ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02185.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummarySand volcanoes have been found in three sedimentary associations in the Upper Carboniferous Bude Formation. In two of these associations they formed when the dewatering of fluidized sand beds, deposited from traction carpets, was temporarily inhibited by the deposition of overlying units. In the third association the volcanoes formed during the normal post‐depositional compaction of fluidized, muddy, poorly sorted units deposited from subaqueous mudflows. While is seems that the tops of fluidized sand beds were characteristically sheared by a fairly powerful current immediately after being deposited, the waters above the recently deposited mudflow units were commonly stagnant, allowing sand volcano growt

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02186.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryScanning and transmission electron micrographs of various shales establish the close correlation between clay‐flake orientation and fissility. The shales with the best fissility have the highest degree of preferred orientation. Randomness of clay flakes prevails in non‐fissile claystones. The results suggest that the fabric of shales may result either from the deposition of dispersed clay or by the collapse of clay floccules after deposit

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02187.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryFabrics of Tertiary shales from the Rhinegraben (southwestern Germany) were studied by methods for fine‐particle measurement including grain‐size distribution, porosity, pore‐size distribution, and specific surface area.The most frequent pore radii (rm) are found to decrease with increasing overburden, this decrease in relation to porosity being more rapid in shales, which are cemented by carbonate. The specific surface area (Sg) is not affected by pressure down to a depth of approx. 1,000 m. With increasing compaction pressure the specific surface areas are found to decrease indicating a fusion of clay‐mineral particles, which corresponds to the alteration of smectite minerals into 10‐Å mica.The sorting index of pore‐size distribution (Sop) remains constant throughout the shallow‐burial range. Below 1,000 m the sorting index increases considerably. This effect is caused by the coarse non‐clay components of the shales, since on both sides of a nearly isometric quartz grain, for instance, large pores may be kept open even under high compaction pressure. This effect is also indicated by the skewness of the pore‐size distribution, which shifts from negative to positive values near 1,000 m of overburden. Above this level fine pores predominate while deeper the relatively coarse pores are more abundant.This study shows that the conventional mechanical model of a clay‐mineral fabric reacting on overburden pressure is applicable to the shallow‐burial range only. After mineral transformations have commenced, the fabrics loose their original grain‐size distribution, so that their porosities are no longer controlled solely by mechanical effects. With the Rhinegraben shales the shallow‐burial range is limited t

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02188.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryPelitic rocks were followed from unmetamorphosed clays and marls of Upper Triassic and Lower Liassic to anchimetamorphosed phyllites of the Alpine border region in Switzerland. Phengite and Al‐rich chlorite formed from mixed‐layer illite/montmorillonite; pyrophyllite from kaolinite. For the formation of paragonite, the following sequence is proposed: irregular mixed‐layer illite/montmorillonite → regular mixed‐layer mica/montmorillonite → mixed‐layer paragonite/phengite → paragonite.Besides the formation of new minerals in the transition zone (anchizone) between diagenesis and greenschist facies, other changes with increasing metamorphic grade are: the crystallinity of illite (in the sense of Kubler, 1967) increases, the intensity ratio 002/001 of the illite basal reflexions increases, 1Mdillite changes to 2M1phengite; the slates change colour from red to pink; the mean density increases; and textural changes due to reactions between clastic quartz and cl

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02189.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryThe results obtained by the author in the study of clay‐minerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates.Kaolinite mineralsare related to the surficial zones of the earth's crust where they are formed. They are characterized by the hexacoordination of aluminium. They furnish paleogeographic indications in ancient sediments. During diagenesis they are very sensitive to the geochemical environment, stable in acid conditions, unstable in alkaline conditions. However, the increase in temperature by burial causes their destruction sooner or later. In the transitional zone to metamorphism (anchizone), kaolinite is not present. Only dickite and nacrite can be observed, provided that the environment is acid.Montmorillonitesare hydrated minerals. The rise in temperature and above all in pressure during burial expels water from the interlayers. Concentrated interstitial solutions of diagenesis provide cations which replace molecules of water between the layers. It is an irreversible reaction which produces 14‐Å minerals (chlorites) or 10‐Å minerals (illites), passing generally through mixed‐layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial.Mixed‐layersare intermediate stages which occur during degradation by weathering and during aggradation by deep diagenesis. This aggradation is the result of an incorporation of certain cations taken up from interstitial solutions, and of a rearrangement within the lattice. There are two major pathways: a potassium and sodium pathway, which produces the illites, then the micas, passing possibly by regular mixed‐layering of the allevardite‐rectorite type; and a magnesium pathway, which produces the chlorites, passing possibly by a regular mixed‐layering of the corrensite type. These mixed‐layers can remain stable until the border of meta‐morphism (anchizone).Micaceous clay minerals or illitesform a very heterogenous group in the sediments which have been hardly diagenetized. Particles of diverse origin are found. They become more regular during burial. In deep diagenesis and the anchizone, crystallo‐graphic parameters of the illite are sufficiently well defined to serve as a scale of recrystallization, a zoneographic index. The morphology of the particles changes. Polymorphic types 1Md and 1M are replaced by the 2M‐type. The sharpness of the 10‐Å peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5‐Å and 10‐Å peaks, which is related to the chemical composition of the octahedral layer.Micasin low‐grade metamorphism, called sericites by petrographers, replace the illites discussed above. They are different from the true micas by a weaker layer charge, less than 0.9 by half‐cell. They often contain sodium (paragonitic muscovites and paragonites). The octahedral charge (zero for the muscovite) is generally high, due to the replacement of Al by Fe2+and Mg (phengites). These transformations should not obscure the fact that metamorphism is also accompanied by crystalline growth and massive neoformation.Chloritesare the least well‐known clay minerals in diagenesis. Detrital particles can be aggraded to chlorite during early diagenesis by passing through the mixed‐layer stage of corrensite. A massive growth of chlorite is observed in late diagenesis and the anchizone. Illite and chlorite slates give place to sericite and chlorite schists. At present, general data are not available on the crystal chemistry of chlorites in the anchizone and the greenschist facies.The stages in the diagenetic evolutionof clay minerals are too little understood to be able to give them precise limits. However, the following provisional scheme can be proposed:(1) Early diagenesis (= “diagenesis” of Russian authors; = the “shallow‐burial stage” of Müller, 1967a). In this stage all the clay minerals are stable; some undergo aggradation by adsorption of Mg, K and Na (various mixed‐layers); some are neoformed (montmorillonites).(2) Middle diagenesis (= “early catagenesis or epigenesis” of Russian authors; the “deep‐burial stage” of Müller, 1967a, includes this stage and all the following until metamorphism). In this stage the sediment becomes compact. It has lost at least 50% of its connate water. Porosity is high and circulation still plays an essential part. Some detrital minerals, such as biotite, are unstable. All the clay minerals are still stable, but many types of replacement take place, due to interstitial circulation. Dickitization of kaolinite and illitization of montmorillonite can already be observed.(3) Deep or late diagenesis (= “late catagenesis or epigenesis” of Russian authors). In this stage the temperature is greater than 100 °C, pressure increases and porosity becomes very weak. Montmorillonites and irregular mixed‐layers disappear. Kaolinite recrystallizes as dickite in acid environment. These changes are irreversible.(4) Anchizone (= “metagenesis” of Russian authors; = “zone anchimétamorphique” of Kubler, 1964). This is the transitional zone to metamorphism. It agrees with temperatures around 200 °C. Illite and chlorite are almost the only sheet silicates. However, dickite can be observed as well as pyrophyllite generally associated with allevardite. The crystallographic parameters of illite define the limit of the following zone, the metamorphic epizone or greenschist facies.The crystallochemical processesthat take place during the diagenetic evolution of clay minerals are schematically the following:(1) Gradual tetracoordination of aluminium.(2) Filling of octahedral sites either by interlayer cations, either by cations derived from outside the lattice, without the distinction dioctahedral‐trioctahedral becoming very clear.(3) Interlayer exchange between crystal lattice and interstitial solution. Gradual closing of the layers by alkaline cations or octahedral brucite‐like sheets.(4) Massive crystalline growth in the anchizone and the epizone.These processes are roughly symmetrical with those which occur during weathering.This review is a summary of the conclusions drawn in a Docteur‐ès‐Sciences thesis (G. Dunoyer deSegonzac, 1969:Les Minéraux argileux dans la Diagenèse. Passage au Métamorphisme, 339 p., 45 tables, 110 illus.) to be published as part of the seriesMémoires du Service de la Carte Géologique d'Alsace et de Lorraine. Most of the evidence on which these conclusions have been based is not cited dire

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02190.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryPhyllosilicates and zeolites grew in Columbia River sediments during hydrothermal experiments at relatively low temperatures and pressures. Although the new minerals may not be equilibrium assemblages, our results strongly support the idea that matrix minerals in graywackes may be the result of alteration of components thermodynamically unstable in the environment of diagenesis. Scanning electron micrographs show that the new minerals have formed as a mesh‐like coating on original grains. The textural relationship of the new minerals to the original minerals resembles graywacke textur

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02191.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryThe Ranger Canyon and Mowitch Formations are the youngest Permian strata in the Rocky Mountain Front Ranges. They constitute a thin, widespread and clearly defined stratigraphic entity covering approximately 60,000 sq. miles; they occur below Triassic beds and above a major, regional, intra‐Permian unconformity, initiated by a transgression which started in the northwest. Beds of the above entity are therefore diachronous. The erosion surface is overlain by polymict, phosphatic conglomerates containing mature lag gravels and immature breccio‐conglomerates and corrosion breccias.Rock types are either sandstones or silty and sandy cherts, phosphorites and occasionally dolomites. Clastic components are dominantly mature quartz (some pseudomorphs gypsum), phosphate, some feldspar, negligible clay, and stable detrital minerals, necessitating: (1) many cycled, clastic sedimentary rock; (2) local gypsum; and (3) phosphate producing, distributive provinces.Secondary features include primary cementation by quartz, chalcedony, dolomite, sulphate and phosphate, with replacement mainly by chalcedony. Contraction fractures are cemented by quartz (after anhydrite and fluorite), calcite and barite. Accessory authigenic minerals are hematite, sulphates (pseudomorphed by quartz), fluorite, apatite and dolomite. Diagenesis therefore occurred within a chemically active environment.Minerals present indicate: (1) phosphate producing and (2) evaporite producing environments, the components for which may be obtained from sea water by: (a) a biogeochemical phosphate‐fixation cycle; and (b) concentration of brines by interstitial refluxion.A Recent environmental parallel occurs along the coast of Baja, California. Phosphate produced off‐shore contributes to quartz‐rich sediments prograding seawards; evaporitic conditions produce minimum carbonate and maximum sulphate precipitation.The sequence of events envisaged for the Permian rocks started with phosphate corrosion of bed‐rock and cementation of lag gravels; some phosphate was contributed to shoreline, with quartz and gypsum sands, prograding over the basal conglomerate. Sand cementation by carbonate occurred in shoreline and intertidal zones, and by sulphate in the supratidal zones. Concentration of brines by refluxion, and local silica enrichment, facilitated silica precipitation and replacement. Penecontemporaneous silicification of Late Permian sediments was therefore instrumental in their ultimate p

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02192.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SummaryExperimental investigation shows that amorphous silica is converted into quartz through cristobalite under hydrothermal conditions. The rate of transformation, essentially dependent on the reaction temperature, was studied on the basis of quantitative analyses of quartz in the products, and the variation of quartz content was elucidated by taking the induction period into consideration. The transformation is a consecutive reaction involving two first‐order steps, from amorphous silica to low‐cristobalite and from low‐cristobalite to low‐quartz. Kinetic data such as the rate constants and the energy of activation are obtained.Mineralogical varieties of silica found in siliceous deposits suggest that the transformation probably takes place under natural conditions. Younger deposits contain amorphous silica or cristobalite, whereas older ones are invariably composed of quartz. By assuming that the transformation process observed experimentally holds in nature, kinetic data can be estimated. Since the process depends upon the thermal history, it is possible to follow the transformation process for a given model of a thermal history. An example of computed results is compared with the geological evidence, and it is concluded that the mineralogical variation of silica is accounted for by the transformation process.Zonal distribution of silica minerals apparently corresponds to that of zeolite minerals, and the transformation of silica is considered to occur during diagenesis. Evidently, almost all diagenetic facies represent intermediate stages on the way to the ultimate equilibrium. The cristobalite stage described in this paper belongs to one of these stages, and is referable to the early stage of diagenesis. It is suggested that silica minerals can be used as clues to understand a progressive change in dia

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1970.tb02193.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY