Late pleistocene deposits at Wretton, Norfolk. I. Ipswichian interglacial deposits.

Interglacial deposits found in the low terrace at Wretton, Norfolk, were formed in the zones II and III of the Ipswichian interglacial. The variety of sediments found is associated with the fluviatile environments of a meandering river. During zone II there was a regional mixed oak forest, with the local development of alder carr, fen, reedswamp and open water communities. During zone III the regional vegetation was more open and Carpinus became an important woodland tree. Locally, fen, reedswamp and open-water communities persisted, but alder carr was absent. The plants give some indication that the climate may have been more continental than at present, a number of species occurring which are not native to the British post-glacial flora but which have a wide distribution on the Continent. A brief comparison of the vegetational history is made with that of other Ipswichian interglacial sites in England and with the correlative Eemian interglacial on the Continent. The interglacial sections at Wretton form one of the richest Ipswichian sites for non-marine Mollusca so far found in England. The presence of a few more southern or more continental species, not now living in England, confirms that the climate was probably slightly warmer than at present, at least in summer. Numbers are large enough for satisfactory analysis in almost all sections, so that the environmental conclusion they suggest can be checked against those deduced from the plants. In general, these conclusions match and indicate a series of deposits laid down by a plant-rich Fenland river, a true ancestor of the present river Wissey, in its channel and neighbouring parts of its floodplain. The occurrence of brackish water species of Mollusca allows levels of marine influence to be clearly integrated with the vegetational history. Brackish horizons occur between - 1.95 m and +0.45 m O.D. in zone II b deposits, giving an indication of sea-level at this stage. The zone III deposits, although at a lower level, show no trace of brackish influences and a possible oscillation of sea-level is inferred.