Llangolman gravel pit -- Anglian fluvio-glacial gravels?

Prof Danny McCarroll examining one of the erratics in the Llangolman gravel pit, adjacent to St Colman's Church

It was good to take another look at this site today, in the company of farmer Huw Absalom and Prof Danny McCarroll and his wife Louise.   It was almost too hot!  And the faces of the gravel pit were so dry that it was quite difficult to pick out the stratigraphy.

But in our discussions Danny agreed that we were probably looking at Anglian fluvio-glacial materials, maybe 450,000 years old.  He agreed with me that the degree of staining by manganese and iron oxide is indicative of great age, as is the extent of pebble "rotting" which is far greater than in the Devensian gravels seen in other pits in the Cardigan - Moylgrove area.

We examined the fossil frost cracks in the upper gravel horizons, which suggested the presence of permafrost during and maybe after a long period of gravel deposition.  Another thing Danny noticed is that one of these frost cracks seems to have a sand layer running across its top edge -- suggesting that this sand layer might have been deposited in a subaerial environment following an episode of ground freezing -- making it a suitable candidate for OSL dating. That's something we need to work on.

On my previous visit I thought that the gravel spread in the vicinity of St Colman's Church was a remnant of a previously much more extensive cover.  But  now I think I agree with Danny that this is probably a mound of fluvio-glacial material which we might call a kame.  It has been eroded away in some places by spring sapping, but it is clearly in a hilltop position, and it is probable that it owes its origin to an accumulation of meltwater debris carried into an open pit in a dead-ice environment.