Diagenetic minerals

Inherent in all these methodologies, which measure either absolute Sr levels or strontium isotope ratios in mineralized tissue, is the assumption that diagenesis has not altered the signal since death. This has been a matter of some considerable debate (e.g., Nelson et al. 1986), but the consensus of current opinion amongst practitioners is that the repeated acid-washing procedures used remove any diagenetic mineral, because it has a higher... 

Force, E.R. Maynard, J.B. 1991. Manganese Syngenetic Deposits on the Margins of Anoxic Basins. In Force, E.R., Eidel, J.J., Maynard, J. B. (eds.), Sedimentary and Diagenetic Mineral... 

In weathering situations, saturation of fluids with SiC relative to any species of pure silica is probably only rarely achieved. In continental and shallow sea deposits, silica is precipitated in some initially amorphous form, opaline or chert when lithified or extracted by living organisms. Authigenically formed silicates are probably not in equilibrium with quartz when they are formed. As compaction increases in sediments, silica concentrations in solution are again above those of quartz saturation (15 ppm) and again it must be assumed that the diagenetic minerals formed are not in equilibrium with a silica polymorph except where amorphous silica is present. It is possible that burial depths of one or two kilometers are necessary to effectively stabilize that quartz form. It must be anticipated that the minerals formed under conditions of silica saturation near the earth s surface will be a minority of the examples found in natural rock systems. 

A wide variety of zeolites are known to form in saline lakes where the species present is dependent upon the chemistry of the solutions. Rapid zeolite formation is aided by the existence of the volcanic glass and high water salinities. Potassium feldspar occurs with the common alkali zeolites (Hay and Moiola, 1963 Hay, 1964 Hay, 1966 Sheppard and Gude, 1969, 1971), however, albite is not evident as a diagenetic mineral in saline lakes. 

The second division of the zeolite facies is based upon the appearance of albite as a diagenetic mineral, usually coexisting with analcite in the initial stages of its development, and also with the widespread development of montmorillonite-illite mixed layered mineral (30 to 90% expandable layers) coexisting with illite. The phase relations of this facies are indicated by Figure 35b. Assemblages can contain natrolite as above. They are ... 

Sheppard and Cude report two sorts of assemblages those where zeolites are dominant, towards the lake edge and those where feldspar is dominant, towards the lake center. There are two groups of assemblages of diagenetic minerals which characterize these two zones ... 

Fig. 58. Diagram of relationships between primary metastable sediments (dashed lines) and stable diagenetic minerals (solid lines) in an open system with ap5 = 10 g ion/1 a—acid b—silicate c—carbonate (beginning of precipitation of FeCOj is shown for bar d—sulfide = 10 ).

The original sediment had a complex composition which was determined by fluctuations in Eh, pH, Pqq, etc. in the sedimentary basin. Magnetite and hematite are believed to be primary sedimentary or diagenetic minerals, essentially unaltered in metamorphism (James, 1954 Huber, 1960 Garrels et al., 1973 Klein, 1973 Klein and Fink, 1976 Drever, 1974). 

Experimental work on the solubility of CH4 (e.g., Haas, 1978 Price, 1979) permits estimation of the solubility of CH4 over much of the range of pressures, temperatures, and salinities characteristic of sedimentary basins (Kharaka et al., 1988 Spycher and Reed, 1988). High concentrations of CH4 have been found in the two-phase fluid inclusions in sedimentary ore deposits and in diagenetic mineral overgrowths, and corrections... 

Figure 3 Eh-pH diagram with sulfides included. Note the large field of stability for Fe sulfide compared to Mn sulfide. The points labeled shallow and deep refer to typical compositions of waters from the Black Sea (reproduced by permission of Society of Economic Geologists from Sedimentary and Diagenetic Mineral Deposits A Basin Analysis Approach to Extraporation (eds. E. R. Force, J. J. Eidel, and J. B. Maynard), 1991, pp. 147-159).

In addition to the grovmdwater pressure distribution, the burial-induced flow of groundwater is associated with several physical and chemical characteristics of the sedimentary basin. These include the distribution of temperature, salinity and chemical composition of the groundwater, and the distribution of diagenetic minerals in the basin. 

Allison, P.A. Pye, K. (1994) Early diagenetic mineralization and fossil preservation in modern carbonate concretions. Palaios 9, 561-75. 

Like other diagenetic minerals in siliciclastic sequences, eogenetic carbonate cements may display a strong relationship with depositional facies in continental and marine settings. 

Fig. 3. Variations in relative importance of the different geochemical zones of diagenesis (see text) and the diagenetic minerals formed in a profile covering proximal to distal continental arid to semi-arid environments, as well as subaquatic marine environments. Mn- and Fe-oxides should be encountered in the oxic zone of these different settings.

Coleman, M.L. Raiswell, R. (1993) Microbial mineralization of organic matter mechanisms of self-organization and inferred rates of precipitation of diagenetic minerals. Philos. Trans. R. Soc. London. Ser. A. 344, 69-87. 

Most diagenetic minerals are the same in the sandstones of the Lower Freshwater Molasse and the Upper Marine Molasse, apd there is no significant difference between the paragenesis of the two units. Minor variations are detected in the diagenetic history preceding the first calcite generation. 

The volumetrically most important cements in the Swiss Molasse basin formed early, and their isotopic characteristics reflect the fluid flow history during subsidence. Furthermore, carbon in the calcite cements is isotopically heavier than that in the bicarbonate of the modem formation waters, and the variation in modern formation waters is not reflected in the diagenetic mineral assemblage. 

Goldstein, R.H. Reynolds, T.J. (1994) Systematics of Fluid Inclusions in Diagenetic Minerals. SEPM Short Course Notes No. 31, Tulsa, 199 pp. 

Standard petrographical and mineralogical techniques, including optical and cathodoluminescence (CL) microscopy. X-ray diffraction (XRD) and electron microprobe analysis (EPMA), were used to characterize detrital and diagenetic minerals and textural relationships. Thin sections were half stained with K-Fe cyanide for rapid identification... 

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