Fresh melt-out till at Nolton Haven

The pretty bay of Nolton Haven is a dangerous place for scientific research because the foreshore is partly man-made -- there has been a lot of activity here, associated with coal-mining, shipping activities, and even the construction of a short-lived narrow gauge railway line.   I looked at one rather convincing exposure and found a piece of an earthenware flowerpot embedded within it.......

But one exposure is very safe -- close to the steps that run down to the beach in the NW corner.

The drift cliff here is around 10m high, and it displays several facies of fresh Devensian till.  The colour is buff - light brown, and in the lower part there is a much higher proportion of silt and sand than we see in most other exposures in the neighbourhood.    This is clearly seen in the photo above.   Above this there is a rapid transition into a much stonier facies, with the same suite of erratics including many of the rock types found at the outer end of the St Davids Peninsula and on Ramsey Island.  The cliff is capped with around 20 cm of sandy loam and soil.

 

In the lower part of the exposure there is one quite distinct silty layer which is relatively free of stones, and below that there is another facies of stony till. At the base of the section we see a blocky slope breccia up to 3-4m thick.  This breccia is also exposed in a more extensive exposure about 20m away and upslope.  Here the breccia is up to 5m thick.  At this site there is no blue-grey clay-rich Irish  Sea till (although it may occur in the valley near the car park); and neither is there any upper slope breccia capping the till.

The full sequence is as follows:

20 cms sandy loam and soil

1m of stony till (gravel and sand matrix -- high concentration of stones and boulders)

3m of more silty till with relatively few stones

15 cm thick silt layer -- relatively stoneless

1.5m of stony till with a sandy and gravelly matrix

3-4m of blocky slope breccia

Interpretation:  this is a deposit of melt-out or ablation till laid down at the end of the Late Devensian glacial episode, following the onset of ice wastage.