Burial Dolomitization of the Upper Devonian Rimbey-Meadowbrook Reef Trend, Central Alberta, Canada

Abstract

Subsurface Leduc buildups (Woodbend Group, Frasnian) of the Rimbey-Meadowbrook Reef trend in Central Alberta, Canada, extend along a linear trend for a distance of 320 km. Most buildups are located on top of the western margin of the underlying Cooking Lake platform (Frasnian). The Leduc buildups are dolomitized only where the margin of the Cooking Lake platform is dolomitized, suggesting that dolomitization of both the platform and the buildups is related. The extent of dolomitization in the Cooking Lake platform ranges from scarce to complete, but the overlying buildups are completely dolomitized. Petrographic data suggest selective replacement of limemud matrix and allochems. The most abundant dolomite type is coarse-crystalline planar mosaic dolomite. It forms dense, nonporous mosaics of subhedral to anhedral crystals, or porous zones characterized by intercrystalline porosity. Replaced allochems are characterized by nonplanar dolomite. Both dolomite types show homogeneous luminescence and exhibit similar isotope values ({delta}{sup 13}C: 2.2 to 3.5{per thousand}, {delta}{sup 18}O: -6.7 to -5.0{per thousand}). Only minor amounts of nonplanar dolomite cements (saddle dolomite) are present, lining pore-spaces and fractures. The observed stratigraphic and spatial distribution of the massive replacement dolomite is compatible with subsurface dolomitization. The Cooking Lake platform margin and the overlying Leduc buildupsmore » were probably dolomitized by the same fluid-flow system. Most of the dolomitizing fluids presumably were derived from downdip areas, utilizing the Cooking Lake platform margin and/or a fracture-fault system as a conduit. Ongoing geochemical analyses will help to constrain the origin of the dolomitizing fluids, their composition, and fluid-flow parameters.« less