Geology Reference
In-Depth Information
(A)
(B)
Figure
2.6.
Landscape elements of the Barn Mountains, interior Yukon Territory. (A) Syncli-
nal ridges and outliers form upland massifs and inselberg-like hills near Sleepy Mountain.
(B) Pediment-like surfaces surround upland massifs. See Figure 2.5.
surfaces truncate dip of the underlying rock (Figure 2.6B), are dissected, occasionally
cross fault lines (see Figure 2.5), and sometimes encroach upon the adjacent sandstone.
For the most part, they are “covered” pediments (Twidale, 1987); that is, they are cut in
weak bedrock and carry a protective veneer of detritus derived from upslope. In the
European literature, such features are commonly termed “glacis” (Dresch, 1982, p. 90) or
“erosion glacis” (Joly, in Demek, 1972b, pp. 189-192). Closely-related features are large
terraces or steps carved in bedrock and occupying hillslope positions (see Figure 9.6).
In all probability, the Barn Mountain landscape is old, dating from the Middle to
Late Tertiary. The pediments, probably in existence prior to the onset of the Quaternary,
would have been effective slopes of transportation of waste material under cold-climate
conditions. At the meso-scale, the bedrock terraces (see Figure 9.6) show no obvious
relationship with geological structures. At the micro-scale, angular rock rubble veneers
many of the upland surfaces. A striking observation is that all these features show little
sign that they are forming under today's climate.
