The mixed‐bed glacial landform imprint of the North Sea Lobe in the western North Sea

Abstract

During the last glacial cycle an intriguing feature of the British‐Irish Ice Sheet was the North Sea Lobe (NSL); fed from the Firth of Forth and which flowed south and parallel to the English east coast. The controls on the formation and behaviour of the NSL have long been debated, but in the southern North Sea recent work suggests the NSL formed a dynamic, oscillating terrestrial margin operating over a deforming bed. Further north, however, little is known of the behaviour of the NSL or under what conditions it operated. This paper analyses new acoustic, sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the NSL offshore from NE England. Subglacial tills (AF2/3) form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor, with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega‐scale glacial lineations and grounding zone wedges. The resultant ‘mixed‐bed’ glacial landsystem is the product of a dynamic switch from a terrestrial piedmont‐lobe margin with a net surplus of sediment to a partially erosive, quasi‐stable, marine‐terminating, ice stream lobe as the NSL withdrew northwards. Glaciomarine sediments (AF4) drape the underlying subglacial mixed‐bed imprint and point to a switch to tidewater conditions between 19.9 and 16.5 ka cal BP as the North Sea became inundated. The dominant controls on NSL recession during this period were changing ice flux through the Firth of Forth ice stream onset zone and water depths at the grounding line; the development of the mixed‐bed landsystem being a response to grounding line instability. © 2018 John Wiley & Sons, Ltd.

Retreat dynamics of the eastern sector of the British–Irish Ice Sheet during the last glaciation

“…Stratified intra‐ and inter‐till beds such as those at Sandy Bay (Eyles et al 1982), Whitburn (Davies et al 2009) and Holderness (Evans et al 1995; Evans & Thomson 2010) record both switches in ice flow provenance as well as phases of sedimentation in subglacial canal fills that in places fed into ice‐marginal lakes. At some locations, multiple tills are separated by stratified sediments of subaerial origin and hence were suitable for optically stimulated luminescence (OSL) dating, best exemplified at sites like Sandsend, north of Whitby (Roberts et al 2013) and Seaham, on the Durham coast (Roberts et al 2019). At Sandsend the stratigraphy displays evidence of an early NSL advance in the form of a bedrock glacitectonite and till which is separated from an upper till, documenting a later readvance, by upward‐coarsening stratified sediments of an ice‐marginal lake and sandur.…”

“…Recent investigations on the floor of the North Sea have identified significant landform‐sediment assemblages that are critical to the reconstruction of the former dynamics and oscillations of the NSL during MIS 2 in offshore locations (Fig. 1; Dove et al 2017; Roberts et al 2018, 2019; Emery et al 2019). In the central North Sea, the prominent feature of the Dogger Bank has been heavily glacitectonised, which Phillips et al (2017) relate to complex thrust moraine construction by a dynamic NSL margin during MIS 2 ice‐sheet recession.…”

“…1). Just offshore, partially excavated, streamlined, mixed‐bed terrain shows the NSL dominating the latter stages of the last glacial cycle, with ice streams such as the Tyne and Tweed either in recession or being deflected south (Everest et al 2005; Livingstone et al , 2010a; Roberts et al , 2019). There is also a clear set of ice‐contact, marginal landforms that document the initial decoupling of the NSL and inland ice (Staines 2009; Teasdale, 2013).…”

“…Additional evidence for ice streaming offshore was linked to deeply incised channels/tunnel valleys and seafloor glacial lineations running southwest–northeast from Montrose. Golledge and Stoker (2006) also suggested that the Wee Bankie Moraine complex may represent a shear margin moraine, although recent work suggests it is more likely to represent the onshore retreat of Firth of Forth ice during deglaciation (Roberts et al 2019).…”

“…The findings of Transect 2 are summarised here based upon new data from a number of localised case studies that were designed to further interrogate the existing glacial geomorphology, Late Quaternary stratigraphy and geochronology in key locations around the British sector of the North Sea Basin (Evans et al 2017, 2018, 2019; Bateman et al 2018; Roberts et al 2018, 2019), as well as concurrent reports on glacial reconstructions prepared outwith, but at the same time complementary to, the BRITICE‐CHRONO project (e.g. Murton et al 2009; Bateman et al 2008, 2015; Fairburn & Bateman 2016; Dove et al 2017; Fig.…”