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.
The 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.
This case study presents the recent development of new 3D geological models for the Low Level Waste Repository in Cumbria through the review of historical and new datasets. The site is located in an area of complex Late Pleistocene glacial geology and geomorphology, which control near-surface groundwater movement, and benefits from extensive historical site characterization data. This work emphasizes the value of a quality review of existing borehole records, drilling techniques and supplementary information to build a predictive geological model. The integration of different datasets has proved crucial to our understanding of the ground conditions, which are characterized by complex Quaternary sequences, and the depositional processes responsible for their formation. The updated geological interpretation suggests that the Low Level Waste Repository is located on a former ice-dammed lake plain. This is contrary to the previous interpretation of multiple and extensive till units in the area. Although the permeabilities may be similar in both interpretations, the extents may be different. Understanding the depositional processes and extent and the hydrogeological characteristics of the deposits is key to developing a hydrogeological model that is appropriate for the assessment of the environmental safety of the site, both now and into the future.Thematic collection: This article is part of the Ground models in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/Ground-models-in-engineering-geology-and-hydrogeology
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