Walker, Michael James Cawthorne

2018-01-31T11:25:39Z

2018-01-31T11:25:39Z

1975

The purpose of the investigation is to present a geographical interpretation of the past environment of part of the Grampian Highlands between ca. 13,000 and 7000 B. P. The study is based principally on pollen analysis, but also draws widely on the results of sedimentological and geomorphologieal investigations. Six sites were selected for analysis, five of which are situated out¬ side the presumed limits of the Loch Lomond Beadvance, while the sixth site is located within those mapped limits. Detailed pollen analyses were carried out on all the profiles, and at three of the sites, organic carbon content, particle size and alkali cation percentages were also determined. Radiocarbon dates on critical horizons were obtained from two of the sites.

The pollen diagrams were divided into individual pollen assemblage zones which enabled the vegetational record at each site to be assessed independently. Correlations between the profiles showed that at the five sites outside the presumed maximal extent of Loch Lomond Readvance ice, the basal deposits were of Lateglacial age with pollen spectra indicati ng a milder Interstadial followed by a harsher Stadial phase. The overlying sediments were found to be Postglacial in age. At the sites within the mapped Loch Lomond Readvance limits, only Postglacial deposits were present. The combined results of pollen analyses, sedimentological and geomorphological studies suggest the following history of landscape evolution.

The Late Devensian ice-sheet, which probably reached its greatest extent 17,000 to 18,000 radiocarbon years ago, had virtually disappeared from the Grampian Highlands by ca. 13,000 B. P. The early Lateglacial pollen spectra at all the sites reflect an initial period of colonisation by open-habitat taxa on freshly-exposed substrates following ice-sheet decay. After this early phase of vegetational development, the plant cover of that area of the Grampians to the north and west of the Ben Nevis-Lochnagar watershed was dominated by Empetrum heaths, while grassland with juniper, dwarf birch, willow and occasional copses of tree birch characterised the southern and eastern slopes. Only in the extreme south of the study area did tree birch become established in significant numbers during the Interstadial. At ca. 11,000 B. P., declining temperatures heralded the onset of colder Stadial conditions with the recrudescence of glacier ice of the Loch Lomond Readvance, and the break-up of existing plant communities through increasingly widespread solifluxion. Open-habitat and chionophilous vegetation proliferated, environmental conditions became increasingly more severe, and a tundra landscape developed. This phase was relatively short-lived however, for rapid climatic amelioration at about 10,000 B. P. saw the final disappearance of glacier ice from Scotland, the cessation of solifluxion, and the initiation of a plant succession which culminated in the establishment of climax forest over much of the area. At that time, mixed woodland covered the southern and eastern Grampian slopes, while to the north and west of the Highland watershed, the landscape was one of coniferous forest.

http://hdl.handle.net/1842/27025

The University of Edinburgh

Annexe Thesis Digitisation Project 2017 Block 15

Already catalogued

Lateglacial and early postglacial environments in part of the Grampian highlands of Scotland

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy