Esker ridges and seismostratigraphic evidence for a southerly ice flow extending onto the present nearshore continental shelf of the Celtic Sea, SE Ireland
Abstract
New evidence is presented supporting a reappraisal of the glacial history of south-east Ireland favouring a southerly flowing ice mass extending beyond the present coastline onto the Irish continental shelf in the Celtic Sea during the last glaciation. The Celtic Sea was not only glaciated, but likely experienced ice-marginal oscillations and multiple phases of ice cover from different sources of the British-Irish Ice Sheet. This is supported by recent sedimentological and chronological constraints upon the south coast stratigraphy. However, ice flow directional information is sparse in the south of Ireland; NNW-SSE and NNE-SSW oriented striae at the coast are the only direct indicators of offshore trending flows. The nearshore area in the Celtic Sea between Dungarvan and Waterford Harbour in southern Ireland was mapped using acoustic Sparker and Pinger data, and the multibeam bathymetry data produced by the INFOMAR programme. The acoustic data reveal evidence of glacial activity in the area: several valleys and large depressions cut into the bedrock, and a buried esker-like ridge at the base of a 20 m deep depression. This ridge is oriented in an N-S direction and its length can be traced in the acoustic profiles for 6 km. The seismic appearance observed in the Sparker data inside the ridge shows stratification, but also large boulders in places. The ridge is covered with a sedimentary unit characterized by a homogeneous and in places weakly laminated seismic unit. Two other elongate linear ridges are observed on the seafloor in the bathymetry data NNE and NNW from the buried ridge. These are oriented in a NNE-SSW and N-S direction and are 6-7 km long. The western ridge on the seabed has a sedimentary fan at its southern end. We interpret these ridges as eskers formed by the sedimentary infilling of subglacial conduits following surges. They were likely deposited during deglaciation behind the northwards retreating margin of the ice sheet or its locally formed lobe, in an inward-transgressive manner. The two phases of esker formation implies a halt in the ice sheet retreat with the short existence of an ice-dammed lake or glaciomarine conditions offshore southern Ireland.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.C53C0749T
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHEREDE: 0730 Ice streams;
- CRYOSPHEREDE: 0774 Dynamics;
- CRYOSPHEREDE: 1621 Cryospheric change;
- GLOBAL CHANGE