SOME PLEISTOCENE PROBLEMS IN SUFFOLK

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GEOSUFFOLK RIGS

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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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SOME PLEISTOCENE PROBLEMS IN SUFFOLK by Suffolk Naturalists' Society - Issuu