Diagenesis characteristic

Few data are available on apertures, heights, lengths, connectivity, and the relation of cleat formation to diagenesis, characteristics that are critical to permeability (Laubach et al., 1998). Moreover, recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well-studied parameters can yield insight into coal permeability. 

An alternative description of iUite—smectite mixed-layer clays begins with megacrystals of smectite that incorporate smaller packets of iUite (163). These constituents are observed as mixed-layer minerals in x-ray analysis. Diagenesis increases the percentage of iUite layer and with increasing alteration the mixed-layer mineral takes on the characteristics of an iUite dominated iUite—smectite. 

Diagenesis and catagenesis can alter the evaporite minerals after burial. For example, high temperatures, pressures, and pore-water salinities characteristic of deep burial lead to the conversion of gypsum into anhydrite. Thus, evaporite mineralogy reflects not only the environmental conditions under which the evaporite was formed, but also those under which diagenesis and catagenesis occurred. 

In order to determine the source composition of sediments using trace elements, it is necessary to ascertain that the element is immobile under conditions of diagenesis and weathering (Spalletti 2008). Several ratios and plots may be used to define the source rocks. The felsic source rock compositions are found in the Co/Th vs. La/Sc diagram (Fig. 3 Table 1). Other trace element characteristics of sedimentary rocks also place some constrains on the nature of the source rock. Floyd Leveridge (1987) used a La/Sc vs. Hf plot to discriminate between different source compositions. In this plot, most data fall in the felsic source to mixed felsic/basic source field (Fig. 4 Table 1). 

Butler, R. D. Pflughoeft-Hassett, D. F. 1995. Diagenesis and Leaching Characteristics of Aged... 

Under the modest temperature and pressure conditions characteristic of the environments in which meteoric diagenesis typically takes place, many of the most important reactions are slow. This has severely constrained the study of the chemical mechanisms and kinetics involved in such fundamental processes as the aragonite to calcite transformation and dolomite formation. Information on these processes obtained under conditions not typical of the meteoric realm (e.g., elevated temperatures) are of questionable applicability to "real world" carbonate diagenesis. 

American Journal of Science, Vol. 291, pp. 109-176 Haszeldine, R.S., Samson, I.M. and C. Cornford, 1984. Quartz diagenesis and convective fluid movement Beatrice oilfield, UK North Sea. Clay Minerals, 19, pp. 391-402 Hedberg, H.D., 1980. Methane generation and petroleum migration. In Roberts III, W.H. and R.J. Cordell (eds.), 1980. Problems of petroleum migration. The American Association of Petroleum Geologists Studies in Geology, no. 10, pp.179-206 Hem, J.D., 1985. Study and interpretation of the chemical characteristics of natural water. 

Figure 2. Mass spectral histograms of tetrapyrrole pigments characteristic of mid-/late-diagenesis. (a) free-base 7,8-dihy-dro-DPEP-series (b) free-base DPEP-series and (c) nickel DPEP (ETIO- omitted)-series. Sample Pliocene/Miocene shale of marine origin (cf. 24).

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