Petrologic and
Geochemical Evidence for Refluxing Brines in the Devonian Wabamun
Group,
Al-Aasm, Ihsan1,
Samantha Raymus1 (1)
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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California