Early and Mid Devensian, Quaternary, Northern England
|From: Stone, P, Millward, D, Young, B, Merritt, J W, Clarke, S M, McCormac, M and Lawrence, D J D. 2010. British regional geology: Northern England.
Fifth edition. Keyworth, Nottingham: British Geological Survey.
Glacigenic deposits of this age are assigned to the Caledonia Glacigenic Group. The continental European record indicates that the Ipswichian Interglacial was halted by rapid climatic deterioration at about 115 ka BP. This was followed by a warmer period at about 100 ka BP (MIS 5c), which probably correlates with the Chelford Interstadial, when mixed birch, pine and spruce forest developed in northern England. Cooling recommenced at about 90 ka BP, followed by another warmer period at about 80 ka BP (MIS 5a), the so-called Brimpton Interstadial. Significant cooling then occurred until about 65 ka BP (MIS 4), when a significant Early Devensian glaciation may have affected northern England. However, uranium-series dating of speleothems from caves in the Craven district indicates that low growth was maintained between 90 and 45 ka BP, implying that a tundra-like environment was more likely than full glaciation. Intervals of faster growth at 76, 57 and 50 ka BP suggest three short, warmer interludes.
The only known representative deposit in northern England for one of these early interstadials is the Mosedale Beck Peat Bed, a poorly preserved deposit of compressed woody peat stratigraphically above the Troutbeck Palaeosol. The lower, silty part of the sequence is dominated by non-arboreal pollen indicative of open grassland, whereas the rest of the peat is dominated by willow that probably formed scrubland. Uranium series dating on twigs has yielded ages of 77 and 91 ka BP, which roughly correlate with MIS 5a.
Boreholes sunk in the 1990s around Sellafield and Drigg in west Cumbria have greatly increased our knowledge of Early Devensian events and contemporaneous relative sea levels. The Maudsyke Till Formation, which overlies the aforementioned Drigg Till in lower Wasdale, records a local, Early Devensian glacial advance (P916097). The till is overlain by varved, glaciolacustrine silt and clay, the Carleton Silt Formation, deposited in a proglacial lake that existed for several thousand years. The glaciolacustrine deposits pass upwards into boreal to Arctic marine rhythmites and shelly sands of the Glannoventia Formation. The gradational transition between the formations at -20 m OD records a marine incursion into the lake basin. Amino acid ratios in shell fragments from the Glannoventia Formation are tentatively commensurate with an age of about 60 ka BP.
The Kiondroughad Formation, known from boreholes in the north of the Isle of Man, comprises 60 m of glacigenic sand, gravel and diamicton containing a suite of clasts typical of the Irish Sea Coast Glacigenic Subgroup. It rests partly on an extensive rock platform at between -41 and -53 m OD, partly on the Ipswichian Ayre Formation, and is tentatively assigned to the Early Devensian. Several boreholes between Luce Bay (off south-west Scotland) and Ramsey Bay (off the north-east coast of the Isle of Man) penetrated laminated glaciolacustrine clays that grade upwards into shelly silts and muddy sands between -50 and -70 m OD. These sequences (Luce Bay Formation) are capped by till. The boreal affinities of the micro-and macrofauna of this formation, and its inferred Early Devensian age, invite correlation with the Carleton Silt and overlying Glannoventia formations of lower Wasdale. However, the contemporary sea level has been calculated to be about -30 m OD during deposition of the Luce Bay Formation, some 10 m below the top of the Glannoventia Formation.
There is apparently no record of the Mid Devensian in northern England apart from some fossil bones: those of woolly mammoth were recovered from Hartlepool Docks and those of woolly rhinoceros from gravel underlying till near West Hartlepool. However, pockets of frost-shattered rock and rubbly periglacial deposits that are quite commonly encountered beneath Late Devensian tills may have formed in this predominantly cold substage. One warmer interlude between 50 and 38 ka BP is known as the Upton Warren Interstadial. Uranium-series dating of speleothems from caves in the Craven district suggest that the period from 44 to 34 ka BP was relatively mild, whereas permafrost or total ice cover then prevailed from 34 to 14.7 ka BP.
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