ABSTRACT: Hydrothermal Karstification and Dolomitization of Upper Devonian (Wabamun Fm.) Medial Ramp Limestones, North-Central Alberta, Canada

PACKARD, JEFF J., Esso Resources Canada Ltd., Calgary, Alberta, Canada, P. CHURCHER, PanCanadian Petroleum Ltd., Calgary, Alberta, Canada, IHSAN S. AL-AASM and IAIN SAMSON, University of Windsor, Windsor, Ontario, Canada, RONALD SPENCER, University of Calgary, Calgary, Alberta, Canada, A. HAMID MAJID, Canadian International Petroleum Consultants, Calgary, Alberta, Canada, and J. G. SEN GUPTA, Geological Survey of Canada, Ottawa, Ontario, Canada

The Upper Devonian (Fammenian) Wabamun Formation is host to a complex play-type, typified by the Tangent field, in the Peace River area of north-central Alberta. Narrow, structurally controlled zones of porous dolomite exist within otherwise impermeable medial ramp limestones. Dolomitization occurs as aureoles surrounding large sediment-filled dissolution cavities. The porosity associated with this oil play is believed to have been created during a hydrothermal event in the Mississippian.

The existing evidence, consisting of detailed core and petrographic observations and geochemical analyses (fluid inclusion, stable isotopes, and rare earth element), point to shallow burial, hydrothermal karstification, and dolomitization that is probably associated with a Tournaisian or Visean sea floor fracture-vent system.

Hydrothermal dolomitization is synchronous with the emplacement of calc-alkaline intrusives and extensional tectonics temporally associated with the evolution of the Fort St. John graben system. Dolomite carbonatite pipes, proximally located to the study area, have yielded radiometric ages of between 339 and 349 m.y. It is postulated that these intrusives provided the thermal pump for the dolomitizing fluids, and/or that juvenile fluids emanating from these intrusives mixed with formation water to create the hot dolomitizing fluids.

Plays of remarkably similar origin have been documented in the Michigan basin and in the Basin and Range Province in Nevada. The latter area's direct association with an intrusive of Tertiary age has been established.

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