Palaeo-Ice Sheet Dynamics and Depositional Settings of the Late Devensian Ice Sheet in South-West Scotland

Recently recognised temporal changes in the configuration of former mid-latitude ice sheets during their long history has introduced doubt over the validity of traditional steady-state equilibrium models delineating Late Devensian glacial and deglacial events in south-west Scotland. This has prompted a reappraisal of the palaeo-ice sheet dynamics and mode of deglaciation in this region. In a wider context, the role played by the Southern Uplands ice sheet in Irish Sea glaciation is considered. Primary emphasis has been placed on addressing the sedimentological and glaciological effects of isostatic submergence, and the character of retreat of the ice sheet onto a part of the Scottish mainland which has remained substantially unconsidered. A strategy for applying Landsat imagery to reconstruct flow geometries has been adopted which has allowed the palaeoglaciological structure of the south-west sector of the Scottish ice sheet to be reconstructed by reference to subglacial bedform alignment and cross-cut and overprinted bedform patterns. Ten major transient ice-flow stages have been identified during the last (Late Devensian) glaciation which demonstrate the style of ice stream development and reflect the time-dependent, dynamic evolution of the ice sheet. These findings provide a significant contrast to previous reconstructions. Zones of extensive pre-lineation deformation are thought to reflect former areas of sustained ice streaming which should be incorporated into future reconstructions of ice sheet elevation and internal flow kinetics, currently based on rigid-bed analogues. During deglaciation, the major valleys of south-west Scotland maintained topographically constrained ice, which underwent a single major readvance during late-stage retreat (Southern Upland readvance). Within the Loch Ryan Basin this readvance was synchronous with reactivated ice flow of Highland origin (Highland readvance) which advanced beyond a previously inferred limit. A subsequent palaeosurge event (Loch Ryan palaeosurge), following the Highland readvance, is strongly suggested by macrofabric data within a far-travelled glacitectonite and the landform assemblage within the Loch Ryan Basin. Available field evidence casts doubt on whether the ice margin retreat onto the south-west Scotland mainland was under marine-influence. A minimum deglacial age of 6 075 +/- 55 years B.P. implies a relative sea-level height of at least 6 m above the present level during the Mid Holocene. This implies that the recession style of Eyles and McCabe (1989a), invoking an ice-contact glacimarine setting, cannot be verified