The glaciation and deglaciation of south east Aberdeenshire

• Main Author: Murdoch, William M.
• Published: University of Aberdeen 1977
• Subjects: 551.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.466614

Evidence resulting from the detailed mapping of the glacial geomorphology and deposits of an area in south east Aberdeenshire is presented and discussed and a model of glaciation and deglaciation is produced. Landforms of glacial erosion are partly masked by the drift cover but glacially abraded and striated bedrock, ice moulded topography and swarms of rock drumlins are all recognised and used in order to determine the amount and mechanisms of glacial erosion that have taken place. Glacial till forms a uniform cover of 2-4m over the entire area and three separate tills are identified. A lodgement till/meltout till couplet of local origin and a meltout till deriving from a sediment source offshore are postulated and the field relations and distribution of these tills suggest that the two parent ice bodies merged in the coastal zone. Meltwater channels are classified and found to be largely of subglacial origin. Deposits of fluvio-glacial material are similarly classified and include terraces, eskers and kames most of which are also interpreted as being of sub-glacial ice-contact oringin. A spatial analysis of all fluvio-glacial phenomena is undertaken incorporating the evidence produced in the discussion of individual channels and deposits. On the basis of this a reconstruction of the hydrological sub-system operating at the base of the former ice-sheet in the area is suggested. This consists of a west to east orientated meltwater system merging with a south to north orientated system in the coastal zone Deposits of glacio-lacustrine and glacio-marine origin are identified and a suggested classification outlined. The low level coastal deposits are interpreted as being marine whilst most of the others are interpreted as being either sub- or supra-glacial lacustrine deposits. Two deposits are interpreted as ice-contact proglacial deposits formed marginal to the ice. No evidence indicating higher sea levels was found in the area. All this information is integrated and compared with theoretical models and with other interpretations for thearea and a new model of glaciation and deglaciation is built up. All deposits, in the area are interpreted as belonging to the last glaciation to effect the area which is believed to be the Devensian. Three main directions of ice movement are idicated a primary easterly direction and two secondary southeasterly and northerly directions. Erosion by the ice is considered to have been more significant than has formerly been thought. The meltwater system is compared with theoretical models based on ice maxima conditions and the pattern of meltwater features in the area is interpreted as reflecting such a system. It is concluded that the ice in the area was temperate and wet based and that the ice margin must have lain some considerable distance away. The hypothesis of both moraireless Buchan and the Aberdeen readvance are both considered and rejected. It is concluded that deglaciation must have taken place by a process of widespread stagnation of ice in situ and that the coastal zone, being an area of ice merging, became an area of very early and rapid deglaciation causing widespread deposition of eskers and kames in this zone. Deglaciation was early, certainly well before 11,500 B.P., and proba.bly before 13,000 B.P. The suggested sequence of events that is produced involves an initial advance of ice from the north west followed by a period of easterly flowing ice merging with a northerly moving ice stream along the coast. Deglaciation took place earliest in this zone. This sequence of events is placed into a suggested regional context.