DIATOM AND POLLEN STUDIES OF A SEDIMENT PROFILE FROM MELYNLLYN, A MOUNTAIN TARN IN SNOWDONIA, NORTH WALES

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Abstract
SUMMARY: Core samples taken from Late Devensian and Flandrian deposits at Melynllyn have been investigated. One profile was sampled at fairly close intervals for diatom and pollen analyses, and a series of radiocarbon dates was obtained. An absolute diatom counting method was used, which enabled the results to be expressed both in terms of annual diatom deposition and as percentages of the diatom sum. The diatom succession indicates that a change from alkaline to circumneutral conditions took place early in the Flandrian period. Diatoms characteristic of acidic, oligotrophic waters have been well established in the tarn from mid Flandrian times to the present day. Pollen analysis serves chiefly as a means of correlating the deposits with those from other sites in the Snowdonia region, although some features of the pollen diagrams are discussed. The data indicate that erosion was accelerated in the drainage basin of the tarn following the decline in Ulmus pollen percentages.