A coupled reaction/transport/mechanical model for intergranular pressure solution, stylolites, and differential compaction and cementation in clean sandstones

Abstract

“Pressure solution” at grain-grain contacts and free-face dissolution and growth kinetics coupled to solute transport and texture-dependent effective stress are shown to lead to pervasive intergranular compaction and the development of stylolites in sandstones. Reaction/transport modeling studies presented here demonstrate that stylolite formation may arise from an instability of a chemically compacting rock, leading to the enhancement of spatial heterogeneities in rock texture. Textural and geochemical criteria distinguishing between conditions favoring stylolites vs. pervasive intergranular pressure solution for both the water film diffusion (WFD) and free-face pressure solution (FFPS) mechanisms (so denoted in Tada et al., 1987) are outlined. WFD and FFPS each show a characteristic grain size dependence which aids in the recognition of the kinetic mechanism responsible for pressure solution. Results from our simulations concerning the effect of grain size on the stable compaction of sandstones compare favorably to observations and data in Houseknecht (1988). They suggest that FFPS is operative in clean sandstones, while WFD is operative in clay-rich sandstones. Spatially discrete domains of heightened cementation and intergranular pressure solution-induced compaction are shown to develop from certain types of initial spatial variations in grain textural parameters. These features, predicted by our computer simulation, show differential cementation/compaction trends similar to examples observed in Paleozoic sandstones. The greatest contrasts in cementation, compaction, and porosity attend the FFPS mechanism.