TWO LATE‐GLACIAL (LATE DEVENSIAN) DIATOM ASSEMBLAGE PROFILES FROM NORTHERN SCOTLAND

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Abstract
SUMMARY: Two profiles of the diatom assemblages in lake sediments of Late Devensian age have been analysed in detail to substantiate a zonation based upon the diatom assemblages from the nearby Loch Sionascaig site, in northern Scotland. The profiles bear out the original divisions into three diatom assemblage zones and indicate some subdivisions; there is close correlation with stratigraphic, pollen and chemical changes. The Cam Loch assemblages did not include the planktonic phase found in the Sionascaig Diatom Zone 2 sediments of Allerød age, despite the proximity of the two sites and a geological location that would suggest a possibly richer environment.It is concluded that the best pioneer forms are those of cosmopolitan distribution and that in the benthos at least there was an alkaline environment with sufficient nutrient status for diatoms typical of present day eutrophic lakes to occur during the period of greatest diatom diversity. The open water planktonic environment probably remained nutrient‐poor with little diatomaceous plankton, a condition resembling some present‐day alpine lakes.The final cold phase of the late‐glacial is characterized by the temporary disappearance of many taxa and the presence of several indicator taxa. Solifluction of the surrounding land surface is indicated by the presence of some subaerial forms. This is also a feature of an earlier slight climatic recession indicated by correlation of pollen and diatom analyses and now correlated with the Bølling/Allerød stade.