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

David J A Evans,Sarah L Bradley,Louise Callard,Alicia Medialdea,Margot Saher,Tom Bradwell,David H Roberts,Jeremy Ely,Steven G Moreton,Chris D Clark,Elena Grimoldi,Dayton Dove,Mark D Bateman,Richard C Chiverrell,Colm Ó Cofaigh,Derek Fabel

doi:10.1002/jqs.3275

Abstract

ABSTRACTThe findings of BRITICE‐CHRONO Transect 2 through the North Sea Basin and eastern England are reported. We define ice‐sheet marginal oscillation between ~31 and 16 ka, with seven distinctive former ice‐sheet limits (L1–7) constrained by Bayesian statistical analysis. The southernmost limit of the North Sea Lobe is recorded by the Bolders Bank Formation (L1; 25.8–24.6 ka). L2 represents ice‐sheet oscillation and early retreat to the northern edge of the Dogger Bank (23.5–22.2 ka), with the Garret Hill Moraine in north Norfolk recording a significant regional readvance to L3 at 21.5–20.8 ka. Ice‐marginal oscillations at ~26–21 ka resulted in L1, L2 and L3 being partially to totally overprinted. Ice‐dammed lakes related to L1–3, including Lake Humber, are dated at 24.1–22.3 ka. Ice‐sheet oscillation and retreat from L4 to L5 occurred between 19.7 and 17.3 ka, with grounding zone wedges marking an important transition from terrestrial to marine tidewater conditions, triggered by the opening of the Dogger Lake spillway between 19.9 and 17.5 ka. L6 relates to ice retreat under glacimarine conditions and final ice retreat into the Firth of Forth by 15.8 ka. L7 (~15 ka) represents an ice retreat from Bosies Bank into the Moray Firth.

Highlights

This paper reviews the results of the BRITICE‐CHRONO Transect 2 through the North Sea Basin and onto the onshore areas of eastern England in the context of pre‐existing knowledge on the behaviour of the British–Irish Ice Sheet (BIIS) in the region
The findings reported in these case studies are critically reviewed in the context of the regional reconstructions of BIIS palaeoglaciology as it pertains to the eastern margins of the ice sheet
The retreat phase boundary for Limit 6 from the Bayesian model is dated to 15.8 ka (Fig. 7a)

Summary

Introduction

This paper reviews the results of the BRITICE‐CHRONO Transect 2 through the North Sea Basin and onto the onshore areas of eastern England in the context of pre‐existing knowledge on the behaviour of the British–Irish Ice Sheet (BIIS) in the region. Following the work of Golledge and Stoker (2006), Hughes et al (2010, 2014) constructed a comprehensive map of bedform types (e.g. drumlins, mega‐scale glacial lineations, crag and tails) in this region and reconstructed complex changes in ice dynamics based on flowset mapping This showed both the Strathmore Ice Stream and the Firth of Forth Ice Stream responding to changes in ice thickness, ice divide migration and topographic influences during the last glacial cycle, but clearly demonstrated that the Strathmore Ice Stream and Firth of Forth Ice Stream were key sources of ice heading northeast, east and southeast into the central North Sea. The behaviour of the Firth of Forth Ice Stream offshore is poorly understood during the build‐up to the LGM, but advances have been made in understanding the role of Firth of Forth ice in controlling the NSL; it is highly likely that the NSL was an offshore extension of the Firth of Forth Ice Stream. This is supported by the imprint of the Bolders Bank Formation, subglacial bedforms, tunnel valleys and moraines on the seafloor as well as onshore stacked tills and ice margin geomorphology down the east coast of Britain and in the vicinity of Dogger Bank (Dove et al 2017; Roberts et al 2018; Emery et al 2019), all of which supports previous work and demonstrates that Scottish ice was flowing from the Firth of Forth into the southern North Sea (Boulton et al 1985; Davies et al 2009; Evans and Thompson 2010; Busfield et al 2015; Dove et al 2017)

Methods

Findings

Conclusions