Geology Reference
In-Depth Information
Figure 12.9.
The various types of non-diastrophic structures observed in Quaternary-age sedi-
ments in eastern Germany. Some are cryogenic (3 and 4), some are glacigenic (1, 2, 3), and one (6)
has no specifi c cold-climate signifi cance. Note that they are not all drawn at the same scale. From
Eissmann (1994). Reproduced by permission of the Mauritianum Altenburg.
pseudomorphs that have already been discussed. Here, attention focuses upon the large-
scale deformations (category 4, Figure 12.9) that are permafrost-related. They take the
form of large diapiric upturning and drop-soil structures within lignite beds. Many are
tens of meters in height. Almost certainly, these massive deformations formed when icy
layers, developed preferentially within and beneath the lignite beds, melted as permafrost
degraded. This cryostratigraphic (i.e. ground ice) situation would have developed during
previous permafrost aggradation because the low thermal conductivity of organic material
such as lignite (see Table 5.1) slowed the downward growth of permafrost and allowed
groundwater to migrate upwards by cryosuction towards the near-stationary freezing
front.
In central Germany, it appears that permafrost aggradation, and the growth of ground-
ice bodies within and beneath the lignite beds, occurred on several occasions during the
Quaternary. This is because different sets of ice-wedge pseudomorphs are preserved
within overlying gravels of Elsterian (Kansan or Nebraskan), Saalian (Illinoian), and
Weichselian (Wisconsinan) age. Thus, there is clear evidence that at least three major
periods of permafrost aggradation and degradation occurred during the Middle and Late
