Stratigraphic and palaeo-geomorphological evidence for the glacial-deglacial history of the last British-Irish Ice Sheet in the north-western Irish Sea

During its maximum extent around 25–23 ka BP, the British-Irish Ice Sheet extended to near the present-day shelf break with a large ice stream, the Irish Sea Ice Stream, occupied much of the present-day Celtic and Irish Seas. The different episodes of advance and retreat of the ice sheet have been extensively constrained onshore, with models based on feature characterisation and dating helping to understand the retreat pattern of the ice sheet. Offshore, glacial geomorphologies in the Irish Sea have been mostly recognised on the United Kingdom side but remains poorly constrained on the Irish side. In this paper, based on the analysis of an extensive seismic dataset, an update of the stratigraphic model of the northern Irish Sea, with new sub-units, is proposed with a mapping of newly discovered buried geomorphology. Characterisation of the geomorphology, including megascale glacial lineations, subglacial meltwater channels, moraines, and iceberg scours, has been used to extend the constraints on ice sheet retreat offshore. The transition from late glacial to marine setting has been constrained based on the mapping of marine sediment subunits and their terminations. This paper brings new constraints offshore, in a previously understudied area, and synthesises all the results into an updated conceptual model highlighting stratigraphic units succession and associated processes linked to geomorphology, within the context of a rapidly retreating ice stream.