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Sunday 25 March 2018

Lydstep Headland -- a key Quaternary site?

Church Door, a very famous arch in vertical strata of Carboniferous Limestone in Skrinkle Haven, near Manorbier.

Yesterday I enjoyed a splendid walk from Manorbier to Tenby (about 11 miles).  It's a number of years since I last walked this stretch of the Coast Path -- it was as enjoyable as ever!    The first part of the route was on Old Red Sandstone, and the later part on Carboniferous Limestone.  As we walked, I kept a careful eye open for anything that might be deemed to be a till, on the clifftops and in stream gullies -- but saw nothing noteworthy.  There are a few erratics around, but they may have nothing to do with the Devensian......

I'm still convinced that Devensian ice has affected Caldey Island and has left till there -- and that's just a few miles further east.  If ice flowed over Caldey it might have touched Old Castle Head, but because of the military presence there it is out of bounds.  I'm now rather convinced that Devensian ice flowed from the west towards the east in this area, and that the great cliff rampart of south Pembrokeshire was an effective barrier which prevented the ice from transgressing inland.  The cliffs are for the most part about 120 ft high, with a further slope of about 30 ft in the tidal and sub-tidal zone before a gently sloping sea bed with considerable irregularities runs further out into Carmarthen Bay.

There is a fabulous resource for looking at the sea bed here:

Check it out!

I need to look in more detail at Manorbier and Swanlake Bays to see if there are any deposits other than churned-up head or slope deposits which attest to a period of severe periglacial climate, probably with permafrost.  But my main priority is to get back to Lydstep Headland,  to take another look at a deposit of cemented till which I saw and recorded many years ago.  Yesterday, my colleagues on our long walk woul have got very irritated with me if I had gone off to do some serious geomorfin'  .    Watch this space......

Coastline and submarine contours (in feet) in the Lydstep area.  This is a classic karst coastline,  with a spectaculat limestone gorge, blow-holes, caves, arches and stacks.  The Carboniferous Limestone strata are here almost vertical.  

Google Earth image of the small peninsula projecting south from Lydstep Headland.  The famous Smugglers Cave is just to the left, off the photo.  This is where the ancient till can be seen.  

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