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Tuesday 25 September 2018

Scilly and South Pembrokeshire -- two of a kind


Fresh till at Ballum's Bay, Caldey


Fresh till near the Caldey Island jetty


Fresh till near Stackpole Head


I'm more and more struck by the extraordinary similarity of  the clifftop tills of the south Pembrokeshire coast and those of the western and northern coasts of the Isles of Scilly.  Take a look at the images here:

https://brian-mountainman.blogspot.com/2018/04/even-more-south-pembrokeshire-till.html

and here:

https://brian-mountainman.blogspot.com/2011/08/devensian-till-at-bullums-bay-caldey.html

and here:

https://brian-mountainman.blogspot.com/2018/04/strange-till-near-stackpole-head.html

Now then -- a few pics from the Isles of Scilly:


Fresh till from Tregarthen Hill, Tresco


Fresh till at Carn Morval, St Mary's Island


Fresh till at Popplestones, Bryher


Fresh till at Gimble Point, Tresco

The most relevant page on this blog:


The similarities are extraordinary, and though I would not go so far as to claim that all these deposits are of precisely the same age, they must have originated in similar ways.  I won't go into too many technical details, but all of these are matrix-supported diamictons containing striated, faceted and rounded pebbles and cobbles from many different source areas.  The matrixes are not particularly clay-rich, and indeed the coarse sand and gravel fractions are well represented.  The deposits are uncemented, even in limestone areas.  Some deposits are iron-stained.  They contain debris from overridden raised beaches and -- in the case of the Stackpole Head deposit -- from what may be Oligocene (?) quartz pebble beds. There are differences, of course -- the Scilly tills have an admixture of loess-like materials indicative of windy and rather arid environments, and the Pembrokeshire tills have more old slope deposits incorporated. 

I would hazard a guess that these deposits were laid down as flowtills very close to an ice edge, and that some of them -- maybe all of them -- have been "paraglacially" redistributed or redeposited in a chaotic ice wastage environment. 

Check out the other photos on the site, and you will -- I hope -- see what I am getting at.......  

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