extensive review of the literature reveals a close correspondence between the high abundance of glauconite and warm climatic intervals during the Paleogene period.The abundance of phosphorite,ironstone,lignite and black shale deposits reveals similar trends.Although investigated thoroughly,the origin of these authigenic deposits is never understood in the background of Paleogene warming climatic intervals.A combination of factors like warm seawater,hypoxic shelf,low rate of sedimentation,and enhanced rate of continental weathering facilitated the glauconitization.The last factor caused the excess supply of nutrients,including Fe,Si,K,Mg and Al through the rivers,the cations needed for the formation of glauconite.The excessive inflow of nutrient-rich freshwater into the shallow seas further ensured high organic productivity and stratification in shallow shelves,causing hypoxia.The consequent rapid rise in sea-level during the warm periods created extensive low-relief shallow marine shelves starved in sediments.Oxygen-deficiency in the shallow marine environment facilitated the fixation of Fe into the glauconite structure.The inflow of nutrient-rich water during the warm climatic intervals facilitated the formation of phosphorite,ironstone,and organic-matter-rich sedimentary deposits as well.Although global factors primarily controlled the formation of these authigenic deposits,local factors played significant roles in some of the deposits.Therefore,phosphorites formed in marine conditions with open circulation within the tropical zone.While lush growth of rainforest covers in the tropical belt facilitated the formation of coastal lignite.展开更多
This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep ma...This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep marine conditions and low seawater temperature discourage formation of glaucony. Around 75% of glaucony is recorded from the Cretaceous to the Holo- eene sediments, which are related to the abundance of the most common substrates, faecal pellets and bioclasts. TFe203 （total）, A1203, K20 and MgO contents of glaucony vary appreciably through geological time. IMhile TFe203 content of most Mesozoic and Cenozoic giaucony ex- ceeds 20%, it is always less than 20% in Precambrian varieties. High K20, A1203, MgO and low TFe203 distinguish the Precambrian glaucony from its Phanerozoic counterpart. Precambrian glaucony, preferably formed within a K-feldspar substrate, is always rich in potassium irre- spective of its degree of evolution, while high K-content in Phanerozoic evolved glaucony in- dicates significant stratigraphic condensation. K20 iJs. TFe203 relationship of glaucony exhibits three different evolutionary trends corresponding to three common modes of origin. Depositional conditions may influence the composition of glaucony as slightly reducing conditions favour Fe enrichment, whereas oxidising conditions cause Fe depletion in giaucony.展开更多
文摘According to the data of the mineral assemblages, the sediment layers with authigenic glauconite were found in the X<sub>1</sub> core collected from the northeast of the Beibu Gulf. Pliocene sediment layer containing a lot of foraminifera shows a shallow sea facies. Its thickness is larger than 30 m and is located at the depth below 59 m of the core.
基金Ministry of Mines, Government of India for financial support through grant F No. 14/77/2015Met. IV
文摘This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.
基金financial support from Space Applications Centre(ISRO)for the project 467 STC0254 entitled“Physico-chemical conditions of formation of bole beds within Deccan basalt for 468 Martian analogue”,CSIR for the fellowship。
文摘Celadonite and glauconite are comparable in terms of physical,chemical and mineralogical characteristics.Formation of both these minerals requires slightly oxygen-depleted conditions in a semiconfined micro-environment,facilitating the uptake of Fe into the structure.Although glauconite is ubiquitous in marine deposits,celadonite forms in both marine and non-marine environments,more commonly by altering intermediate to mafic rocks.A review of data across the geological column shows that both these minerals are more common in the Mesozoic and Cenozoic,which may be related to extensive volcanism.The composition of celadonite and glauconite is highly variable and is controlled by the availability of cations within the pore water micro-environment.The major element composition of celadonite overlaps with that of evolved to highly evolved glauconite to a large extent.Existing data and representative samples of celadonite and glauconite reveal subtle differences in X-ray diffraction parameters and Fourier transform infrared(FTIR)spectra.Celadonite shows sharper basal and hkl reflections than glauconite.It characteristically exhibits distinct 111-021,003-022,023 and 130-131,and 060 reflections at less than 1.51A,indicating a betterordered crystallographic structure than glauconite.The FTIR spectra of celadonite and glauconite show similar absorption bands although Si-O bending,Si-O stretching and OH-stretching bands are sharper and well resolved in celadonite than that of glauconite.For palaeoenvironmental interpretations,it is,therefore,necessary to examine the subtle differences in X-ray diffraction parameters and FTIR spectra to confirm the identification of these two minerals.The composition of celadonite relates closely to the host rock and depositional environment.The celadonite associated with mafic rock shows relatively high Fe,Mg and low Al contents.In contrast,those associated with felsic to intermediate composition rocks show slightly higher contents of Al and lower content of Fe,Mg.The mineral chemistry of celadonite varies from marine to continental settings.Marine celadonite contains higher Fe,Mg and lesser Al than their non-marine counterpart.Celadonite with relatively higher Al may show slightly lower interlayer K than Fe and Mg-rich celadonite for charge balancing.
文摘Drill cuttings,though rarely used,are crucial subsurface samples to understand petrographic properties affecting reservoir quality.Unlike core material,cuttings are continuously available along the wellbore and can be used during drilling to monitor progress.Therefore,cuttings may allow a semi-quantitative,statistical calibration of rock properties from the subsurface,but they are often underutilized.Although fracture and vein orientations cannot be reconstructed from drill cuttings,the presence of veins and their internal textures(open,partially sealed or sealed) in specific formation sections and depths can be identified and analyzed using e.g.,transmitted light microscopy and cathodoluminescence to supplement characterization at the well site and subsequently assess production behavior.Borehole gamma ray logs in combination with handheld portable X-ray fluorescence(pXRF) analyses on cleaned and dried drill cuttings can be used to further improve the depth accuracy of the cutting samples and to geochemically fingerprint the samples,based on the Si/Al ratio,as a proxy for sandstone-rich and mudrock-rich sections of the well.In this study,eighty-three sandstone cutting samples from two wells,covering~400 m of stratigraphy targeting the Paleocene-Eocene Greifenstein Fm.equivalent(Glauconite Sandstone,GLS) in the Vienna Basin(Austria),were studied.They also cover parts of three different reservoir sections(1.to 3.GLS).The Flysch play in the Vienna Basin hosts several sand stone-mud rock interbeds and is composed of several nappes,forming complex reservoir compartments.The glauconite contents vary between different sections of the GLS,where the highest is observed in the 3.GLS.The sandstones are predominantly cemented by ferroan calcite,resulting in low optical porosity(<5 %)in both wells,with only individually elevated porosity,related to partially dissolved K-feldspar grains.A paragenetic sequence solely based on cuttings further highlights that reservoir quality in the studied section is independent of sandstone compaction,but is related to lower optical porosity in finer-grained sa ndstones and higher carbonate vein cement conte nts.Furthermo re,productive intervals are related to lower Fe+Mg contents.The understanding of reservoir properties,diagenesis,and their influence on fluid flow is crucial for successful exploration and reduction of uncertainty in reservoir production and development.The diagenetic variations from cuttings and the geochemical fingerprint by pXRF are linked to reservoir quality and production performance of individual well perforations.This approach can provide additional information on reservoir quality where core material is unavailable.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFF0803600)National Natural Science Foundation of China(Grant Nos.42302009,42072003,and W2441016)+3 种基金HYZ thanks the Shaanxi Province postdoctoral research project and China Scholarship Council(202306970031)We also thank the Department of Science and Technology of Shaanxi Province(2022TD-11)TPT also acknowledges the Swedish Research Council(VR2017-05183 and VR2021-04295)This is also a contribution to the project of Theory of Hydrocarbon Enrichment under MultiSpheric Interactions of the Earth(THEMSIE04010106).
文摘Small shelly fossils(SSFs)have long been recognized as important to the studies of both metazoan evolution and the onset of biomineralization during the Cambrian radiation.The marked decline in the occurrence,diversity and abundance of SSFs in the middle to late Cambrian,when compared with the early Cambrian,has often been regarded as a result of the closure of a phosphatization window.Despite this,there have been numerous and consistent reports of SSFs from the middle Cambrian and younger deposits.To identify possible factors influencing SSF preservation,five microfacies including bioclastic limestone,flat-pebble conglomerates with bioclasts,hummocky cross-stratified grainstone with bioclasts,bioclastic grainstone in hardgrounds and glauconite bioclastic wackstone-packstone,from Cambrian Series 2 to Miaolingian in North China are compared to assess how differences in lithology impact the preservation potential of SSFs.Our results,based on 35,161 SSF specimens from deposits across six sections,suggest that there are still abundant and diverse SSFs in the middle Cambrian of North China preserved in ways not exclusively reliant on the presence of phosphate and that SSF preservation can be linked to the differences in microfacies in the early to middle Cambrian of North China.
基金supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China (Nos. 2011ZX05002-004-006HZ, 2016ZX05002-004-010)
文摘Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow into the ocean, especially in deltaic environments with high hydrodynamic conditions. At the same time, sandstone sequences with grain-coating chlorites also tend to have relatively high glauconite and pyrite content. EPMA composition analysis shows that glauconites with ‘‘high Al and low Fe’’ content indicate slightly to semi-saline marine environments with weak alkaline and weakly reducing conditions. By analyzing the chlorite-containing sandstone bodies of the southern Sichuan Xujiahe Formation, this study found that chlorite was mainly distributed in sedimentary microfacies, including underwater distributary channels, distributary channels, shallow lake sandstone dams, and mouth bars. Chlorite had a tendency to form in the upper parts of sandstone bodies with signs of increased base level, representing the influence of marine（lacustrine）transgression. This is believed to be influenced by megamonsoons in the Middle and Upper Yangtze Region during the Late Triassic Epoch. During periods of abundant precipitation, river discharges increased and more Fe particulates flowed into the ocean（lake）. In the meantime,increases or decreases in lake level were only affected byprecipitation for short periods of time. The sedimentary environment shifted from weakly oxidizing to weak alkaline, weakly reducing conditions as sea level increased, and Fe-rich minerals as authigenic chlorite and glauconite began to form and deposit.
基金The National Programme on Global Change and Air-sea Interaction under contract No.GASI-02-SCS-CJ03China Geological Survey:Continental Shelf Drilling Program under contract No.GZH201100202China-Thailand Cooperation Project"Research on Vulnerability of Coastal Zones"
文摘Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the Mn O content in siderite decreases, but FeOand Mg O content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains,which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The KO content of glauconite is low or absent, indicating its short formation time.
文摘The objective of this work is to study the efficiency of some surface modified phyllosilicate minerals （bentonite and glauconite） in the removal of dyes from textile waste water. It is found that complete dye removal was achieved by using 10-25g modified glauconite from solutions having a dye concentration of 10-50 mg/L. Adsorption data were modeled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. Adsorption capacities and optimum adsorption isotherms were predicted by linear regression method. The analysis of experimental isotherms showed that Langmuir isotherm reasonably fit the experimental data in the studied concentration range for the adsorption of dye onto glauconite mineral surface where Freundlich isotherm fit the experimental data for the adsorption of dve onto bentonite mineral surface.
基金SB is thankful to Ministry of Mines,Government of India for financial support through grant F No.14/77/2015-MetIV.TRC is thankful to Council of Scientific and Industrial Research,India for the financial support.
文摘Although Paleogene warm climatic intervals have received considerable attention for atmospheric and oceanographic changes,the authigenic mineralization associated with these time spans remains overlooked.An extensive review of the literature reveals a close correspondence between the high abundance of glauconite and warm climatic intervals during the Paleogene period.The abundance of phosphorite,ironstone,lignite and black shale deposits reveals similar trends.Although investigated thoroughly,the origin of these authigenic deposits is never understood in the background of Paleogene warming climatic intervals.A combination of factors like warm seawater,hypoxic shelf,low rate of sedimentation,and enhanced rate of continental weathering facilitated the glauconitization.The last factor caused the excess supply of nutrients,including Fe,Si,K,Mg and Al through the rivers,the cations needed for the formation of glauconite.The excessive inflow of nutrient-rich freshwater into the shallow seas further ensured high organic productivity and stratification in shallow shelves,causing hypoxia.The consequent rapid rise in sea-level during the warm periods created extensive low-relief shallow marine shelves starved in sediments.Oxygen-deficiency in the shallow marine environment facilitated the fixation of Fe into the glauconite structure.The inflow of nutrient-rich water during the warm climatic intervals facilitated the formation of phosphorite,ironstone,and organic-matter-rich sedimentary deposits as well.Although global factors primarily controlled the formation of these authigenic deposits,local factors played significant roles in some of the deposits.Therefore,phosphorites formed in marine conditions with open circulation within the tropical zone.While lush growth of rainforest covers in the tropical belt facilitated the formation of coastal lignite.
基金Department of Science and Technology,Government of India for financial support through Grant IR/S4/ESF-16/2009(2)DST-IITB National Facility for EPMA,Department of Earth Sciences,Indian Institute of Technology Bombay
文摘This study presents a review on palaeogeographic implications and temporal variations of giaucony coveringboth modern and ancient records. Phanerozoic giaucony preferably forms in a shelf depositional setting. Deep marine conditions and low seawater temperature discourage formation of glaucony. Around 75% of glaucony is recorded from the Cretaceous to the Holo- eene sediments, which are related to the abundance of the most common substrates, faecal pellets and bioclasts. TFe203 （total）, A1203, K20 and MgO contents of glaucony vary appreciably through geological time. IMhile TFe203 content of most Mesozoic and Cenozoic giaucony ex- ceeds 20%, it is always less than 20% in Precambrian varieties. High K20, A1203, MgO and low TFe203 distinguish the Precambrian glaucony from its Phanerozoic counterpart. Precambrian glaucony, preferably formed within a K-feldspar substrate, is always rich in potassium irre- spective of its degree of evolution, while high K-content in Phanerozoic evolved glaucony in- dicates significant stratigraphic condensation. K20 iJs. TFe203 relationship of glaucony exhibits three different evolutionary trends corresponding to three common modes of origin. Depositional conditions may influence the composition of glaucony as slightly reducing conditions favour Fe enrichment, whereas oxidising conditions cause Fe depletion in giaucony.
