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by drowning, and they were subsequently covered by grey marine shales and
argillaceous limestones of the Ireton Formation.
The reefs seem to have influenced the environment to the south-east of
the Stettler area because evaporites become more important in the Duvemay
Formation and the equivalents in that direction.
No obvious structural feature caused the trends, and the Leduc is litholog-
ically indistinguishable from the Cooking Lake under the reefs. But the trends
themselves are of interest because, like the other reef areas of the Western
Canada basin, there is very little deformation.
The Redwater field, discovered in 1948 by seismic reflection survey, pro-
duces oil of 34-36"API gravity from the most imporant undolomitized reef.
It lies at a depth of about 1000 m, but, because only the top 50 m or so con-
tains oil, little is known of the complex as a whole. The main frame builders
in the oil-bearing part of the reef were stromatoporoids, and the biosomes
and lithosomes show a general parallelism with the reef trend from NW to SE
(Andrichuk, 1958; Klovan, 1964).
Klovan distinguished seven facies: a Megalodon (pelecypod) facies along
the outer edge, and then successively the facies are, tabular stromatoporoid
reef, massive stromatoporoid detritus, skeletal calcarenite, and a back reef
facies that encloses an Amphipora limestone facies. Corals (Phillipsastreu and
Alueolites) occur in most areas of the reef and appear to have been important
frame builders locally. AZueolites is found commonly in all but the back-reef
facies and so seems to have been able to adjust to the various environments.
Syringopora and Syringoporella are found in the fore-reef, in which original
dips of 20" have been recorded (Klovan, 1964).
Golden Spike (west of Leduc) is also undolornitzed, and Duhamel is partly
dolomitized. We cannot be sure that the dolomitized reefs were similar in

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Fig. 12-9. Stratigraphic relationships of formations of the Woodbend Group in the Leduc
trend.