dolomitisaation

Dolomitization is a diagenetic process by which calcium carbonate rocks, primarily limestone, are converted into dolomite rock (dolostone). This transformation involves the substitution of magnesium for some of the calcium ions within the crystal lattice of the original calcium carbonate mineral, calcite. The resulting mineral is dolomite, which has the chemical formula CaMg(CO3)2.

The process requires a source of magnesium-rich fluids. These fluids, often seawater or pore waters with elevated magnesium concentrations, interact with the existing limestone. The magnesium ions in the fluid replace calcium ions in the calcite structure. This replacement can occur in several ways. One common model involves the dissolution of calcite and subsequent precipitation of dolomite. Another mechanism suggests a solid-state exchange where magnesium ions directly substitute for calcium ions within the calcite lattice.

Dolomitization can occur under various conditions, both during shallow burial (eogenetic) and at greater depths (mesogenetic). Eogenetic dolomitization is often associated with the movement of magnesium-rich brines through porous sediments shortly after deposition. Mesogenetic dolomitization occurs later, after the sediments have been buried and lithified, and is typically driven by more extensive fluid flow through fractures and permeable zones.

The presence of dolomite significantly alters the physical and chemical properties of the rock. Dolomite is generally harder and less soluble than calcite. The dolomitization process can also lead to an increase in porosity and permeability within the rock, which is crucial for the formation and storage of hydrocarbons. Therefore, understanding dolomitization is vital in fields such as petroleum geology, sedimentology, and hydrogeology.