Submarine deglacial sediment and geomorphological record of southwestern Scotland after the Last Glacial Maximum

In this paper new seismo-stratigraphic analysis is correlated with bathymetry data, sediment cores and relative sea-level (RSL) curves to provide new insights on the retreat dynamics of the Hebrides Ice Stream following the Last Glacial Maximum in the southern Hebrides region of Scotland.
Revising the submarine Quaternary stratigraphy within the region for the first time in over 30 years, we observe two primary glaciogenic units (Units III and IV). Unit III partly corresponds to the previously defined Barra Formation (Davies et al. 1984), but is expanded and re-interpreted here as a time-transgressive subglacial to ice-proximal deposit. On the mid-shelf, this unit comprises grounding-zone wedges (GZWs), deposited at a time when RSL was between +5 and -5 m OD. Within inshore waters and sea lochs Unit III can be found at or near seabed, where it is associated with retreat moraines, as well as with proglacial outwash sediments near the Kyntire coast (RSL ~ +10 m OD). The younger Unit IV represents instead ice-proximal to hemipelagic conditions, (equivalent to the Jura Formation).
From these new observations and associations we demonstrate that retreat dynamics followed three main stages: i) tidewater margin retreat punctuated by stillstands on the inner shelf with lower relative sea-level, ii) topography-controlled fjordic retreat, with evolution from a coherent ice-sheet to separate tidewater glaciers, and iii) stabilisation at the transition between tidewater to land-based ice margin.