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Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Friday, 18 February 2011

Glacial Lake Teifi


The recent work on Glacial Lake Teifi and the other temporary lakes formed during the advance and retreat of the Devensian Irish Sea Glacier onto the North Pembs - South Cardiganshire coast is interesting in several respects. One of the most interesting is the presence of varves and rhythmites in the lower deposits on the lake beds, some of which were laid down in water up to 100m deep. These rhythmites are described in some detail, but the two key papers about them fail -- as far as I can see -- to address the question of the length of time that elapsed from the beginning to the end of the glacial episode in this area. Are we talking about decades or centuries?

In Sweden it was established long ago that many of the varves in clay deposits had annual layers in them, so that they could be counted -- and matched up across many sites (like tree rings) until a comprehensive chronology of deglaciation and varve deposition was worked out. Are the rhythmites real annual layers in these Teifi Valley lakes, or are the rhythms related more to oscillations of melting and water flow into the big bodies of standing water? I'll try to get some answers....

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Development of glacial Llyn Teifi, west Wales: Evidence for lake-level fluctuations at the margins of the Irish Sea ice sheet, by Fletcher, C J N, Siddle, H J , Journal of the Geological Society, Mar 1998.
Palaeoenvironmental interpretation of an ice-contact glacial lake succession: an example from the late Devensian of southwest Wales, UK.
by James L. Etienne, Krister N. Jansson, Neil F. Glasser, Michael J. Hambrey, Jeremy R. Davies, Richard A. Waters, Alex J. Maltman and Philip R. Wilby,
Quaternary Science Reviews, Volume 25, Issues 7-8, April 2006, Pages 739-762

3 comments:

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I was very encouraged to find this site. I wanted to thank you for this special read. I definitely savored every little bit of it and I have you bookmarked to check out new stuff you post.

Amber said...

Diolch yn fawr, Brian, for the remarkable blogsite! :) I've bookmarked your blog for daily musings, as the majority of my exhibited/published paintings and illustrations are of British megalithic sites, and Cymru in particular. We actually met several times, years ago, when I lived at Penty Parc near Clarbeston Road and spent thoughtful time in Newport and Castell Henllys with reenactments as well. You are a gift to the region.
This topic of varves et al... mind candy. I'm sharing it with many...

BRIAN JOHN said...

Thank you, folks. Glad you like the site! Been putting a lot on in recent days, in a flush of enthusiasm ...... soon I will have to get the garden into shape, and blogging will have to take 2nd place in the grand scheme of things......