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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Abstract
Diagenesis of an Upper Devonian Carbonate-Evaporite Sequence: Birdbear Formation, Southern Interior Plains, Canada
Steve G. Whittaker (*), Eric W. Mountjoy
ABSTRACT
to -5)
relative to coeval open marine settings reflect the restricted paleoenvironment
of the shelf. Limestones are present only in the eastern part of the study
area, and were altered by meteoric and burial diagenesis and do not retain
marine d18O values. d18O
values of replacement dolomites have limited range (-3
to -5)
and may indicate dolomitization by hypersaline marine waters having low
d18O
values. 87Sr/86Sr ratios of the replacement dolomites
are variable (0.7082-0.7085), but also suggest that reflux of Late Devonian
seawater, possibly Famennian, was the principal dolomitizing mechanism
in the Birdbear shelf. Most bedded anhydrites have d34S
values (22
to 24
CDT) and 87Sr/86Sr ratios (ca. 0.7081) that record
Frasnian seawater. Dissolution and reprecipitation of sedimentary sulfates
resulted in sulfate cements having up to 2
higher d34S values and slightly higher
87Sr/86Sr
ratios (ca. 0.7083). Fluids associated with anhydrite dissolution may have
been derived from the overlying Famennian shelf. Late diagenetic cements
in the Birdbear Shelf precipitated during the Late Cretaceous and early
Tertiary during maximum burial from hot, evolved residual evaporitic brines.
Residual evaporitic brines that originated on the shallow eastern Upper
Devonian shelves were likely important agents of diagenesis throughout
th basin.
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