The Formation of Dolomite in Sediments

Abstract

Dolomite forms in two ways: 1. The origin of dolomite on the surface of the earth, i.e., the early diagenetic formation of dolomite and 2. the origin of dolomite in sedimentary rocks, i.e., the late-diagenetic formation of dolomite. In both cases, pre-existing CaCO3 reacts with solutions, resulting in the formation of dolomite. The reaction solution of the early diagenesis is modified, pre-concentrated sea water. The reaction solution of the late diagenesis consists of pore solutions. Both reactions proceed as follows: Metastable CaCO3 which forms in place of stable dolomite is changed into dolomite by diagenetic solutions which generally contain abundant Mg. Different amounts of dolomite are thus formed from a definite amount of CaCO3 depending on the anion content of the solutions. These processes are discussed with the aid of solubility equilibria of the Ca-Mg-carbonates, -sulfates and -chlorides.