ABSTRACT

Some processes of vadose and phreatic diagenesis in carbonate rocks have been simulated in the laboratory, using CO₂-charged water to leach a "source bed" of carbonate sand. Precipitation of calcite cement in a second sand body, above and below an artificial water table, was induced by CO₂ evasion. Magnesian calcite was preferentially leached from the source bed, and calcite was precipitated as cement in the second sand unit. More cement was produced in the "vadose" zone than in the "phreatic" zone.

Cement formed in the vadose zone is composed of micron-sized crystals, and occurs as abundant rim cement and grain contact cement. Crystal size increases with distance from grain boundaries. Rounding of intergranular void spaces is common. Cement formed in the phreatic zone is more coarsely crystalline (50 microns) than in the vadose and abuts directly against original skeletal grain boundaries. The texture of the vadose cement closely resembles textures observed in vadose cementation of skeletal calcarenites in Bermuda.