53
AGE OF FAULTS

The faults of McConnell Creek map-area may have formed at different
times in its geological history, but, as evidenced by the Sustut strata,
major, although not necessarily the greatest, displacements took place in
post-Paleocene time. So far as known all significant faults are older than
the Tertiary and Recent basaltic rocks. The probable occurrence of Kast-
berg intrusions in the Omineca and Genlyd fault zones, but not in the
adjacent rocks, suggests that these structures existed prior to the emplace-
ment of the intrusions, but does not preclude the possibility of some fault
movement after intrusion. The post-Paleocene displacements may be in
part a phase of an early Tertiary period of orogeny that resulted in the
folding of the Sustut formations and presumably culminated with the
emplacement of the Kastberg porphyritie rocks.

FOLDS

As previously described, most strata have been folded along north-
westerly trending axes, and many of the resultant structures plunge north-
west. These folds were formed mainly during two intervals. Although it
is possible that some folding occurred prior to the deposition of the Takla
strata, the first clearly defined interval of major folding was probably related
to the emplacement of the Omineca intrusions: it followed the deposition
of the Takla formations and preceded the accumulation of the Sustut rocks.
As a result, Takla, Cache Creek, and Asitka rocks are folded to about the
same degree. In general they are tightly folded. So far as known, the
folding stresses of this interval were about equally effective throughout
the map-area on assemblages of equivalent competency.

The second interval of major folding followed the deposition of the
Paleocene, Sustut strata. During this interval the Sustut rocks southwest
of the faulted belt were subjected, as previously explained, to a thrust from
the southwest and warped into a series of open folds. However, to the north,
near Thutade Lake, they remain only gently inclined or horizontal. Thus
the thrust appears to have achieved nearly complete relief within at least
the northwest part of the faulted belt. Furthermore, it seems reasonable to
expect that, despite the lack of direct evidence of Sustut strata, similar
relief was attained elsewhere along the belt. If so, it is probable that much
or all of the map-area northeast of the belt (that is northeast of the
Omineca fault) remained almost unaffected by the post-Paleocene folding,
stabilized in part, no doubt, by the Omineea intrusions.