ABSTRACT: Formation of Presqu'ile Dolomite in the Middle Devonian Presqu'ile Barrier, Northwest Territories and Northeastern British Columbia, Canada

QING, HAIRUO, University of Ottawa, Ottawa, Ontario, Canada, and ERIC MOUNTJOY, McGill University, Montreal, Quebec, Canada

Presqu'ile dolomite consists of two types of dolomites: (1) light brown, coarsely crystalline replacement dolomites and (2) vug and fracture-filling saddle dolomite cements. It is most abundant in the Middle Devonian Presqu'ile barrier, which hosts MVT deposits at Pine Point, and also serves as hydrocarbon reservoirs in the subsurface west of Pine Point area.

Petrographic study suggests that the Presqu'ile dolomites formed during burial because they replace blocky sparry calcite cements, postdate stylolites, overlap with MVT deposits at Pine Point, and locally occur continuously across the sub-Watt Mountain unconformity. The average Oxygen 18 values of Presqu'ile dolomites decrease gradually from -9.1o/oo PDB at Pine Point to -13.9o/oo PDB in the subsurface of northeastern British Columbia, whereas the corresponding homogenization temperatures of saddle dolomite fluid inclusions increase from 99 degree C to 168 degree C. The 87Sr/86Sr ratios of Presqu'ile dolomite also increase westward along the Presqu'ile barrier, averaging 0.7083 at Pine Point and 0.7097 in the subsurface of northeastern British Columbia.

The gradual increase in 87Sr/86Sr ratios and homogenization temperatures with corresponding decrease in oxygen 18 values westward along the Presqu'ile barrier suggests a basin-scale migration of hot, radiogenic dolomitizing fluids updip from west to east along the Presqu'ile barrier. Fluid movements probably were most active during Late Cretaceous and early Tertiary as a result of tectonic and sedimentary loading and uplift of the foreland basin west of the Presqu'ile barrier.

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