Overgrowth cements

Reed R. M. and Laubach S. E. (1996) The role of microfractures in the development of quartz overgrowth cements in sandstones new evidence from cathodoluminescence smdies. Geolog. Soc. Am. Annual Meeting, 28(7),... 

Franks and Forester (1984) have discussed this mechanism in detail for Gulf Coast sediments, with particular emphasis on pre- and post-secondary porosity mineral assemblages. For many localities they found strikingly similar mineral assemblages (Table 8.1). Early carbonate cements had precipitation temperatures in the range of 40° to 75°C. Quartz overgrowths were observed to precipitate... 

It is generally agreed on the basis of TEM evidence (e.g., Rask et ai, 1997) and on the basis of chemical substitution in the several structural sites of illite (e.g., Lanson and Champion, 1991 Awwiller, 1993 Lynch et ai, 1997) that the illitization of smectite, like other replacement reactions in late diagenesis, proceeds through a dissolution/precipitation mechanism. Similar to other replacement minerals, illite also occurs as cements in sandstones as well as in shales, where it forms overgrowths on detrital illite particles and discrete crystals (cements) (e.g., Lanson and Champion, 1991 Rask et at, 1997). 

Figure 18. Wavelength-dispersive electron microprobe image of a cluster of pyrite framboids within coal from the Black Warrior basin Alabama. Bright colored areas show the presence of arsenic, nickel, and sulfur. Arsenic is concentrated in epigenetic overgrowths and cement surrounding the framboids, while the diagenetic framboid interiors them.selves contain little or no arsenic. This indicates that the arsenic was added after earliest diagenesis.

Opaline/fine-grained massive Quartzitic No detrital component, massive, comprising opaline, chalcedonic or cryptocrystalline silica Grain supported fabric cemented by overgrowths on detrital quartz... 

GS-fabric Grain supported fabric - skeletal grains (i.e. grains >30 pm diameter) constitute a self-supporting framework. Subdivided by cement type (a) optically continuous quartz overgrowths (b) chalcedonic overgrowths (c) microquartz/cryptocrystalline/opaline silica in-fill... 

Smith, 1975 Shaw and Nash, 1998 Webb and Golding, 1998 Figure 4.7A). Gradations between overgrowth and less well-ordered silica cements may also occur (Ullyott et al., 2004 Ullyott and Nash, 2006). 

Cement crystals are commonly bladed, equant or syntaxial in shape. Syn-taxial overgrowths are precipitated in optical continuity with the substrate... 

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