Page 289 - Petroleum Geology

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KILOMETERS
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100 50 0 100 U. S. A
MILES
Fig. 12.5. Devonian reefs of the Western Canada basin. (Reproduced, with permission,
from Barss et al., 1970, p. 20, fig. 1.)

these periods before the opening of the Atlantic ocean). Of particular impor-
tance to petroleum geology are the Devonian reefs of the Western Canada
basin. The discovery of oil at Leduc in 1947 was an event of great significance
not only to Alberta and Canada, but also to the petroleum industry at large,
because it reminded the industry of the great potential of fossil coral reefs
and encouraged a wave of research into ancient and modern reefs around the
world.
The Western Canada basin (Fig. 12-5) lies east of the Rocky Mountains and
extends from the Arctic Islands in the north, through the Northwest Territo-
ries and Alberta, to the Williston basin in north-central United States. A pro-
minent feature of the basin is the Peace River arch, in British Columbia and
Alberta, which influenced sediment and its accumulation throughout most
of the Palaeozoic, forming in late Devonian seas an island of Precambrian
granodiorites, schists and gneisses. Around this grew fringing reefs, and cycles
of reef rock, detritus and clastic limestones (commonly dolomitic) accumu-
lated (De Mille, 1958).