Petrologic and Geochemical Evidence for Refluxing Brines in the Devonian Wabamun Group, West-Central Alberta*
Ihsan Al-Aasm1 and Samantha Raymus1
Search and Discovery Article #50046 (2007)
Posted July 30, 2007
*Adapted from oral presentation, AAPG Annual Convention (with SEPM), Long Beach, California, April 1-4, 2007
1University of Windsor, Windsor, Ontario, Canada ([email protected])
Recent sedimentological and geochemical investigations on several Devonian Crossfield reservoirs from Burnt Timber, Panther River, Moose Mountain, and Benjamin Ghost region west of the Crossfield trend, Alberta, provided new evidence for the role of reflux brines on the formation of pervasive fine-crystalline matrix dolomite and modification of porosity in these reservoirs. Other associated diagenetic processes that formed during early and late burial history include compaction, recrystallization of early matrix dolomite, precipitation of secondary anhydrite, blocky calcite, saddle dolomite and thermal sulphate reduction (TSR)-related diagenetic minerals. The evidence for density-driven refluxion from the Stettler brines for the formation of the fine-crystalline matrix dolomite include: (1) dolomitization occurs in sediments that are relatively uncompacted, and the degree of preservation of the original fabrics is quite significant in the dolomicrite and fine- to medium-crystalline matrix dolomite, (2) fabric-destructive stylolitization and the development of dissolution seams cross-cut dolomite matrix fabrics, (3) matrix dolomite is relatively fine- to medium-crystalline (<10 µm–200µm), planar-S to nonplanar, non-luminescent to very dully luminescent, (4) oxygen isotopic values range from -2.82 to -6.17 ‰ and carbon isotopic values from 0.22 to 1.47 ‰. These values are comparable to slightly more depleted than Famennian seawater isotopic signatures. The depletion is likely the result of recrystallization that has affected the matrix dolomite during subsequent burial and (5) 87Sr/86Sr ratios indicate that the dolomicrite and fine-crystalline dolomite precipitated from Famennian seawater. The associated primary evaporites show also values close to Famennian seawater, suggesting that the dolomicrite and fine-crystalline matrix dolomite precipitated from Famennian seawater.
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