Dolomitization closed system

Figure 6.14 Idealized, end-member approaches to mineral saturation of groundwater, dissolving calcite or dolomite at 12°C and 1 bar total pressure. Open-system dissolution pathways are labeled with hxed values of PCOj- Closed-system pathways are labeled no CO2 added. Reprinted from Geochim. et Cosmochim. Acta, 35, D. Langmuir, The geochemistry of some carbonate ground waters in central Pennsylvania, 1023-45, 1971, with permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington 0X5 1GB, U.K.

The amount of carbon observed in the Shullsburg waters was less than the modeled carbon in a closed system. An increase in the amount of sulfide oxidation implies an increase in the amount of carbonate dissolution in a 1 1 stoichiometric ratio (Equation 2). When calcite precipitation, driven by dolomite dissolution, is included in reaction modeling, the relationship between sulfate and carbon becomes nonlinear (Figure 3). Even for this nonlinear model, there is a discrepancy between measured carbon concentrations and modeled closed system carbon concentrations. 

Sperber et al. (1984) conducted an extensive examination of Paleozoic dolomites from North America that provides general insight into how different types of dolomitization processes may be reflected in carbonate rocks. Their data indicate that two separate processes may lead to two distinctive populations of sedimentary dolomite. The processes are divided into closed and open system... 

The patterns of diagenetic evolution recognized in this study allow discussion of the conditions for optimum porosity preservation and/or enhancement in the Serraria reservoirs. The best reservoirs of the unit occur in the Caioba area of the distal domain, where porosity was enhanced by dissolution of detrital feldspars and dolomite cement during telogenetic influx of meteoric waters. Similar conditions are expected for other structural blocks of the basin affected by post-rift uplift and erosion, or blocks bounded by major fault systems in which the Serraria Formation was relatively close to the... 

Many natural aquatic systems have a chemical composition close to saturation with respect to calcite or even dolomite. This is the case, for instance, for seawater, which is usually slightly oversaturated in the upper part of the water column and slightly undersaturated at greater depths. Under these conditions, the rates of both precipitation and dissolution contribute significantly to the overall rate of reaction. Even though the reaction paths may be very complex, there is a very direct and important link between the kinetic rate constants, according to which the rates of forward and reverse microscopic processes are equal for every elementary reaction. The fundamental aspect of this principle forms the essential aspect of the theory of irreversible thermodynamics (Frigogine, 1967). 

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