Nechako River Map-Area

andesite, porphyritic andesite, quartz, and grey chert in order of abundance. The
matrix may contain much hematite or chlorite, a calcite or a siliceous cement.
The make-up of the cement determines the compactness and colour of the rock—
green, grey, red or reddish brown.

Along Frangois Lake a unique section, at least 100 to 200 feet thick of
well-bedded red shales, white to greenish orthoquartzites, fine reddish pebble-con-
glomerate, and black limestone, forms what is believed to be the base of the Red
Bed Unit. Individual beds are 6 inches to a foot thick, well bedded, and without
crossbedding or graded bedding. One bed of black limestone carries indeterminate
marine shells and this, coupled with the complete dissimilarity of this section
with the rest of the unit, leads to the conclusion that this whole section was laid
down under marine conditions.

Origin

The red beds and their origin have been described and discussed more
fully elsewhere (Tipper, 1959a, pp. 18-19). Briefly stated, there is ample evi-
dence to indicate a non-marine environment of deposition. Largely on negative
evidence and physical dissimilarities they are considered to be primary red
beds that have been eroded and transported from a deeply weathered regolith of
an old land area to the north. It is suggested that late Permian or Triassic red
soils were produced on a land area north of Francois Lake and these were rapidly
eroded, transported, and dumped on a marginal area, possibly a coastal plain, and
rapidly buried to preserve the red coloration (Krynine, 1949, p. 61; Van Hou-
ten, 1948, pp. 2083-2126).

Structural Relations of Takla Group

Little is known of the internal structural relations of the Takla Group as no
complete controlled section was studied. The red beds are interbedded with the
main unit, and many flows are mapped with the red beds. The nature of two
units in Nechako River area suggests very strongly that the group is not a con-
formable succession—certainly a short distance north of the area erosion was
apparently active while deposition was occurring within the area.

The relation of the Takla Group to the Cache Creek Group is not known in
the area, but in Fort St. James area Armstrong stated “that the Takla group
lies unconformably above the Cache Creek group [Permian] and that the period
between Middle Permian and Upper Triassic was apparently one of igneous
intrusion, uplift, erosion, and probable deformation” (Armstrong, 1949, p. 56).

The chert-pebble conglomerate unit of the Hazelton Group overlies the Takla
Group unconformably.

The Topley Intrusions cut the main unit of the Takla Group and the marine
part of the red beds, but not the non-marine. The intrusions are therefore younger
than at least part of the group.

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