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1.
Nicholas J. Tosca David T. Johnston Daniel H. Rothman Andrew H. Knoll 《Geochimica et cosmochimica acta》2010,74(5):1579-15096
Clay minerals formed through chemical weathering have long been implicated in the burial of organic matter (OM), but because diagenesis and metamorphism commonly obscure the signature of weathering-derived clays in Precambrian rocks, clay mineralogy and its role in OM burial through much of geologic time remains incompletely understood. Here we have analyzed the mineralogy, geochemistry and total organic carbon (TOC) of organic rich shales deposited in late Archean to early Cambrian sedimentary basins. Across all samples we have quantified the contribution of 1M and 1Md illite polytypes, clay minerals formed by diagenetic transformation of smectite and/or kaolinite-rich weathering products. This mineralogical signal, together with corrected paleo-weathering indices, indicates that late Archean and Mesoproterozoic samples were moderately to intensely weathered. However, in late Neoproterozoic basins, 2M1 illite/mica dominates clay mineralogy and paleo-weathering indices sharply decrease, consistent with an influx of chemically immature and relatively unweathered sediment. A late Neoproterozoic switch to micaceous clays is inconsistent with hypotheses for oxygen history that require an increased flux of weathering-derived clays (i.e., smectite or kaolinite) across the Precambrian-Cambrian boundary. Compared to previous studies, our XRD data display the same variation in Schultz Ratio across the late Neoproterozoic, but we show the cause to be micaceous clay and not pedogenic clay; paleo-weathering signals cannot be recovered from bulk mineralogy without this distinction. We find little evidence to support a link between these mineralogical variations and organic carbon in our samples and conclude that modal clay mineralogy cannot by itself explain an Ediacaran increase in atmospheric oxygen driven by enhanced OM burial. 相似文献
2.
River water quality in weathered limestone: A case study in upper Mahanadi basin, India 总被引：1，自引：0，他引：1
Stromatolitic limestone and calcareous shale belonging to Chattisgarh Supergroup of Proterozoic age dominate the upper part
of the Mahanadi river basin. X-ray diffractogram (XRD) of limestone rocks show presence of a significant amount of calcite,
dolomite and ankerite. Shales of various colours contain calcite and dolomite. It is observed that congruent dissolution of
carbonate minerals in the Charmuria pure limestone has given rise to a typical karst topography. On the other hand, limestones
are also seen to support red and black soil profiles. This indicates that the limestone bedrock undergoes a parallel incongruent
weathering, which leaves a residue of decomposed rock. The XRD analyses reveal that the limestone soils thus formed contain
an assemblage of quartz, clays and Fe-oxides. It is likely that the silicate component trapped during deposition of the stromatolitic
limestone weathers incongruently resulting in diverse soil profiles. Carbonate and silicate mineral weathering schemes have
been worked out to explain the soil formation, fixation of Al in clay minerals, and Fe in goethite. The water quality parameters
such as Ca, Mg and HCO3 in the river water suggest under saturation with respect to calcite and dolomite. The mineral stability diagrams indicate
that kaolinite and Ca-smectite are stable in the river water environment, hence they occur in suspended sediments and soils.
The dominant influence of carbonate weathering on the water quality is observed even in the downstream part of the river outside
the limestone terrain. 相似文献
3.
第四纪红色粘土在我国南方分布很广,最典型的分布在华中岗地上,土层较厚,上部土质均匀,下部具有红白网纹并含砾石,大都是中更新世的洪积-冲积或残积-坡积物,笔者认为可能是间冰期比较暖热气候条件下的产物。熊毅早就指出:各地环境殊异,地形复杂,母岩不同,其理化特征将随之而异。第四纪红色粘土来自不同的堆积相,和经受不同的风化和成土过程,这将在矿物组成方面反映出来。土壤普查的结果表明,第四纪红色粘土按其分布的地形部位,成因和物质来源,可分成两类:一类是残积坡积相，为中更新世较早的暗红色沉积物，即Q2另一类是冲积相，为中更新世较晚的红化程度较轻的淡红色沉积物。它们都经历了中更新世至今的成土过程1)”。为了查明它们的差异，并有助于第四纪沉积物的研究，笔者用部分标本进行矿物分析，并对初步结果进行讨论。 相似文献
4.
The distribution of the clay minerals of the Banco Negro Inferior-Río Chico Group succession (BNI-RC), a middle Danian–middle Eocene mainly continental epiclastic–pyroclastic succession exposed in the Golfo San Jorge Basin, extra-Andean Patagonia (∼46° LS), is assessed in order to determine the possible origin of clay and specific non-clay minerals using X-ray diffraction and scanning electron microscopy analyses. The control over the clay mineralogy of the sedimentary settings, contemporary volcanism, paleoclimate and weathering conditions is considered. A paleoclimatic reconstruction is provided and correlated with the main global warming events that occurred during the early Paleogene.Mineralogical analyses of BNI-RC demonstrate that smectite and kaolin minerals (kaolinite, halloysite and kaolinite/smectite mixed layers) are the main clay minerals, whereas silica polymorphs (volcanic glass and opal) are common non-clay minerals. Throughout the succession, smectite and kaolin minerals are arranged in different proportions in the three clay–mineral assemblages. These show a general vertical trend in which the smectite-dominated assemblage (S1) is replaced by the smectite-dominated assemblage associated with other clays (S2) and the kaolinite-dominated assemblage (K), and finally by S2 up-section. The detailed micromorphological analysis of the clay and non-clay minerals allows us to establish that the origins of these are by volcanic ash weathering, authigenic and pedogenic, and that different stages in the evolution of mineral transformations have occurred.The supply of labile pyroclastic material from an active volcanic area located to the northwest of the study area could have acted as precursor of the authigenic and volcanogenic minerals of the analyzed succession. Diverse fine-grained lithological facies (muddy and tuffaceous facies) and sedimentary settings (coastal swamp and transitional environments, and different fluvial systems) together with variable climate and weathering conditions controlled the mineralogical transformations and the arrangement of clay–mineral assemblages. The paleoclimatic reconstruction suggests a general warm and humid climate. However, the temporal trend of the clay–mineral assemblages, the ratios between smectite and kaolinite and the micromorphological analysis of clay minerals contrasted with evidence from sedimentological analyses suggest a warm and seasonal climate for the basal part of the unit, a warm and humid climate with a relatively more perennial rainfall regime in the middle part of the unit, and a warm and less humid, probably subhumid, climate up-section. Such a reconstruction makes it possible to establish a correlation with some of the hyperthermal events of the Early Paleogene Global Warming (EPGW) and, consequently, constitute one of the most complete time records of the EPGW in South America. 相似文献
5.
Two weathering profiles developed over disseminated Cu mineralization hosted by granodiorites (porphyry type) and felsic volcanics respectively, in a savannah tropical environment (Burkina Faso) have been studied in detail. A mineralogical and geochemical study was carried out in order to determine the characteristics of both profiles and the behaviour of Cu in such deeply weathered environments. Our investigation was focused on the upper part of the weathering profile, respectively 4.0 and 10.5 m below the surface.The mineralogical study reveals that in the first case (profile A) the predominant clay minerals are smectites and kaolinite while in the second (profile B) a more kaolinitic composition is indicative of more severe leaching. In fact, field observations seem to demonstrate that the latter situation is more clearly related to an ancient lateritic-type weathering while the first one results from more recent processes.In both cases the Cu contents through the profiles are high (several thousands of ppm) and in good agreement with the grades obtained in depth, in the mineralized rock. Nevertheless, some leaching can be observed in the upper soil horizons, but the contents still remain highly anomalous, in the 1000 ppm range.It is shown that Cu is distributed in the main secondary minerals constituting the weathering products, whether they are silicates (smectites, phyllites, kaolinites) or oxides (goethite, hematite, Mn oxides).The main stable Cu-bearing mineral seems to be the kaolinite: indeed, smectites turn into kaolinite in the upper part of the profiles while goethite seems to be depleted in Cu under the same conditions.As concerns geochemical exploration, two observations can be noted. Firstly, Cu is very stable in such supergene environments, and secondly, the best size fraction in which to detect the Cu secondary dispersion haloes in soil or stream sediment samples is the <63 μ fraction, in terms of anomaly intensity or contrast. 相似文献
6.
Chemical processes affecting alkalis and alkaline earths during continental weathering 总被引：10，自引：0，他引：10
The alkali and alkaline earth concentrations in the Toorongo Granodiorite weathering profile are controlled by two competing processes; leaching of cations from primary minerals during their degradation to clays; fixation, by exchange and adsorption, of the same cations onto the secondary clay minerals. Degradation and leaching dominate the early weathering stages whereas during the advanced stages, exchange and adsorption onto clays are of most influence.The alkali and alkaline earth compositional changes in the Toorongo Granodiorite weathering profile are typical of changes occurring during weathering of the continents, consequently the following generalizations apply to continental weathering. Ca, Sr and Na are most rapidly and most strongly removed (as dissolved species) during weathering of fresh continental rocks. Although large quantities of Mg are transported to the marine environment as dissolved species, appreciable amounts remain (fixed in secondary clay minerals) at the weathering site to be removed during mass wasting of continental weathering profiles. Large quantities of Rb, Cs and Ba, fixed in continental weathering profiles by exchange and adsorption onto secondary clays, are transported from the continents only during mass wasting of the continents. 相似文献
7.
Laboratory experiments indicate that clay particles of the <2-üm fraction can be considerably degraded by the bivalve Mytilus edulis: dickite, kaolinite, smectite, chlorite and illite particles are partially dissolved and rounded by the digestive processes. Structural changes and a decrease in crystallinity of kaolinites, dickites and illites are striking. Investigations of clay minerals from tidal flat sediments highly populated by marine invertebrates, from marine suspensions and samples from profiles across Mytilis edulis beds on the North Sea coast of Germany show, however, that these materials have a uniform mineral composition. This uniformity of clay mineralogy can be explained by the hydrodynamic conditions in the nearshore area, where tidal currents and waves cause a periodic resuspension and transport of sediments introduced into the Wadden Sea from different sources (glacial, fluviatile). Processes of bioturbation also redistribute the sedimentary material. These mixing processes effectively erase any evidence of local enrichment of the biogenically degraded clays. However, the disordered clays should react more sensitively (i.e. have higher adsorption capacities for organic substances, hydroxides and metals) in sediments than untreated materials, so that biodegradation is of basic importance for clay diagenesis. During these processes, Pb, V, Ni and Fe are dissolved from the digested particles. 相似文献
8.
9.
GU Shangyi WAN Guojiang MAO Jianquan 《中国地球化学学报》2007,26(4):434-438
The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO* Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase. 相似文献
10.
本区燕山早期花岗岩发育的风化壳中的粘土矿物以高岭石和埃洛石(7Å)为主;蒙脱石、三水铝石及其它为新查明矿物。据粘土矿物组合特征,自风化剖面深部到地表分为三个带:含蒙脱石带,高岭石和埃洛石(7Å)带,含三水铝石带。本文探讨了矿物在风化过程中的生成演化顺序,并进行了热力学的解释。据各带粘土物质的阳离子交换量与稀土含量变化的不一致关系认为,稀土在C带中的富集是化学风化的结果,与粘土矿物组合无关。 相似文献
11.
二长花岗岩风化壳自下而上划分为原生带、微风化带、弱风化带和强风化带。风化壳中粘土矿物主要为埃洛石,其次为高岭石及少量伊利石。微风化带下部以高岭石为主,往上埃洛石逐渐占优势,并于弱风化带中、上部和强风化带中局部富集,这与当时地下水活动状态有关。高岭石结晶程度随风化程度的增强而提高。在弱酸性介质条件下及水分丰富、溶出条件强烈时,从长石解理面上和长石的“溶蚀”空隙中可以直接形成高岭石或埃洛石,而过渡阶段的伊利石很不发育或不存在。 相似文献
12.
台湾海峡表层沉积物中黏土矿物特征及物质来源 总被引：4，自引：1，他引：3
利用X射线衍射仪,对比分析台湾海峡及周边表层沉积物的黏土矿物特征,讨论长江、福建和台湾河流对海峡黏土矿物的贡献程度。福建河流（闽江）的黏土矿物以高岭石为主（>40％）,其次是伊利石（30％）和绿泥石,不含蒙脱石;长江和浙闽泥质区的黏土矿物特征是伊利石含量最高（61％～66％）,其次是绿泥石（16％～17％）和高岭石（10％～13％）,少量蒙脱石（6％～9％）。台湾河流（浊水溪）黏土矿物组合为伊利石（>70％）和绿泥石,不含高岭石和蒙脱石为特征。台湾海峡高岭石含量由西向东明显减少,说明高岭石主要来自福建的河流。〖JP2〗台湾海峡50 m等深线以东区域的黏土矿物具有高的伊利石和绿泥石含量,低的蒙脱石和高岭石含量,且伊利石的化学指数和结晶度值都明显低于长江和福建的河流,反映台湾河流的物质来源。在台湾暖流作用下,台湾河流为台湾海峡中北部提供了大量的伊利石和绿泥石。福建近海的黏土矿物主要是由福建河流提供的,但在平潭岛周边海域的黏土矿物可能有长江物质的混合。〖JP〗 相似文献
13.
M. Cathelineau 《Mineralium Deposita》1983,18(1):89-97
A comprehensive study of alteration minerals, especially clays, developed around or within French hydrothermal uranium ore bodies (Vendée and Margeride), generally associated with leucogranitic rocks, using optical examinations, classical methods of clay mineralogy and electron microprobe determinations, demonstrates the general feature of potassic minerals as products of reaction between ore forming fluids and host rocks. Six stages of alteration follow the typical metallogenic sequence established for numerous deposits: early stages and uranium stages 1) 2) 3) with phengites, illite, mixed layered illite and K-montmorillonites; 4), early reworking of pitchblende 1 to pitchblende 2 with complex zoning around ores: illite, illite-K-montmorillonites; 5) then to coffinite-smectites; 6) sooty pitchblende, during supergene weathering, with smectites and kaolinite. Potassic metasomatism by fluids in desequillibrium with the minerals of the granitic host rocks, essentially albite, explains the complex alterations in K-smectites, mixed layered minerals and adularia. Variety of alteration products in each alteration zone indicate incomplete reactions of the solids and chemical potential gradients on a small scale. 相似文献
14.
J. P. Shrivastava Mansoor Ahmad Surabhi Srivastava 《Journal of the Geological Society of India》2012,80(2):177-188
Clay minerals associated with intra-volcanic bole horizons of varied colours and thicknesses contain montmorillonite, halloysite and kaolinite, show distinct microstructures and microaggregates. In kaolinite, Fe3+ ions substitute for Al3+ at octahedral sites. Most of these clays are dioctahedral type, show balance between net layer and interlayer charges. The interstratified illite — smectite (I/S) mixed layers containing variable proportions of montmorillonite. Illite contains sheet-like, well oriented microaggregates. The parallel stacks of chlorite sheets show chlorite/smectite (C/S) mixed layers. Progressive enrichment of Fe and depletion of Al ions with the advancement of kaolinization process is observed. High order of structural and compositional maturity observed in these bole clays, indicate long hiatus between the two volcanic episodes. 相似文献
15.
山西、河南高铝粘土铝土矿矿床矿物学研究 总被引：5，自引：0，他引：5
耐火材料工业把Al2O3>46%（熟料）的耐火粘土称为“高铝粘土”。从理论上应把铝硅比≥2.6的称为耐火用铝土矿,惟我国《储量规范》为了勘探工作方便仍称其为高铝粘土。而普通耐火粘土（熟料Al2O3<46%,但实际应用扩大到50%）与高铝粘土中的易熔杂质总量不超过6%,灼减一般不大于16%,Fe2O3一般不大于3%或3.5%。 相似文献
16.
K. Rajkumar A. L. Ramanathan P. N. Behera 《Journal of the Geological Society of India》2012,80(3):429-434
Clay minerals, byproducts of chemical weathering, are important group of minerals found in rivers, estuaries, and marine sedimentary environments, which include mudstones, clay stones, and shales. In the present study, FTIR and SEM investigation on the clay minerals in Sundarban mangrove core sediments collected from Moipith Matla and Belamati Island are carried out. The study indicated the dominant association of kaolinite with subordinate amount of quartz, illite and chlorite. The abundance of kaolinite, illite chlorite and clay with quartz helps in increasing sediment in the islands region. The geochemical and mineralogical evolution of mangrove sediments are results of the interaction of biotic and abiotic parameters, whose balance is conditioned by the climate that governs the hydrologic regime, the sedimentation dynamics and the organic matter. This study on the charaterstation of clay provides us with substantial impact in the water holding capacity, productivity and mineralogical and chemical transformation in order to establish much more and intermediate equilibrium between marine influence and continental contribution, as part of the estuarine environment, than to the tropical climate conditions. 相似文献
17.
Altered crystalline rocks occur at the peneplain exposed in southern Israel and in other localities across North Africa and Arabia where they underlie an extensive blanket of Cambro–Ordovician sandstones. This study focuses on the petrography, mineralogy and geochemistry of top basement rocks of the northern Arabian‐Nubian Shield. The altered rocks are shown to be weathering profiles that can be subdivided into three horizons interpreted as apparently unweathered granite, or saprock, which grades upwards to a saprolite, topped by a thin clayey plasmic zone. The plasmic zone is enriched in iron and aluminium and is depleted in silicon, calcium, magnesium and potassium relative to the underlying saprolite. The chemical index of alteration increases upward, but does not exceed 90 and, therefore, lags behind values observed in strongly leached present‐day tropical soils. Petrographic examinations reveal iron mobility under local fluctuating redox conditions, similar to modern and Proterozoic soils. A variety of birefringence fabrics induced by shrinkage and expansion of clays during wetting and drying cycles and clay illuviation strongly indicate pedogenic processes rather than a post‐depositional alteration. Illite and ordered illite‐smectite phases coexist with smectitic illite‐smectite in the lower part of the saprolite and with kaolinite in the plasmic zone, in line with increasing chemical index of alteration. Observations are in accordance with the current profile being a remnant of a thick weathering profile whose top was truncated by fluvial incision just prior to deposition of the overlying Early Cambrian sequence. A previously documented Devonian thermal event reaching temperatures of at least 200°C overprinted the studied rocks. During burial diagenesis, illitization affected original smectite rather than kaolinite. However, in spite of the elevated temperatures, illitization was incomplete implying restricted potassium addition. The sub‐Cambrian weathering reflects warm and humid conditions in a tropical or sub‐tropical climate, in line with several plate reconstructions placing Israel at low latitudes during Cambrian time. 相似文献
18.
《Geochimica et cosmochimica acta》1999,63(23-24):4013-4035
The effect of organic matter during soil/water interaction is still a debated issue on the controls of chemical weathering in a tropical environment. In order to study this effect in detail, we focused on the weathering processes occurring in a small tropical watershed (Nsimi-Zoetélé, South Cameroon). This site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry.The lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones: unsaturated slope soils on the hills and/or elevated areas; and water-saturated soils in the swamp zone which represent 20% of the basin surface. The study present chemical analysis performed on water samples collected monthly from different localities between 1994–1997 and on soil samples taken during a well drilling in December 1997. The results suggest the existence of chemical and spatial heterogeneities of waters in the basin: colored waters flooding the swamp zone have much higher concentrations of both organic matter (i.e., DOC) and inorganic ions (e.g., Ca, Mg, Al, Fe, Th, Zr) than those from springs and groundwater from the hills. Nevertheless, these organic-rich waters present cation concentrations (Na, Ca, Mg, K) which are among the lowest compared to that of most world rivers. The main minerals in the soils are secondary kaolinite, iron oxi-hydroxides, quartz, and accessory minerals (e.g., zircon, rutile). We mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through SEM observations the textural characterization of weathered minerals such as kaolinite, zircon, rutile, and the secondary recrystallization of kaolinite microcrystals within the soil profile. Water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin. Thus, in order to explain the increase of element concentration in the organic-rich waters, we suggest that organic acids enhance dissolution of minerals such as kaolinite, goethite, and zircon and also favors the transport of insoluble elements such as Al, Fe, Ti, Zr, and REE by chemical complexation. SiO2(aq) concentrations in these waters are above saturation with respect to quartz. Dissolution of phytholithes (amorphous silica) may be responsible for this relatively high SiO2(aq.) concentration. Al/Mg ratios obtained for the soil and the Mengong river waters show that a significant amount of Al does not leave the system due to kaolinite recrystallisation in the swamp zone soils. Geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone. Quantitatively we propose that the increasing amount in total dissolved solid (TDS) due to organic matter and vegetation effect is about 35%. In summary, this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements. Thus, the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils. 相似文献
19.
粘土矿物钝化改性和钝化机理初步研究 总被引：1，自引：0，他引：1
在岩土工程中,进行灾害防治和软基处理的一个核心问题是把粘土矿物由亲水性改造成疏水性,抑制和降低其含水量,使得粘土遇水后不再吸水膨胀,从而保持土壤的稳定性。岩土力学工程中以保持土壤稳定性为目的对粘土的改性称为“钝化”。所谓钝化就是用 钝化剂与粘土矿物表面发生反应,改变粘土矿物的表面结构,提高憎水性,增加粘土整体的力学性质,从而达到稳定土体的目的。在粘土矿物钝化中表面活性剂是一个重要的组成部分 ,但是表面活性剂在固液界面的吸附,除决定于其本身的性质外,还决定于固体的性质、溶 液的pH值和温度等。因此,研究粘土矿物表面结构和性质以及与钝化剂的相互作用是提高粘 土矿物钝化效果的重要途经。利用近代分析方法（XRD、IR、Raman、MAS NMR、TEM、AFM和S EM）,对粘土矿物（高岭石、蒙脱石和伊利石）钝化前后的表面结构和性质进行了系统研究 ,并结合相关的土力学、工程力学参数的测定,阐明粘土矿物钝化的机理,剖析和研制粘土 矿物钝化剂,为解决各类工程和灾害问题中的土壤稳定提供理论依据。 相似文献
20.
《Applied Geochemistry》2004,19(4):633-643
Banana plants (Musa spp.) are very sensitive to Al, which is mobilized in acid soil conditions. These plants may, however, contribute to their own intoxication because their roots can excrete protons in large quantities. The authors studied the mobilization of Al by banana roots from clay minerals in experimental designs exacerbating the root–mineral contact. The plants were grown on agarose-gel or sand substrates previously mixed with smectite (montmorillonite) and kaolinite as sole source of Al. The pH and the ion concentrations in the aqueous and exchangeable phases of the substrates were determined as concentrations of Al, Ca, Mg and K in plants. In both agarose and sand substrates, pH significantly decreased in the close vicinity of roots, relative to the bulk substrate. This root-induced acidification involved a preferential mobilization of Al in kaolinite substrates and of Mg in smectite substrates, and thereby a significant plant uptake of Al and Mg from these respective substrates. Root-induced weathering of kaolinite and montmorillonite thus suggests that the mobilization of, respectively, Al and Mg are the limiting steps in the dissolution of these respective minerals, just as demonstrated in previous chemical weathering studies. 相似文献