Geology Reference
In-Depth Information
geocryology adopt holistic all-encompassing approaches whereas North American perma-
frost studies are characterized as being either “science” or “engineering” in nature. Thus,
there is no North American text that equals the breadth and depth presented by the most
recent Russian and Chinese texts,
General Geocryology
(Yershov, 1990) and
Geocryology
in China
(Zhou Youwu et al., 2000). Third, permafrost studies sit awkwardly between the
disciplines of geography and geology. For example, in North America and much of Europe,
periglacial geomorphology is taught usually in geography departments while permafrost
is within geology, geophysics, or earth science departments. Similar fractionation occurs
in Russia and China.
The most obvious areas of overlap between periglacial geomorphology and geocryology
lie in the problems associated with ground freezing and the occurrence of ground ice.
1.2.2. The Changing Nature of Quaternary Science
Advances in Quaternary science, and in particular the expansion and proliferation of
sophisticated dating techniques, mean that studies involving paleo-environmental recon-
struction no longer rely solely upon the morphological and stratigraphical evidence (Büdel,
1951, 1953; Poser 1948; Smith, 1949) that was typically used in traditional Pleistocene
periglacial studies. Instead, a broader range of evidence now includes biological pheno-
mena such as fauna and fl ora, arboreal and non-arboreal pollen, temperature-sensitive
insects such as beetles (coleoptera sp.), and geochemical indicators such as isotopes.
Stratigraphy is increasingly being supplemented by the study of ground ice, or cryostrati-
graphy. Thaw unconformities, truncated ice bodies, and cryostructures are now used to
infer previous freezing and thawing events or early Holocene climate change (Burn, 1997;
French, 1999; Melnikov and Spesivtsev, 2000). One must conclude that much of traditional
Pleistocene periglacial geomorphology has been largely replaced by cryostratigraphy and
cryolithology.
1.2.3. Modern Periglacial Geomorphology
As noted by M. Church (2005), geomorphology is no longer the preserve of geographers
and geologists. However, periglacial geomorphology continues to be identifi ed as a process
sub-discipline of geomorphology that is distinct from both geocryology and Quaternary
science. The key processes are those associated with seasonal and perennial frost.
While geocryologists concentrate upon the thermal implications of terrain and the
presence of ice within the ground, periglacial geomorphologists emphasize the associated
landforms, and their growth and modifi cation through time. Obviously, there is consider-
able overlap between the two. For example, the recognition of anti-syngenetic wedges on
hillslopes (Mackay, 1990a, 1995b) is an illustration of the overlap between landscape
evolution (geomorphology) and permafrost-related processes (geocryology). Likewise, as
discussed above, there is a complex overlap between periglacial geomorphology and
Quaternary science via cryostratigraphy and cryolithology.
Permafrost cannot be the only diagnostic criterion for periglacial geomorphology. This
is because permafrost is a thermal concept while geomorphology is concerned with land-
forms that are not controlled by ground temperature alone. On the other hand, permafrost
and ground ice must be central to periglacial geomorphology in the same way that hills-
lopes and running water are central to geomorphology at large.
It is easy to forget that the broad features of cold-climate terrain are largely infl uenced
by lithological variability, the nature and distribution of ice contained within bedrock or
