Diagenesis variables

Program SEOS04 solves diagenesis in carbonate sediments Variable layer thicknesses... 

The rate at which metastable phases dissolve or are replaced is an important problem in carbonate diagenesis. Carbonate mineral assemblages persist metastably in environments where they should have altered to stable assemblages. The question is "what are the time scales of these alterations" They are certainly variable ranging from a few thousand to a few hundreds of millions of years. Even calcites in very old limestones show chemical and structural heterogeneities, indicating that the stabilization of these phases is not complete. Unfortunately, it is difficult, but not impossible, to apply directly the lessons learned about carbonate mineral dissolution and precipitation in the laboratory to natural environments. 

We shall see, though, that the environment does not yield totally to simple models of chemical equilibrium and chemical kinetics, and laboratory determined constants often cannot explain the field observations. For example, organic matter degradation rate constants determined from modeling are so variable that there are essentially no constraints on these values from laboratory experiments. In addition, reaction rates of CaCOa and opal dissolution determined from modeling pore waters usually cannot be reproduced in laboratory experiments of these reactions. The inability to mechanistically understand reaction kinetics calculated from diagenesis models is an important uncertainty in the field today. 

After application of the diagenesis equations to a variety of marine environments, it became clear that the organic matter degradation rate constant, k, derived to fit the pore water and sediment profiles, was highly variable. The organic fraction of such sediments is thus often modeled as a mixture of a small number of discrete components (Gi), each of which has a finite initial amount and... 

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