Showing papers in "Sedimentology in 1970"
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TL;DR: The results obtained by the author in the study of clayminerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates as discussed by the authors.
Abstract: Summary
The 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 minerals are 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.
Montmorillonites are 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-A minerals (chlorites) or 10-A minerals (illites), passing generally through mixed-layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial.
Mixed-layers are 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 illites form 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-A peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5-A and 10-A peaks, which is related to the chemical composition of the octahedral layer.
Micas in 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.
Chlorites are 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 evolution of 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 Muller, 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 Muller, 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 anchimetamorphique” 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 processes that 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-es-Sciences thesis (G. Dunoyer de Segonzac, 1969: Les Mineraux argileux dans la Diagenese. Passage au Metamorphisme, 339 p., 45 tables, 110 illus.) to be published as part of the series Memoires du Service de la Carte Geologique d'Alsace et de Lorraine. Most of the evidence on which these conclusions have been based is not cited directly in this article, but can be found in the thesis mentioned above, to which the reader is referred.
382 citations
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TL;DR: In this paper, the authors compare the sedimentary structures in modern point bar deposits of the Amite River in Louisiana and the Colorado River in Texas are analogous to features observed in Eocene Simsboro and Pleistocene Colorado River deposits.
Abstract: SUMMARY
Primary sedimentary structures in modern point bar deposits of the Amite River in Louisiana and the Colorado River in Texas are analogous to features observed in Eocene Simsboro and Pleistocene Colorado River deposits of the Texas Gulf Coastal Plain.
Short-duration peak flow, channel pattern, average stream gradient of about 2–3 ft./mile, and bank stabilization by dense vegetation are major parameters controlling the depositional pattern of coarse sand and pebble gravel of the Amite and Colorado rivers. Stratification is directly related to specific depositional features and consists of: large-scale trough-fill cross-stratification in the scour pool; trough-fill cross-stratification and foreset cross-stratification in the lower point bar; parallel laminae, large foreset cross-stratification, and trough-fill cross-stratification in the chute bar; parallel inclined laminae, climbing ripple laminae, and mud drapes in the chute fill; and parallel inclined laminae, mud drape, and foreset cross-stratification in overbank, flood-plain deposits.
Fundamental differences between point bars of bed-load streams (low suspended load/bed load ratio) and mixed-load streams (high suspended load/bed load ratio) are that upper point bar sediments with small trough sets and parallel inclined laminae occur only in fine-grained (mixed load) fluvial deposits, and large scale foresets of chute bars are common to coarse-grained (bed load) fluvial deposits but are not found in fine-grained fluvial deposits. Upward fining sequences, characteristic of fine-grained fluvial deposits, are uncommon in sediments deposited by bed-load streams such as the Amite and Colorado rivers.
The Simsboro Sandstone consists mainly of scour pool, lower point bar, and chute bar sediments. Chute fill and flood-plain deposits are preserved only in the highest stratigraphic sequence. Pleistocene Colorado River deposits display the same sequence of stratification types as the Simsboro but are composed of coarser material.
265 citations
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TL;DR: The Middle Pleistocene Belmont Formation of Bermuda consists in part of beach-dune biocalcarenites which underwent intense contemporaneous cementation and diagenesis.
Abstract: SUMMARY
The Middle Pleistocene Belmont Formation of Bermuda consists in part of beach-dune biocalcarenites which underwent intense contemporaneous cementation and diagenesis. The beach deposits were contemporaneously cemented by fibrous isophacous cement to form beachrock, whereas previously deposited eolianites further inland underwent intense meteoric phreatic diagenesis, resulting in coarse-grained cementation and stabilization of most of the metastable components of the rock. Above the Belmont water table, vadose diagenesis was relatively ineffective in cementing and altering the biocalcarenites. Phreatic meteoric diagenesis is interpreted to be a very rapid process, relative to vadose meteoric diagenesis, and to result in a much coarser-grained sparite.
160 citations
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TL;DR: In this article, the rotatable-drum principle is used to measure the critical angle of repose (ac) and the angle of rest (aR) of a mass of granular material.
Abstract: SUMMARY
A simple apparatus for measuring the angles of repose of masses of granular material in various media, based on the rotating-drum principle, is described. Two angles of repose are measured by this method. The critical angle of repose (ac), is defined as the angle through which a mass of granular material can be rotated before it fails by avalanching, and the angle of rest (aR), is defined as the inclination of the slope after avalanching has ceased.
Measurements of the angles of repose of several materials in air and under water with the “rotatable-drum apparatus” indicate that for materials with similar surface characteristics the angles of repose increase with departure of the grains from a spherical form. For masses of spherical particles the angles of repose increase with increasing intergranular friction caused by changes in the surface characteristics of the spheres. For mixtures of spheres and cubes the angles of repose are proportional to the volumes of the end members present. For natural quartz sands the critical angle of repose (ac), is always greater in air than under water, but the angle of rest (aR), is the same in both media. Measurement of the inclinations of slip faces of subaerial dunes and subaqueous deltas indicates that these faces stand at, or less than, the angle of rest (aR), of the sand from which they are built.
It is concluded that shape and surface characteristics of the particles have the greatest effect on the angles of repose.
153 citations
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TL;DR: In this paper, side-scan Asdic and echo-sounder data was used to investigate the widespread occurrence of sand ribbons, sand waves and sand patches on the continental shelf west of the British Isles and France.
Abstract: SUMMARY
Extensive data obtained by side-scan Asdic and echo-sounder equipments, viewed in conjunction with bottom notations on navigational charts and some seabed samples, show the widespread occurrence of sand ribbons, sand waves and sand patches on the continental shelf west of the British Isles and France. The close similarity of their directional trends with those of the strongest tidal currents strongly suggests a causal relationship which applies to much of the continental shelf, parts of the upper continental slope and also to off-lying shoals such as Rockall Bank. The sand transport paths broadly parallel the coasts in the epicontinental seas and on the open shelf west of the British Isles. In contrast, the paths are substantially normal to much of the coast of western France.
142 citations
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TL;DR: In this article, a sequence of irregular mixed-layer illite/montmorillonite was proposed for the formation of paragonite, and the following sequence was proposed: irregular mixed layer illite, regular mixed layer mica, mixed layer phengite/phengite.
Abstract: Summary
Pelitic 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, 1Md illite changes to 2M1 phengite; the slates change colour from red to pink; the mean density increases; and textural changes due to reactions between clastic quartz and clay cement occur.
120 citations
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TL;DR: In this article, the angle of climb of ripples in cross-laminated deposits is governed by a simple relation, in which ζ is the angle to climb, M is the rate of sediment deposition normal to the rippled bed, H is the ripple height, and Jb is the bedload sediment transport rate.
Abstract: SUMMARY
The angle of climb of ripples in cross-laminated deposits is governed by the simple relation:
in which ζ is the angle of climb, M is the rate of sediment deposition normal to the rippled bed, H is the ripple height, and jb is the bedload sediment transport rate. After introducing sediment transport functions, this relation is developed using the assumptions of gradually varied flow to predict the spatial patterns of cross-lamination types in deposits due to pure non-uniform flow, pure unsteady flow, and simultaneous non-uniform and unsteady flow. Most of the predicted patterns can be matched from the geological record, and the analysis affords a hitherto missing insight into the environmental significance of climbing-ripple cross-lamination. The analysis also results in a rigorous definition of the kinds of environmental interpretation that may legitimately be made from examples of this structure.
103 citations
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TL;DR: In this paper, an experimental investigation showed that amorphous silica is converted into quartz through cristobalite under hydrothermal conditions, and the rate of transformation, essentially dependent on the reaction temperature, was studied on the basis of quantitative analyses of quartz in the products.
Abstract: Summary
Experimental 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 diagenesis.
98 citations
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TL;DR: The development of optically continuous quartz overgrowths is governed by the atomic structure and crystallographic orientation of the detrital quartz grains as mentioned in this paper, and growth is particularly rapid along the direction of the c-axis.
Abstract: SUMMARY
The development of optically continuous quartz overgrowths is governed by the atomic structure and crystallographic orientation of the detrital quartz grains. Initial growth commences with the appearance of numerous oriented projections, with rhombohedral and prismatic form, on grain surfaces. Merging and overlap of the projections results in the formation of large crystal faces whose form is dependent upon the initial location of the projections with respect to the internal crystallographic axes. Growth is particularly rapid along the direction of the c-axis. For unicrystalline quartz grains the ultimate growth phase is the production of polyhedral quartz crystals having the appearance of hexagonal dipyramids. In polycrystalline grains each quartz unit within a single grain develops a separate overgrowth, the form of which is similarly controlled by the internal structure of the individual quartz units. Hence, the completed overgrowth shows an irregular distribution of diversely oriented prism and rhombohedral faces.
88 citations
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TL;DR: In this article, the late Pleistocene reefs of North Jamaica are attributed to reaction with meteoric water, including dolomitization, including the dolomerization of red algae.
Abstract: SUMMARY
Diagenesis, including dolomitization, of Late Pleistocene reefs of North Jamaica is due to reaction with meteoric water. Although the reactions:
Mg-calcite—calcite
Aragonite—calcite
Mg-calcite—dolomite
retain microarchitectural information, complete chemical redistribution takes place so that incongruently dissolved Mg-calcites, aragonite inversion mosaics (neomorphosed aragonite), and dolomitized red algae have similar isotopic compositions, resembling precipitated calcite cements. The minerals all appear to have stabilized in the meteoric water environment. The dolomite is not widely distributed, and is restricted to replacement of red algae. There has been no net addition of magnesium to the red algal clasts.
81 citations
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TL;DR: In this article, scanning and transmission electron micrographs of various shales establish the close correlation between clay-flake orientation and fissility, and the shales with the best fissibility have the highest degree of preferred orientation.
Abstract: Summary
Scanning 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 deposition.
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TL;DR: In this article, Malekula Island pre-Miocene pelagic red mudstones are in tectonic contact with a thick marine succession of Early Miocene age, which is intruded by basaltic and andesitic dykes and sills with a calc-alkaline composition and by plutons.
Abstract: SUMMARY
On Malekula Island pre-Miocene pelagic red mudstones are in tectonic contact with a thick marine succession of Early Miocene age, which is intruded by basaltic and andesitic dykes and sills with a calc-alkaline composition and by plutons. This succession is in faulted contact with Middle Miocene sedimentary rocks.
The Lower Miocene succession consists of quartz-free volcanoclastic rocks, detrital limestones and pelagic sediments, and rare lava flows. Fifteen sedimentary facies have been recognized, all of which accumulated below the zone of strong wave or current action. Vertical changes in facies are common; facies relationships and associations and internal sedimentary structures indicate that many facies were transported by mass gravity processes. Texture and composition of clasts in the volcanoclastic rocks show that some facies were derived from subaerially erupted volcanic rocks, and others from submarine volcanoes. Clastic limestones consist largely of algal and coral fragments and benthonic foraminifers.
The Lower Miocene palaeogeography resembled that in and around volcanic chains in present island arcs. Subaerial and submarine volcanoes fed by minor intrusions supplied epiclastic, pyroclastic and autoclastic debris which accumulated in deep water around the volcanic chain. Carbonate detritus was derived from reefs bordering the volcanic islands.
The Middle Miocene succession consists of volcanic and reef-derived turbid-ites, pelagic sediments and tuffs. The epiclastic rocks in this succession were derived from the uplifted rocks of Early Miocene age and from bordering reefs.
The presence of some ancient volcanic arcs, now located either within existing ares or within geosynclinal successions lying in or on the borders of continents, may be indicated only by quartz-poor turbidites containing abundant calc-alkaline volcanic detritus.
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TL;DR: In this article, the authors studied grain orientation and size in eight turbidite greywacke beds from the Cloridorme Formation (Middle Ordovician), Gaspe, Quebec, Canada.
Abstract: SUMMARY
Longitudinal and vertical variation in grain orientation and size has been studied in eight turbidite greywacke beds from the Cloridorme Formation (Middle Ordovician), Gaspe, Quebec, Canada. The beds are exposed on a wave-cut platform near Grande Vallee, Gaspe. These beds were traced for about two miles along the strike (276°), which is almost parallel to the average current direction (274°) as indicated by sole marks.
Agreement between grain orientation and other internal current-direction indicators such as graptolites and intra-bed lineation shows that grain fabric is primary in nature and that grains are typically aligned parallel to the current direction. Grain orientations are generally statistically non-significant in the upper massive part of the beds in the proximal region and significant in the rest of the beds. Most of the significant grain orientations are close to the sole direction in the proximal region and deviate from the sole direction by as much as 90° in the distal region. Grain orientations are increasingly divergent from the base towards the top of the bed. Current-normal grain orientations are observed in a plane-laminated part of a bed.
The beds show a good grading in the proximal area and are ungraded or slightly reverse graded in the distal area. These grading characteristics are exhibited by both the mean and maximum grain size. Most beds show no appreciable variation in the mean grain size at the base of the bed along the strike. However, for one bed, the largest mean size at the base occurs in the middle of the outcrop and grain size decreases from this point both in the upstream and downstream directions.
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TL;DR: In this paper, the authors studied fabrics 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, showing that the conventional mechanical model of a clay-mineral fabric reacting on overburden pressure is applicable to the shallow-burial range only.
Abstract: Summary
Fabrics 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-A 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 to a depth of about 1,000 m.
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TL;DR: In this article, the relationship between crystal chemistry and genetic conditions is presented for a series of dioctahedral micaceous minerals, including Al-micas, Fe-illites, and glauconites.
Abstract: SUMMARY
Relationships between crystal chemistry and genetic conditions are presented for a series of dioctahedral micaceous minerals. Using a ferruginicity index, three groups of micaceous minerals are distinguished: Al-micas, Fe-illites, and glauconites. The degree of Al-for-Si substitution in the tetrahedral sheets of micaceous minerals depends on their thermodynamic genetic conditions. If pressure and temperature increase, the Al-IV content increases and the octahedral sheet is “cleaned” from divalent cations. This process is accompanied by structural alteration with a polytype sequence 1Md-1M-2M1. Tetrahedral and octahedral charges are the same for micaceous minerals formed at the surface (sedimentogenesis/diagenesis) and are independent of the iron content. For most illites of sedimentary rocks an authigenic origin is suggested.
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TL;DR: In this paper, the diagenesis of calcareous algae was investigated by electron microprobe and the results showed that the highest magnesian values in Recent algae specimens were found to be in high Mg calcites rather than in any other phase.
Abstract: SUMMARY
Initial results of investigation of the diagenesis of calcareous algae by electron microprobe are:
1
A few conceptacles and other cavities in Recent algae specimens are partly to completely filled with younger carbonate In contrast to the surrounding skeleton of about 10–20% mol MgCO3-calcite, these deposits are either very low (0–2%) or very high (15–50%) in MgCO3 content
2
Highest magnesian values in Recent algae studied are thought to be in high-Mg calcites rather than in any other phase, with very few possible exceptions
3
Calcian dolomite replacing fossil algae in cores from Eniwetok Atoll commonly has Ca-rich lenses resembling exsolution laminae
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TL;DR: In this article, the dynamics of the structural change of triclinic kaolinite and its polymorphous modifications at different stages of sedimentary rock formation are presented. But, the authors do not consider the effects of metagenesis filling of fissures with dickite.
Abstract: SUMMARY
The paper presents the dynamics of the structural change of kaolinite and its polymorphous (polytype) modifications at different stages of sedimentary rock formation.
Sedimentogenesis is characterized by a gradual disordering of structure of triclinic kaolinite, the degree of disorder produced being proportional to the intensity and duration of the influence of the hydrodynamic medium.
Epigenesis (deep) is connected with gradual transformation of kaolinite into dickite through the stage of mixed-layer growths inheriting the structure of twin rotations of disordered kaolinite from the sedimentogenesis stage.
In metagenesis filling of fissures with dickite or nacrite takes place. The former is peculiar to the general thermodynamic medium of deep epigenesis/metagen-esis, whereas nacrite is an indicator of intense stress and seems to be due to transformation of dickite.
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TL;DR: In this paper, electron micrographs show that the new minerals have formed as a mesh-like coating on original grains and the textural relationship of the new materials to the original minerals resembles graywacke texture.
Abstract: Summary
Phyllosilicates 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 texture.
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TL;DR: Sand volcanoes have been found in three sedimentary associations in the Upper Carboniferous Bude Formation as discussed by the authors, where they formed when the dewatering of fluidized sand beds, deposited from traction carpets, was temporarily inhibited by the deposition of overlying units.
Abstract: Summary
Sand 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 growth.
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TL;DR: In this article, the 17th horizon of north Sakhalin has been studied and the areas within and beyond oil and gas pools, near the top and at the flanks of structures were compared with areas where the horizon under study was waterbearing.
Abstract: SUMMARY
One of the productive horizons (17th) of north Sakhalin has been studied. The areas within and beyond oil and gas pools, near the top and at the flanks of structures were compared with areas where the horizon under study was waterbearing. The rocks were least transformed by secondary processes within oil accumulations, where a sudden increase was observed in the content of feldspars and accessory minerals (epidote, ilmenite and sphene) which had not undergone intrastratal solution. Inside gas pools, however, no deceleration of epigenesis has been observed. This points to a more recent (post-Pliocene) accumulation of gas, whereas the first oil migration in these Miocene strata occurred in the Upper Pliocene, according to the hampered epigenesis.
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TL;DR: In this paper, a method for determining the time of formation of oil and gas accumulations on the basis of the number of epigenetic minerals contained in granular reservoir rocks is described.
Abstract: SUMMARY
The paper describes a method for determining the time of formation of oil and gas accumulations on the basis of the number of epigenetic minerals contained in granular reservoir rocks. The beginning of the accumulation is established by comparing the epigenesis stage in the oil- or gas-bearing crest areas of the trap with the water-bearing part of the reservoir at different depths of the geological section. This takes into account that the epigenetic processes tend to intensify with depth and to slow down after the rocks become filled with hydrocarbons.
The time of accumulation completion is found by comparing the degree of epigenetic alteration of the oil- and gas-bearing reservoirs with the water-bearing reservoirs occurring at the oil (gas)-water interface in the trap. The greater the differences, the older is the age of the pool completion. Lack of a difference indicates a youthful pool completion.
In this paper, the ratio of detrital to authigenic titanium minerals, the quantity of regenerated quartz grains, and the pelitization of feldspars have been used.
The application of this method is exemplified by oil deposits occurring in the productive Valangien and Hauterive beds (Lower Cretaceous) of the Ust-Balyk and Megion fields of western Siberia.
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TL;DR: In this paper, a historical review of the development of quartz-grain morphoscopy is presented, where some unsolved problems such as the real aspects of the details on frosted grain surfaces and the interpretation of the origin of different surface textures are elaborated.
Abstract: SUMMARY
In a historical review of the development of quartz-grain morphoscopy some unsolved problems such as the real aspects of the details on frosted grain surfaces and the interpretation of the origin of different surface textures are elaborated. Discrepancies in the presentation of quartz-grain types as observed by electron microscopy are mentioned. It is proposed to relate such investigations to CAILLEUX's (1942) classical morphoscopic method; this could be facilitated by the modern scanning electron microscope. The possibilities and advantages of this instrument for morphoscopic research are presented by first results concerning the surface textures of original quartz grains derived from a weathered granite and of experimentally and naturally etched grain surfaces. For generalized conclusions a greater number of further observations must be made.
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TL;DR: The main trends in epigenetic research in the U.S.R. in the last few years are:==================\/\/\/\/\/\/£££€££$££ £££• as mentioned in this paper
Abstract: SUMMARY
This paper presents the main trends in epigenetic research in the U.S.S.R. in the last years:
1
Study of epigenetic zonality in thick series of sedimentary rocks of various ages and tectonic regions, (zones of unaltered clay matrix, of altered clay matrix, of quartzitic structures and hydromica-chloritic cement, and of prick-like structures and phyllite-like schists).
2
Principles of stadial analysis and mineral indicators of different epigenetic stages (clay minerals, organic matter, zeolites, feldspars, sulfides).
3
Facies of regional epigenesis connecting the main petrographic families of unaltered terrigenic rocks (quartz sandstones with kaolinitic matrix and the same composition of associated clays, acidic arkoses with hydromicaceous clays, lithoclastic sands with several matrix components and associated clays, and volcanogenic greywackes) with “related” facies of regional metamorphism.
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Some practical aspects of epigenesis are: for petroleum geology: maximum depth of burial according to porosity, interruption of quartz, feldspar, sphene, epidote, carbonate, biotite, and clay mineral epigenesis by oil migration; and for ore geology: (a) initial epigenesis: ore impregnation (e.g., volkonskoite in wood remains) due to intrastratal solution of heavy minerals and leaching of rock fragments; (b) deep epigenesis: e.g., galena impregnations due to release of trace elements during dissolution of rock forming minerals e.g., feldspars; and (c) metagenesis: “Alpine” veins across and along bedding, filled, e.g., with copper ores.
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TL;DR: In this paper, the relationship between phosphate content and the foraminiferal plankton/benthos (P/B) ratio in Senonian-Maastrichtian chalks of Galilee, Northern Israel was investigated.
Abstract: SUMMARY
Two environments of phosphate deposition within carbonate rocks are distinguished on the basis of the relationship between phosphate content and the foraminiferal plankton/benthos (P/B) ratio in Senonian-Maastrichtian chalks of Galilee, Northern Israel:
(1) A normal marine environment of phosphate deposition during Santonian time. This environment is characterized by a low, normal P2O5 content and a positive correlation between P/B ratio and P2O5. Since it is assumed that the P/B ratio increases with the depth of the sea, it is suggested that the phosphate content in carbonate rocks can be employed as a bathymetric indicator.
(2) An “abnormal” high phosphate deposition environment, found mainly in Upper Campanian sediments and related genetically to the economic phosphorite deposits in the Negev (Central Israel). The negative correlation of P/B ratio to P2O5 is caused by a shallowing of the sea and a continuous increase in P2O5, (e.g., by upwelling currents or a terrigenous supply) throughout the Upper Campanian.
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TL;DR: In the course of deep weathering of a biotite gneiss, Biotite is transformed into mixed-layer biotitite-vermiculite hydrobiotite as discussed by the authors.
Abstract: SUMMARY
In the course of deep weathering of a biotite gneiss, biotite is transformed into mixed-layer biotite-vermiculite hydrobiotite. Later biotite-vermiculite is transformed into biotite-chlorite under the action of hydrothermal solutions at the stage of epigenesis.
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TL;DR: In this article, the combined use of size analysis and electron microscopy has indicated the presence of beach sands within the Lower Carboniferous Fell Sandstone of southeast Scotland and northern England.
Abstract: SUMMARY
The combined use of size analysis and electron microscopy has indicated the presence of beach sands within the Lower Carboniferous Fell Sandstone of southeast Scotland and northern England.
Environmental interpretations are based on a comparison of the statistical parameters summarizing the size distributions of the Fell Sandstone specimens with similar data from modern sediments. The spread of standard-deviation values (sorting coefficients) indicates the presence of littoral, alluvial, and possibly offshore marine environments within the Fell Sandstone. These environments are further defined by plotting standard deviation against skewness on a scatter diagram.
Electron micrographs (E.M.G.'s) of the quartz grain surface textures of selected Fell Sandstone specimens corroborate the interpretations based on the size analysis.
E.M.G.'s of the Fell Sandstone beach specimens show all the diagnostic surface features developed on modern quartz beach sand grains.
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TL;DR: The Ranger Canyon and Mowitch Formations are the youngest Permian strata in the Rocky Mountain Front Ranges as mentioned in this paper and they constitute a thin, widespread and clearly defined stratigraphic entity covering approximately 60,000 sq. miles.
Abstract: Summary
The 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 preservation.
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TL;DR: In this paper, a new turbidimetry method is proposed based on the relation between gamma activity and turbidity T, such as Nt=aTb (Nt counting rate caused by turbidity, a and b experimental coefficients).
Abstract: SUMMARY
The determination of the natural radioelements in suspended matter in rivers and estuaries, lead to a simple relation between gamma activity and turbidity T, such as Nt=aTb (Nt counting rate caused by turbidity, a and b experimental coefficients). A new turbidimetry method is based on this relation and discussed here. In situ measurements have been conducted with field gamma scintillometers and compared with different turbidimetry methods, such as nephelometry, gravi-metry and gamma ray absorptiometry. This method has been particularly convenient to continuous in situ measurements of turbidity from 0.5 g to several hundreds of g/1. This broad range is very well adapted to turbidity studies in estuaries.
The new method has been applied to study suspended matter dynamics in the Gironde estuary (France) during November 1968, as a part of a more general study of natural radioactivity in terrigenous sediments brought into the ocean.
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TL;DR: In this paper, a new apparatus, the "buret cylinder" was constructed in order to increase the efficiency of the size analysis of fine-grained sediments, and an ALGOL-program was compiled to compute all data, obtained from the granulometric analysis of the entire sediment.
Abstract: SUMMARY
A new apparatus, the “buret cylinder”, was constructed in order to increase the efficiency of the size analysis of fine-grained sediments. Its uncomplicated operation and automatic levelling enables working in series of ten samples or more at a time. This method, an improvement of the “pipet method”, works with an accuracy comparable to that of the “Atterberg method”.
An ALGOL-program was compiled to compute all data, obtained from the granulometric analysis of the entire sediment. In the output, the numerical parameters are printed out and a simple frequency and a cumulative diagram is plotted. The computer program works for grain sizes from −6 phi (64 mm φ) to +9 phi (2 u φ). Two procedures can be applied alternatively: (a) sieving—buret analysis; and (b) sieving—visual accumulation tube—buret analysis.
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TL;DR: Experimental studies on saturation of montmorillonite with potassium showed that sorption of potassium tends to produce a regular alternation of the interlayer regions as mentioned in this paper, which formed the basis of the epigenetic formation of rectorite.
Abstract: SUMMARY
Experimental studies on saturation of montmorillonite with potassium showed that sorption of potassium tends to produce a regular alternation of the interlayer regions.
The sorptive nature of the potassium fixation by montmorillonite appears to form the basis of the epigenetic formation of rectorite.