British and Fennoscandian Ice-Sheet interactions during the quaternary

Abstract

Northeastern England and the North Sea Basin is a critical location to examine the influence of glaciation in the northern Hemisphere during the Quaternary. This region was a zone of confluence between the British and Fennoscandian Ice Sheets, and harboured several dynamic ice lobes sourced from northern Scotland, the Cheviots, the Lake District and the Southern Uplands. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings, and being sourced from both the British Isles and northern continental Europe. The research undertaken involved a thorough reinvestigation of the Quaternary sediments of northeast England, making use of enhanced exposures in coastal sections following the cessation of colliery waste dumping, and in boreholes from the North Sea. It used detailed sedimentological, stratigraphical, chronostratigraphical, lithological, petrological, and geochemical techniques to investigate their depositional processes, age, provenance signatures, and regional correlatives to construct an independent model of the eastern margin of the British-Irish Ice Sheet (BUS) throughout the Quaternary, and its interaction in the North Sea Basin with the Fennoscandian Ice Sheet (PIS). This region was a zone of confluence between ice lobes sourced from northern Scotland, the Cheviots, the Lake District and the Southern Uplands, and is ideally placed for investigating the geological record of the North Sea Lobe during the Late Devensian. In addition. County Durham has one of the most northerly exposures of Middle Pleistocene sediments in Britain, including a raised beach and a Scandinavian till. This project focussed on a variety of localities in northeastern England and in the North Sea Basin, including Whitburn Bay, Shippersea Bay, Hawthorn Hive, and Warren House Gill. At Whitburn Bay, the Blackhall and Horden glacigenic members are exposed in superposition and are Late Devensian in age. The lower Blackhall Member here is interpreted as a subglacial traction till with a high percentage of locally derived erratics. A boulder pavement at the top of the till points to a switch in ice-bed conditions and the production of a melt-out lag prior to the deposition of the upper, Horden Member. This second traction till contains erratics and heavy minerals derived from crystalline bedrock sources in the Cheviot Hills and northeast Scotland, including tremolite, andalusite, kyanite and rutile. Within the Horden Member are numerous sand, clay and gravel-filled channels incised into the diamicton, which are attributed to a low energy, distributed, subglacial canal drainage system. Coupled with the hydrofractures and the boulder pavement, this suggests that a partly decoupled, fast flowing ice stream deposited the Horden Member. The eastward, on-shore direction of ice movement indicates that the ice stream was confined in the North Sea Basin, possibly by the presence of Scandinavian ice. From Hawthorn Hive to Warren House Gill, the Blackhall and Horden members are separated by the Peterlee Sands and Gravels, ice-proximal outwash sediments. Beneath the glacial sequence, some 500 m to the south is the Easington Raised Bench. The partly calcreted interglacial beach lies directly on Magnesian Limestone bedrock at 33 m O.D., and consists of beds of unconsolidated, well-bedded, imbricated, well- rounded sands and gravels. It has been dated to MIS 7 by amino acid geochronology and OSL dating. The beach contains exotic gravel, including flint, and previous workers have reported Norwegian erratics. The only currently extant source for these is the Scandinavian Drift at Warren House Gill. Warren House Gill is a classic Middle Pleistocene site, and has a complex stratigraphy, consisting of a lower "Scandinavian Drift" with overlying estuarine sediments, and an upper "Main Cheviot Drift", which comprises two tills and glaciotectonised, interstratified sands and silts, traditionally interpreted as Devensian in age. The lowest grey Scandinavian Drift is a grey, laminated clay with dropstones. It contains marine bivalve fragments, foraminifera, and clasts of northeastern Scotland and Norwegian provenance, as well as Magnesian Limestone, chalk, flint, and Triassic red marl from the North Sea. Reworked palynomorphs include Eocene dinoflagellate cysts. This is interpreted as a Middle Pleistocene glaciomarine deposit, and is renamed the 'Ash Gill Member' of the Warren House Formation, with inputs from both Scottish and Scandinavian sources. It is dated to the Middle Pleistocene by AAR dates on the shell fauna, and by the relationship to the MIS 7 age raised beach. The overlying well sorted pink and red interbedded sands and silts contain carbonate nodules and rare clasls. These shallow subaqueous sediments were deposited through suspension settling and bottom current activity, and they may be reworked loess. They are named the 'Whitesides Member' and are the highest member in the Warren House Formation. The overlying "Cheviot Drift" consists of two ice-marginal traction tills (the Blackhall and Horden members), separated by interbedded glaciofluvial red silts and sands. The till lithologies are indicative of a northern British provenance, and are rich in limestone, coal, sandstone, greywacke and dolerile. The Blackhall Member was deposited by ice during MIS 4, during a period of maximum extent of the British and Fennoscandian ice sheets and contact in the central North Sea. The Horden Member was deposited in an ice- marginal landsystem by the Late Devensian North Sea Lobe, and is correlative with the Skipsea Member in Yorkshire and the Bolders Bank Formation offshore. The Swarte Bank, Coal Pit, Fisher and Bolders Bank formations from the North Sea Basin were also examined. These subglacial and glaciomarine sediments, ranging from MIS 12 to MIS 2 in age, were all found to show a similar provenance from the Grampians, Aberdeenshire and the Scottish Highlands, indicating repeat ice-flow pathways during the Quaternary. This research has significant implications for British Quaternary stratigraphy, as it indicates that Fennoscandian ice was a significant influence on the BIIS throughout the Quaternary, and that on multiple occasions, Fennoscandian ice directly impacted the coast of eastern England. During MIS 12, a marine embayment opened in northeast England between the British and Fennoscandian ice sheets. Ice rafted material derived from both Scottish and Norwegian sources was deposited in this marine embayment. The Ash Gill Member of the Warren House Formation is an isolated remnant of this ancient glaciomarine environment, and it is separated from the overlying Devensian sediments by a substantial unconformity. During the Early Devensian, ice sourced in Scotland flowed eastwards through the Tyne Gap, where it was joined by a minor component of Lake District ice. This was a stage of maximum configuration of the BIIS, with contact with the FIS offshore. During the Last Glacial Maximum, the North Sea Lobe was constrained by the FIS offshore, forcing the North Sea Lobe onshore. This project found no evidence of Lake District erratics in County Durham, but found detrital material in the subglacial tills from the coast of northeastern Scotland.