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Tuesday, 22 May 2018

Fossil ice wedge, Manorbier

This is a very fine fossil ice wedge, seen in the cliff face at Manorbier, overlooking the beach.   There's broken bedrock at the base, then about 1.5 m of pseudo-stratified ORS head, and about 50 - 75 cm of sandy loam and modern soil.  The wedge fill consists of sandy loam and small fragments of soliflucted ORS debris, with one or two larger fragments as well.  Note how many of the fill fragments are arranged vertically.  There is no till exposed here.    But clearly permafrost was present after the formation of the head horizon, at the time of sandy loam / colluvium accumulation.

Were features such as this formed at the peak of the Late Devensian Glaciation -- around 20,000 years ago, or much later, in the Zone III / Younger Dryas cold snap around 10,500 years ago?

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