Arkell.1956.Jurassic..

WESTERN CANADA 539
Trias. Above follow more than 1500 m. of greywackes, shales and
argillites, with subordinate tuffs. Towards the coast thicknesses are
smaller and much of the Jurassic is locally cut out by disconformities and
minor unconformities: for instance on Vancouver Island, where Callovian
rests on Toarcian, and on Queen Charlotte Islands where Albian rests on
Callovian.
The inner or Rocky Mountains trough has no volcanics and consists
mainly of shale, with minor quantities of fine sandstone and, sometimes,
black limestone. At the top coarser sandstones come in, their constituents
felspathic, and thickening westward as if derived from the rising Cordilleran
geanticline. These rocks, called the Fernie group and (p. 540)
basal Kootenay Sandstone, comprise representatives of nearly all the
stages present in the western geosyncline, with close correspondence in
most of the faunas, but the thicknesses are of the order of a tenth or
twentieth: the total for the Fernie varies from 66 m. to 330 m.
The deepest part of the trough lay under the front ranges and foothills
of the Rockies in Alberta and eastern British Columbia. The western
boundary cannot be clearly defined (Warren, 1951). To the east the
shallow sea passed far over the southern prairies, for marine Jurassic has
been proved in borings under the Cretaceous of southern Saskatchewan
and SW. Manitoba. These epicontinental sediments are or were continuous
with those which come to the surface in the Black Hills uplift
of South Dakota.
If the local unconformity and incoming of coarse sand grains at the
base of the Kootenay betokens the climax of the Nevadan orogeny in the
western geosyncline, the contribution of Canada to the dating of that
event depends mainly on the single giant ammonite mentioned on p. 540.
It appears to be Upper Portlandian, which would make the Nevadan
orogeny Lower Portlandian or Upper Kimeridgian.
In the western geosyncline in Canada, however, no major unconformity
or conglomerate that can be correlated with the Nevadan orogeny has
yet attracted attention. Instead, in the Harrison Lake area of British
Columbia a 900 m. conglomerate is intercalated between Oxfordian
Cardioceras beds and Callovian with Cadoceras. This, the Kent Conglomerate,
is said to rest discordantly on the Callovian and is believed to
represent the upheaval and erosion of the Agassiz Mountains, and it has
been equated with the Chisik conglomerate of Alaska (Crickmay, 1933a,
p. 358). The Canadian batholiths, though 'Nevadan' in the loose sense of
the term, are probably Cretaceous, like the Idaho batholith and those in
Lower California.
The lion's share in unravelling and publishing the Jurassic faunas of
Canada has been taken by Dr F. H. McLearn, as shown by the long series
of papers cited in the bibliography. More recently, important contributions
have also been made by Warren, Frebold, and others. I am deeply
indebted to these correspondents for reprints and to Dr Frebold for an
advance copy of the typescript of his masterly summary of the Jurassic
http://jurassic.ru/