Late‐Pleistocene tidewater glaciers and glaciomarine sequences from north County Mayo, Republic of Ireland

Abstract

Late-Pleistocene deposits in north County Mayo were deposited in three main glacigenic environments. 1 . Drumlins and basal tills were formed when ice moved from the Irish lowlands and local mountain catchments into Donegal Bay. 2. Gilbert-type deltas accumulated up to 80m I.O.D. on the lowlands and subaqueous moraines formed across minor valleys when marine-based ice grounded inland. 3. A thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice-rafting immediately outside of these ice limits. The muds contain an flphidium clavatum-dominated, low-diversity microfauna which is characteristic of cold-water conditions adjacent to glacier termini. Valves of Macoma calcarea from the mud have been 14C dated at 16 940 k 120 and 1 7 300 k 100 BP.The high-level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north County Mayo. Although the field evidence cannot be used to determine former sea level history with any accuracy, it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of Ireland. Raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in Ireland and represent marine transgressions prior to glacial unloading. It is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in Ireland than hitherto real ised.Journal of Quaternary Science

Glacial rebound of the British Isles-II. A high-resolution, high-precision model

“…The initial northwards retreat of the ice across southern Ireland and the Irish Sea is assumed to have been rapid such that by 18000yr BP the ice margin stood north of the Galtrim Moraine and at the Isle of Man (Stephens & McCabe 1977) (Figs 1 and 2a), consistent with ice-free conditions having existed in northeastern Wales by this time (Bowen 1973). Along the western margin in Ireland the ice sheet -is assumed not to have extended much beyond the present shoreline such that the coastal fringe was ice free before 17000yr BP (McCabe, Haynes & MacMillan 1986;Bowen et al 1986). …”

Radiocarbon constraints on the history of the western Irish ice sheet prior to the Last Glacial Maximum

“…1). McCabe et al (1986) described three facies in this deposit from an exposure at Brookhill that indicate deposition as a Gilbert delta. The tops of the gravelly foresets are between 74 and 78 m asl.…”

“…New chronological data, however, demonstrate that the IIS was a more dynamic system with several ice-margin fl uctuations comparable to the LGM event over the past 45 k.y. (McCabe et al, 1986(McCabe et al, , 2005Clark, 1998, 2003;Bowen et al, 2002). For example, at least three advances occurred in the Irish Sea Basin: a maximum advance ca.…”

Geomorphic evidence for active and inactive phases of Late Devensian ice in north-central Ireland

“…1) flowed mainly westwards into Donegal Bay (Knight and McCabe, 1997a). Drumlinisation (sediment shaping) of previously-formed Rogen moraine ridges in the Omagh Basin region is dated to~17 14 C kyr BP (cal 19.6 kyr BP) from articulated shells of Macoma calcarea within icemarginal sediments in Donegal Bay (McCabe et al, 1986). Following drumlinisation, ice-bed conditions in the Omagh Basin changed from warm-to cold-based, thereby preserving these bedforms intact.…”