Microbial micritization

Diagenesis is the conversion of sediments into rock by organic, physical and chemical processes. Six main processes have been identified for limestone [2.3] — microbial micritization, cementation, neomorphism, dissolution, compaction and dolomitization. 

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... 

Loisy, C., Verrecchia, E.P. Dufour, P. (1999) Microbial origin for pedogenic micrite associated with a carbonate paleosol (Champagne, France). Sedimentary Geology 126, 193-204. 

---