Geology Reference
In-Depth Information
clinal ridges. The main range of the Barn Mountains consists of faulted Paleozoic shale
and limestone bedrock interbedded with quartzite, chert, and conglomerate.
The Barn Mountains, like the Beaufort Plain, appear to fulfi ll the main requirements
for periglacial designation. First, the mountains lie beyond the maximum limit of
Pleistocene glaciation. The last major ice advance, termed the Buckland Glaciation
(Duk-Rodkin et al., 2004; Hughes, 1972; Rampton, 1982), was from the Mackenzie Delta
along the coastal plain to the north. Evidence of glaciation, in the form of either till
deposits or glacially-sculptured landforms, is absent from the Barn Mountains. Second,
the present climate is cold and dry. Data recorded at Shingle Point, on the Beaufort Sea
coast, and at Eagle Plain, some 150 km inland, indicate local conditions (Table 2.1B). In
winter, because of inversion effects, the Eagle Plain data are more representative. In
summer, because of elevation, the Barn Mountains are slightly cooler than both Shingle
Point and Eagle Plain. Precipitation, in the form of both rain and snow, is probably similar
to that at Eagle Plain, with more than half falling as rain, between June and September.
The landscape of the Barn Mountains is also instructive as far as periglacial terrain is
concerned. The mountains consist of structurally-controlled upland massifs surrounded
by extensive pediments. The latter are dissected by streams that drain towards the Arctic
coast (Figure 2.5). The pediment surfaces, fi rst reported upon by O. L. Hughes (1972),
are best developed where less resistant Mesozoic-age shale outcrops adjacent to more
resistant sandstone. In places, sandstone outliers are completely surrounded by gentle
pediment surfaces, forming isolated inselberg-like hills (Figure 2.6A). The pediment
Figure
2.5.
Vertical air photo of part of the Barn Mountains is annotated to show main structural
elements. The geology is after Norris (1977). The area has been subject to folding and faulting. The
uplands are synclinal in structure and formed by relatively resistant Lower Cretaceous sandstone
and quartzite (Kwc). The pediments are developed upon softer shale and siltstone (JKk). Faulting
has resulted in an inlier of Ordovician-age shale (Osh) that also results in upland terrain. The pedi-
ments are dissected. Air Photograph A 24502-160, National Air Photo Library © 1996. Produced
under licence from Her Majesty the Queen in Right of Canada, with permisssion from Natural
Resources Canada.
