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(A)
(B)
(C)
(D)
Figure 7.6. Ground ice in bedrock. (A, B): Ground ice in shale bedrock, Melville Island, exposed
in section excavated during the winter of 1983-1984. The ice crystal structure has been destroyed
by blasting. (A) cryoturbated ice-rich shale in upper 0.6-1.25 m; (B) brecciated ice-rich shale at
1.7-3.0 m depth. A thaw unconformity separates these two cryostratigraphic units. See Figure 7.8A.
From French et al. (1986). (C) Ice fi lls a 50 cm wide expanded joint in the main tunnel of the Gruve-7
coal mine, Adventdalen, Svalbard . The ice is clear and contains mineral inclusions. Oxygen-isotope
values suggest the ice is basal meltwater/subglacial regelation ice. See Table 7.6. From Christiansen
et al. (2005). (D) An expanded joint, previously fi lled with ice, occurs in shale bedrock and is
exposed here in a borrow pit, kilometer 366, Dempster Highway, Yukon Territory, Canada.
under pressure are all possible reasons why apparently non-frost-susceptible materials
may, in fact, possess high ice content. This is also true for deltaic sediments, where high
ice-content permafrost may be associated with a range of grain sizes. For example, in the
Mackenzie Delta, the sand and clay content of ice-rich sediments (
70% moisture content)
was between 5% and 45%, and 7% and 24%, respectively (Kokelj and Burn, 2005). It is
unwise to assume that all coarse-grained sediments are ice-poor.
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7.4. CRYOSTRATIGRAPHY AND CRYOLITHOLOGY
Cryostratigraphy refers to study of frozen layers in the Earth's crust. Central to cryos-
tratigraphy is the fact that ice within perennially-frozen sediment imparts structures
distinct from those found in other sedimentary environments. These structures are
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