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Thursday, 17 January 2019

Penfro Formation -- a lexicon correction needed

A type locality for the Penfro Till Formation?  Cemented till exposed at Black Mixen, Lydstep.

A type locality for the Penfro Till Formation?  Cemented and stained till near the coast at Ceibwr, overlain by cemented glacifluvial gravels and fresh grey-blue till.

I have sent this message off to BGS with a view to getting the lexicon record corrected, with respect to the Penfro Formation.    I don't object to the name -- some name has to be used for the ancient till deposits, and "Penfro" is as good a name as any.  But the record is misleading since neither West Angle nor Llandre should be used as a type location.

So what are the candidates for type localities?  I am suggesting Ceibwr and Black Mixen (Lydstep) since these are the two sites where an old cemented till can be seen in close proximity to a fresher till.  Other sites are Witches Cauldron and Whitesands -- but I need to do some more checking at both......

We'll see how we get on.  It would be good to visit the sites in the company of a BGS geologist, if we can organize that.

Penfro Till Formation.

I cannot work out where the type locality is supposed to be.  Is it Pencoed?
The two "partial type sections" referred to are highly misleading, and should be removed from the Lexicon.  West Angle does NOT reveal an ancient till (Penfro Till) beneath the raised beach.  Both Dixon and Bowen have misinterpreted the stratigraphy.  There is a till at the site, but it is of late Devensian age, and rests ABOVE the silt and clay series assumed to be interglacial.  Llandre is a useless site too -- there are apparently glacifluvial gravels there, but there are no stratigraphic markers that can be used to tie in with any regional stratigraphy.

The only two convincing sites where an ancient till can be seen in close proximity to a more recent till are Black Mixen (Lydstep) and Ceibwr.  Please use these as type localities instead.  What is the process for correcting the lexicon?

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