Stabilization burial diagenetic

In nodular cemented sandstones, the areas left uncemented often reveal evidence of later burial diagenetic modifications, such as compaction and quartz cementation (Morad et al., 1995). Burial cements are believed to be sourced from meteoric or dissolution of detrital carbonates and bioclasts (cf. Wilkinson, 1991). As the sandstone framework is expected to be stabilized due to early cementation, the burial dissolution of bioclasts may be recognized by oversized pores and mouldic pores filled with cement. 

N NaCl exchanges used to study diagenetic I/S (44). Thus, the illite layers remaining in the WD clays after three Sr-exchanges may be of comparable stability to those formed by burial diagenesis. 

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. 

It has been shown by mineralogical, chemical and X-ray-diffraction analyses that the major part of reduced sulfur occurs in the form of pyrite in ancient sediments (Lein, 1978)81). It has been also established that pyrite may form rapidly in muds of recent sediments. In anoxic bottom waters, pyrite formation can take place before and after burial even during sedimentation (Berner, 1984)89). Also the geological occurrence and chemical stability relations indicate that authigenic pyrites can be synsedimentary or diagenetic (Kalliokosky, 1966)90). 

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