Ice limits in the Chilterns and elsewhere

Two reconstructions of ice limits in the Lower Thames - Chiltern area

Grateful thanks to Philip for this interesting piece of research:

According to the "Victoria County History of Wiltshire”, there are deposits “ … of glacial drift south of the town [of Cricklade] and at the west end of the parish.” (Quoting the geological survey map, sheet 252.) This is well to the south of the ice margin line on Ixer & Co's map which you illustrate in your previous post. If correct, it would support the bulge of the ice margin reaching Stonehenge depicted on the map in your present post. 

Also, the Chiltern Society’s document on Marlow Common says “The geology of this site is unique and unlike the rest of the Chilterns. Glacial deposits from the last ice age mask the chalky geological base and create acidic soils, … ” (I don’t know on what authority. I suppose they could be fluvioglacial.) Marlow Common is at the foot of the chalk dip slope, some 35 km south of the supposed ice margin. There are other proposals about a line of "drift" along the foot of the Chiltern dip slope (distinguished from the "Plateau Drift", said to be somehow related to the Clay-with-Flints, and by some, to be partly affected by a glacier. The terminology is very confused.) Also about Puddingstones (a kind of Sarsen) allegedly moved by ice partly across the Chilterns, and about glacial deposits elsewhere in the Chilterns, again well outside all the ice margin lines I have seen on maps. I am in the process of investigating these proposals.

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Cricklade is on the River Thames, between Swindon and Cirencester.  To the north, in the Thames valley, there has been a vast amount of gravel extraction from the Thames terraces. To the south, the modern geological map shows a patch of something or other -- variously referred to as  head or alluvial clay, depending on which map you are looking at. It's fair to say that the deposits around Swindon are not very well investigated or defined.......

As for the Chilterns, let's see what Philip's research shows up.....

And thanks to Philip for drawing attention to this comprehensive paper by Murton et al (2015) which I have read before but never quite latched onto.

Murton, Julian, Bowen, David Q, Candy, Ian, Catt, John A, Currant, Andrew, Evans, John G, Frogley, Mick, Green, Christopher P, Keen, David H, Kerney, Michael P, Parish, David, Penkman, Kirsty, Schreve, Danielle C, Taylor, Sheila, Toms, Phillip S et al. (2015) Middle and Late Pleistocene environmental history of the Marsworth area, south-central England. Proceedings of the Geologists' Association, 126 (1). pp. 18-49. ISSN 0016-7878

http://sro.sussex.ac.uk/id/eprint/52890/

The authors publish this map:

It shows a tongue of ice (assumed to be of Anglian age) pushing into the St Albans - Welwyn Garden City area from the NW, but they also refer to other glacial deposits to the south of the ice limits shown in the Vale of Aylesbury, and they admit that some of the clay-with-flints deposits shown on the Chilterns look suspiciously like fresh or reworked glacial and fluvioglacial deposits. While the chalk escarpment must have presented a barrier to ice coming down from the north, there are signs that the Chiltern Hills might well have been overridden by active ice on at least one occasion.

There's another map in a presentation by my old friend Chris Green (he and I read geography in Oxford at the same time), and in the accompanying text he refers to "glacially disturbed Tertiary deposits on the Chilterns ('Plateau Drift')". This is the map:

Chris Green's map of the Plateau Drift and other deposits on the Chilterns.  The areas shown in brown represent exposed surface Plateau Drift.  The green is the chalk scarp.  The grey areas represent "drift" or Pleistocene sediments on bedrock, in the Vale of St Albans.

It's interesting that Chris refers to glacial (rather than periglacial) involvement in the formation of the plateau drift; if he is right, then the whole of the Chilterns must have been glaciated.

And here is yet more information from Phil, for which many thanks:

In a webpage on Marlow Common (not far from Henley) by the Chiltern Society, it is stated “The geology of this site is unique and unlike the rest of the Chilterns. Glacial deposits from the last ice age mask the chalky geological base and create acidic soils, generating rare heathland habitat of conservation priority.”

According to a 1962 article by Loveday, “The formation of Plateau Drift, which is thought to be a more or less crude mixing of Clay-with-flints with Reading Beds and, at particular elevations, with marine and fluviatile gravels and sands, may have resulted from either periglacial or glacial conditions early in the Pleistocene.” 

More and more intriguing........... and it is more and more likely that the glacial ice from the north actually reached the position of the present Thames near Henley and Reading and around the Goring Gap.