The influence of organic matter in organogenic dolomitization

Abstract

We hypothesize that the decomposition of organic debris derived from plants, planktonic animals, and algae by sulfate-reducing bacteria, and specifically by the enzymatic degradation of protein, is vital to organogenic dolomitization. The role of this degradation is to increase both alkalinity and pH of the pore waters, providing the necessary solution and surface chemistries for dolomitization to occur. Ammonia, derived by the enzymatic breakdown of proteins, is the only simple base available to supply the pH conditions necessary for dolomitization. Protein is abundant in organic matter derived from a marine source. Because of the large enthalpies of hydration of Mg (super +2) and Ca (super +2) ions, we propose that dolomitization proceeds with the transfer of neutral ion pairs, CaCO 3 and MgCO 3 , to and from the dolomite surface within a replacement zone. For this reason, dolomitization will occur only when the concentration of the CO 3 (super -2) ion is high and in large excess to the HCO 3 (super -) ion in solution and at the carbonate crystal surface. These conditions will be met when the pH and/or ionic strength is high and the carbonate alkalinity is also high.