ABSTRACT: Fracture and Fault-Controlled Burial Dolomitization, Late Devonian Wabamun Group, Alberta

HALIM-DIHARDJA, M. K., Norcen Energy Resources Limited, Calgary, Alberta, Canada, E. W. MOUNTJOY, E. W., McGill University, Montreal, P.Q., Canada

The Famennian Wabamun Group is comprised of cyclic, shoaling upward shallow marine carbonates and evaporites. In the Tangent, Normandville and Eaglesham fields, dolomitization is part of a complex diagenetic history related to multiple phases of faulting and fracturing in

the Peace River Arch region.

Petrographic and geochemical data indicate a range of dolomite textures and types that are variable distributed within the reservoir. Dolomites consist of (1) widespread early microdolomite, floating dolomite crystals, and stylolite-precipitated dolomite, (2) intermediate stage matrix and sucrosic dolomite, and (3) later saddle and reworked fine crystalline dolomites.

During marine and early burial diagenesis, calcite cementation, mechanical compaction and minor dissolution occurred. Microdolomite and scattered dolomite crystals were formed during shallow burial. More pervasive matrix dolomite and sucrosic dolomite is associated with extensive phases of fracturing related to faulting. Saddle dolomite precipitated during later stage fracturing and fine crystalline dolomite was derived from the fracturing, brecciation, and reworking of earlier matrix dolomites.

The timing of dolomitization and fracturing is difficult to determine. Early fractures most likely initiated in the Late Devonian to Early Carboniferous during early burial and compaction. Another phase of fracturing probably occurred during the Mississippian to Pennsylvanian when the Normandville, Dunvegan, and other subsidiary faults underwent movement during the collapse of the Peace River Arch. Later phases of fracturing and possible fault reactivation may have continued over a long period of time as a result of more rapid subsidence and burial by the Cretaceous and Early Tertiary clastic wedge.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)