Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea

Abstract

Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice-stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice-sheet reconstructions.

Response of salt structures to ice-sheet loading: implications for ice-marginal and subglacial processes

“…The more rapid decay of permafrost in the vicinity of salt structures may increase the drainage capacity of the substratum and thus increase the ice-bed coupling. Increased ice-bed coupling slows down the sliding ice sheet (Narloch et al, 2013;Szuman et al, 2013) and favours glacitectonic thrusting at the ice margin (Van der Wateren, 2002;Passchier et al, 2010;Phillips et al, 2013). On a regional scale, the influence of the thermal conditions above salt structures will probably have a greater influence on the behaviour of an ice sheet than the localised obstacles formed by rising salt structures.…”

The glaciogenic unconformity of the southern North Sea

“…In the Dutch sector, all the valleys are considered to be of Elsterian age and are confidently mapped in highfrequency 2D seismic lines (Huuse & LykkeAndersen 2000, fig. 4;Praeg, 2003;Passchier et al 2010).…”

Reconstructing Quaternary Rhine–Meuse dynamics in the southern North Sea: architecture, seismo‐lithofacies associations and malacological biozonation

“…(); Saalian ice limit 2 from Passchier et al . (); Open valleys not infilled (dark grey patches) and Undefined valley fills (light grey patches) in Dover Strait from Laban et al . (); these valleys coincide largely with those mapped by Gupta et al .…”