| Summary: | This thesis describes the author^ investigation of ice-limits and raised shorelines in the Lorn and eastern Mull areas of western Scotland. Criticism of many of the methods used by previous workers led to the adoption of the following techniques in this study» detailed morphological aerial photograph mapping of all identifiable raised marine and fluvioglacial landforms at the 1:10,560 scale followed by careful checking and modification in the field; stratigraphic investigations involving the study of sections, augering and the use of a limited amount of borehole data; accurate levelling from bench marks of the shorelines and other terraces at close intervals; the use of radiocarbon dates, pollen analyses and macrofossil investigations; analysis of the height data using height/ distance diagrams and employing linear regression and trend surface analysis. By using principally these techniques the following sequence of events has been established. The first definitely recognisable shoreline to be formed was the Main Rock Platform which probably dates from a late inter-glacial period. Despite its age it is very well developed and associated with it are some very impressive examples of raised marine erosion. The main trend of the shoreline is a westward slope from 10.5 m O.D. at Connel to 5 m O.D. at Carsaig and Salen on Mull, a gradient of 0.16 m/km, though it is distorted by a number of bends and one possible fault. Most of the deformation is probably explicable in terms of tectonic movement, and long distance correlation of rock platforms is therefore unwise. Lithology and exposure have been important factors in influencing the height and development of the platform and related landforms. Higher and lower rock benches exist but these pose problems of origin, correlation and chronology. Ice-limits related to high sea levels are found at and south of Oban but probably mark only brief, diachronous halts during deglaciation from a more extensive ice cover, possibly the Perth Readvance. As the ice retreated, relative sea level was falling rapidly and lateglacial beaches are therefore only poorly developed and can rarely be correlated. How far sea level fell and the ice retreated are unknown. Ice readvanced during the Zone III or Loch Lomond Readvance. On the mainland glaciers reached the seaward ends of lochs Etive and Creran and advanced to the head of Loch Feochan, while on Mull a small ice-cap and several separate corrie and valley glaciers existed. Sea-level at this time was below 13-14 m O.D. at lochs Etive and Creran and below about 10 m O.D, at Glen Forsa and Loch Ba on Mull, During retreat from the maximal extent of this readvance massive outwash spreads were deposited particularly at Loch Etive and Loch Creran. Around 6,500 B.P. relative sea level reached its post-glacial maximum and formed the Main Post-glacial Shoreline (PSl) which is the best developed depositional shoreline in the study area. It slopes from 14 m O.D, at Glennoe on Loch Etive to 12 m O.D. at Flshnish Bay and the head of Loch Buie on Mull, a gradient of 0.05 m/km. During the fall of relative sea level from the Main Post-glacial Shoreline to its present level two fairly clear shorelines were formed at about 8 m O.D. (PS3) and 4 m O.D. (PS5) with gradients of only about 0.01 ra/km. The influence of exposure and the Connel rock bar on the heights of the post-glacial shorelines and present high water mark has been considered. There are also traces of 2 vague post-glacial shorelines (FS2 and FS4) between the three well marked ones. The sequence of events identified in this study compares reasonably well with the work in S.E. Scotland but previous work in the study area has been criticised and several alternative interpretations have been put forward, The thesis concludes by stressing the need for further detailed studies of this type.
|
|---|