ABSTRACT

Textural observation of quartz dissolution at mica-quartz interfaces in sandstones from the Norwegian continental shelf show that mica grains have penetrated into quartz grains without being significantly deformed. Theoretical calculations of the mechanical properties of the mica suggest that quartz dissolution takes place at pressures less than 10 bars, i.e., at pressures only a fraction of the overburden load. Cathodoluminescence and element mapping show that K-and Al-bearing material (probably illitic and/or micaceous clay) is present at all interfaces where quartz-to-quartz dissolution and interpenetration is observed. Because illitic and micaceous clay is likely to have an effect upon quartz dissolution similar to that of mica, this suggests that what has been considered to be a ressure-solution process may instead be a clay-induced dissolution process. Because quartz-to-quartz dissolution is not observed in the absence of illitic or micaceous clay, this suggests that quartz dissolution is not mainly controlled by pressure. In a quartz-mica or quartz-illite system the rate of quartz precipitation, which is strongly controlled by the temperature, may therefore be the main control on quartz cementation (Oelkers et al. 1992, and in press).