Box 91 Megascale Thrustfault Complex In Northwest Russia

Larsen et al. (2006) describe a large glaciotectonic moraine system on the northern coast of the Kanin Peninsula in northwest Russia. Exposed on the coast is a 20 km long section up to 80 m high, which is composed of alternating layers of diamict, glaciofluvial, glaciolacustrine and marine sediment. These sediments have been dated to the first part of the last glacial cycle and were initially deposited in marine embayments and ice-dammed lakes between ice of the Barents Sea Ice Sheet and the Kanin Peninsula, which formed a reverse bedrock slope against which the ice advanced. As the ice advanced at the Last Glacial Maximum these sediments were moved onshore as large thrust nappes to create a large glaciotectonic moraine system.

Source: Larsen, E., Kjaer, K.H., Jensen, M., et al. (2006) Early Weichselian palaeoenvir-onments reconstructed from a mega-scale thrust-fault complex, Kanin Peninsula, northwestern Russia. Boreas, 35, 476-92. [Modified from: Larsen et al. (2006) Boreas, 35, figure 5, p. 489]

|_| Glacier ice (clean) |_| Sand (gravelly) | - | Bedding or foliation o I • • a I [A Z~1 I — 1

I * | Glacier Ice (with basal debris) | a I Diamicton | x | Folds

° _|-1 Glaciomarine/glaciofluvial i-1 i-1

|_| Glacier ice (clean) |_| Sand (gravelly) | - | Bedding or foliation o I • • a I [A Z~1 I — 1

I * | Glacier Ice (with basal debris) | a I Diamicton | x | Folds

° _|-1 Glaciomarine/glaciofluvial i-1 i-1

Figure 9.5 Schematic cross-section through the Uversbreen push moraine in Svalbard.

[Modified from: Hambrey and Huddart (1995) Journal of Quaternary Science, 10, figure 11, p. 324]

the glacier snout terminated (Figure 9.6). A moraine system created by subglacial deformation has also been described from a surge of Bniarjokull in Iceland. Here variation in the geometry of the moraine can be attributed to the hydrogeological properties of the foreland (Box 9.2).

Large glaciotectonic moraine systems may also incorporate bedrock rafts. One of the most famous examples is M0ns Klint in Denmark, where large thrust-blocks of Cretaceous Chalk occur in tectonic slices with glacial sediment forming a series of ridges, the structures of which are revealed in spectacular coastal cliff sections. Similar, although older, chalk rafts are exposed in coastal cliffs at Sidestrand Norfolk, England and other examples of systems incorporating rock rafts include the Dirt Hills in Saskatchewan, Canada. The Dirt Hills have been pushed up over 300 m and have been partly overridden by an ice sheet during the last glacial cycle. They consist of hundreds of parallel ridges, transverse to the former ice flow, between which there are small linear lakes. The ridges comprise blocks of sandstone bedrock that have been thrust forward over a basal decollment surface located in softer clay-rich beds beneath. It has been suggested that rapid glacial

Figure 9.6 Push moraine and crevasse-squeeze ridges formed by a surge of Sefstrombreen in Svalbard. This moraine system appears to be the product of subglacial deformation as the ice advanced across glaciomarine and marine muds on a fjord floor before mounting and terminating on the island of Coraholmen. [Modified from: Boulton et al. (1996) Quaternary Science Reviews, 15, figure 22, p. 144]

Figure 9.6 Push moraine and crevasse-squeeze ridges formed by a surge of Sefstrombreen in Svalbard. This moraine system appears to be the product of subglacial deformation as the ice advanced across glaciomarine and marine muds on a fjord floor before mounting and terminating on the island of Coraholmen. [Modified from: Boulton et al. (1996) Quaternary Science Reviews, 15, figure 22, p. 144]

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