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Middle Upper Cretaceous Marine Expansion

The Dunvegan marginal alluvial plain retreated and the seas spread
over most of the site ot the Foothills and Plains and may even have inun-
dated the site or the present Rocky Mountains. Most, or all, of them
extended from the Gulf to the Arctic Ocean, dividing the continent, but
only, of course, by a shallow sea. The paleogeography of this time is
commonly illustrated in current textbooks on Historical Geology. Mostly
fine-grained sediments were deposited on the sea bottom, and are now pre-
served as shale. Finer sediments, speckled calcareous shale, and even some
limestone formed in places, particularly in the east. Some sand accumu-
lated in the extreme west. Little, if any, evidence of delta building is
preserved. The sandstones, however, may have fringed, that is, lain out
in front of, marginal alluvial plains on the site of the Rocky Mountains,
but any evidence of such plains was destroyed during the deep erosion that
the Canadian Rockies have undergone.

The Dunveganoceras sea is recorded by shale and sandstone near the
base of the Kaskapau formation on Pouce Coupé River, near the eastern
border of the map-area, by shale at the base of the Kaskapau at Dunvegan,
by shales low in the Blackstone formation in southwestern Alberta, and by
beds of the same age in Wyoming (Haas, 1949). It, doubtless, had a much
wider distribution than the fossil record shows, and spread some distance
into northeastern British Columbia.

The Watinoceras and Prionotropis seas inundated the interior of the
continent, and records ot them are preserved from Mackenzie River Valley
to Texas. In northeastern British Columbia, sand was deposited in the
vicinity of Pine River Valley, where Watinoceras has been collected on
Tuskoola Mountain. Finer sediment was laid down farther east, in the
Pouce Coupé area.

In Scaphites ventricosus time both fine and coarse sediment accumu-
lated in the sea, and some of the sand was carried to the site of lower Smoky
River, far beyond the east border of British Columbia. The question might
well be asked whether alluvial plains existed at this time to the west on the
site of the Rocky Mountains. Like the Prionotropis and Watinoceras seas
the Scaphites ventricosus sea has left its mark on the interior of the continent
from the Arctic to the Gulf.

The later sea, recorded by Inoceramus of the lobatus species group, had
a wide and probably a similar distribution to that of Scaphites ventricosus
time. Fine sediments accumulated in this sea, mostly now preserved as
shale, but calcareous deposits formed in the eastern part, particularly on
the Manitoba escarpment. A little sand enters in the extreme western
sections. ‘bis sea is recorded in northeastern British Columbia by sand-
stone and shale near the top of the Kotaneelee formation on lower Liard
River. It may well have spread widely over northeastern British Columbia
and Jeletzky (1950) suggests an extension to the Arctic.

Eastern Advance of the Delta Plains

In northeastern British Columbia the last middle Upper Cretaceous
sea was expelled by the advance of a delta or marginal alluvial plain, which
covered all of this part of the continent. This was in early Belly River,
possibly about late Santonian or early Campanian time. Here the advance

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