micritedominated

Micrite-dominated refers to carbonate rocks in which the fabric is largely or wholly made up of micrite, a fine-grained, microcrystalline form of calcium carbonate. Micrite itself consists of tiny calcite crystals typically less than about 4 micrometers across and forms a carbonate mud that can be either biogenic or inorganic in origin. In micrite-dominated rocks, micritic matrix or cement comprises the majority of the rock, with only minor amounts of coarser grains such as skeletal fragments, peloids, or sparry calcite.

Formation and origins: micrite forms in low-energy marine or lacustrine environments where fine carbonate mud can settle and accumulate, often in lagoons, calm shelves, or outer-shelf settings. Micrite can also develop diagenetically through micritization, in which skeletal grains are dissolved and replaced by microcrystalline calcite, or by the precipitation of micritic cement around grains. Distinguishing primary, depositional micrite from diagenetic (micritized) micrite is a key petrographic challenge.

Texture and lithology: micrite-dominated rocks typically display a uniform, fine-grained matrix under hand lens and microscope, with limited visible fossils and little to no sparite cement in their primary fabric. When sparry calcite cements dominate, the rock would be less accurately described as micrite-dominated.

Porosity and diagenesis: micritic textures can reduce primary intergranular porosity due to pervasive fine-grained cement, yet diagenetic processes such as dissolution or karstification can enhance secondary porosity. In some settings, micrite accumulation contributes to relatively dense, mudstone-like limestones.

Significance: micrite-dominated textures are diagnostic of low-energy depositional environments and can reveal diagenetic histories in carbonate successions. They are important in carbonate petrology, sedimentology, and hydrocarbon reservoir characterization.