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1.
The Holocene lacustrine diatomaceous earth of Fayium,South West of Cairo,has been studied to define its minerals,chemistry,petrography and physical properties.Minerals were processed by way of calcination at 550℃ ,followed by acid leaching to reduce levels of mineral impurities.The diatomite is of biogenic opal A.with calcite as the main ganue mineral,quartz and clay minerals(smectite followed by kaolinite in abundance and a trace amount of illite).Silica in the diatomaceous earth accounts for about 63% on average.Positive correlation between CaO and CO2 indicates that Ca is present mainly as calcite.Al2O3,Fe2O3,MgO and K2O are attributed mainly to clay minerals.However,the physical properties of the diatomaceous earth as filter-aids and filler for paints and plastics are poor because of general high levels of impurities.The technological performances of the diatomaceous earth have been significantly improved owing to upgrading of diatoms through mineral processing trical.  相似文献   

2.
The mineralogy of the high-volatile bituminous coals and associated strata from the Greta seam, Sydney Basin, Australia, has been evaluated in this study. Although the seam is not immediately overlain by marine strata, percolation of marine water into the original peat bed is indicated by the petrological, mineralogical and geochemical characteristics, which resemble those of coals with marine roof strata. The upper and lower sections of the seam have contrasting mineralogy. Pyrite typically comprises 40 to 56 wt% of the mineral assemblage in the marine-influenced upper part of the seam section. The lower part contains much less pyrite (typically <5 wt%, organic-free basis), and also relatively abundant dawsonite (up to 14 wt%, organic-free basis). The minerals within most coal plies are largely of authigenic origin. These include pyrite, siderite, clay minerals (mainly kaolinite and Na-rich mixed-layer illite/smectite), and quartz, most of which have a relatively early, syngenetic origin. Minor Ti-bearing minerals, anatase or rutile, and phosphate minerals, fluorapatite and goyazite, were probably also formed during early diagenesis. Other minerals have features that indicate late-stage precipitation. These include abundant cleat- and fracture-filling dawsonite, which may be the result of reactions between earlier-precipitated kaolinite and Na2CO3- or NaHCO3-bearing fluids. Minor albite may also be epigenetic, possibly precipitated from the same Ca–Al bearing fluids that formed the dawsonite. The most abundant detrital minerals in the Greta coals are quartz, poorly ordered kaolinite, illite and mixed-layer illite/smectite (I/S). These occur mainly in the floor, roof and other epiclastic horizons of the seam, reflecting periods of greater clastic influx into those parts of the original peat-forming environment. Detrital minerals are rare in the coals away from the epiclastic horizons, probably owing to almost complete sediment bypassing in the depositional system. Alternatively, any detrital minerals that were originally present may have been leached from the peat bed by diagenetic or post-diagenetic processes.  相似文献   

3.
This study focused on typical injection layers of deep saline aquifers in the Shiqianfeng Formation used in the Carbon Capture and Sequestration Demonstration Projects in the Ordos Basin, Northwest China. The study employed experiments and numerical simulations to investigate the mechanism of CO2 mineral sequestration in these deep saline aquifers. The experimental results showed that the dissolved minerals are plagioclase, hematite, illite–smectite mixed layer clay and illite, whereas the precipitated minerals are quartz (at 55, and 70 °C) and kaolinite (at 70 °C). There are rare carbonate mineral precipitations at the experimental time scale, while the precipitation of quartz as a product of the dissolution of silicate minerals and some intermediate minerals rich in K and Mg that transform to clay minerals, reveals the possibility of carbonate precipitation at the longer time scale. These results are consistent with some results previously reported in the literature. We calibrated the kinetic parameters of mineral dissolution and precipitation by these experimental results and then simulated the CO2 mineral sequestration under deep saline aquifer conditions. The simulation results showed that the dissolved minerals are albite, anorthite and minor hematite, whereas the precipitated minerals are calcite, kaolinite and smectite at 55 and 70 °C. The geochemical reaction of illite is more complex. At 55 °C, illite is dissolved at the relatively lag time and transformed to dawsonite; at 70 °C, illite is precipitated in the early reaction period and then transformed to kaolinite. Based on this research, sequestrated CO2 minerals, which are mainly related to the temperature of deep saline aquifers in Shiqianfeng Fm., are calcite and dawsonite at lower temperature, and calcite at higher temperature. The simulation results also establish that calcite could precipitate over a time scale of thousands of years, and the higher the temperature the sooner such a process would occur due to increased reaction rates. These characteristics are conducive, not only to the earlier occurrence of mineral sequestration, but also increase the sequestration capacity of the same mineral components. For a sequestration period of 10,000 years, we determined that the mineral sequestration capacity is 0.786 kg/m3 at 55 °C, and 2.180 kg/m3 at 70 °C. Furthermore, the occurrence of mineral sequestration indirectly increases the solubility of CO2 in the early reaction period, but this decreases with the increase in temperature.  相似文献   

4.
采用X射线衍射、扫描电镜分析方法,对兰州盆地永登剖面晚古新世—早渐新世沉积物中粘土矿物的相对含量、伊利石结晶度、显微形貌及其古气候意义进行深入研究。结果表明:晚古新世—早渐新世沉积物中粘土矿物主要为伊利石、蒙脱石、绿泥石和少量的坡缕石,其中伊利石的含量最高,而且从晚古新世到早渐新世,沉积物中伊利石的含量呈明显升高的趋势,蒙脱石则呈明显减少的趋势;在大约55 Ma处伊利石含量急剧减小,而蒙脱石含量急剧增大。此外,可见到毛发状的自生坡缕石沿蒙脱石晶片边缘交代生长,而碎屑成因的坡缕石则主要呈破碎的短棒状。粘土矿物分布特征表明,兰州盆地晚古新世—早渐新世的古气候以干旱为主导,并且经历了由相对温暖湿润到半干旱半湿润或干旱炎热的转变,这种气候转型主要受全球气候的影响,即受行星风系的控制;而在大约55 Ma处伊利石、蒙脱石的含量变化则记录了全球性的PETM事件。  相似文献   

5.
From 14 deeps and other regions of the Red Sea totally 226 samples from 28 cores recovered during the VALDIVIA cruises (1971, 1972) were investigated according to their clay mineral content (<2μm resp. < 6.3 μm) after carbonate dissolution. Three facies groups are to distinguish:
  1. normal sediments: dominance of chlorite, kaolinite, illite, small amounts of smectite and sepiolite. Two palygorskite types are present only in a few samples.
  2. normal sediments with hydrothermal influence: clay mineral paragenesis similar like that of normal sediments; but increase of smectite and presence of goethite in each sample; partly small contents of talc.
  3. heavy metal deposits: dominance of iron-bearing smectite, partly with amorphous components resp. pure ore mineral assemblages with authigenic silicates (talc, quartz, opal, chrysotile, sepiolite, palygorskite, chlorite).
Crystallinity of the clay and ore minerals is independent from sedimentary overburden. Sepiolite shows in small amounts a wide distribution; palygorskite2 (d110=11.3 Å) yields locally an increased concentration in the range of pteropod layers cemented by aragonite. The environment of ore deposits is characterized by iron-bearing smectite besides the ore minerals.  相似文献   

6.
准噶尔盆地南缘新生界粘土矿物分布及影响因素   总被引：10，自引：8，他引：10       下载免费PDF全文
根据粘土矿物的相对含量研究了准噶尔盆地南缘新生界砂岩粘土矿物类型、组合特征及纵、横向分布规律及其主要影响因素。划分出无序伊/蒙混层型、部分有序伊/蒙混层型、伊利石+伊/蒙混层型、蒙皂石型以及含坡缕石型等5类粘土矿物组合。按照伊/蒙混层相对含量的变化,粘土矿物纵向上演化呈正常转化型(伊/蒙混层相对含量降低)、反向转化型(伊/蒙混层相对含量增加)和“S”型(伊/蒙混层相对含量呈曲线变化)3种形式。平面上,伊/蒙混层和伊利石这两类主要粘土矿物从湖盆的边缘向中心分别呈现减少和增多的趋势,湖盆边缘相带以无序伊/蒙混层型、蒙皂石型和含坡缕石型为主,湖盆中心则为部分有序伊/蒙混层型和伊利石+伊/蒙混层型组合等类型。上述分布规律的控制因素主要有沉积环境、构造运动及层序发育等。  相似文献   

7.
Neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto-frictional regime, but neither the conditions nor the processes which wall-rock is transformed into clay minerals are well understood. Yet, understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults. We therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low-angle normal faults (LANF's) in the American Cordillera to demonstrate the range and type of clay transformations in natural fault gouges. The sampled faults juxtapose a wide and representative range of wall rock types, including sedimentary, metamorphic and igneous rocks under shallow-crustal conditions. Clay mineral transformations were observed in all but one of 28 faults; one fault contains only mechanically derived clay-rich gouge, which formed entirely by cataclasis.Clay mineral transformations observed in gouges show four general patterns: 1) growth of authigenic 1Md illite, either by transformation of fragmental 2M1 illite or muscovite, or growth after the dissolution of K-feldspar. Illitization of fragmental illite–smectite is observed in LANF gouges, but is less common than reported from faults with sedimentary wall rocks; 2) ‘retrograde diagenesis’ of an early mechanically derived chlorite-rich gouge to authigenic chlorite–smectite and saponite (Mg-rich tri-octahedral smectite); 3) reaction of mechanically derived chlorite-rich gouges with Mg-rich fluids at low temperatures (50–150 °C) to produce localized lenses of one of two assemblages: sepiolite + saponite + talc + lizardite or palygorskite +/− chlorite +/− quartz; and 4) growth of authigenic di-octahedral smectite from alteration of acidic volcanic wall rocks. These transformation groups are consistent with patterns observed in fault rocks elsewhere. The main controls for the type of neoformed clay in gouge appear to be wall-rock chemistry and fluid chemistry, and temperatures in the range of 60–180 °C.  相似文献   

8.
Core U1359 collected from the continental rise off Wilkes Land, east Antarctica, is analyzed for the clay mineralogy and carbon content. The temporal variation of the clay mineralogical data shows a dominance of illite with chlorite, smectite and kaolinite in decreasing concentration. Clay mineral illite is negatively correlated with smectite which shows enrichment during 6.2–6.8, 5.5–5.8, 4.5 and 2.5 Ma. The mineralogical analyses on the silt size fraction (2–53 μm) of some selected samples were also carried out. The combined result of both the size fractions shows the presence of chlorite and illite in both size fractions, smectite and kaolinite only in clay size fraction (<2 μm) and similarity in the crystallinity and chemistry of illite in both fractions. Similar nature of illite in both fractions suggests negligible role of sorting probably due to the deposition from the waxing ice sheet. During times of ice growth, nearby cratonic east Antarctica shield provided biotite-rich sediments to the depositional site. On the other hand, the presence of smectite, only in the clay size fraction, suggests the effective role of sorting probably due to the deposition from distal source in ice retreat condition. During times of ice retreat, smectite-rich sediment derived from Ross Orogen is transported to the core site through surface or bottom water currents. Poor crystallinity of illite due to degradation further corroborates the ice retreat condition. The ice sheet proximal sediments of U1359 show that in the eastern part of Wilkes Land, the ‘warming’ was initiated during late Miocene.  相似文献   

9.
The x-ray powder diffraction identification of clay minerals both in bulk samples and in separated clay fraction confirmed the presence of palygorskite in samples of cave sediments from Wadi Haqil (the western slopes of Musandam Mountains; Ras Al-Khaimah Emirate, UAE). Samples contain quartz, gypsum, smectite, kaolinite, calcite, and palygorskite, some of them chlorite, illite, feldspars, and goethite. Calcite dominates in most samples; smectite prevails in clay fraction. After heating, the 001 reflection of chlorite shifts to higher diffraction angles and its intensity decreases; these features indicate that the chlorite represent a Fe-dominant species. Unit-cell dimensions of major phases as refined by the Rietveld method are in agreement with literature data. Chemical composition of palygorskite was derived from unit-cell dimensions as follows: MgO content is 11–14 wt% and Al2O3 10–13 wt%. Clay mineralogy is only hard to ascertain from the scanning electron microscope (SEM) images even after being combined with the energy-dispersive spectrometer data. The SEM was also used to characterize gypsum grains; they often display flow deformation features. Studied cave sediments represent palygorskite-bearing weathering products and desert soils re-deposited from the cave surroundings by slope processes and wind and/or surface runoff. The mixture with other clay minerals, quartz, feldspars, etc. supports this interpretation. Fine-grained quartz fraction is probably wind-blown. Gypsum and calcite are the precipitates (crusts and/or cements), although gypsum can also be re-deposited from omnipresent gypsum-cemented surface sediments.  相似文献   

10.
Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.  相似文献   

11.
In this study a series of CH4 adsorption experiments on clay-rich rocks were conducted at 35 °C, 50 °C and 65 °C and at CH4 pressure up to 15 MPa under dry conditions. The clay-dominated rock samples used are fresh samples from quarries and mines. Samples are individually dominated by montmorillonite, kaolinite, illite, chlorite, and interstratified illite/smectite. The experimental results show that clay mineral type greatly affects CH4 sorption capacity under the experimental conditions. In terms of relative CH4 sorption capacity: montmorillonite ? illite/smectite mixed layer > kaolinite > chlorite > illite. Physisorption is the dominant process for CH4 absorption on clay minerals, as a result, there is a linear correlation between CH4 sorption capacity and BET surface area in these clay-mineral dominated rocks. The abundance of micro-mesopores in the size range of a few to a few 10 s of nanometers in montmorillonite clay and illite–smectite interstratified clay results in large BET surface area values for these mineral species.  相似文献   

12.
The Jurassic shale is an important source rock for the found gas reservoirs in the Tarim Basin, northwestern China, but has never been researched for shale gas potential. The geological effects on methane adsorption capacity for the gas shale have been investigated in this paper through the geochemical, mineralogical and adsorption analyses on samples from wells and sections. The methane adsorption capacity ranges from 0.58 to 16.57 cm3/g, and the total organic carbon (TOC) content is between 0.5 and 13.5 wt%. The organic maturity measured by Tmax is between 410 °C (immature) and 499 °C (overmature). The methane adsorption capacity of the Jurassic continental shale in the Tarim Basin is affected by many geological factors, including the TOC content, organic matter maturity, mineral composition, surface area and pore size distribution. The TOC content is the most significant factor with a positive effect on the adsorption capacity of the Jurassic shale, and the influence varies piecewise according to the TOC content. The TOC content contributes much more to the methane adsorption capacity of organic‐rich shale samples (TOC content > 0.7 wt%) than to the organic‐lean samples (TOC content < 0.7 wt%). The mineral composition is a secondary factor, and the abundance of clay content has a positive effect on the methane adsorption capacity despite its relatively weaker adsorption ability compared to TOC. The pore size distribution has different effects on surface area and pore volume. Mesopores and micropores provide the major surface area and are mainly derived from TOC and illite, which has a positive influence on the adsorption capacity. Mesopores and macropores offer the major pore volume and are mainly formed by illite, which is the major contributor for pore volume rather than surface area. In addition, the TOC and illite contents of the Jurassic shale in the Tarim Basin are closely related to the origin, maturity and diagenesis evolution of the shale: (1) both TOC and illite content variations are related to the different provenances and depositional environments of shale; (2) the decrease of TOC content with increasing maturity is also partly attributed to hydrocarbon generation; and (3) the increase of illite content with increasing maturity is due to illitization in the diagenesis of shale. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

13.
The results of the study of clay mineral alterations in Upper Pleistocene sediments of the southern trough in the Guaymas Basin (Gulf of California) due to the influence of hydrothermal solutions and heat produced by sill intrusions are discussed. Core samples from DSDP Holes 477 and 477A were taken for the analysis of clay minerals. Application of the method of modeling X-ray diffraction patterns of oriented specimens of the finely dispersed particles made it possible to establish the phase composition of clay minerals, determine their structural parameters, and obtain reliable quantitative estimates of their contents in natural mixtures. The modeling data allowed us to characterize reliably the transformation of clay minerals in sediments of the hydrothermally active southern trough in the Guaymas Basin. In Upper Pleistocene sandy–clayey sediments of the southern trough, changes in the composition of clay minerals occurred under the influence of a long-living hydrothermal system. Its lower part (interval 170.0–257.5 m) with maximum temperatures (~300°C) was marked by the formation of chlorite. Terrigenous clay minerals are not preserved here. Saponite appears at a depth of 248 m in the chlorite formation zone. Higher in the sedimentary section, the interval 146–170 m is also barren of terrigenous clay minerals. Sediments of this interval yielded two newly formed clay minerals (chlorite and illite), which were formed at lower temperatures (above 180°C and below 300°C, approximately up to ~250°C), while the relatively low-temperature upper part (110–146 m) of the hydrothermal system (from ~140°C to ~180°C) includes the mixture of terrigenous and newly formed clay minerals. Terrigenous illite is preserved here. Illitization of the mixed-layer illite–smectite was subjected to illitization. The terrigenous montmorillonite disappeared, and chlorite–smectite with 5–10% of smectite layers were formed. In the upper interval (down to approximately 110 mbsf), the composition of terrigenous clay minerals remains unchanged. They are composed of the predominant mixed-layer illite–smectite and montmorillonite, the subordinate illite, mixed-layer chlorite–smectite with 5% of smectite layers, mixed-layer kaolinite–smectite with 30% of smectite layers, and kaolinite. This composition of clay minerals changed under the influence of sill intrusions into the sedimentary cover at 58–105 m in the section of Hole 477. The most significant changes are noted in the 8-m-thick member above the sill at 50–58 m. The upper part of this interval is barren of the terrigenous mixed-layer illite–smectite, which is replaced by the newly formed trioctahedral smectite (saponite). At the same time, the terrigenous dioctahedral smectite (montmorillonite) is preserved. The composition of terrigenous clay minerals remains unchanged at the top of the unit underlying the sill base.  相似文献   

14.
四川广安地区侏罗系粘土矿物类型主要为绿泥石、高岭石、伊蒙混层和伊利石;同一口井随着深度的增加,伊利石、绿泥石含量增加,伊蒙混层中的蒙脱石混层比降低。粘土矿物特征与储集层物性的相关性分析认为:伊蒙混层含量、伊利石含量均与储集层孔渗性能呈负相关,绿泥石与高岭石含量与储集层孔渗性呈正相关;通过对伊蒙混层中蒙脱石的混层比的计算,大多数为有序混层,说明该区凉高山组处于生油高峰期,这与岩石中TOC(%)介于0.8与1.3,Ro(%)介于0.7与1.2相吻合。  相似文献   

15.
杭州湾潮滩沉积物黏土矿物空间差异与物源指示   总被引：4，自引：1，他引：3  
通过对杭州湾潮滩沉积物中主要黏土矿物成分及组合类型的研究,分析了杭州湾潮滩沉积物黏土矿物的空间分布特征。借助聚类分析等手段,同时结合杭州湾水动力特征,探讨了研究区黏土矿物的来源和成因。研究结果表明,杭州湾潮滩表层沉积物主要为黏土质粉砂,其余为砂质粉砂。本区沉积物黏土矿物成分复杂,主要为伊利石,其次是高岭石和绿泥石;还有少量蒙皂石和蛭石及1.4 nm过渡矿物。根据其相对含量可分为3种组合类型:Ⅰ型为伊利石-高岭石-绿泥石-蛭石类-蒙皂石型,Ⅱ型为伊利石-绿泥石-高岭石-蒙皂石-蛭石类型,Ⅲ型为伊利石-高岭石-绿泥石-蒙皂石-蛭石类型。在空间上,北岸的蒙皂石和绿泥石平均含量高于南岸,而伊利石、高岭石和蛭石(含1.4 nm过渡矿物)平均含量则低于南岸。高潮滩和中潮滩黏土矿物对比,除了蒙皂石含量高潮滩大于中潮滩外,其他矿物含量均无明显规律。表层沉积物黏土矿物的分布特征与水动力条件和物质来源密切相关,杭州湾北岸乍浦以东潮滩受潮流和长江沿岸流影响明显,沉积物主要为长江和东海源的;南岸由于曹娥江和甬江两条河流的注入,流域物质所占比例明显比北岸高。柱状岩芯样品中各黏土矿物含量自下而上的变化则反映了物源区风化强度的波动特征。  相似文献   

16.
《Chemical Geology》2003,193(3-4):167-179
REE analyses were performed on authigenic illitic clay minerals from Late Permian mudrocks, sandstones and bentonites from the Bowen Basin (Australia). The mixed-layer illite–smectite exhibit REE patterns with an obvious fractionation of the HREE from the LREE and MREE, which is an apparent function of degree of illitization reaction. The highly illitic (R≥3) illite–smectite from the northern Bowen Basin show a depletion of LREE relative to the less illitic (R=0 and 1) clays. In contrast, an enrichment of HREE for the illite-rich clays relative to less illitic clays is evident for the southern Bowen Basin samples. The North American Shale Composite-normalized (La/Lu)sn ratios show negative correlations with the illite content in illite–smectite and positive correlations with the δ18O values of the clays for both the northern and southern Bowen Basin samples. These correlations indicate that the increasing depletion of LREE in hydrothermal fluids is a function of increasing water/rock ratios in the northern Bowen Basin. Good negative correlations between (La/Lu)sn ratios and illite content in illite–smectite from the southern Bowen Basin suggest the involvement of fluids with higher alkalinity and higher pH in low water/rock ratio conditions. Increasing HREE enrichment with δ18O decrease indicates the effect of increasing temperature at low water/rock ratios in the southern Bowen Basin.Results of the present study confirm the conclusions of some earlier studies suggesting that REE in illitic clay minerals are mobile and fractionated during illitization and that this fact should be considered in studies of sedimentary processes and in identifying provenance. Moreover, our results show that REE systematic of illitic clay minerals can be applied as an useful technique to gain information about physico-chemical conditions during thermal and fluid flow events in certain sedimentary basins.  相似文献   

17.
We analyzed the clay mineral assemblages, content and mineralogical characteristics of Hole U1438A sediment recovered from Amami Sankaku Basin during International Ocean Discovery Program (IODP) expedition 351. The results show that the clay minerals are mainly composed of illite (average 57%), smectite (average 26%), chlorite (average 14%) and minor kaolinite(average 3%). The crystallinity of illite in all samples are good (<0.4 Δ° 2θ), and the chemical indexes of illite in all samples are low (<0.4). Both indicate that illite in Hole U1438A formed in cold and dry climate. By comparing clay mineral assemblages of hole U1438A and the potential sediment sources, we suggest that smectite be mainly derived from the volcanic materials around Amami Sankaku Basin. Illite, chlorite and kaolinite are mainly derived from the Asian dust. The ratios of (illite+chlorite)/smectite show a phased increase over the last 350 ka, which is consistent with the cold and drying trend of the Asian continent since late Pleistocene. The high ratios of (illite+chlorite)/smectite and (illite+chlorite)/kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.  相似文献   

18.
苏北盆地粘土矿物转化模式与古地温   总被引：16，自引：0，他引：16  
以苏北盆地为例,系统研究了火成岩发育区粘土矿物组合特征及其控制因素;建立了粘土矿物转化模式;根据粘土矿物成岩演化特点,进行古地温分析。研究表明,苏北地区粘土矿物的分布主要受埋藏成岩作用、岩浆侵入、母质来源三种因素的影响,发育四种类型的粘土矿物组合和三种粘土矿物转化模式;火山碎屑岩母岩区和基性岩浆侵入区具有特殊的粘土矿物组合和成岩演化模式,前者以富含蒙皂石矿物为特点;后者出现高岭石与伊/蒙有序间层矿物共生组合,并具有不连续的演化序列;苏北盆地短有序I/S矿物出现于镜质组反射率 0.5 %～ 0.5 5 %的深度,伊/蒙间层矿物转变成伊利石在镜质组反射率 0.75 %～ 0.8%,可以用于热成熟度和古地温的估算;而蒙皂石消失的界面则不具有指标意义  相似文献   

19.
In order to investigate changes caused in clay mineralogy and potassium (K) status by different land-use types, 42 soils samples (0–30 cm) were monitored and analyzed. Soil samples belonging to Reference Soil Groups of Cambisols and Vertisols were collected from three neighboring land uses involving cropland (under long-term continuous cultivation), grassland, and forestland. The soils reflected an alkaline and calcareous aspect as were characterized by high pH (mean of 7.1 to 7.5) and calcium carbonate equivalent (mean of 35 to 97 g?kg?1) in the three land-use types. X-ray diffraction patterns of the clay fraction showed that the soils were mainly composed of illite, smectite, chlorite, and kaolinite. Chlorite and kaolinite remained unweathered irrespective of land use and soil types, soil processes, and physicochemical attributes assessed. Some changes in the XRD diffractograms of illite and smectite (the intensity or the position of peaks) were observed in the cultivated soils compared to those of the adjoining grassland that may explain the dynamics of the K trapped in illite interlayer sites. Potassium issues reflected a heterogeneous response to changes in land-use types. In light of this, a pronounced variation in soluble K (4–22 mg?kg?1), exchangeable K (140–558 mg?kg?1), and non-exchangeable K (135–742 mg?kg?1) appeared among the land-use types for both Cambisols and Vertisols, corresponding to variability in clay content, nature and type of clay mineral (mainly illite and smectite), cation exchange capacity (CEC), and soil organic carbon (SOC). In general, the largest amounts of soluble K and exchangeable K were recorded in the forestland, whereas the highest contents of non-exchangeable K were found in the grassland for both Cambisols and Vertisols. Exchangeable K, available K, CEC, and clay contents in the soils with higher smectite values (25–50 %) were significantly different (P?≤?0.05) compared to those of the lower smectite values (10–25 %). This suggests that smectite is a major source for surface sorption of K in the studied soils.  相似文献   

20.
《Applied Geochemistry》1999,14(5):559-568
Salt marshes are the major areas for net sedimentation in many estuaries such as the Delaware Bay, and their diagenetic chemistry is harsh and extreme with large seasonal excursions in chlorinity (1–50 ppt), pH (4–6), and Eh (−240+120). Such diagenesis is driven by organic matter decomposition using redox cycles of S and Fe materials imported primarily as tidal sea water SO4 and Fe silicates, respectively.Important and quantitative changes in clay mineralogy occur within a decade at the redox boundary in a high marsh sediment near Lewes, Delaware. The clay mineralogy consists initially of a micaceous illite and chlorite mixture accumulating at the salt marsh surface. It is comprised of relic glacial sediments deposited on the continental slope during their net tidal movement from the sea to land. Once buried, these detrital clays are transformed into a new assemblage containing an illite/smectitic mixed layer mineral of poor crystallinity. Using curve decomposition techniques on complex X-ray traces, it is estimated that this new phase constitutes 45–55% of the clay fraction.The redox boundary where the sharp transition occurs is only about 20 a old as determined by 210Pb and 137Cs geochronology, and, thus, the clay mineral transformation is rapid. The occurrence of the new, abundant clay mineral is very abrupt (less than 1 cm at 12 cm in depth) and, thus, may itself occur in as little as three years. Once formed, the new mixed layer phase remains stable during the subsequent 40 a of burial from the time of formation at the oxic/anoxic boundary.Slow transformations of unstable primary clay reactants such as illite and chlorite are a common process of soil formation. However such rapid clay reactions have rarely been documented in either subaerial or submerged soil settings. The formation of a smectite mineral product of high chemical reactivity for a significant portion of the clays in a soil is unusual. In fact, the abrupt change in clay mineralogy in the salt marsh occurs precisely at the sharp evolution in salt marsh geochemistry from oxidized to reducing conditions where there is extensive redox cycling of Fe and S phases. A large seasonal oscillation in interstitial pH and Eh probably contributes to the rapid clay transformation. Such clay transformations may have important implications for the retention of other trace elements entering the salt marsh by atmospheric fallout and tidal cycles, or the release of such metal inventories after burial.  相似文献   

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