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Thursday, 6 March 2014

Newgale Submerged Forest - 2014 exposures

 



Been over to Newgale today, to inspect the exposures of the submerged forest.  Very interesting.  It was raining and blowing, but at least I managed to get some photos......

The top three photos are of the peat beds which are normally covered by sand -- the beach is now about 2m lower than it was, following the winter storms.  As we can see, some of the peat bed exposures are coherent, and other sections are being broken up into rills by water streaming up and down the beach.  Most of the pebbles you can see around these rills have been dragged down from the storm beach and dumped here to replace sediments that have been destroyed. 

The lower two photos show some of the woodland remains.  The exposures here are very different from those at Ynyslas, where actual tree stumps are exposed at the moment -- here we just get occasional traces of root systems, and a lot of debris embedded in the peat.  There are wood fragments everywhere, especially on the southern part of the beach, near the southern cafe and caravan park.  The biggest piece of wood which I found was a long tree trunk about 6m long; and the thickest was about 1m across.  So we are talking about a woodland of quite mature trees.

The stratigraphy is much more complex than I had imagined.  I hope some bright young thing from one of the universities has been looking at it, and making an accurate record......

In Newport the peat bed and submerged forest lies directly on till and frost-shattered (periglacial) debris -- but here, in a much more open environment, the peat bed is quite thin -- mostly less than 50cms thick -- and is resting on a variety of different materials -- sandy gravelly material in some places and actually on beach pebbles in other places.  These beach pebbles are loose and unconsolidated, but in a few places there are exposures of solidly concreted beach and river gravels which may even be interglacial in age.  All very complicated.....


 The peat beds in this area are quite thin, and are underlain by sandy and gravelly 
unconsolidated material.


Here the peat bed is also thin -- just a few cm thick -- and is underlain by unconsolidated storm beach material.  Was this material thrown over an advancing storm beach ridge into the boggy area beyond the ridge, in exactly the same fashion as we have seen in recent weeks when the storm beach advanced across the road?


A patch of solidly cemented beach or river gravel exposed through the sand.  One cannot see the precise stratigraphic relationship with the peat beds.   Is this material the same age as the cemented interglacial raised beaches that we see in other parts of Pembrokeshire?


Another much larger exposure of this cemented beach - river gravel material, standing up as a pedestal.

In trying to work out what has happened here, my best bet is as follows.  There are some very old deposits here -- maybe dating from the last interglacial.  These materials must have been overridden during the Devensian ice advance of the Irish Sea Glacier, but we see no signs of till or periglacial materials out here in the open bay.  Peat beds and woodland then started to form after the ice retreat, when the coastline was far out to the west. So some peat beds might be more than 7,000 years old.  I think these peat beds and the forest might have survived for at least 5,000 years -- this could be established by pollen analysis and examination of the tree species represented.  The sea rose inexorably, and as it did so it drove a storm beach ridge eastwards, covering the old peaty / woodland area bit by bit, leaving it submerged beneath pebbles and sand.  Within the last 2,000 years or so the eastwards advance of the storm beach ridge has slowed down as sea level has stabilised, but we know that it has continued because historical records show that there have been at least two other inns at Newgale, each of them in the area now submerged beneath the beach.  The current Duke of Edinburgh Inn, alongside the road that has been blocked by pebbles several times this winter, is equally vulnerable -- and one wonders how long it will survive!

The interbedding of storm beach pebbles and peat beds suggests to me individual storm events in which waves have overtopped the ridge, flinging pebbles onto the peaty boggy area on the landward side -- then followed by more peat formation, when "normal" waterlogged or lagoonal conditions returned.

So it is quite possible that the peat beds are of all sorts of ages, with some of them shown in the photos above no older than a few centuries........







7 comments:

Anonymous said...

look out for a thin post with an arrow saying "Stonehenge 183 miles"
:)
PeteG

BRIAN JOHN said...

Yes -- I looked for it but didn't find it. Must have been looking in the wrong place. It's a very big beach.....

Anonymous said...

Think you might have stumbled onto something important there!

The "peat" beds in photos 2 and 3 look suspiciously like a giant Xylophone to me?

Did you get manage to get a tune out of them?

Alex G

ND Wiseman said...

Hi Brian,
I have watched with much interest these past weeks - as well as with consternation - the storms that have raged across the UK. Nasty business and apparently uncommon. I hope all is well in Pembrokeshire.

I live on Cape Cod, in Massachusetts, northeast US. A quick review will show it as a peninsula jutting into the Atlantic in the shape of a flexed arm. (Defiantly shaking its fist at those dastardly, oppressive Brits!)

The Gulf Stream comes along the outer Cape on its journey North and East and in simple terms, the back-swirl creates a counter-clockwise rotation in Cape Cod Bay.
Most of the inner Cape is Glacial while the Outer Cape is created by sand carried north from the old moraines. There's an unending ballet that occurs, as the Outer Cape is viciously eroded by storm, while the inside is constantly being replenished by the back-swirl.

The North Side is largely protected from the direct vagaries of southern storms, though our fickle, notorious Nor'Easters often raise the devil with the inner beaches.

The point of this little geography lesson is that the pictures you show could easily have been taken on the North Side. The 'peat' seen here also sits on stoney gravel, is both thick and thin in places, is alternately exposed then covered with sand, and is quite expansive; the tides almost almost a mile in and out due to shallow grade. We also have the run-off gullies, though not as drastic as you've shown in north Wales.

I've never seen footprints or the like in this tough, hardened muck, but storm exposure often reveals old branches and stumps from who knows how long ago.

I did once find a spindly old sign that said: 'Stonehenge: 2,856 Miles', but that's another story ...

Neil

BRIAN JOHN said...

Thanks Neil -- all sounds very familiar. Without cecking it out, the situation might be similar, with a similar relative sea-level history and maybe a similar isostatic recovery regime as well, following the Devensian Glaciation. The key thing at Newgale is the "migrating storm beach ridge" which has marched across the landscape, impounding a lagoon or boggy area on its landward side and occasionally flinging lots of pebbles into it during extreme storms....

chris johnson said...

Nice to be reminded of Cape Cod so eloquently. I spent some time in West Dennis and found it to be a charming and mysterious misty other land. A bit like Pembrokeshire actually. Lovely golf too.

TonyH said...

Used to enjoy investigating the submerged forest at Westward Ho!, round the western corner from the Torridge/Taw estuary, with my kids as they were growing up. Rudyard Kipling used to reside there, not sure what he made of these prehistoric relics though. Good views of Lundy Island (between North Devon and South West Wales) from Westward Ho! which takes its name from Charles Kingsley's seafaring book.