The glaciogenic unconformity of the southern North Sea

Abstract

The southern North Sea is a shallow epicontinental sea that was glaciated several times during the Quaternary. The area is known for its remarkable record of tunnel valleys, the age and origin of which are debated. The recent availability of continuous three-dimensional seismic data between the coasts of Britain and the Netherlands provides the opportunity to establish a new seismic interpretation workflow adapted to the intracratonic glaciogenic successions. By analysing the geomorphology of the buried basal glaciogenic unconformity, four distinct major ice fronts are identified and correlated onshore. The ice fronts provide robust relative timelines, and the analysis of tunnel-valley orientations and their merging points indicates that the number of glacial phases has been underestimated. By comparing the erosion capacities of sand and chalk substrates, it is suggested that mechanical abrasion processes are also involved during tunnel-valley genesis. The methods and observations used in this study are applicable to the ancient glaciogenic record in general and constitute a basis for the sedimentological analysis of tunnel valleys

Morphological properties of tunnel valleys of the southern sector of the Laurentide Ice Sheet and implications for their formation

“…The spacing metrics are within the range of previously reported values for tunnel valleys (Praeg, 2003;Jørgensen and Sandersen, 2006;Stackebrandt, 2009;Moreau et al, 2012;Kehew et al, 2013) but smaller than the average spacing of eskers (Storrar et al, 2014a, and references therein). Theory suggests that the spacing of subglacial conduits is controlled by substrate properties, basal melt rate and the hydraulic potential gradient (e.g.…”

Sedimentary imprints of former ice-sheet margins: Insights from an end-Ordovician archive (SW Libya)

“…Individually, both dyke types are poorly differentiated from dykes occurring in other non-glacial systems (Parize and Friès, 2003;Arnaud, 2012;Moreau et al, 2012). They cannot be used alone to differentiate a subglacial to proglacial context, yet their occurrence attests to overpressures, one of the key elements in ice-marginal depositional systems.…”

“…Tunnel valleys are identified across most of the Late Quaternary ice-marginal areas characterised by a sedimentary subglacial substrate (Huuse and Lykke-Andersen, 2000;Kluiving et al, 2003;Lutz et al, 2009;Janszen et al, 2012;Kehew et al, 2012;Moreau et al, 2012;Van der Vegt et al, 2012). Models usually invoke hydrostatic overpressure generated by the icesheet load but alternative models based on erosion by steady-state meltwater flows have also been proposed.…”

North Sea palaeogeographical reconstructions for the last 1 Ma

“…The latter are elongated and remarkably deep features presumably formed by pressurised, super-cooled sub-glacial flows of water controlled by ice-sheet hydrology (e.g. Moreau et al, 2012). Relatively small-scale tunnel valleys occur on Chalk bedrock of East Anglia (Anglian age; Woodland, 1970) and immediately offshore (Anglian/Wolstonian/Devensian age).…”