Late Pleistocene deposits at Wretton, Norfolk. I I. Devensian deposits

• Published in: Philosophical Transactions of the Royal Society of London. B, Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1974
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.1098/rstb.1974.0004; https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1974.0004

The low terrace at Wretton, Norfolk, is shown to consist of up to 6 m of mainly fluviatile sands and gravels of Devensian age. It contains many organic horizons rich in plant remains, molluscs and bones, and shows well-developed periglacial structures, including involutions and ice-wedge casts. Organic deposits lie in channels beneath, within and above the fluviatile sediments, and also within small depressions, a few metres across, which are interpreted as features formed by the melting of ground-ice mounds. The succession within the terrace is complex, but the detailed sections observed, with petrographical, palaeobotanical and molluscan studies, allow a synthesis of the environmental changes which accompanied terrace formation. The petrography of the sediments in the depressions indicates that certain of the ground-ice mounds formed in lenses of sandy clay derived from weathered interglacial sediments. The sediments redeposited on the melting of the mounds have a characteristic particle-size distribution. Times of coversand formation within the terrace sequence are identified. The palaeobotanical study, by analysis of pollen and macroscopic plant remains, reveals a sequence of pollen assemblage biozones. There are three periods with biozones characterized by herb pollen spectra. These are separated by periods with biozones characterized by pollen spectra indicating the presence of woodland. The earlier sequence of the woodland biozones, named the Wretton interstadial, shows birch-pine woodland and heath. The later sequence shows pine-birch-spruce woodland and heath, and is correlated with the Chelford interstadial. A detailed consideration of the flora and vegetation of the herb biozones is given, with a comparison of the pollen spectra with recent pollen spectra from the Arctic. It is concluded that in these biozones vegetation physiognomically akin to grassland prevailed in the region. Molluscan faunas, found at several horizons, are typical of Early Devensian deposits in other parts of the Fenland drainage ...