Deep-Burial Dissolution of Devonian Carbonates in Western Canada—More Common Than You Think!

Jeffrey J. Dravis¹ and Iain Muir^2
1 Dravis Geological Services, Houston, TX
² Suncor Energy Inc, Calgary, AB

Deep-burial dissolution promoted substantial secondary porosity development in several Devonian limestone and dolostone sequences in western Canada. This process is very common but under appreciated because of inadequate petrography. Devonian limestone sequences exhibiting substantial deep-burial dissolution and secondary porosity development include those in the Jean Marie, Slave Point, and Ramparts Formations. Dolostones in the Keg River and Wabamun Formations underwent deep-burial dissolution of dolomitized fabrics.

Evidence for deep-burial dissolution in limestones includes: (1) secondary porosity cutting across pressure solution seams, or seams “floating” in secondary porosity; (2) dissolution of grains already sutured by pressure solution; (3) secondary porosity preserved along stylolites and burial fractures, or termination of these fabrics into such pores; and (4) leaching of calcitic grains.

Dissolution of dolomitized grains produces randomly scattered secondary pores, not partial molds confined to grain centers, as is typically seen when limestones are progressively dolomitized and remnant calcites leached. Criteria for burial dissolution of dolostones are similar to that for limestones, and often include saddle dolomite dissolution. Rotated stylolitic breccia clasts represent a grander scale of burial dolostone dissolution.

Resolution of the timing of secondary porosity development allows one to infer the chemistry of pore fluids and their movement through a sequence, creating new exploitation opportunities. Unlike near-surface dissolution, deep-burial dissolution is controlled on a larger scale by faults and associated facture systems. On a finer scale, fractures and pressure solution seams transport dissolving fluids, often reflecting a strong facies control on burial dissolution, in both limestones and dolostones.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005