SOME PLEISTOCENE PROBLEMS IN SUFFOLK

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SOME PLEISTOCENE PROBLEMS IN SUFFOLK PETER ALLEN Within the Pleistocene of Suffolk, many problems remain to be solved. The history of the early Thames in the county exemplifies this.

The earliest Thames debouched into the Crag Sea which at the time extended to the western part of the London Basin. As the Crag Sea withdrew, so the Thames extended, eventually to cross Essex, Suffolk and, arguably, Norfolk. The gravels deposited by the river collectively are known as the Kesgrave Formation in East Anglia, and the deposits of the individual terraces form Members, as indicated Table 1.

Table 1 Stratigraphy of the early Thames in Suffolk and the London Basin Region Formation Members

Middle Thames Essex Suffolk Middle Thames Kesgrave (part) (part) Rassler Waldringfield Waldringfield Diversion of Thames into new valley east of Colchester Gerrard’s Cross Moreton Claydon Beaconsfield Bures Baylham Common Satwell Stebbing Westland Green Bushett Farm

The terrace sequence can be traced, from quarries and boreholes, as far east as the Gipping Valley (Green and McGregor, 1999; Rose et al., 1999). Further east, mapping of the terraces is not possible and palaeographical maps show only generalised outlines of the changing course of the river (e.g. Rose, et al., 2002), leaving many questions to be investigated. For example, the two highest terraces, associated with the Bushett and Bures Members, are not represented in Suffolk, though normally the sedimentary records of the lower reaches of rivers are well preserved. As a second example, the terrace sequence falls in a normal fashion from Great Blakenham to the coast, but unusually low crops of gravel occur north of Great Blakenham, exposed at Creeting St Mary (TM09/55) and Badwell Ash (TL 99/69), corresponding to the Moreton Member. Possibly these anomalies are related to tectonic activity.

The strike of the underlying Chalk changes from south-west – north-east to south – north in the Bury St Edmunds area, which must have been accompanied by tectonic flexing. At the coast, Boswell (1915) recorded anticlinal tectonic activity during Tertiary times between the Stour and the Deben. Possibly the two are linked and a stress zone could have existed between Bury and the Suffolk coast affected the deposition and preservation of the Thames deposits. It is interesting to note that the Orwell receives very few tributaries and those that do occur are very short. The watershed is very close to the river. As an example, the upper reaches of the Mill River are little more than a 1 km from the Orwell, but the river flows to the Deben, over 10 km away. Possibly anticlinal tectonic activity was still exerting an influence in relatively recent times.

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The pre-Quaternary bedrock surface of the Ipswich area. Contours in metres O.D. Arrows indicate palaeoflow directions. Based on Woodland (1942–1946), Allender and Hollyer (1972, 1973) and Hollyer (1974).

On a more local scale, there are several locales where the palaeogeography of the Kesgrave Thames can be reconstructued in detail. Two examples are at Barham and on the peninsula between the Orwell and the Stour. The quarry at Barham (TM 133515) lies on the terrace of the Moreton Member, with the gravels lying between 38 and 41 m OD. The regional palaeogeographical reconstruction shows that the Kesgrave Thames flow from south-west to north-east, but at Barham palaeocurrent measurements show that the flow direction was only just east of north and that to the south-west, the Chalk and overlying Crag sands reach over 40 m OD, often over 50 m as at Great Blakenham. The palaeocurrents and palaeotopography suggest that the river must have flowed to the south of the higher ground, probably through Valley Farm (TM 116433) where the gravels are 37–41 m OD, and then almost northwards to regain its alignment (Fig. 1). Establishing the detail of this route will make an interesting study for the future.

On the Orwell-Deben peninsula, the Waldringfield Gravel Member lies in a different, lower channel from that associated with the higher terraces.

Between the two courses, the Red Crag rises to over 25 m OD, forming the Rushmere-Kesgrave Ridge , whereas the height range of the Waldringfield Gravels on the peninsula is 20–26 m OD. Thus the Waldringfield Gravel is contained to the south and east of the Ridge. Palaeocurrent measurements

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from the Kesgrave quarry (TM 228465) indicate flow to the NNE, whereas those at Foxhall Heath (TM 239438) and Waldringfield (TM 257448) show flow to the north-east or east. The river flow at Kesgrave may have been influenced by the proximity of the Ridge. Bridgland (1999) also describes the later gravels of the Thames as occupying a separate channel in the Colchester Area. The implication of this is that the Kesgrave Thames did not migrate downslope in a simple fashion to the Waldringfield Gravel terrace, but was diverted into the channel, possibly by river capture, effected by a tributary of the early Medway (Bridgland, 1999).

Many other challenges exist within the Pleistocene sequence. There is controversy concerning the number of terraces that are associated with the Ingham River, broadly contemporary with the Kesgrave Thames, which flowed through Lakenheath and along an alignment now occupied by the Lark and Waveney. The relationship of this terrace sequence to pre-Anglian glacial events is another matter of discussion, as indeed is the extent of these glaciations in Suffolk. Another exciting avenue would be to explore the preAnglian and post-Anglian human landscapes of Suffolk. The former signals virtually the oldest human occupation of Britain. The latter may be more tangible to explore as there is more evidence from which to reconstruct the landscape, as at Hoxne and Foxhall Road, Ipswich. Re-examination of other sites, such as Dales Road, Ipswich, could give valuable contextual information, while the Foxhall Road site, at the head of the Mill River, suggests that re-investigation of other post-Anglian valley heads could be rewarding. Straying beyond the Pleistocene, reconstruction of the Medieval coastline of the county, before the formation of the gravel spits and nesses, would show a very different picture from today.

There remain many possibilities for future work on the Pleistocene of Suffolk. Many of these are relatively small, but nevertheless important, and particularly suited to investigation by RIGS groups.

References Allender, R. and Hollyer, S. E. (1972). The sand and gravel resources of the area south and west of Woodbridge, Suffolk. Description of 1:25000 resource sheet TM24. Report of the Institute of Geological Sciences, 72/9.

Allender, R. and Hollyer, S. E. (1973). The sand and gravel resources of the country around Shotley and Felixstowe, Suffolk. Description of 1:25000 resource sheet TM23. Report of the Institute of Geological Sciences, 73/13.

Bridgland, D. R. (1999). ‘Wealden rivers’ north of the Thames: a province study based on gravel clast analysis. Proceedings of the Geologists’ Association, 110: 133–148.

Green, C. P. and McGregor, D. F. M. (1999). Pre-Anglian gravel deposits of the River Thames and its tributaries between Goring and Cromer.

Proceedings of the Geologists’ Association, 110: 117–132.

Hollyer, S. E. (1974). The sand and gravel resources of the country around Tattingstone, Suffolk. Description of 1:25000 resource sheet TM13.

Report of the Institute of Geological Sciences, 74/9.

24 Rose, J., Whiteman, C. A., Allen, P. and Kemp, R. A. (1999). The Kesgrave Sands and Gravels: ‘pre-glacial’ Quaternary deposits of the River Thames in East Anglia and the Thames valley. Proceedings of the Geologists’ Association 110: 93–116.

Rose, J., Candy, I., Moorlock, B. S. P., Wilkins, H., Lee, J. A., Hamblin, R. J. O., Lee, J. R., Riding, J. B. and Morigi, A. N. (2002) Early and Middle Pleistocene River and Neotectonic Processes, Southeast Norfolk, England.

Proceedings of the Geologists’ Association 113: 47–67.

Woodland, A. W. (1942) Water supply from underground sources of the Cambridge-Ipswich district (quarter-inch Geological Sheet 16). Wartime Pamphlet No 20, Geological Survey, U.K. Peter Allen 13 Churchgate Cheshunt Hertfordshire EN8 9NB.