Geology Reference
In-Depth Information
Figure 11.8.
Distribution of frozen Pleistocene mammalian carcasses in Siberia, Alaska and
northwestern Canada. Compiled from Sutcliffe (1985), Guthrie (1990), and others.
indicative of epigenetic freezing (see Figure 8.7). Often ice wedges act as lines of prefer-
ential thaw-erosion. These secondary or modifi ed deposits are described as pseudomorphs.
Cryostructures, and gravel, sand, silt, and ice pseudomorphs have all been discussed in
Chapter 8.
Syngenetic permafrost growth is an important concept when understanding the nature
of Pleistocene loess and “muck” deposits.
11.4.4. Loess Deposition
Wind action played a dominant role in fashioning the Pleistocene periglacial environments
of high northern latitudes. The evidence lies in the form of extensive and thick deposits
of loess-like silt (dust) that mantles extensive areas of central Alaska, south-central
Yakutia, the Qinghai-Xizang Plateau, and other areas (Péwé and Journaux, 1983; Péwé
et al., 1995). These wind-blown dust layers, generally termed loess (see Chapter 10), com-
monly contain ash layers from volcanic eruptions, ancient tree trunks and other plant and
animal remains. They are well sorted; the typical grain size is shown in Figure 10.10.
Loess deposition in the high latitudes was favored by well-developed high-pressure
systems that formed over the continental ice sheets and the gravity-induced (katabatic)
winds that fl owed outwards as a consequence. Other factors included the abundance of
fi ne-grained material available for wind transport on the outwash plains and braided
channel systems that were adjacent to the ice margin. For example, in central Alaska,
much of the loess was derived from the alluvial fl oodplains of the Tanana and Yukon
Rivers. In Siberia, the origin of the silt is more complex since much was probably derived
