General Geology

Red Bed Unit

Distribution

This unit occurs in several disconnected areas south of Francois Lake, east
of Uncha Mountain, along both sides of Ootsa Lake, along Chelaslie River, and
near the east end of Cheslatta Lake. The Chelaslie River occurrence is the most
southerly, and all are confined to the northwest quarter of the area. No comparable
strata are reported in adjoining areas to the west and north.

Lithology

The Red Bed Unit is an assemblage of sedimentary rocks consisting primarily
of red and brown shales and interbedded conglomerate and lesser amounts of
green and grey shales, orthoquartzite, greywacke, and black limestone. It is
distinguished from the main unit by its red colour and its coarse clastic com-
ponents. In this respect it bears a closer lithologic relation to the type Hazelton
Group but, because it underlies Middle Jurassic strata and is in part interbedded
with typical Takla rocks, it is preferable to map it as a local, non-typical part
of the Takla Group. The red beds are non-marine, except for a part at or near
the base.

Shales form the most important part of the unit. They are fine grained,
poorly to moderately well sorted, and lack graded bedding and distinct stratifica-
tion lines. Ill-defined conglomerate beds or conglomeratic lenses are commonly
interbedded with the shales. Shale beds, where distinguishable, are 2 to 3 feet thick
but may be as much as 50 feet thick. A red, brown, or reddish brown coloration,
due to disseminated hematite, is a dominant feature but a few green or grey
shales are interbedded with the red shales and are identical in all respects except
colour.

The conglomerates of the Red Bed Unit vary in composition, colour, and
physical characteristics. They are interbedded with the shales of the unit wherever
they occur but are more common along Francois Lake and southward decrease in
pebble-size, thickness of beds, and amount. The conglomerate beds vary in thick-
ness from 6 inches to 150 feet. They have sharp, distinct contacts with shale beds
and rarely grade into them. Although channelling and erosion of shales before
deposition of the conglomerates was deduced from the evidence at several places,
generally the conglomerate appeared to have been spread sheet-like over the
shale with little intermixing at the contacts.

The conglomerates are, in general, moderately to well sorted, generally
distinctly stratified, and in places are crossbedded; many beds, however, are poorly
sorted and unstratified. The pebbles of the conglomerate vary from sand size to
18 inches across, but the usual size is one half inch to 2 inches. Where fine
conglomerates occur, greywackes may form beds or lenses. The greywackes
apparently are similar in all respects to the conglomerates, differing only in grain
size. Pebbles are subrounded to well rounded and are made up of fine-grained

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