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Wednesday 8 November 2023

More on the Nevern Estuary washed till

 I have discussed (on several occasions) the exposure of till in the Nevern Estuary -- sometimes nicely exposed in the inside of the coastal dune belt.  I have also speculated on the possibility that the last active ice in this area might have been Welsh Ice, not Irish Sea Ice.........

On our walk today I noticed a distinct gradation in the washed till / pebble accumulations on the tidal shoe on the inside of the dune belt.  This is all very unscientific, since I have done no pebble collecting or counting, but I think there is a far greater range of rock types represented on the washed till surface towards the southern end of the exposure, and a far greater percentage of grey and brown gritstones, sandstones and shales (typical of the rock types exposed in Ceredigion) towards the north.  If we take igneous pebbles as a proxy for debris derived from Irish Sea till, they are far more numerous in the south and diminish in frequency northwards over a distance of c 100m.

So was there a contact zone between Irish Sea Ice and Welsh Ice during the Late Devensian here in the Nevern Valley?  It's quite possible.......

Southern exposure of pebbles washed out of till -- with abundant quartz and igneous materials including lavas and tuffs 

Northern exposure with a much greater concentration of grits, sandstones and shales (from the Ceredigion coastal strip?)

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