Abstract: How Important is Pressure in Causing Dissolution of Quartz in Sandstones?

Per Arne Bjorkum

Textural observation of quartz dissolution at mica/quartz interfaces in sandstones from the Norwegian Continental Shelf shows that mica grains have penetrated into quartz grains without being significantly deformed. Theoretical calculations of the mechanical properties of mica suggest that the pressure involved in the dissolution cannot have exceeded 1/10 of the overburden load (i.e. 25 bars).

Cathodoluminescence studies and element mapping of 30 thin sections from different sandstones from the North Sea shows that whenever evidence of grain to grain quartz dissolution is observed, K- and Al-bearing minerals are present at the interface. This is interpreted as indicating illitic/micacous clay present at the interface. Since dissolution of quartz in contact with mica may take place at pressures much lower than the overburden load, this suggests that what has been considered to be a pressure solution process may instead by a clay induced dissolution (CID) process. Since quartz to quartz dissolution is not observed in the absence of clay, this suggests that the quartz cementation process is not primarily controlled by pressure. The rate of quartz precipitation, which is strong y controlled by the temperature, may therefore be the primary control on the quartz cementation process (Oelkers et al., 1992).

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994