Raised beach and sandrock exposure at Ragwen Point

The Ragwen Point cemented raised beach -- grid ref SN 21874 07188

I have seen various passing references in the literature to the raised beach and sandrock exposure at Ragwen Point, but it was quite exciting to come across it quite by accident during yesterday's visit to the Pendine area.  The officers of the Geological Survey mentioned it in 1909, and David Bowen published a simplified section from the site in 1970.  DQB referred to TWO raised beaches in the exposure, which made things rather confusing -- so it was good to be able to check that out.........

The exposure is tucked into the western corner of the little bay to the west of Ragwen Point proper, and is very well protected from storm waves except when they are rolling in from due south.  There is a sandy beach and a storm beach, and the slopes at the back of the embayment are chaotic, with cliff collapses and debris movement so frequent that except at the top of the cliff, almost nothing is in its original stratigraphic position. 

Accumulated rockfall / cliff collapse / slope breccia near Ragwen Point.  The local rocks are highly fractured Namurian (Marros Group) sandstones, shales and mudstones, overlain by Lower Coal Measures.  Rockfalls and debris flows are frequent.

The cemented raised beach has a somewhat sandy matrix and consists of well-rounded pebbles of many different sizes, mostly of local rock types, resting on small small and irregular rock platform remnants and ledges and plastered against the cliff face.  Some huge boulders are incorporated, all with smoothed corners and apparently much affected by wave action.

The cemented beach is up to 2m thick, and it incorporates patches of sandrock and also some relatively unmodified rockfall debris.  It is overlain by buff-coloured sandrock, but in one exposure reddish sandrock is seen to be overlain by another "raised beach layer" about 50 cm thick and made of well-rounded pebbles in a sandy matrix.  David Bowen wondered whether there might be two "raised beach episodes" or interglacials represented here -- but I think all these deposits belong to the same episode, with the upper pebble bed simply representing an exceptional stormy episode in which pebbles were flung up onto pre-existing sandy beach or dune material.  

Above this layer there are about 2m of buff coloured sandrock with occasional beach pebbles or rockfall fragments, with traces of stratification. There are many irregular cavities, presumably caused by the washing out of weathered material.   This grades up to a 1m thick layer of foxy-red sandrock that looks as if it contains colluvium or slopewash material.  This contains fewer rockfall fragments than the layer below.  

Above that is a disturbed dark-coloured layer that cannot be reached -- is it an organic-rich layer, and is it in its "correct" stratigraphic position?  Somebody younger and fitter than I needs to climb up and check it out........  However, it's interesting that in 1970 DQ Bowen described a "sandy silty mud"  with abundant organic remains above the raised beach and beneath brecciated slope deposits at Marros, just around the headland to the west.  The organic remains which were identified were listed on P 223 of "The Glaciations of Wales" and were interpreted as typical of a largely treeless environment from the end of the Ipswichian Interglacial.  This deposit at Ragwen Point is in a stratigraphically identical situation.......

At the top of the colluvial layer is another layer about 50 cms thick and which is clearly stratified -- with some flat-lying slabs of rock and with what appear from below to be bands of iron-rich hardpan. Again this layer needs to be examined.

Above this level the slopes at the head of the embayment have been so mobile, with rockfalls and debris flowage all over the place, that it is very difficult to see what material is in its correct stratigraphic position and what is rearranged or redistributed.  In the slump scar we can see up to 4m thickness of brecciated slope deposits that have clearly accumulated on the coastal slope.

In some places these slope deposits appear to have no stratigraphic junctions within them, but elsewhere there appear to be interbedded grey-blue deposits with a high percentage of clay and silt, and containing abundant fragments of shale and mudstone that appear to have come from the Coal Measures to the west.  There are also some foreign erratics with abraded edges, and I interpret this deposit as Irish Sea Till.  Very little of it is in its original (primary) position, and in places masses of it have slumped or flowed down to beach level.

Brecciated slope deposits (partly periglacial?) exposed in the slump scar.  Here there is no trace of till. 

A patch of blue-grey till in a secondary position, but still as a coherent mass.  Note the staining where material has been washing down over the exposure of colluvium and sandrock.

Near the top of the slope in the photo above, we can see material of this colour in the sediment exposure, overlain by some slope breccia and underlain by similar material.  My interpretation is that patchy till has been deposited here in an environment dominated by frost shattering and slope breccia accumulation.  Was there a complete ice cover?  Quite possibly.  Where did the ice come from?  My best guess is that it was flowing eastwards along the coast, since the till consists almost entirely of silts and clays from the floor of Carmarthen Bay, with comminuted fragments of  Coal Measures mudstones, shales and even coal-bearing beds.  There are a few sub-rounded boulders as well, unfortunately in inaccessible positions on the cliff face.  

In a number of publications DQ Bowen insisted that there was a complete lack of glacial deposits and a complete lack of foreign erratics at Ragwen Point -- but he was wrong on both counts.  I found as very distinctive cobble of red granite on the beach, which could have come from any one of the glaciations that have affected this area.  There are other small igneous erratics on the beach which I did not recognise. And the till in the exposures and on the coastal slope is uncemented and therefore almost certainly of Late Devensian Age. In any case it is in the "right" stratigraphic situation as compared with Abermawr, Druidston, Porthclais, Whitesands and a host of other locations around the Pembrokeshire coast. 

So the stratigraphy at Ragwen Point is as follows:

Modern soil and "slopewash"  30 cms

Upper slope breccia -- up to 2m

Patchy blue-grey clay till -- c 2m?

Lower slope breccia and rockfall debris -- up to 4m

Hardpan / cemented silty layers c 40 cm

Dark organic silts 30 cm

Iron-stained sandy layer (cemented)  1m

Buff coloured sandrock with cavities and rockfall inclusions  2m

Raised beach with large embedded boulders and sandrock layers  2m

Further work is needed both here and around the corner in Marros Bay -- but this section confirms that the Ipswichian / Devensian history here at the SE extremity of Pembrokeshire is exactly the same as that  of the Cardigan Bay coast.