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Monday, 9 December 2013

Bancywarren geology lesson


How about this for a geology lesson?  Faulted fluvioglacial sands and gravels at Bancywarren, north of Cardigan.  These sands and gravels were emplaced during a Devensian ice ADVANCE -- that's a bit counter-intuitive, since big fluvioglacial sequences are normally laid down during ice wastage phases.

The faults are so sharp here that the mass of sand and gravel must have been frozen by permafrost when the faulting took place.  The structures here are very different from those formed by settling / compaction / loading when the mass of fluvioglacial material is in a semi-liquefied state.  So what we have here is an example of a frozen body of sediment which has been subjected to pressure either from the side (eg by an advancing ice front) or by a great weight of ice or other sediments exerting pressure from above.


4 comments:

CharlieD said...

A fascinating bit of geology. How was it determined to have been deposited during an advnce?

BRIAN JOHN said...

Charlie -- a number of very detailed papers by people from Aberystwyth for the most part. Here is one of the papers: http://cadair.aber.ac.uk/dspace/handle/2160/1585

There's a complicated sequence of sedimentation, including thick lacustrine clays accumulated in Lake Teifi as the ice was advancing.

Anonymous said...

Same old rock from MPP
http://www.youtube.com/watch?v=81owUAZJ4Qk

PeteG

chris johnson said...

Very good presentation. I thought from the first slide that MPP would be beating a dead horse (or two) but it looks like this is still a runner.