Diagenesis of carbonate rocks

Abstract

Introduction Chapter 8 discusses the processes that bring about diagenesis of siliciclastic sediments. In that chapter, the terms eodiagenesis, mesodiagenesis, and telodiagenesis are used to describe the stages of diagenesis that occur in siliciclastic sediments as they are progressively buried and subsequently uplifted. Significant differences exist between siliciclastic and carbonate sediments; therefore, the course of diagenesis differs in these two fundamentally different kinds of rocks. To illustrate, carbonate sediments are intrabasinal deposits, which are precipitated in some manner from the water in which they are deposited. Thus, initially, carbonate minerals are more or less in chemical equilibrium with the waters of their depositional environment. By contrast, siliciclastic sediments are brought into the depositional basin from outside. Further, carbonate sediments are composed of only a very few major minerals (aragonite, calcite, dolomite) in contrast to a much larger variety of minerals and rock fragments that may be present in siliciclastic sedimentary rocks. Carbonate minerals are more susceptible in general to diagenetic changes such as dissolution, recrystallization, and replacement than are most silicate minerals. Also, they are generally more easily broken down by physical processes, and they are much more susceptible to attack by organisms that may crush or shatter shells or that may bore into carbonate grains or shells. Nonetheless, carbonate sediments proceed in a general way through the same diagenetic regimes as siliciclastic sediments. That is, carbonate sediments go through early (shallow-burial), middle (deep-burial), and possibly late (uplift and unroofing) stages of diagenesis.