Left High and Dry: Deglaciation of Dogger Bank, North Sea, Recorded in Proglacial Lake Evolution

Abstract

Reconstructions of palaeo-ice sheet retreat in response to climate warming using offshore archives can provide vital analogs for future ice-sheet behavior. At the Last Glacial Maximum, Dogger Bank, in the southern North Sea, was covered by the Eurasian Ice Sheet. However, the maximum extent and behavior of the ice sheet in the North Sea basin is poorly constrained. We reveal ice-marginal dynamics and maximum ice extent at Dogger Bank through sedimentological and stratigraphic investigation of glacial and proglacial lake sediments. We use a large, integrated subsurface dataset of shallow seismic reflection and geotechnical data collected during windfarm site investigation. For the first time, an ice stream is identified at Dogger Bank, based on preserved subglacial bedforms, eskers and meltwater channels. During ice-sheet advance, a terminal thrustblock moraine complex formed, whose crest runs approximately north-northeast to south-southwest. Subsequent ice stream shutdown caused stagnation of ice, and rapid retreat of the ice-sheet margin. The moraine complex, and outwash head from an adjacent ice-sheet lobe to the west, dammed a large (approximately 750 km 2) proglacial lake. Subsequent sedimentation infilled the lake with 30 m of glacial outwash sediments. A lobate subaqueous fan formed at the ice-sheet margin, which thins toward the southeast with iceberg scours and ice-rafted debris at the base, and is onlapped by lake sediments calibrated to core as alternating clay and silt laminae, interpreted to be varves. The lake became isolated from the retreating ice-sheet margin, and ice-sheet retreat slowed. Sediment-laden meltwater was supplied to the ice-distal proglacial lake for c. 1500-2000 years. Subsequent ice-sheet retreat off Dogger Bank was more rapid due to the negative subglacial slope. The stepped retreat of rapid downwasting, slow retreat, and a final rapid phase off Dogger Bank occurred after the LGM at around 27 ka and before formation of a ribbon lake, dated previously to 23 ka and approximately 60 m lower in elevation, formed to the north of Dogger Bank. The complicated stratigraphic architecture revealed through these data improves forecasting of ground conditions for turbine footings at Dogger Bank, an important step in the provision of clean, sustainable energy.

Ice sheet and palaeoclimate controls on drainage network evolution: an example from Dogger Bank, North Sea

“…The channel network was buried during subsequent marine transgression which began at around 10 ka at Dogger Bank, with complete inundation occurring around 8.5-8 ka (Brooks et al, 2011;Emery et al, 2019b;Shennan et al, 2000;Sturt et al, 2013). Shallow marine sand, varying in thickness from 0 m up to 25 m, was then deposited during the Late Holocene (Cotterill et al, 2017b;Emery et al, 2019b).The stratigraphy provides an archive of the transition (Cotterill et al, 2017b;Emery et al, 2019a, b), with the incised channels and Horizon Z observed in this study. from MIS 5 marine sediments, through to glacial and terrestrial environments, followed by a return to marine conditions during MIS 1, 11.7 ka to present (Cotterill et al, 2017a, b;Emery et al, 2019a, b;Phillips et al, 2018).…”

“…These channels form part of the extensive networks of post-Last Glacial Maximum North Sea channel fills mapped by the North Sea Palaeolandscape Project (Fitch et al, 2005;Gaffney et al, 2007Gaffney et al, , 2009 and other studies (Cameron et al, 1987;Coughlan et al, 2018;Hepp et al, 2017Hepp et al, , 2019van Heteren et al, 2014;Hijma et al, 2012;Prins and Andresen, 2019;Salomonsen, 1993). The channel network was buried during subsequent marine transgression which began at around 10 ka at Dogger Bank, with complete inundation occurring around 8.5-8 ka (Brooks et al, 2011;Emery et al, 2019b;Shennan et al, 2000;Sturt et al, 2013). Shallow marine sand, varying in thickness from 0 m up to 25 m, was then deposited during the Late Holocene (Cotterill et al, 2017b;Emery et al, 2019b).The stratigraphy provides an archive of the transition (Cotterill et al, 2017b;Emery et al, 2019a, b), with the incised channels and Horizon Z observed in this study.…”

“…The basal seismic unit comprises three main seismic facies, with minor contributions of other seismic facies. Generally, the area east and southwest of the study area is characterised by high-amplitude, varying frequency reflections and asymmetric and symmetric serrate, inclined, patchy and sporadic reflections (see Emery et al, 2019b, for description of terminology), termed sub-unit 1 (Fig. 2a).…”

“…Sub-unit 3 is interpreted to be glacial outwash deposited subaerially in outwash fans during ice-sheet retreat. A full description of these glacial and proglacial sedimentary environments and their implication for landscape evolution during ice-sheet advance and retreat is provided in Emery et al (2019b).…”

“…This relatively constant width implies the existence of a topographic constraint, such as the low-relief valleys (Fig. 3d), with the possibility that these valleys were once deeper, and the surrounding higher topography has been subsequently removed through wave ravinement during marine transgression (Emery et al, 2019b). It is difficult to test whether significant erosion has taken place due to the lack of a stratigraphic datum to correlate within the proglacial lake sediments, and such a correlation would require high vertical and spatial resolution of stratigraphic detail from borehole logs and seismic data that are beyond the capability of this dataset.…”