Glaciation of the Oxford area

Plateau or Northern Drift occurrences in the Oxford area, after Shotton et al, 1980.  The consensus seems to be that many of these deposits are of glacial origin, heavily weathered and eroded, and sometimes redistributed or rearranged as slope deposits.  Note that this map shows an area to the south of the assumed Anglian ice limit.

There is a huge literature on the glaciation of the middle Thames basin and the Oxfords area, and I think it is fair to say that when it comes to ice limits, confusion reigns. Many years ago, when I was a student at Oxord, I remember going on a field trip with Dr Kenneth Sandford, during which he showed us exposures of the "Northern Drift" or "plateau Drift" which cap many of the hilltops to the north of the city.  He was quite convinced that at one time ice from the north extended at least as far south as Oxford, and I found his evidence quite convincing. Others disagreed with him, and said that the Northern Drift was not glacial at all, but was a weathered residue of destroyed or disaggregated Pliocene and older deposits.  In one of the most influential articles, Prof Fred Shotton (a very famous and powerful figure in his day who tried to shut down some of my early research until he had to accept that I was correct) and others undertook a comprehensive analysis of the deposits of the Cotswolds and Oxford area.  They concluded that everything was very confusing!  This is what they said:

1. Much of the Plateau Drift is water-deposited, but where it was originally gravel, decalcification by solution of limestone clasts, together with cryoturbation, may give it a spurious resemblance to till. This interpretation does not preclude the original occurrence of some true till.

2. The lowest occurrences of 'Plateau Drift' along the Evenlode Valley lie on a surface that is a continuation upstream of the Sugworth Bench.

3. The high level occurrence of Plateau Drift represents the original incursion of west Midland erratic material on to the Cotswold Scarp and its dip plane to the southeast and must be ascribed to glacial action, though it is probable that the more easterly outcrops represent fluvio glacial outwash rather than till.

4. Intermediate levels of Plateau Drift are suggested to be the result of redistribution of original material at various times between the early glaciation and the stage of the Sugworth Bench (i.e. Terrace).

In other words, almost anything could have happened, and probably did............

Cromerian Interglacial Deposits at Sugworth, Near Oxford, England, and Their Relation to the Plateau Drift of the Cotswolds and the Terrace Sequence of the Upper and Middle Thames Author(s): F. W. Shotton, A. S. Goudie, D. J. Briggs and H. A. Osmaston
Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 289, No. 1034 (May 7, 1980), pp. 55-86

http://www.jstor.org/stable/2395507

Here is a more recent paper:

The terraces of the rivers Thame and Thames and their bearing on the chronology of glaciation in central and eastern England
M.G. Sumbler
Proceedings of the Geologists' Association
Volume 106, Issue 2, 1995, Pages 93-106

Abstract
The newly surveyed terraces of the River Thame are correlated with those of the Upper Thames, principally on the basis of apparent continuity of long profiles. This fixes the levels of the terraces of the Upper Thames at the Thame/Thames confluence at Dorchester, close to the ‘Goring Gap’, allowing correlation with the terraces of the Middle Thames to be more firmly established than hitherto. Anglian glacial deposits in the headwaters of the Thame appear to be broadly contemporaneous with those of the Wolvercote Terrace of the Upper Thames and Evenlode. An analogous relationship between the Wolvercote Terrace deposits and the glacial ‘Moreton Drift’, previously suggested by many workers is upheld, supporting the view that the Moreton Drift is itself Anglian. However, the relationship of the Wolvercote Terrace with the Middle Thames terrace succession suggests that the Anglian deposits of the Evenlode and Thame valleys are significantly younger than those in the Vale of St Albans. An hypothesis which explains these observations is that the Anglian Stage comprised two separate glacial phases together with an intervening temperate episode. Published amino acid racemization data suggest that the glaciations correspond with Oxygen Isotope stages 12 and 10 of the deep sea record, and the temperate phase with Oxygen Isotope Stage 11; the deposits of the latter ‘Swanscombian Interglacial’ are similar in palynological character to those of the Hoxnian of Hoxne (Oxygen Isotope Stage 9). It is suggested that deposits ascribed to the Anglian glaciation include deposits from both stages 12 and 10, and that much of the Anglian glacial succession of central and eastern England, hitherto ascribed to Stage 12, including the ‘Wolston Series’ of the original ‘Wolstonian’ stratotype and perhaps also the Lowestoft Till of the Anglian stratotype, were deposited during the younger Stage 10.

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What emerges from these and many other papers is great uncertainty regarding the definition of "till" -- only partly resolved by the fact that more recent researchers have actually visited glaciers and have studied modern ice edge environments.  They know that till is highly variable lithologically, and can in some circumstances be composed largely of older and overridden terrace gravels or slope deposits.  Some of the convoluted arguments about the genesis and survival of glacial deposits, in the 1980 paper by Shotton et al, seem today to be curiously dated......

Whatever the truth of the matter, it seems clear that there is good evidence of glaciation in the Oxford area (Middle Thames basin) around 40 km south of the position of the "accepted" Anglian limit.

Anyway, the two messages for me, from looking at these old research articles, are that:

(a) there is huge doubt still about the age of the deposits examined, with some (such as Sumbler) assuming that many or most of them are of Anglian age, with at least two different glacial episodes, while others argue that some of the deposits are of Cromerian or Baventian age;

(b)  the Anglian ice limit, used by many to represent the "maximum southward extent of ice in the UK" is completely inadequate.  Large areas beyond that line on a map have clearly been affected by ice from the north.

Ice limits map from the Oxford Geology Group -- showing, interestingly enough, Anglian ice from the Bristol Channel extending all the way to Stonehenge.......

This is a somewhat crude map purporting to show the extent of "pre-Anglian fluvial deposits" -- including the "Northern Drift" deposits which include sediments of many different types.