Intergranular Pressure Solution in Four Quartzose Sandstones

Abstract

ABSTRACT Cathodoluminescence petrography and scanning electron microscopy reveal that several geologic variables significantly influenced intergranular pressure solution and quartz cementation in the Bromide (Ordovician, Oklahoma), Upper Minnelusa (Permian, Wyoming), Nugget (Jurassic, Utah), and Tuscarora (Silurian, Pennsylvania) sandstones. A linear relationship exists between mean grain size and intergranular pressure solution, with finer-grained samples having experienced more intergranular pressure solution than coarser-grained ones. Samples that display pervasive illite grain coatings have also experienced more intergranular pressure solution than those with no or poorly developed grain coatings. Sorting and limited framework-grain compositional variability have exerted little influence o intergranular pressure solution. Silica budgets indicate that in the Bromide, Upper Minnelusa, and Nugget sandstones, more quartz has been dissolved by intergranular pressure solution than is present as cement; these sandstones have exported silica during burial diagenesis. In the Tuscarora, the amount of quartz dissolved by intergranular pressure solution is about equal to the amount of quartz cement present, implying approximate mass balance. However, petrographic evidence suggests that most of the quartz cement in at least three of these sandstones predates most intergranular pressure solution, implying that they acted as silica importers during shallow diagenesis and silica exporters during deeper diagenesis. Intergranular pressure solution has played varying roles in determining the ultimate porosity of these four sandstones. In the Nugget, intergranular pressure solution was the single most important diagenetic process that influenced porosity evolution. In the Bromide, intergranular pressure solution was slightly more important than mechanical compaction and considerably more important than cementation. In the Tuscarora, intergranular pressure solution was slightly more important than mechanical compaction and of about equal importance to quartz cementation. In the Upper Minnelusa, intergranular pressure solution was less important than both mechanical compaction and gypsum/anhydrite cementation.