Ipswichian Interglacial, Quaternary, Northern England

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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.

Introduction[edit]

During this interval of climatic amelioration, the district became cloaked in mixed deciduous forest, which eventually included a peculiarly large proportion of hornbeam and alder in addition to birch, pine, oak and holly. Representative deposits are not common, most being only tentatively dated and lacking in stratigraphical continuity. One well-documented terrestrial deposit that crops out in a river cliff of the Scandal Beck, at the southern edge of the Vale of Eden drumlin field, is the Scandal Beck Peat Bed (P916098)a. It comprises at least 4 m of organic mud, sand, gravel and compressed peat containing pollen, coleoptera and plant macrofossils indicative of the closing stages of an interglacial. The organic deposits occur in the core of a drumlin, overlain by two units of till, but stratigraphical uncertainties remain because weathered diamicton similar to the lower till unit also occurs beneath the organic deposits, suggesting that the latter may have been ice-rafted, although probably not very far. Another possibly Ipswichian organic deposit was found between tills in a borehole near Dalton-in-Furness, south Cumbria.

Elsewhere in northern England, construction of a cutting on the A19 trunk road at Hutton Henry, near Peterlee, revealed a unit of very strongly compressed peat. It contained well-preserved fragments of moss and some samples contained high percentages of hornbeam pollen. The peat bed occurred 6.7 to 8.5 m below ground level near the base of glacial till, which boreholes revealed rested on a sequence of plastic clays, sands and gravels at least 24.4 m thick. The peat was sheared, folded and streaked out towards the south-west in continuity with the fabric of the enclosing till. Field relationships confirmed that it formed a glacial raft.

Weathering profiles of supposed Ipswichian age have been tentatively identified sporadically across northern England, including the Troutbeck Palaeosol. This truncated palaeosol is developed on the Thornsgill Till (see above) and is overlain by younger till. The palaeosol results from the severe in-situ chemical breakdown of mudstone, volcanic and granitic clasts, many of the last being pitted and bleached; it has also been periglacially disturbed, with frost shattering of stones and cryoturbation. The weathering profile is 14 m deep locally, decreasing in severity downwards, and probably required 100 000 to 150 000 years of temperate conditions to form; these could have occurred cumulatively during the Ipswichian and several earlier interstadials of the Mid Pleistocene.

Boreholes drilled at the northern end of the Isle of Man proved 8 m of shelly silts and sands at depths of -65 to -73 m OD. The shell fauna of the unit, named the Ayre Formation, probably represents an in-situ interglacial marine assemblage that can be correlated with the Ipswichian. On the mainland, lenses of buff-coloured clay within red clay were found beneath till and gravel in a borehole drilled near Wigton, Cumbria. The clays apparently rested on bedrock within a buried channel at about -21 m OD and contained the marine snail Turritella communis, foraminifera and ostracods. These fossiliferous deposits may be Ipswichian in age, but were possibly transported as glacial rafts from the Solway Firth during an early stage in the last glaciation, if not earlier, when Scottish ice flowed up the Vale of Eden.

Bibliography[edit]

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