Field evidence to constrain models of glacio-isostatic uplift in Scotland

The Scottish glacio-isostatic uplift centre has been used to develop glacio-hydro-isostatic models which have subsequently been used to constrain the rheology of the mantle. The models have tended to be based upon relative sea level curves derived from the study of isolation basins or Holocene marine deposits and occasionally have utilised morphological features of unknown age.

The current study presents new evidence from northern Scotland which indicates that high relative sea levels were present during the retreat of the Late Devensian ice sheet. The field evidence indicates that in Northern Scotland (Strath Halladale and Armdale Bay) relative sea level fell from 27.3 m O.D to 15.9 m OD whilst an active ice margin was retreating down the valleys.

The presence of marine shoreline fragments at 15-18.6m OD, and possibly up to 27.3m OD, contrasts markedly with the relative sea level histories predicted from visco-elastic geophysical models (e.g. Lambeck, 1995; Peltier et al., 2002). The field data indicates that either the basic geophysical parameters associated with the models needs to be refined or the volume of ice across northern Scotland needs to be dramatically increased. Since research by Ballantyne et al. has indicated that the elevation of the actual ice surface probably lay below that used in the model, it suggests that the basic geophyisical parameters need to be revised.