Stylolitization Mechanisms, Permeability Barriers and Pressure Solution Generated Cements: Examples from the Lockport Formation (Middle Silurian) of Dundas, Ontario and Nisku Formation (Upper Devonian) of Central Alberta

Abstract

<p>The study of stylolites found in the Lockport (Middle Silurian) dolostones and Nisku Formation (Upper Devonian) limestones has led to the development of two stylolitization mechanisms. The amalgamation mechanism (Lockport Formation) forms a stylolite by the amalgamation of microstylolites through pressure solution of intervening dolomite. Microstylolites originated as primary "organic" layers. Dolomitization-stylolitization (Nisku Formation) forms a stylolite by pressure-dissolution of matrix calcite against concentrations of dolomite. Dolomite acts as a stress perturbation that ultimately leads to pressure solution and stylolitization.</p> <p>Statistical analysis of Nisku Formation core data suggests that there is a reversal in the trend of vertical permeability reduction once a stylolite grows to centimetre-scale. The most effect permeability barriers are millimetre- and millimetre to centimetre-scale stylolites.</p> <p>Cathodoluminescent observations suggest that stylolites generate carbonate cements. The mode of transport of dissolved material away from the stylolite is by ionic transfer in porosity and diffusion through intra-crystalline/matrix micrite mediums. Stylolitization is responsible for recrystallization and dedolomitization textures seen in the vicinity of stylolites. The isotopic composition of main mineral phases in the Nisku Formation supports these interpretations.</p>