Illite authigenic

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. 

Kozlowska, A. 2006. K-Ar dating of authigenic illite from sandstones and thermal history of the Lublin Carboniferous basin (SE Poland). Sediment 2006. Gotingen, Abstracts, 106. 

Chamberlain et al. (1999) measured the oxygen isotope composition of authigenic kaolinite, smectite and illite in weathered horizons from intermontane basins on the east side of the Southern Alps. Neither smectite nor illite produced useful results, as reflected in the... 

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. 

The concentrations of potassium in the samples obtained from the Norphlet Formation in the central Mississippi Salt Dome Basin are those expected from the Louann Salt bittern potassium values in other samples obtained from reservoirs of Jurassic age are lower by a factor of —2 (Kharaka et al., 1987). The decrease in the dissolved potassium in these samples is attributed to the formation of authigenic illite and potassium feldspar (Carpenter et al., 1974 Kharaka et al., 1987). 

Lynch F. L., Mack L. E., and Land L. S. (1997) Burial diagenesis of illite/smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones. Geochim. Cosmochim. Acta 66, 439—446. 

Clays are volumetric ally the most abundant mineral group in coal. They can be authigenic or detrital in origin. Kaolinite is the most common clay and the most common authigenic mineral in coals. The silicon and aluminum in kaolinite are, perhaps, residual from the dissolution of ferromagnesian minerals and feldspars. Illite and mixed layer clays in coal are almost exclusively detrital in origin. Chlorites, smectites, and other clay minerals may be abundant locally. 

The sources of Si for cave-authigenic silicates were most likely the silicates disseminated in the dolostone units of the Permian Capitan reef complex. Silt-sized quartz and minor feldspar, and clays such as illite and dickite, made up approximately 1-5% of the dolostones. 

Chemical conditions within the peat swamp influenced the clay mineral assemblage. Kaolinite is enriched towards the margins of the depositional basin an authigenic origin in acidic freshwater conditions is proposed for much of this clay. Illite/mica is primarily detrital, as indicated by the presence of the... 

Authigenic clay minerals identified by SEM/EDS include minor amounts of kaolinite, chlorite, illite and mixed-layer illite/smectite, which form grain coatings, platelets or fibrous cements. 

Authigenic illite forms characteristic grainbridging cements, as seen by SEM. In very few samples, rims of illite of uniform thickness were found lining the pores (Fig. 14D) and contributing substantial amounts (2-5%) of cement, but in general illite cement, like chlorite, is negligible in Hibernia Field. 

Tirrawarra Sandstones in the Moorari and Fly Lake Fields consist mainly of medium-grained, moderately sorted sublitharenites (mostly mica schist and phyllite, shale and siltstone clasts) (classification of Folk, 1974). A variety of authigenic minerals are recognized, including syntaxial quartz overgrowths, minor illite, patchy kaolinite and siderite. Attention is focused on the siderite and only a short description of the other diagenetic minerals is provided here. 

The authigenic nature of illite is evident from its rare fibrous, lath-like habit. XRD analysis indicates that the mineral is a dioctahedral 2M1 variety with a relatively broad base to the 10 A peak, indicative of either a poorly crystalline nature or possible interstratification with other minerals. The mineral... 

Freed RL, Peacor DR (1992) Diagenesis and the formation of authigenic illite-rich I/S crystals in Gtrlf Coast shales TEM study of clay separates. J Sed Petrol 62 220-234 Frey M (1969) A mixed-layer paragorrite/phengite of low-grade metamorphic origin. Contrib Mineral Petrol 14 63-65... 

Based on analysis of authigenic smecite formed at 1°C (A(sm-H2O)=30.3 %o), natural smectite-illite pairs, the quartz-illite curve of Eslinger and Savin (1973), and the quartz-H20 curve of Matsuhisa et al. (1979). 

Hydromicas are authigenic minerals rather easily forming in a sedimentary environment. Fe-illites would be the analogs of glauconites in gradually salting-up basins. The out-flow of bottom waters and the fixation of the bivalent cations Ca and Mg " (in dolomite) in case of a relatively low concentration of the latter (sodic-calcic lakes) lead to the relative enrichment of these in potassium. The latter will then be fixed by the silicate compounds in solution leading to the synthesis of Fe-illites. In case... 

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