Late Glacial to Holocene relative sea-level change in Assynt, north west Scotland

Abstract

This thesis aims to improve the relative sea-level (RSL) reconstruction for the Assynt region, a previously under-studied region of the British Isles, to provide important further constraints on glacial isostatic adjustment (GIA) models for the British Isles. The lack of geological data from this region means that the GIA models are currently poorly constrained for this region of north west Scotland. Evidence from four isolation basins on the north coast of the Assynt region reconstructs post-Last Glacial Maximum (LGM) RSL for previously unstudied time periods, including the Late Glacial and early Holocene. This thesis produces the first Late Glacial sea-level index points for Assynt, providing a critical additional constraint on the GIA model predictions for this early deglacial period, which in general is poorly constrained throughout the British Isles.

Sediment cores were taken at a range of altitudes above present sea level from four isolation basins. Reconstruction of the palaeoenvironment focused on diatom analysis, supported by organic content, particle size and qualitative pollen analysis. A number of clear transitions, from marine to brackish to freshwater conditions, document the isolation or ingression of the basins investigated at Duart. AMS radiocarbon dating of these contacts produced new sea-level index points for the Late Glacial, early and late Holocene for Assynt.

These new sea-level index points show there is poor fit between the model predictions for the Late Glacial RSL fall following the Late Glacial highstand and the RSL rise to the mid-Holocene highstand. There is reasonable data-model fit however from the mid- to late-Holocene as RSL falls to present. This misfit, evident elsewhere in north west Scotland, is potentially due to uncertainties associated with both the global and local ice model employed in the GIA models, providing a context for future study.