Modeling Diagenetic Bedding, Stylolites, Concretions, and Other Mechanochemical Structures

A quantitative reaction-transport-mechanical model of pressure solution is used to explain a variety of differentiated features in carbonate rocks. The development of stylolites, bands of compaction alternating with bands of augmented cementation, and carbonate bands in sandstones are shown to be the consequence of an unstable dynamic that takes place during compaction. This dynamic leads to the intensification of textural contrasts during burial diagenesis. The quantitative model allows for the prediction of the range of existence and properties of these phenomena with respect to constraints. These constraints include carbonate grain size, clay content, burial and thermal history, and fluid chemistry.The theory is applied to the analysis of diagenetically differentiated marl/limestone alternations. Observed trends with grain size and clay content are explained, as is the anti-correlation between regions of compaction and highest porosity.An analysis of the growth of quartz concretions in a sponge spicule-bearing limestone is carried out via a closely related mechanochemical model designed to characterize low-porosity rocks. Simulations of the model yield the temporal evolution of the concretion from its nascent state as a domain of quartz nucleation to one in which all calcite has been removed by a force of crystallization mechanism. Our conclusion is that the above range of phenomena from concretions to stylolites and differentiated marl/limestone sequences are all endmember responses of the mechanochemical dynamics of carbonate rocks and are to be understood in terms of a unified perspective as presented.