Dalsetter erratic

ice flow models

styles of glaciation

The approximate extent of the Scandinavian ice sheet at 22 ka

What should we be looking for to demonstrate that ice originating from Scandinavia did once cross Shetland?

1. Scandinavia erratics including the distinctive rhomb porphyry of the Oslo region and the striking Dalarnia porphyries.

2. Pollen and spores derived from Mesozoic and Tertiary sediments on the bed of the North Sea.

3. Shell or foraminifera fragments or other fossils from the North Sea bed

 

Ice from Scandinavia?

Since Peach and Horne's pioneering investigation, there has been much speculation that ice from Scandinavia reached Shetland during or prior to the last glacial maximum. This possibility has received new impetus from the recent realisation that the North Sea was completely covered by ice between 30 and 20 ka. Moreover the latest BGS work on Shetland shows that glacial streamlines appear to extend from east to west across the island chain, requiring an ice shed east of the islands. Yet the evidence for the presence of ice flowing from Scandinavia remains elusive. Arguments against a former cover of Scandinavian ice include:

  • the Dalsetter erratic is undoubtedly derived from the Oslo region but there is no certainty that it is a glacial erratic carried by ice from its source. The block could have been brought to Shetland by Norse settlers.

  • despite searches, no other Scandinavian erratics are known from Shetland, aside from the former contents of ship's ballast at two localities. This situation can be contrasted with the Buchan coastal fringe, where around a dozen Norwegian erratics have been recorded or with the rich erratic assembly in eastern Orkney.

  • the transport of material to the northwest across southern Shetland can be achieved by Shetland ice if the ice shed lies east of south Mainland. Under these circumstances it would be possible to first raft erratic material from Scandinavia on icebergs and then to carry material westwards beneath Shetland ice at a later stage (Ross, 1996)

  • unlike Orkney, no shelly tills derived from the erosion of glacimarine sediment has been found on the eastern fringes of Shetland, indicating that ice has not moved across the bed of the northern North Sea to reach Shetland

  • a cover of Scandinavian ice can only occur when the Scandinavian ice sheet is sufficiently thick to cross the Norwegian Trench. This implies conditions close to those of glacial maxima when ice on Shetland would also be thick and act to exclude external ice.