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Monday, 12 March 2012

Irish Sea Till


The famous Irish Sea Till has been mentioned often enough on this site.  I took this photo of an exposure at Abermawr, on the North Pembrokeshire coast, yesterday.  It's typical -- this is a rather dried-out surface with a grey-blue colour.  When seen wet and fresh, the colour is much darker.   At the top edge of the exposure, in the weathered horizon,  there is some iron staining, so the till is a foxy red colour;  and this colour can also be seen in the basal layers of the till, where it is in contact with underlying periglacial deposits -- as a result of water percolation upwards into the (largely impervious) till from beneath.

If you click to enlarge the photo you can see some interesting details -- pebbles of various shapes and sizes and origins, some clearly striated, and also fragments of shells and lignite (carbonized or hardened fossilized wood).  These organic materials have come from the bed of St George's Channel.  The till itself is made up almost entirely of old sea-floor sediments, dredged up and transported by the overriding ice of the Irish Sea Glacier around 23,000 years ago.  The till is also highly calcareous, and reacts with hydrochloric acid.

How was the till emplaced?  There's a lot of debate about this -- but it is probably for the most part a lodgement till, created by material being "plastered" onto the glacier bed by ice sliding along on its base.

5 comments:

Anonymous said...

Wow, I never knew looking at mud could be so exciting!!

I bet your a 'hoot' at dinner parties.

Liz Windsor

BRIAN JOHN said...

Wonderful stuff, I can assure you.... mind you, I try not to talk about it too much, and the wonders of Irish Sea till must remain a secret, shared by just you and me.

Ellie Rigby said...

Didn't Dorothy Squires and my old mate Tom sing a song that was based on 'Till' in the 1970's?

Anonymous said...

I've known a foxy red Tilly in my time: does this count in the records? (but she wasn't Irish)


Leslie Phillips

BRIAN JOHN said...

The sex was on the other thread -- this one is about serious science.....