Clays authigenic

MacKenzie and Garrels equilibrium models. Most marine clays appear to be detrital and derived from the continents by river or atmospheric transport. Authigenic phases (formed in place) are found in marine sediments (e.g. Michalopoulos and Aller, 1995), however, they are nowhere near abundant enough to satisfy the requirements of the river balance. For example, Kastner (1974) calculated that less than 1% of the Na and 2% of the K transported by rivers is taken up by authigenic feldspars. 

Weathered fragments of continental crust comprise the bulk of marine sediments. These particles are primarily detrital silicates, with clay minerals being the most abmidant mineral type. Clay minerals are transported into the ocean by river runoff, winds, and ice rafting. Some are authigenic, being produced on and in the seafloor as a consequence of volcanic activity, diagenesis and metagenesis. 

THE PRODUCTION OF CLAY MINERALS FROM AUTHIGENIC PROCESSES... 

Over longer time scales, clay minerals can undergo more extensive reactions. For example, fossilization of fecal pellets in contact with a mixture of clay minerals and iron oxides produces an iron- and potassium-rich, mixed-layer clay called glauconite. This mineral is a common component of continental shelf sediments. Another example of an authigenic reaction is called reverse weathering. In this process, clay minerals react with seawater or porewater via the following general scheme ... 

The Production of Clay Minerals from Authigenic Processes 363... 

Finally, some authigenic clay minerals are produced by the reaction of seawater with fresh volcanic glass. This commonly occurs near mid-ocean ridges and rises or where lava from coastal volcanoes flows into the sea. Clay minerals produced by this process are primarily smectites, such as montmorillonite, and a type of framework silicate called zeolites of which phillipsite and clinoptilite are the most common marine examples. Zeolites are characterized by three-dimensional frameworks with large cavities that... 

The production of illite from chemical weathering occurs at all latitudes. It dominates the clay mineral assemblage in the North Atlantic and North Pacific Ocean, particularly at 40° reflecting aeolian transport by the westerlies (Figure 14.11). In the southern hemisphere, the input of illite by the westerlies is diluted by a large input of authigenic montmorillonite in the South Pacific and Indian Oceans and in the South Atlantic by a large input of kaolinite. 

Zeolites Authigenic clay minerals whose production is associated with geochemical processes occurring at spreading centers, including volcanism and chemical weathering of ocean crust by seawater. 

The sandstones studied contain different types of cements, such as clay, quartz and carbonate cements. Clay cements are often a mixture of alio- and authigenic minerals. Kaolinite is the main component... 

Coal contains detrital minerals that were deposited along with the plant material, and authigenic minerals that were formed during coalification. The abundance of mineral matter in coal varies considerably with its source, and is reported to range between 9.05 and 32.26 wt% (Valkovic 1983). Minerals found in coal include (Table 2) aluminosilicates, mainly clay minerals carbonates, such as, calcite, ankerite, siderite, and dolomite sulphides, mainly pyrite (FeS2) chlorides and silicates, principally quartz. Trace elements in coal are commonly associated with one or more of these minerals (see Table 2). 

Na and Ca to play equivalent roles in zeolites, as well as K, and if we consider A1 and Si as the major variables combined with K and Na in the phyllosilicates, we can adequately represent the phases in a (Ca-Na)-K-Al-Si system where H O is in excess in the fluid phase. If the system has four chemical variables and the natural assemblages are frequently found to contain four authigenic minerals, we must assume that most chemical variables are inert or extensive variables of the chemical system which controlled the crystallization of the zeolite-clay mineral containing sediments. ... 

Quartz is the dominant form in which silica is found in coals, and it is ubiquitous. There is some distinction between clastic grains of quartz introduced by wind or water and authigenic quartz deposited from solutions. Quartz is also a major component of clay and siltstone partings in coal that are of detrital origin. 

Chamberlain CP, Poage M, Craw D, Reynolds R. (1999) Topographic development of the Southern Alps recorded by the isotopic composition of authigenic clay minerals, South Island, New Zealand, Chem Geol 155 279-294... 

Trioctahedral illites have been reported by Walker (1950) and Weiss et al.(1956). Walker s analysis, which he considers only a rough approximation, is given in Table XI. The clay biotite occurs in a Scottish soil and is believed to be authigenic however, it weathers so easily to vermiculite that unweathered material is difficult to find. Due to its instability, it is not likely that much clay-sized biotite exists although trioctahedral biotite-like layers may occur interlayered with dioctahedral illite layers. Such interlayering has been reported by Bassett (1959). 

Some of the lMd material (either illite or mixed-layer illite-montmorillonite) presumably formed authigenically on the sea bottom or on land from the weathering of K-feldspars however, much of it was formed after burial. Studies of Tertiary, Cretaceous, and Pennsylvanian thick shale sections (Weaver, 1961b) indicate that little lMd illite was formed at the time of deposition. These shales and many others contain an abundance of expanded 2 1 dioctahedral clays with a lMd structure, some of which is detrital and some of which formed by the alteration of volcanic material on the sea floor. With burial the percentage of contracted 10A layers systematically increases. 

Nontronite apparently forms under the same general environmental conditions as the low-iron montmorillonites. It is formed by hydrothermal alteration and as vein fillings. It is commonly formed by both the hydrothermal alteration and surface weathering of basalt. Nontronite is the dominant clay in some soils (Ross and Hendricks, 1945). Arrhenius (1963) found that much of the authigenic montmoril-lonite in the pelagic muds of the Pacific Ocean has a relatively high iron content. 

The material from the Hector area of California is believed to have formed by the action of hot spring waters containing Li and F on clinoptiolite. The Mg was obtained from the alkaline lake waters (Ames and Goldich, 1958). The material from Morocco is associated with marls and is believed to be authigenic. These two types of trioctahedral smectite appear to be the only ones with a relatively pure Si tetrahedral sheet. No analyses were found which indicated tetrahedral Al values between 0.02 and 0.30. Analyses of saponite indicate there is complete isomorphous substitution between the range Si3.70 Al0.3o and Si3.0s Al0.92 (Table XXXIX). Caillere and Henin (1951) reported an analysis of a fibrous expanded clay (diabantite) which had a tetrahedral composition of Si3.i7 Alo.49 Fe3+0.34. There is some question as to whether this should be classified as a smectite regardless, it indicates the possibility of Fe3+ substitution in the tetrahedral sheets of the trioctahedral 2 1 clays. 

Sudo (1954) authigenic clay matrix in tertiary iron sand bed, Moniwa, Japan. 

Most of the saponites described have a hydrothermal origin and have usually been formed by the action of either hydrothermal or surface waters on basic rocks. The iron-rich saponite described by Sudo (1954) occurs as a clay matrix in a Tertiary iron sand bed and is presumably authigenic. A metamorphic origin is proposed for saponite from metalimestones (Wilson et al., 1968). 

Rex, R.W., 1967. Authigenic silicates formed from basaltic glass by more than 60 million years contact with sea water, Sylvania Guyot, Marshall Islands. Clays Clay Miner., Proc., 15 195-203. 

Michalopoulos, P., and Aller, R.C. (2004) Early diagenesis of biogenic silica in the Amazon Delta alteration, authigenic clay formation, and storage. Geochim. Cosmochim. Acta 68, 1061-1085. 

Pottery is produced by the conversion of sedimentary clay (produced by the weathering of rocks) into hard rocklike objects. The clay minerals, which were formed by the chemical decomposition of certain rock-forming minerals, contain trace elements. The sediments in which these clays are found, however, also contain fragments of the primary minerals from the parent rock (including grains of silica sand). These detrital components, which result from the physical and chemical breakdown of minerals, are often accompanied by authigenic minerals that are chemically precipitated from aqueous solutions. In some ceramics, additional components were added as temper during production. 

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