Abstract
Abstract. Submerged landscapes on continental shelves archive drainage networks formed during periods of sea-level lowstand. The evolution of these postglacial drainage networks also reveals how past climate changes affected the landscape. Ice-marginal and paraglacial drainage networks on low-relief topography are susceptible to reorganisation of water supply, forced by ice-marginal rearrangement, precipitation and temperature variations, and marine inundation. A rare geological archive of climate-driven landscape evolution during the transition from ice-marginal (ca. 23 ka) to a fully submerged marine environment (ca. 8 ka) is preserved at Dogger Bank, in the southern North Sea. In this study, our analysis of high-resolution seismic reflection and cone penetration test data reveal a channel network over a 1330 km2 area that incised glacial and proglacial lake-fill sediments. The channel network sits below coastal and shallow marine sediments and is therefore interpreted to represent a terrestrial drainage network. When mapped out, the channel form morphology reveals two distinct sets. The first set comprises two low-sinuosity, wide (>400 m) channels that contain macroforms of braid and side bars. These channels are interpreted to have originated as proglacial rivers, which drained the ice-sheet margin to the north. The second set of channels (75–200 m wide, with one larger, ∼400 m wide) has higher sinuosity and forms a subdendritic network of tributaries to the proglacial channels. The timing of channel formation lacks chronostratigraphic control. However, the proglacial rivers must have formed as the ice sheet was still on Dogger Bank, before 23 ka, to supply meltwater to the rivers. Ice-sheet retreat from Dogger Bank led to reorganisation of meltwater drainage and abandonment of the proglacial rivers. Palaeoclimate simulations show a cold and dry period at Dogger Bank between 23 and 17 ka. After 17 ka, precipitation increased, and drainage of precipitation formed the second set of channels. The second set of rivers remained active until marine transgression of Dogger Bank at ca. 8.5–8 ka. Overall, this study provides a detailed insight into the evolution of river networks across Dogger Bank and highlights the interplay between external (climate) and internal (local) forcings in drainage network evolution.
Highlights
This study provides a detailed insight into the evolution of river networks across Dogger Bank and highlights the interplay between external and internal forcings in drainage network evolution
Postglacial drainage patterns in the North Sea have become a focus of interest in recent years since the growth in archaeological exploration of the submerged landscapes of the northwest European continental shelf (Bailey et al, 2017; Coles, 1998; Flemming et al, 2017)
Mapping of Horizon Z revealed a network of channels that incise and postdate glaciogenic and proglacial lake sediments but are buried under shallow marine sand. These channels, along with Horizon Z, are interpreted to represent the terrestrial landscape at Dogger Bank that developed during the period between ice sheet retreat and marine transgression
Summary
Postglacial drainage patterns in the North Sea have become a focus of interest in recent years since the growth in archaeological exploration of the submerged landscapes of the northwest European continental shelf (Bailey et al, 2017; Coles, 1998; Flemming et al, 2017). Previous explorations of submerged landscapes have used low-resolution 2D or 3D seismic reflection surveys designed to target deeper oil and gas reservoirs (Fitch et al, 2005; Gaffney et al, 2007, 2009) or combine oil and gas datasets with sparse high-resolution 2D seismic reflection data (Coughlan et al, 2018; Hepp et al, 2017, 2019; Prins and Andresen, 2019) Whilst this enables drainage networks to be identified, there is little information to constrain sedimentary and geomorphic processes and the controls on landscape evolution. Dogger Bank is covered by a large (1500 km2), 2D seismic reflection data grid and geotechnical logs acquired as a site investigation for the Forewind wind-farm projects
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