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Outlines of Deltas in Middle Fort St. John Time

The outlines of delta or alluvial plains shown on paleogeographic maps
in 1932 by McLearn were revised in 1944 by the same author. Whatever
further drastic revisions may be necessary as new stratigraphic data and
new correlations become available, it does appear that some unusual
outlines were traced by the fronts of these deltas. North-south replace-
ment of marine by non-marine strata, and of shale by sandstone, noted by
McLearn (1932, 1944), Wickenden and Shaw (1943), Nauss (1945A), and
Wickenden (1948), call for somewhat unorthodox paleogeography. Mc-
Learn has inferred that some of the delta fronts extended in an approxi-
mately east-west direction. The deltas advanced and retreated in a more
or less north-south or southwest-northeast direction. Apparently a
delicate balance was maintained at times between sea, on the one hand, and
coastal swamp and alluvial plain on the other, so that marine and non-
marine beds are, in places, intimately related in some formations.

In northeastern British Columbia, the marine sand bottoms and
alluvial plain or coastal swamps of middle Fort St. John time are recorded
by the Commotion and Gates formations. The non-marine beds included,
along with marine beds, in the Commotion on Pine River, disappear to the
north on Peace River, as already noted, and point to an old coastal swamp or
delta front between the sites of these two rivers.

An important event in late Lower Cretaceous or Albian history was
the appearance in abundance of dicotyledons, or plants with leaves, pro-
ductive of a marked change in the forest landscape of the delta plains.

’ They are recorded in northeastern British Columbia by the flora of the
Commotion formation.

Late Fort St. John Marine Sands

A widespread sandy sea floor is recorded by beds of the Goodrich
formation and its correlatives. This floor covered the site of the western
part of the Plains, at least from Pine River north to Steamboat Mountain,
but may not have extended very far out on the Plains. As knowledge of
the stratigraphy increases, it will be interesting to determine to what
extent the outline and location of this sand bottom differed from the out-
lines of the deltas in middle Fort St. John time, and to what extent they
were prophetic of the outline and the localities of the later Dunvegan delta
or marginal alluvial plain.

This sand covered a large area for a littoral marine sand. It may
indeed have had an even wider extent than the known outcrops of sand-
stones of the Goodrich and Sikanni formations indicate; for it may have
spread west or southwest across the site of the Rocky Mountains to the
western shore of the Goodrich or Neogastroplites sea. It may, however, not
have extended so far west or southwest and have lain, as a wide, fringing,

sandy sea floor, on the site of the Foothills and western part of the Plains, .

in front and east or northeast of a marginal alluvial plain, on the site of the
Rocky Mountains. In either case the unusually large area of marine sand
floor requires an explanation: subsidence of the sea floor may have been too
rapid to permit growth of a delta or marginal alluvial plain, which so com-
monly formed when sediment of sand grade was being carried into the
interior Cretaceous sea; or subsidence was rapid enough to impede advance