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Thursday, 17 October 2019

Caldey Island -- a till or not a till?




In the summer issue of Quaternary Newsletter Prof John Hiemstra and several colleagues published a short note on the "diamicton" at Ballum's Bay on Caldey Island, which I have referred to on a number of occasions on this blog.

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

I have been convinced since 2011 that this deposit is a Late Devensian till, and I have not changed my mind.  Anyway, I encouraged John and others to go and have a look at it, which they duly did, and they decided that it is "probably" an old Anglian deposit which has been redistributed and redeposited under periglacial conditions in the Late Devensian -- some way from the nearest glacier.  Their article is available on Researchgate, where it can be scrutinised.

https://www.researchgate.net/publication/333998714_Caldey_%27Kald_ey%27_in_Old_Norse_was_literally_a_%27cold_island%27_but_was_it_under_Devensian_ice

I didn't like their line of reasoning, and say so in the new edition of QN, just published:

https://www.researchgate.net/publication/336614738_COMMENT_ON_CALDEY_'KALD_EY'_IN_OLD_NORSE_WAS_LITERALLY_A_'COLD_ISLAND'_BUT_WAS_IT_UNDER_DEVENSIAN_ICE_QUATERNARY_RESEARCH_FUND_REPORT_BY_JOHN_HIEMSTRA_ET_AL

I didn't expect them to row back on their earlier opinions, and of course they have responded to my published points by saying that they still think they are right -- and to give a proper picture of their arguments I have added their comments after my own.  All good fun.

Of course, it's easy for them to say that I am basing my conclusions on "basic" rather than intensive fieldwork and on my detailed knowledge of the Pembrokeshire coastal exposures -- and they are right that I have no detailed laboratory studies or dating results to back up what I am saying.  The joys of being old, retired and disreputable!

But I will maintain, until something strong comes along to prove me wrong, that the Caldey till exposure is unexceptional, and that there are many other similar till exposures along the south Pembrokeshire coast -- as itemised on this blog -- that show that the Late Devensian ice pressed far to the east.  I repeat -- their explanation of the deposit as a "redistributed ancient till" is more convoluted than it needs to be, and is unsupported by any convincing evidence.


Of course, none of us ever looks at an exposure in a completely impartial way, and I dare to suggest that John and his colleagues may be just a little influenced, in their attitude to the Ballum' Bay exposure, by their interpretation of some of the deposits on the Gower coast, and at Rotherslade in particular.  They claim that in the cliffs on the south Gower coast there are great thicknesses of "redistributed till" which were rearranged beyond the edge of Late Devensian ice.  On balance, I disagree with that too, since I consider that the authors have not demonstrated in their paper that the studied deposits were not simply deposited (and maybe rearranged) in a highly dynamic and changeable ice wastage environment at or near the peak of the Late Devensian glaciation.........

That paper is here:

https://www.academia.edu/11862453/Reinterpreting_Rotherslade_Gower_Peninsula_implications_for_Last_Glacial_ice_limits_and_Quaternary_stratigraphy_of_the_British_Isles?auto=download

Hiemstra, J. F., Rijsdijk, K. F., Shakesby, R. A. and McCarroll, D. Reinterpreting Rotherslade, Gower Peninsula: implications for Last Glacial ice limits and Quaternary stratigraphy of the British Isles.
J. Quaternary Sci., (2008). ISSN 0267-8179









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