micritization

Micritization is a diagenetic process in carbonate rocks in which grains, shells, or fossils become coated with or converted to micrite, a microcrystalline form of calcite. In thin section, micritized grains show fine-grained, micritic rims or are encased by micritic cement, altering the original skeletal fabric and the rock’s pore structure.

The process occurs through two main pathways. Biogenic or microbial micritization involves microboring organisms and microbial mats that bore into skeletal material and stimulate micrite precipitation on exposed surfaces, producing micritic envelopes. Abiotic or chemical micritization transpires when carbonate-saturated pore waters precipitate microcrystalline calcite directly onto grain surfaces or within pore spaces, binding grains together. Both pathways are common in shallow, agitated, or diagenetically active carbonate settings where fluid compositions and saturation levels favor micrite precipitation.

Micritization affects rock properties and interpretation. It commonly reduces primary porosity and modifies permeability by cementing grains with micrite, though it can also create small-scale porosity around micritic rims. As a diagenetic marker, micritization records fluid-rock interactions, carbonate saturation, and microbial activity, helping to reconstruct diagenetic histories and depositional environments in carbonate platforms, shoals, and tidal flats.

Identification and study rely on petrographic analysis. Thin sections reveal micritic rims around grains, micrite cement, and changes in fabric from skeletal to micritic textures. Complementary methods include scanning electron microscopy and cathodoluminescence to distinguish micrite from primary mud and to characterize the timing and sequence of diagenetic events.