The Main Postglacial Raised Beach

Detail of the base of the raised beach, with a dyke of till injected into an open joint of the raised shore platform

The section facing Skateraw Harbour shows the Main Postglacial Raised Beach, deposited around 5500 years ago. It was a high energy storm beach, with abundant shell debris. The raised beach rests on a raised shore platform which seems to have been refashioned from existing old platform. Open joints in the limestone contain plugs of till and the platform on the east side of Skateraw Harbour shows a cover of till.

The outer shore platform at Chapel Point. On the right, a zone of abrasion; on the left, a zone of undercutting and block release at the edge of the limestone bed.

 

shore platforms

shore platform morphology

shore platform processes             

Chapel Point

Significance: an extensive shore platform developed across Carboniferous Limestone that shows a variety of processes of weathering and erosion, backed by a raised rock platform and raised beach

This shore platform is up to 300 m wide and dips gently seawards. The Chapel Point Limestone dips west so that a small cliff faces into Skateraw Harbour. Moving seawards from the edge of the raised beach we find a sequence of process zones:

Weathering pits1. above the high water mark, subaerial solution processes dominate. The joints are open. Small weathering pits are being deepened by carbonation and salt weathering (left).

  • 2. around the high water mark, where the raised beach material is eroded and mobilised during storms, lies a zone of abrasion. This has smooth rock surfaces (above).
  • 3. between the high and low tide marks lies an extensive zone where water-layer weathering and undercutting combine to detach blocks ready for wave transport (below).
  • 4. at the low water mark biogenic weathering dominates, with loss of material to boring worms and to pull-away by kelp.

It is clear that the platform is being lowered by a range of processes. Assuming that the modern platform has been fashioned from the higher platform below the raised beach, the long term rate of lowering is around 1 m in 5000 years.

shore platform abrasion