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'Fluvial responses to rapid climate change in Eastern England during the last glacial period'

Ph.D. thesis 2002 by Rebecca Briant, University of Cambridge

Abstract

The response of lowland fluvial systems to rapid climate changes has been investigated using as case studies the Rivers Nene and Welland, two medium-size lowland catchments draining into the Fenland Basin. This is particularly timely because recent evidence from ice-core and marine records suggests that climate was considerably less stable during the last glacial period (Devensian Stage, Marine Isotope Substage 5d - Stage 2) than previously thought.

On the basis of detailed description of sediments exposed in quarries in the two river valleys, site-specific sequences of facies associations have been identified which reflect changes in the fluvial system. They were correlated, using significant bounding surfaces and facies similarities, and used to construct catchment-scale sequences of fluvial activity during the period. Palaeontological analyses (plant macrofossils, pollen, Mollusca, Coleoptera) show that the river systems were active under a periglacial climate, with a nival discharge regime grass- and herb-dominated vegetation of varying abundance and sparse molluscan and coleopteran faunas adapted to arctic conditions. Age control on the sequences is provided by substantial numbers of both radiocarbon and optically-stimulated luminescence (OSL) age estimates, which were cross-calibrated by dating samples from the same channel-fills.

The Nene and Welland rivers were both active throughout the Devensian Stage, with lower-energy deposition in the Early Devensian Substage (~50-115 ka) than in the later Middle and Late Devensian Substages (~11-50 ka). An significant hiatus in sedimentation during the Late Devensian appears to relate to decreased fluvial activity and increased permafrost development at the Last Glacial Maximum (~22 ka), particularly in the Welland valley. These changes are similar to those recorded in other lowland British rivers, and systems across North-West Europe, although the type of sediments representative of high- and low-energy conditions varies significantly.

It is concluded that there are clear responses to climate at the interglacial/glacial scale and to larger-scale trends and fluctuations within the Devensian such as those recorded by Marine Isotope Stages and Substages. However, river systems of this type do not respond to the small-scale Stadial/Interstadial events recorded in the Greenland ice-cores. In addition, this is the first study of Devensian fluvial sediments in lowland Britain to use OSL dating in conjunction with radiocarbon and has allowed the reliability of each technique to be assessed.