A Pliocene age and origin for the strandflat of the Western Isles of Scotland: a speculative hypothesis

A series of very wide (> 5 km) raised shore platforms in the Scottish Hebrides are identified and described for the first time. The features are considered to be part of a high rock platform shoreline that occurs throughout the western isles of Scotland and described by W B Wright 100 years ago as a ‘pre-glacial’ feature. Subsequent interpretations that the platforms were produced during the Pleistocene are rejected here in favour of the view that the features are part of the well-known strandflat that is extensively developed across large areas of the northern hemisphere. It is argued that the Scottish strandflat developed during the Pliocene and was later subjected to extensive Pleistocene glacial erosion such that only a few areas of platform have survived in the Scottish Inner Hebrides (ice-proximal) while they are well-preserved in the Outer Hebrides (ice-distal). Support for a Pliocene hypothesis is provided by the marine oxygen isotope record for this time interval which points to prolonged periods of relative sea level stability such as would be required for the production of such wide features. It is argued here that the exceptional widths of the platforms and their development in Lewisian gneiss points to chemical weathering during the Cenozoic as having been a key factor in the development of saprolites which, in turn, enabled marine erosion during the Pliocene to produce wide platform surfaces in the Hebrides. This hypothesis for the formation of a Scottish strandflat not only provides an elegant explanation for the origin and age of the raised rock platform fragments that occur throughout the western isles of Scotland, but it may also have relevance for other coastal areas of northern hemisphere (e.g. Norway, Greenland, Alaska) where the strandflat is a well-developed feature.