Glauconite formation

The material within the pellet would be then more reducing than the sediment in which it lies, and would have a higher local Eh potential. Thus, the initial impetus to the process is a A Eh between sediment and pellet. The concentrations of the elements which must be present in the sea water solution to promote glauconite formation are largely governed by the type of sediment in contact with the water. Equilibrium is thus established punctually between pellet and sea water effecting a transfer of material between the two media. On a larger but still somewhat local scale the dissolution of detrital silicates in sea water provides the basic "reservoir" of material in solution and hence determines the activities of various elements in the solution. 

Two minerals frequently encountered in sediments and sedimentary rocks are not accounted for in the Figures 48a to c. These are glauconite and chlorite, the two major iron-bearing phyllosilicates in sediments and sedimentary rocks. Glauconite formation can be explained on the basis of... 

Ehlmann, A.J., Hulings, N.C. and Glover, E.D., 1963. Stages of glauconite formation in modern foraminiferal sediments. J. Sediment. Petrol, 33 87-96. 

The Nishikurosawa Formation is composed of siltstone, mudstone, conglomerate and sandstone. Siltstone and mudstone contain foraminiferal fossil such as Globorotalia birnageae, and G. denseconnexa, indicating Zone N. 9 by Blow (1969). The upper part is characterized by glauconite-bearing sedimentary rock. The total thickness is about 150 m. 

Sediments formed by the abiogenic precipitation of solutes from seawater are termed hydrogenous. Unequivocal examples of hydrogenous sediments are ones formed from the evaporation of seawater. The minerals deposited are collectively called evaporites and are the subject of Chapter 17. Others form with the assistance, to varying degrees, of marine microbes. For example, bacteria seem to play a role in the formation of Fe-Mn nodules and crusts. Some hydrogenous minerals, such as barite, celestite, glauconite, and francolite, are produced from the precipitation of elements... 

The mineral content of the Rose Run Sandstone is similar to other deep formations that are being considered for sequestration of C02, including other Cambrian sandstones deep beneath Ohio (Janssens 1973) and the glauconitic sandstone in the Alberta Basin of Canada (Gunter et al. 1993). Like the Rose Run, these... 

The formation of sedimentary glauconite is rather similar in mode to that of chamosite or berthi rine except in the greater range of depth,... 

Thermodynamic Description of the Formation of Sedimentary Glauconite Pellets. 

In addition to proper biotic factors, it appears that the oxidation state of the iron in the sediment is critical to the formation of sedimentary 7 8 chlorites these conditions are more reducing than those which form glauconites (Porrenga, 1967b Leclaire, 1968). As is the case for... 

It is possible that the mechanism of berthierine formation in this example is one of accretion, i.e., the grain would accumulate material at the exterior and this is eventually transformed into a chlorite composition. None of the grains was noted to have the form of a shell test as is often noted glauconite pellets. However the meta-berthierine pellets reported by Velde, et al.. (1974), were often found inside foraminifera tests. 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

The initial increase in hydrostatic pressure in a sedimentary basin appears not to change mineral stabilities from those of the weathering environment. The formation of potassic, iron-rich micas such as ferric illite and glauconite both in lacustrine and shallow ocean basins demonstrates their stability at low pressures and temperatures. The same is true of the 7 8 chlorite chamosite or berthierine. Most likely the chemical variables of pH, Eh and the activity of the various ions in solution are predominant in silicate phase equilibria in sedimentary environments. 

It might be noted that, upon burial in an argillaceous matrix, the process of both glauconite and 7 8 chlorate formation is largely stopped. 

It is only implied that the process of formation of sedimentary glauconites and 7 X chlorites in pelletal form is restricted to areas near the sediment-water interface. Given the proper chemical conditions, these minerals will form at depth. These conditions, however, are probably unusual. 

KELLER (W.D.), 1958. Glauconitic mica in the Morrison formation in Colorado. Clays and Clay Min. 5, 120-28. 

OWENS (J.P.) and MINARD (J.P.), 1960. Some characteristics of glauconite from the coastal plain formations of New Jersey. U.S. Geol. Sur. Special Papers. 

The marine formations of late Cretaceous-Paleogene age on the southern part of the Russian Platform can be traced along strike for more than 2500 km and across it for more than 1000 m. They consist mostly of siliceous rocks (gaizes), clays, marls, chalk, and a small amount of sandstones and siltstones of quartzose composition. The rocks abound in glauconite and often contain phosphorites the clays are of a montmoril-lonitic composition, and a few pure bentonites have been found. Clinoptilolite occurs in almost all types of rocks of these formations. It fills pores and chambers of foraminifera and radiolaria and varies from fractions of a percent to 2-3% of the rock. It commonly makes up 70-80% of the 0.01- to 0.001-mm fraction. 

Cretaceous secondary glauconite after Precambrian iron-formation, Auburn mine, Minn., U.S.A. Tyler and Bailey (1961). 

Too few chemical analyses are available of glauconites from one formation to provide much indication of the amount of variability at the formation level. However, Table XXII lists 14 potassium analyses of glauconites from the Upper Cambrian Franconia Formation of Minnesota and Wisconsin. 

The conditions favoring the formation of glauconite have been discussed by most of the authors referenced in this review and will only be summarized here. 

Keller, W.D., 1958. Glauconite mica in the Morrison Formation in Colorado. Proc. Natl. Conf. 

Tyler, S.A. and Bailey, S.W., 1961. Secondary glauconite in the Bivabic iron-formation of Minnesota. Econ. GeoL, 56 1030- 1044. 

Chemical conditions. The occurrence of glauconites in sandstones (acid) and carbonates (basic) indicates that pH is not of great importance to their formation. They are found in sedimentary rocks ranging in age from Precambrian to the present day. Hence, their formation seems to be constrained by chemical and physical conditions rather than by specific events. There is no apparent time-dependent reaction which transforms them into new phases. 

Some glauconites have been identified in hydrothermally altered basalts together with celadonites (Alt et al., 1992 Clayton and Pearce, 2000). This material appears to form a mixed-layer mica-ferric smectite series. The formation of glauconite mixed-layer minerals is therefore not restricted to peloids under shallow-ocean-bottom conditions. However, the identification of glauconite as distinct from ferric Ulite is difficult. Perhaps these mineral occurrences should be given another name. 

Normally weathered (subaerial, surface alteration) basalts can contain nontronite (a ferric smectite) and celadonite which form at the same time but by pseudomorphism of different basalt mineral grains during intermediate stages of alteration (i.e., between rock and soil) as summarized by Righi and Meunier (1995). These observations would lead one to beheve that celadonite can be formed in terrestrial environments. If so, celadonite is not entirely restricted to relatively low-temperature hydrothermal formations in marine environments. It does not, apparently, form a significant mixed layer mineral series with smectite minerals as do glauconite and ilhte. 

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