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.