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Wednesday 19 August 2020

The interglacial - glacial sequence at West Angle Bay


I have been looking again at some of my research material relating to West Angle Bay, and regret that I never did publish a full research monograph back in the 1970's!  Because I didn't, a good deal of material on this location was published by others who had not had the chance to examine the sequence properly -- so speculation took the place of accurate observations and measurements.  Such is the way of the world.......

Anyway, the site is in danger of disappearing because of ongoing coastal erosion, and this is seriously bad news since West Angle has to be the most important interglacial site in Wales, as well as telling us a lot about the extent of Late Devensian Irish Sea Glaciation.

My blog entries on West Angle contain most of the key information, and my analyses of past research work which has appeared in print.  The most important records appear in the three blog posts under the title of "The West Angle Enigma" (1) (2) and (3):

https://brian-mountainman.blogspot.com/2017/02/the-west-angle-enigma.html
https://brian-mountainman.blogspot.com/2017/03/the-west-angle-enigma-2-silt-and-clay.html
https://brian-mountainman.blogspot.com/2017/03/the-west-angle-enigma-3-two-tills-or-one.html

See also:

https://brian-mountainman.blogspot.com/2020/08/the-west-angle-sediment-sequence-moreys.html

https://brian-mountainman.blogspot.com/2017/03/west-angle-gallery.html

https://brian-mountainman.blogspot.com/2017/03/west-angle-bay-classic-coastal-section.html

For the record, I have re-scanned one of the key diagrams which was very faded and discoloured, and assembled the other measured sections into one place, so here they are:



The outer (northern) end of the drift cliff at West Angle. Here, overriding ice has removed the bulk of the interglacial sediments, and the bulk of the sediments exposed in the cliff face are related to the Devensian glaciation. The raised beach is at considerable depth, or is absent. The best exposures of Irish Sea till occur around point B.


The middle part of the surveyed section. At E we can see the slip face / slump face / erosional contact, to the left (north) of which the bulk of interglacial sediments have been cut out. At D the bulk of materials exposed are glacially related. Between F and H the bulk of the exposed sediments are fine-grained interglacial silts and clays overlying the raised beach.



The southern part of the surveyed section, extending northwards from the bedrock slope. The bulk of the deposits exposed are interglacial, resting on the raised beach. Around J and K glacially-related materials sit on these deposits at the top of the section.



ThisThe key part of the West Angle sequence, near point (E) on the levelled section -- the erosional contact between the interglacial silt and clay series (to the right) and the dark red Late Devensian till (to the left).  The glacitectonic features need to be studied by a specialist!


A careful plot of the lower part of the sediment sequence at point (H), showing the transition between  the raised beach (near present-day HWM) at the base and the organic-rich interglacial sediments above.  The peat bed has not been exposed at all in recent years, and may never be found again.


A slab or lump of material from the interglacial silt and clay series incorporated into the dark red till in the glacitectonic "contact zone".  There are many detached slabs and fragmented layers in this zone, which explains why past researchers at this site have been very confused about the true sediment sequence.  Unravelling the story is made even more difficult by the frequent slumping on the cliff face and by the fact that every observer sees a different sediment sequence!

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