Micritic envelopes

Calvet, F. (1982). Constructive micrite envelope developed in vadose continental... 

Bathurst, R. G. C. (1966). Boring algae, micrite envelopes and lithification of molluscan biosparites. Geological Journal, 5, 15-32. 

Figure 5.6 Micritic envelopes developed around a former shell fragment that has undergone dissolution and has been partially replaced by secondary porosity and neomorphic spar, Campo de Tiro, Mallorca (cross-polarised light, x10 magnification).

Cements near the vadose end-member are associated with typical vadose features however, these features are less apparent than in type 2 tabular units, and sparry void filling cements are sometimes more abundant than micrite. As stated previously, micrite-spar cement textures could have initially formed in the vadose zone as pendant and meniscus envelopes around grains or groups of grains (Jacka, 1974 Reeves, 1976 Warren, 1983). Upon burial, these initial vadose cements would provide sites for further calcite precipitation and the unfilled voids could subsequently be filled with sparry calcite in the phreatic zone (Jacka, 1970 Funk, 1979). The vadose contribution to cementation may have been overlooked in the past because of this overprinting. 

Microbial micritization. Many organisms bore into carbonate deposits. The most important one is cyanobacteria, but others include cliona sponges, bivalves, polychaetes and fungi. The bore-holes become filled with a calcium carbonate structure called micrite, which typically forms an envelope around... 

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