Ground-Water Chemistry and Diagenetic Reactions in Tertiary Sandstones of the Green River and Wasatch Formations, Uinta Basin, Utah (Chapter X)

摘要

An integrated study of ground-water chemistry and aquifer petrology reveals close correspondence between the chemical evolution of ground water and observed authigenic mineral assemblages. In recharge areas, authigenic kaolinite is observed in the rocks, and ground-water compositions plot within the stability field for kaolinite in a variety of activity-activity diagrams. Feldspar is dissolved from the updip rocks, also in accordance with thermodynamic predictions from the water chemistry. In down-gradient reaches of the flow system, authigenic clay, including smectite and illite-smectite, is present and feldspar destruction still prevalent. Near discharge areas, feldspar may be stable, although authigenic feldspar is not common. Throughout the basin, authigenic calcite and dolomite commonly replace detrital feldspar grains. Precipitation of carbonate minerals probably is driven by an increase in pH and by release of calcium associated with feldspar dissolution. Chalcedony, rather than quartz, probably is the silicate phase controlling dissolved silica levels. The good agreement between the petrographic relationships and the present-day ground-water chemistry suggests either that the observed authigenic mineral assemblages are still forming or that the ground water has had sufficient time to approach equilibrium with respect to the assemblage.