Petrographic constraints on models of intergranular pressure solution in quartzose sandstones

Abstract

Petrographic and SEM observations on 478 samples of six quartzose sandstones provide a data base that can be used to evaluate the role of intergranular pressure solution (IPS) in sandstone diagenesis and to constrain predictive models of the pressure solution process. SEM examination of grain contacts that have experienced pressure solution suggests that IPS occurs at the interior portions of contacts where the greatest stress is concentrated and that granulation of quartz grains at points of contact may contribute to the process. The chemical compaction fabrics that result from IPS suggest that the process is most commonly induced by effective lithostatic stress and that the resulting strain is uniaxial. Numerous geological variables influence IPS. Grain size exerts a fundamental influence, with finer grained samples experiencing more IPS than coarser grained samples. On both local and regional scales, IPS is inhibited by poor sorting, an abundance of ductile grains, the presence of “shallow” cement, slow rates of shallow burial, and overpressured conditions. In contrast, IPS is enhanced by the presence of illite grain coatings, increased maximum burial depth, rapid rates of shallow burial, longer times spent at great depths, higher temperatures, and high volumes and rates of fluid flow. Silica budgets indicate that some of the analyzed sandstones approximate mass balance whereas others have exported silica. Calculations of fluid flow requirements indicate that advanced stages of IPS are favored by high volume, high velocity fluid flow. Such flow can occur as a result of uplift of basin margins, which is typical of foreland and intractonic basins.