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Saturday, 2 May 2015

Ice-moulded surfaces, Carn Goedog






There are many ice-moulded or scoured surfaces dotted about in the midst of the jumble of rocks on Carn Goedog.  This suggests quite powerful ice action at some stage -- maybe more than once.

Like the other ice-moulded surfaces in other parts of Preseli they look quite fresh -- but there is always the chance that they are very old (maybe Anglian?) and that they have simply been freshened up during the late Devensian glaciation.  I have not seen any obvious grooves, striations of crescentic gouges.  The dating problem will only be resolved when somebody does some cosmogenic dating here.......

For the moment, I will go with the thesis that these surfaces are signs that the Devensian Irish Sea Glacier pressed against the north face of the Preseli ridge about 20,000 years ago, and possibly over-topped it in a few places.  Maybe the ice was in occupation for a few centuries.

3 comments:

Myris of Alexandria said...

Hmmmm to my, untrained, eye these look very convincing. How thick is the weathering crust.
M

BRIAN JOHN said...

Weathering crust? I wish I knew -- I didn't see any conveniently broken slabs on these surfaces. But yes, they will give us an indication as to age of exposure -- but I suppose somebody at some stage will have to take cores and analyse them properly.

BRIAN JOHN said...

If you do a search for "ice moulded surfaces" via the seqarch box, you'll see more examples from N Pembs and elsewhere.