The rocks and soils above and below the raised beaches at the southern tip of the Isle of Portland in Dorset, England, exhibit features that are believed to be associated with freeze-thaw periglacial conditions. These photographs show interesting rock features in the Upper Jurassic limestone that I think may possibly relate to the cold period prevailing prior to the interglacial period in which the younger of the two raised beaches known as Portland East Beach (as shown in the previous post) were formed. Pugh & Shearman (1967) first described these cryoturbation features on the Isle of Portland, and later (Goudie & Brunsden, 1997) stated that:
At the base of the raised beach gravels, the shore platform is heaved, cracked, and warped to a depth of up to 3m. The meticulous observer will also be able to reconstruct crude polygons of angular boulders which stand on edge. Such features are thought to be caused by frost action under cold conditions and are commonly known as periglacial (tundra) patterned ground and, more specifically as rock blisters.
REFERENCES
Goudie, A. and Brunsden, D. (1997) Classic Landforms of the East Dorset Coast, Series Editors Rodney Castleden and Christopher Green, The Geographical Association, ISBN 1 899085 28 9.
Pugh, M. E. and Shearman, D. J. (1967) Cryoturbation structures at the south end of the Isle of Portland in Proceedings of the Geologists’ Association, 78, pp 463 – 471.
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