Ice sheets grow and decay in response to climate change and can leave a rich geological record of their former behaviour and extent after retreat. Although the British-Irish Ice Sheet (BIIS) has been investigated for over 100 years, it is only in recent years that we are beginning to unravel the history of the glaciated margin that surrounds Britain and Ireland. For example, recent studies conducted about ice extent show that the western Irish shelf has undergone major glacial advances at least since the earliest Pleistocene. The aim of this study is (1) to investigate the extent and timing of major glaciations and their influence on sedimentary processes on the western Irish continental shelf throughout the Quaternary period and (2) to correlate the onshore and offshore glacial record in western Ireland.
To achieve this a multi-proxy approach is adopted and includes the investigation of marine geophysical data, analysis of glacial material deposited in marine and terrestrial settings, as well as cosmogenic nuclide (CN) and radiocarbon dating. The study area stretches from nearshore to the outer shelf, from west of Donegal Bay (55°N) to the Porcupine Ridge (51°N).
A Cenozoic stratigraphy, with a focus on the Quaternary, was produced from borehole data and a marine geophysical dataset of 69 seismic lines, including airgun, sparker and pinger data of varying vertical resolution. The lithology, radiocarbon dating, and micropalaeontology of sediment cores allowed for the interpretation of depositional processes and palaeoevironmental changes on the shelf. A transition from stiff towards soft diamicton and an increasing planktonic to benthic foraminifera ratio suggest a change from glacial proximal to glacial distal environments. These sediments are overlain by gravel and Holocene marine sand. Some cores were collected on a set of moraines at southern Donegal Bay, representing a glacial re-advance after the last glacial maximum (LGM) ice sheet retreated. Radiocarbon dates should provide a chronology for this re-advance that can be traced back onshore and linked to a northward-flowing ice stream. Age estimates of ice retreat onshore will be obtained through CN analysis of 22 erratics, sampled at key sites around southern and eastern Donegal Bay, and should provide ice landfall chronology for both the LGM ice sheet and the post-LGM re-advance.
This presentation will discuss the main results of this multi-proxy approach and their implications for future detailed reconstructions of the BIIS dynamism during the Quaternary and more specifically during the last glacial period.