Den Wick, Deerness
Significance: this site provides evidence for changing ice-flow conditions during the last ice sheet glaciation

Den Wick is a coastal section on the Deerness peninsula in the eastern part of Mainland Orkney (HY 580089) which shows two superimposed tills (Gordon in Hall, 1993).

Wilson et al. (1935) first reported the occurrence of multiple drift units on Orkney, noting a grey or yellowish clayey rubble below the more usual grey, red or purple till of sandy clay composition. They concluded that the former was little more than fractured and locally transported bedrock. Subsequently, Rae (1976) formally established and defined the existence of more than one till on the basis of colour, lithology and sedimentology. He argued that the till characteristics at a site reflect the bedrock composition up-ice and that contrasts between individual till units at a site relate to changing ice-movement patterns. Rae (1976) recorded twenty multiple till sections in Orkney.

At Den Wick, Rae (1976) noted the following sequence:

  1. Red till                        1.5->3 m
  2. Brown till                     >5.5 m
  3. Striated bedrock

The contact between the two tills is sharp and undulating, and locally a thin sand and gravel horizon, 0.1-0.15 m thick, lies between the two tills. Rae considered at this and all the other sites that there was no firm evidence to support more than one glacial episode, and therefore the multiple tills were deposited by the last ice sheet to cover Orkney.

From the orientations of striae on the bedrock beneath the brown till, the lithological composition of the till ( a relatively high percentage of Lower Eday Sandstone) and clast fabric measurements, Rae concluded that the ice movement associated with the lower till was from between south and south-east. Ice following such a flow pattern would have traversed the Lower Eday Sandstone most of the way across the Deerness peninsula and avoided the Middle Eday Sandstones.

The overlying red till has a relatively higher content of red sandstone clasts similar to the Middle Eday sandstone. Since no onshore outcrop of this lithology appeared to fit with the pattern of striation observed beneath the red till elsewhere in Deerness where it rests directly on bedrock, Rae postulated an offshore outcrop, an interpretation supported by the presence of chalk erratics in the red till but not in the brown till. The red till was therefore associated with ice flow from a more easterly azimuth than the underlying brown till. Shell fragments have been recovered from both till units (Gordon, 1993).

Den Wick is an important section representing one of the key elements of the till stratigraphy of Orkney. The multiple till sequences, of which Den Wick is a particularly good example, are important in several respects. First, their lithological and sedimentological characteristics demonstrate close relationships with the source bedrock traversed by the ice. Second, the superimposition of the different till units indicates changes in ice-flow direction, thus supporting the inferences based on striation patterns. Third, the contacts between the different units a individual sites provide no conclusive evidence for deposition during more than one glacial period. Fourth, the superimposition of multiple till units in consistent fashion (Rae, 1976) and the inferred shifts in the direction of ice flow provide important evidence for the dynamics of the ice-sheet and its driving forces. Further study at both regional and national scales, coupled with ice-sheet modelling, is required to elaborate the origins of these changes and the extent to which they may relate to climatic factors and other variables which determine ice-sheet flow patterns. Multiple till sequences, like that at Den Wick, will be an important source of field evidence to provide constraints on the appropriate mathematical models.

J E Gordon SNH

Key Geomorphological Sites

  • Significance: a coastline noted for its Devonian geology and coastal geomorphology

  • Significance: this bay lies adjacent to Skara Brae and provides evidence of the interaction between coastal processes and human disturbance between 6600 and 4400 radiocarbon years ago. The settlement first re-emerged from the dunes after a storm in 1850.

  • Significance: this site provides evidence for changing ice-flow conditions during the last ice sheet glaciation

  • Significance: the construction of the Churchill Barriers started in 1940 and led to a fundamental change in the pattern of tidal flow around Scapa Flow. A range of coastal landforms have been created subsequently which illustrate the fundamental control of coastal configuration on the transport and deposition of sand.

  • Significance: Rackwick lies at the southern end of two major glacial breaches on Hoy. Its well-developed moraines indicate that at the close of the last glaciation two lobes of ice retreated northwards at a time when the Pentland Firth was probably still occupied by ice.

  • Significance: The Old Man is the tallest sea stack in Britain, 137 m high

  • Significance: a superb corrie formed at an unusually low elevation that was last occupied by a small glacier only 11,000 years ago

  • Significance: Ward Hill provides examples of a range of active and fossil periglacial landforms. As the highest point on Orkney it also provides evidence of the thickness of the last ice sheet

  • Significance: the site of a former small corrie glacier on Hoy

  • Significance: the site of a small corrie glacier during the Loch Lomond Stadial

  • Significance: a raised beach deposit at 6-12 m asl buried by till

  • Significance: a possible Scandinavian erratic on Orkney.

  • Significance: a peat deposit with willow boles formed 6500 years ago and now lying below sea level

  • Significance: the Kilns of Brin-Novan is an excellent example of an interconnected series of caves, arches and blow-holes which illustrate the sequential development of these features.

  • Significance: this coastal section provides perhaps the best available exposure of the shelly till which is characteristic of the eastern part of Orkney

  • Significance: exceptional cliff scenery and dramatic cliff-top storm deposits