A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain, the Celtic shelf and adjacent continental slope

Abstract

Scourse, J. D. and Furze, M. F. A. 2001. A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain, the Celtic shelf and adjacent continental slope.ABSTRACT: In support of their 'glaciomarine' model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach-face gravels and sands around the shores of the Celtic Sea. Glacial and sea-level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south-central Celtic Sea. Relative sea-levels were lower, and therefore glacio-isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice-rafting at a time of high relative sea-levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation.

Ice sheet extension to the Celtic Sea shelf edge at the Last Glacial Maximum

“…Our results thus support previous interpretations linking IRD flux in deep-sea cores to a short-lived advance and retreat of the Irish Sea Ice Stream (Scourse and Furze, 2001;Scourse et al, 2009a,b). However, they further indicate that the BIIS extended across the Celtic Sea to the Irish-UK continental shelf edge, up to 150 km seaward of previously proposed limits (Fig.…”

“…This compares with evidence from deep-sea cores on the Celtic margin for increases in ice-rafted debris (IRD) of IrishCeltic Sea provenance, with a smaller peak at c. 25.5e24.5 ka BP and a main peak at 23.6e23.4 ka BP encompassing Heinrich Event 2 (HE2; Scourse et al, 2001Scourse et al, , 2009aAuffret et al, 2002). These peaks are consistent with evidence from southern Ireland and the Isles of Scilly for the advance and retreat of the Irish Sea Ice Stream (ISIS) around 25e23 ka ( O Cofaigh and Evans, 2007;O Cofaigh et al, 2012;McCarroll et al 2010;see Chiverrell and Thomas, 2010;Chiverrell et al, 2013).…”

“…1), which grain size analyses show to consist of sandy silt to silty sand, almost entirely lacking in gravel, and containing an ostracod fauna indicating extremely low energy conditions of almost no currents (Scourse et al, 1990Scourse and Furze, 2001). Scourse et al (1990Scourse et al ( , 1991 acknowledged that the presence of such deposits across an open Atlantic shelf was difficult to explain by iceberg rafting, especially given modelling evidence that glacially lowered sea levels resulted in significantly increased tide and wave energies in the Celtic Sea (Belderson et al, 1986;Uehara et al, 2006;see Scourse et al, 2009b).…”

“…The southernmost extent of the last BritisheIrish Ice Sheet (BIIS) has long been disputed (e.g. Mitchell et al, 1973;Scourse, 1991;Scourse and Furze, 2001;Bowen et al, 2002), but it is now agreed that onshore glacigenic deposits in Ireland and southern Britain provide evidence of an advance of the Irish Sea Ice Stream into the Celtic Sea during the Last Glacial Maximum (LGM), around 25e23 ka BP 1 (Scourse, 1991;Evans, 2001, 2007;Greenwood and Clark, 2009;Chiverrell and Thomas, 2010;Clark et al, 2010;McCarroll et al, 2010;O Cofaigh et al, 2012;Chiverrell et al, 2013). The extent of this advance across the continental shelf has been constrained by a dozen vibrocores acquired in the late 1970s that penetrated surficial sand and gravel to reach sediments of glacial character ( Fig.…”

“…These undated sediments were interpreted to include subglacial till and glacimarine mud, their distributions used to propose a grounding line on the mid-shelf, correlated to an LGM limit across the Isles of Scilly ( Fig. 1; Scourse et al, 1990Scourse et al, , 1991Scourse and Furze, 2001;Scourse et al, 2009b). Till-like sediments at the base of two cores near the shelf edge were suggested to represent residual ice-rafted deposits ( Fig.…”