ABSTRACT

Intergranular pressure solution is believed by many sandstone petrologists to be the major source of silica for the cementation of orthoquartzites, although there is no quantitative supporting evidence from thin-section petrology. The white Tuscarora orthoquartzite, often cited as a good example of cementation by pressure solution, has been studied using luminescence petrology to evaluate this hypothesis.

Point counts were made to determine the amount of pressure solution and authigenic silica in 183 thin sections of samples of the Tuscarora orthoquartzite from Pennsylvania, Virginia, and West Virginia. Luminoscope measurements show large amounts of pressure solution to be an uncommon phenomenon in the Tuscarora throughout the study area. Pressure solution can account for only 30-35% of the pore-filling quartz cement.

Proximity to folds, grain size, sorting and clay content are factors that have been suggested as controls on the amount of pressure solution in orthoquartzites. Of these, only clay appears related to the occurrence of pressure solution in the Tuscarora. Furthermore, the well-cemented samples show less pressure solution than more friable samples, but contain more pore-filling cement.

We conclude that initiation of cementation by silica during early diagenesis has prevented widespread development of intergranular pressure solution by equalizing the distribution of stress along grain boundaries. Of the many possible sources of silica other than pressure solution, transport of H₄SiO₄ in surface-derived ground water seems the most likely source of the majority of the cement found in the Tuscarora.